Coexistence of Superconducting Gap and Pseudogap in Underdoped Bi2212
K.-W. Nga, Anjan Guptab
aDepartment of Physics and Astronomy, University of Kentucky, Lexington, KY 40506-0055, U. S. A.
bCNRS-CRTBT, 25 Avenue des Martyrs, 38042 Grenoble, France
The pseudogap in high Tc cuprates is an established phenomenon, although its origin is not clear yet. We have carefully studied the temperature dependence of tunneling spectra in underdoped and slightly overdoped Bi2212 single crystals. The underdoped spectra clearly show a pseudogap above Tc, while this gap features get very weak in slightly overdoped crystals. Without the pseudogap depression, the states in slightly overdoped spectra are always conserved. However, underdoped spectra do not conserve states even at temperatures when the material is in its superconducting state. More interestingly, we found that the conservation of states can be recovered by normalizing the superconducting spectra with the normal state pseudogap spectra. This clearly indicates the coexistence of pseudogap and superconducting gap.
Mechanism of hole carrier generation and pseudogap nature in doped La214.
Olga Ivanenko, Kirill Mitsen
Lebedev Physical Institute, 119991 Moscow, Russia.
The generation of hole carriers in HTS is considered in the framework of model [JETP, 91 (2000) 579]. According to this model the hole conductivity starts up at the dopant concentration exceeding the percolation threshold for chain of -U centers. The conductivity (and superconductivity) takes place in the band formed by the oxygen pp-orbitals hybridized with the pair orbitals of -U centers. It is shown that the inclusion of two-particle hybridization results in the temperature dependences of hole carrier concentration n(T) µ T and resistivity R(T) µ T. As far as the mechanism of superconducting gap suppression in HTS is the occupation of pair level with electrons, the superconducting gap (pseudogap) in small nonpercolative clusters containing short chains of -U centers has to open at T above Tc because of the large relative fluctuations of the number of particles between pp-band and pair level in small clusters.
Fermi surface and ARPES of CuO2 planes - violation of Luttinger's theorem?
Thomas Pruschke
Center for Electronic Correlations and Magnetism, Theoretical Physics III, Institute for Physics, University of Augsburg, 86135 Augsburg, Germany
We employ the dynamical cluster approach to the 2D Hubbard model in the intermediate coupling regime. For small to intermediate doping we observe strong deviations from conventional Fermi liquid behaviour and evidence for a violation of Luttinger's theorem. Without next-nearest neighbor hopping t¢ the calculated Fermi surface shows a crossover to a conventional Fermi liquid at larger doping while for physically sensible values of t¢ there remain strong deviations from the non-interacting Fermi surface even for large doping. Our spectra and Fermi surface data compare well with recent experiments on high-Tc compounds suggesting that certain pecularities observed experimentally may indeed be traced to a violation of standard Fermi liquid relations.
Effects of thermal fluctuations and magnetic field in the SO(5) theory
Xiao Hu
National Institute for Materials Science, Tsukuba 305-0047, Japan
The SO(5) symmetry is expected as the result of the competition between magnetism and superconductivity orders. According to the RG theory, however, an O(n) isotropic fixed point becomes unstable for n > 4 in 3D because of thermal fluctuations. We have performed Monte Carlo simulations on a classical SO(5) model, which can describe the long-wave-length behaviors of the SO(5) theory. We have found, in contrast to RG theory, that the SO(5) symmetric point is stable when biquadratic coupling between AF and SC is repulsive, which is shown to be realized in high-Tc cuprates by the Gutzwiller projection. We derive a scaling theory for the bicritical phenomena which can be used test the SO(5) theory quantitatively in experiments. Under an external magnetic field, a first-order normal state to AF phase transition is predicted near the AF-SC phase boundary, which has been confirmed in organic superconductors.
On the Limit of Tc in C60-Based Superconductors
Eiko Matsushita
Faculty of Engineering, Gifu University, Gifu 501-1193 JAPAN
Ionic superconductors (C603-, C603+) in the
field-effect transistor (FET) are tried to explain in the unified
picture with alkali-doped A3C60 superconductors.
The simplified extended BCS-like theory is presented in success in
analyzing explicitly various roles of some kinds of phonons playing
on the transition temperature Tc: the phonon
to make the basic mechanism of weak-coupling s-wave superconductivity,
the phonon to enhance Tc, and the phonon to
adjust whether assisting or preventing superconductivity.
Within the present theory for phonon-mediated superconductivity,
the possibility of higher Tc and the limit of
Tc are predicted and discussed in comparison
with experimental results reported by Schön et al.1.
1J.H.Schön et al., Science 288 (2000) 656;
Nature 408 (2000) 549; Science 293 (2001)
2432).
Pseudogap phenomena in the BCS pairing model
Satoshi Fujimoto
Department of Physics, Kyoto University, Kyoto 606-8502, Japan
Recently, the pseudogap phenomena observed in the high-Tc cuprates have attracted much interest. It has been proposed by some authors that its origin may be attributed to the superconducting fluctuation in the normal state. Here, we investigate pseudogap phenomena realized in the BCS pairing model with a long but finite interaction range. We calculate the single-particle self-energy corrections by the superconducting fluctuation in all orders exactly in the temperature range where the superconducting fluctuation is Gaussian-like. The pseudogap behavior of the density of states is obtained in the substantially wide temperature ranges in the two-dimensional case. It is found that vertex corrections to the self-energy, which are discarded in the previous studies, are crucially important for the pseudogap phenomena in higher order calculations.
Novel Metallic and Superconducting States in Doped High-Tc Cuprates
Safarali Dzhumanov
Institute of Nuclear Physics, 702132 Tashkent, Uzbekistan
The current understanding of the nature of the novel pseudogapped metallic and superconducting (SC) states in doped high-Tc cuprates is reviewed taking into account recent theoretical and experimental results obtained for underdoped, optimally doped and overdoped cuprates. We prove that the pseudogap formation and superfluid condensation phenomena can be understood properly within the continuum model of carrier self-trapping and the novel two-stage Fermi-Bose-liquid model of superconductivity. It is argued that the pseudogap phenomena is irrelevant to superconductivity. The possibility of pseudogap formation above Tc and the coexistence of two preudogaps and true SC gap below Tc as well as doping and temperature dependences of these pseudogaps and SC gap are studied. The obtained results are consistent with numerous experiments.
Variational Monte Carlo Study on the Dependence of ep - ed of the Two-Dimensional d-p model
Soh Koike
JST, Domestic Research Fellow, and AIST, Tsukuba, Ibaraki, 305-8568, Japan
The superconducting condensation energy as a function of the energy difference (ep-ed) between the oxygen and copper site in the two-dimensional d-p model has been estimated by use of the variational Monte Carlo method. We have found that the superconducting condensation energy increases when ep-ed increases. We also have calculated the numbers of the d- (nd) and p-holes (np) and compared to those estimated from the NQR/NMR experiments. The obtained phase diagram, the superconducting condensation energy, which is correlated with the superconducting critical temperature, in the d-p model seem to be considerably agreement with those of the cuprate superconductors from the view point of nd and np.
Theory of Nernst Coefficient and Magnetoresistance
in High-Tc Cuprates:
the Role of Superconducting Fluctuations
Hiroshi Kontani
Department of Physics, Saitama University, 255 Shimo-Okubo, Saitama-city, 338-8570, Japan.
The Nernst coefficien (n) in hole-doped compounds increases drastically below the pseudo-gap temperature, T*. Here, we study this mysterious behavior of n in terms of the FLEX+T-matrix approximation. We analyze the role of the vertex corrections (VC's) both for the electronic current and the heat one, which are indispencable to keep the conservation laws. According to the present analysis, the abrupt increase of n below T* is well understood as the reflection of the enhancement of the d-wave superconducting fluctuations (SCF), because the VC's due to the SCF make the total current [J\vec]k much singular. As a result, the striking behaviors of n as well as the magnetoresistance below T* are naturally understood in terms of the AF and SC fluctuation scenario based on the Fermi liquid theory.
Sb NQR study of superconducting YbSb2
Y. Kohoria, T. Koharab, N. Satoc, T. Kinokirid
aDepartment of Physics, Faculty of Science, Chiba University, Inage-ku, Chiba 263-8522 Japan
bDivision of Material Science, Graduate School of Science, Himeji Inst. of Tech. Ako-gun, Hyogo 678-1297 Japan
cDepartment of Physics, Nagoya University, Chikusa-ku, Nogoya 464-8602, Japan
dGraduated School of Science, Tohoku University, Sendai 980-8577 Japan
We have measured 121Sb and 123Sb NQR spectra and nuclear spin- lattice relaxation rate 1/T1 both in normal and superconducting states of YbSb2. 1/T1 in the superconducting state has coherence peak just below the transition temperature and exponential temperature dependence at lower temperatures, which indicate occurrence of the s-wave superconductivity in YbSb2.
Unusual ferromagnetic behavior in UGe2
Takashi Nishioka, Gaku Motoyama, Setsushi Nakamura, Noriaki K. Sato
Department of Physics, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan.
We have measured high pressure ac magnetic susceptibility (cac) and dc magnetization on a ferromagnetic superconductor UGe2, especially in a pressure region at which ferromagnetism (FM) and superconductivity (SC) coexist. As the pressure (P) increases above ~ 10 kbar, at which SC sets in, a peak temperature in cac(T) corresponding to the Curie temperature begins to deviate from a characterestic temperature (Tm) below which spontaneous magnetization appears. This deviation increases with P, and even above pressures at which both FM and SC disappear, Tm remains at around 40 K. In addition, FC and ZFC magnetization separate below about Tm. These results seem to suggest that tiny ferromagnetic clusters are formed below Tm and they behave as superparamagnetism. Thus, we conjecture that the FM at higher pressures is inhomogeneous, which may allow the coexistence of FM and SC in UGe2.
115In-NQR study of magnetic properties of CeIn3 under pressure
Shinji Kawasakia, Takeshi Mitob, Guo-qing Zhenga, Yu Kawasakia, Yoshio Kitaokaa, Shingo Arakic, Rikio Settaic, Yoshichika ¯Onukic
aDepartment of Physical Science, Graduate School of Engineering Science, Osaka University, Machikaneyama-cho, 1-3 Toyonaka, Osaka 560-8531, Japan
bFaculty of Science, Kobe University, Kobe, Hyogo 657-8501, Japan
cDepartment of Physics, Graduate School of Science, Osaka University, Machikaneyama-cho, 1-3 Toyonaka, Osaka 560-0043, Japan
We report the pressure(P)-temperature phase diagram of antiferromagnetism and superconductivity in CeIn3 based on the 115In nuclear-spin-lattice-relaxation (T1) measurements under P. We found that the localized magnetic character is robust against the application of P up to P ~ 1.9 GPa, beyond which the system evolves into an itinerant regime in which the resistive superconducting phase emerges.
Magnetic order in heavy electron system CeRh1-xIrxIn5
Norihiko Yamaguchia, G.-q. Zhenga, K. Tanabea, Y. Kitaokaa, J. Sarraob, J.D. Thompsonb
aDepartment of Physical Science, Osaka University, Osaka 560-8531, Japan
bLos Alamos National Laboratory, Los Alamos, NM 87545, USA
CeRh1-xIrxIn5 is an alloy of new heavy fermion compounds CeRhIn5 and CeIrIn5. CeRhIn5 is an antiferromagnet (TN= 3.8K) and CeIrIn5 is a superconductor (Tc= 400mK). In the range of x=0.3-0.6 coexistence of antiferromagnetic order and superconductivity was reported. We have investigated the electronic states of the x=0.35 and 0.25 samples using 115In-NQR and confirmed the antiferromagnetic order in both alloys from the measurement of spectrum and spin-lattice relaxation time.
Critical magnetic fluctuations induced superconductivity and residual density of states in CeRhIn5 superconductor
Yunkyu Banga, I. Martinb, A.V. Balatskyb
aDepartment of Physics, Chonnam National University, Kwangju 500-757, Korea
bTheoretical Division Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
We propose the multiband extension of the spin-fermion model to address the superconducting d-wave pairing due to magnetic interaction near critical point. By solving the unrestricted gap equation with a general d-wave symmetry gap, we find that divergent magnetic correlation length x leads to the very unharmonic shape of the gap function with shallow gap regions near nodes. This unharmonic gap is extremely sensitive to the small amount of disorder and we propose that we can understand the large Nres(0) = limT® 0 Cp(T)/T value and its pressure dependence of the recently discovered CeRhIn5 superconductor under pressure within this approach.
High-temperature superconductivity: not due to cuprate-planes.
John D. Dow, Dale R. Harshman
Physics Department, Arizona State University, Tempe, Arizona 85287 U.S.A.
The superconducting compound Sr2YRu1-uCuuO6 (for 0.05 £ u £ 0.15) has two types of layers: YRuO4 doped on Ru sites with Cu, and (SrO)2. It superconducts in its SrO layers with an onset temperature of » 49 K, and with an absolute critical temperature of 23 K, which coincides with the N\' eel temperature TN of the fluctuating Ru moments. Near 29.3 K, spin-glass fluctuations are observed. Interestingly, the doped Cu moments spin-order at » 86 K. The YRuO4 layers are ferromagnetic in their planes, but stacked antiferromagnetically, so that there is no field in the SrO layers. The SrO superconductivity of Cu-doped Sr2YRuO6 is analogous to the BaO-layer superconductivity of PrBa2Cu3O7, and suggests that all cuprates superconduct p-type in their SrO or BaO layers, or in interstitial regions. We know of no credible evidence supporting the common viewpoint that the cuprate-planes superconduct.
Effect of Adsorbed Molecules of Phenidone and Hydroquinone on the Critical Superconducting Parameters of Ceramics Y-Ba-Cu-O
Lev L. Makarshin, Natalia A. Golikova, Dmitry V. Andreev, Valentin N. Parmon
Boreskov Institute of Catalysis, pr. akad. Lavrentieva 5, Novosibirsk 630090, Russia
Hydroquinone (p-dihydroxybenzene) and phenidone (1-phenyl-3-pyrazoline) react effectively with Y-Ba-Cu-O ceramics and change its critical parameters. As the results: (1) Tc increases from 89.5 to 93 K; (2) fraction of the intergranular contacts engaged in the transport critical current conductivity increases; (3) total fraction of the superconducting phase increases; (4) transport critical current density decrease by a factor of 2.5-5. We suggest that an increase in Tc is associated with formation of Cu(III) in the ceramics lattice in the reaction course, and an increase in the number of intergranular contacts is due to the surface chemical reaction resulting in modification of the superconducting granules.
Structural Sensitivity of Superconducting Properties of Mercury-Based Copper Oxides and Other Layered Systems
Alexander L. Kuzemskya, I.G. Kuzemskayab
aJoint Institute for Nuclear Research , Dubna, Moscow Region, 141980, Russia
bHigh Pressure Physics Institute, Russian Academy of Sciences, Troitsk, Moscow Region, 142092, Russia
We discuss the different factors which govern the unique physical properties of the mercurocuprate family HgBa2Can-1CunO2n+2+d . The relationships between structural and superconducting properties are discussed and particular attention is paid to layered structure. The dependence of a superconducting critical temperature for different members of mercurocuprate family is analyzed in terms of workable model of layered superconductors, taking into account possible charge redistribution. This lead to observable non-monotonic "bell"-shaped dependence of Tc(n) and fits the experimental data well.
Electron-doped superconductivity in (Sr,Ca)CuO2 infinite-layer thin films
J.C. Niea, P. Badicab, M. Hiraic, Y. Kodamaa, A. Crisanb, A. Sundaresana, Y. Tanakaa, H. Iharaa
aNeRI, AIST, Tsukuba, 305-8568 Japan and CREST, JST, Kawaguchi, Saitama, 332-0012 Japan
bNeRI, AIST, Tsukuba, 305-8568 Japan and Nat. Inst. Mat. Phys., POB MG-7, Bucharest, Romania
cNeRI, AIST, Tsukuba, 305-8568 Japan and Sci. Univ. of Tokyo, 2641 Yamazaki, Noda, Chiba, Japan
The infinite-layer compound (Sr,Ca)CuO2 thin films have been prepared by off-axis rf magnetron sputtering. The c-axis lattice parameters of the infinite-layer phase are contracted with increase of deposition temperature, whereas the reversed changes in the a-axis lattice parameters are observed, suggesting the incorporation of oxygen vacancies in CuO2 planes. A superconducting transition with on-set at 40-50 K was obtained for the first time, induced by the electron-doping with suitable oxygen vacancies in CuO2 planes. Further increase of doping showed to destroy superconductivity.
The influence of superconductivity on the positronium in a void
Victor L. Sedov, Oleg A. Tsigel'nik
Department of Physics, Moscow State University, Moscow 119992, Russia
At present it has been established by experiment that the high-temperature superconductivity transition exerts a noticeable influence on positron annihilation effects. These effects are mainly connected with positrons trapped by lattice defects. The lifetime of such positrons decreases discontinuously at the superconductivity transition. In the present study this phenomenon is associated with an sharp formation of the energy gap when the superconductivity state arises in HTSC. We believe that the observed effect of the influence of superconductivity on the positron lifetime arises due to formation of a positronium in microvoids. When a superconductivity energy gap is formed the filling of the positronium level is decreased. Estimation of this phenomenon in HTSC carried out on the basis of the BCS theory gives the jump of the Dt ~ 1-10ps.
Superconductivity in NCCO thin films and effect of Gd and Ni doping
Bambang Prijamboedia, Satoshi Kashiwayaa, Hajime Shibataa, Yukio Tanakab
aNanoelectronics Research Institute of AIST&CREST, Tsukuba, Ibaraki 305-8568, Japan
bDepartment of Applied Physics, Nagoya University&CREST, Nagoya 464-8603, Japan
In order to clarify the electronic states of electron-doped cuprates superconductor, Nd2-xCexCuO4-y (NCCO), Nd1.8-xGd0.2CexCuO4-y (NGCCO) and Nd2-xCexCu0.998Ni0.002O4-y (NCCNO) thin films were fabricated for Ce concentration range of 0.08 £ x £ 0.15 by pulsed laser deposition technique on SrTiO3 (100) substrate. The superconductor-insulator transition occurs at Ce concentration of ~ 0.095 for NCCO, ~ 0.105 for NGCCO and ~ 0.11 for NCCNO. In all compositions, Tc gradually decreases as Ce concentration decreases. The presence of the superconductivity for x £ 0.12 suggests the apparent presence of underdoped region of NCCO.
Determination of structural changes of YBa2Cu3O6.94 by X-Ray diffraction
Margarita Yu. Kameneva, Anatoly I. Romanenko, Nina V. Kurat'eva, Nikolai Yu. Naumov, Olga B. Anikeeva
Institute of Inorganic Chemistry, Siberian Branch of Russian Academy of Science, Novosibirsk, Russia
X-ray diffraction (XRD) patterns of the samples YBa2Cu3O6.94 after slow heating from 300 K to 530 K (less than 1K/hour) and annealing at 530 K during one month demonstrate the decreasing of intensity of diffraction peaks and its broadening. Peak broadening is often assumed to results from coherent scattering domain sizes, its distribution, strain and disorder. Modelling of all possible contributions to XRD profiles were carried out. Usefulness of such approach for correlation of superconducting properties to actual structure is discussed.
Pinning Properties of Gd-Ba-Cu-O Bulk Superconductor Fabricated by Cold Seeding Method
Kazuo Inoue, Naomichi Sakai, Shinya Nariki, Masato Murakami
Superconductivity Research Laboratory, ISTEC, 1-16-25 Shibaura, Minato-ku, Tokyo, 105-0023, Japan
Gd-Ba-Cu-O bulk superconductor was fabricated by the cold seeding method. We have optimized the growth conditions that make it possible to grow a single domain. The critical current density of the central part of the bulk was lower than the other parts in a lower magnetic field. However, the secondary peak effect was more remarkable. Such results are correlated with spatial fluctuation in the volume fraction of 211 phase as evidenced by the SEM observation of microstructure.
Capacitive and Inductive Effects in Multi-Josephson Junction Model in High Tc Superconductors
Hideki Matsumotoa, Shoichi Sakamotob, Satoshi Katohb
aInstitute of Physics, University of Tsukuba, Ibaraki 305-8571, Japan
bDepartment of Applied Physics, Seikei University, Musashino 180-8633, Japan
I-V characteristics of high Tc superconductors, such as Bi2Sr2CaCu2O8, are well described by use of the multi-Josephson junction model. There are capacitive and inductive effects as mechanisms of inter-layer couplings. By numerical simulation, I-V characteristics are investigated, including both effects. It is shown that the inductive effect makes phase differences of layers to behave coherently, while the capacitive effect works to form a pattern of phase-rotating layers. Both effects are equally important to get systematic changes of I-V characteristics from short junctions to long ones, and their dependence on the applied magnetic field.
Inhomogeneous electronic structures in heavily Pb-doped Bi2Sr2CaCu2Oy single crystals probed by low temperature STM/STS
Go Kinodaa, Shoichiro Nakaob, Teruki Motohashia, Yuri Nakayamab, Keisuke Shimizub, Junichi Shimoyamab, Koji Kishiob, Tetsuo Hanagurib, Koichi Kitazawab, Tetsuya Hasegawaa
aMater. and Struct. Lab., Tokyo Institute of Technology, Midori-ku, Yokohama 226-8503, Japan
bDept. of Applied Chemistry, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
We have perfomed cryogenic STM/STS of heavily Pb-doped Bi2Sr2CaCu2Oy single crystals to investigate the two-phase microstructures possibly responsible for the flux pinning. The obtained STM/STS results at 4.3K clearly showed local inhomogeneity of gap structure D (D=20-60 meV) in a scale of several nm, suggesting the coexistence of sperconducting and pseudogap-like regions, even in the overdoped regime. We also comfirmed an abrupt change in D across the phase boundaries, indicating that they could act as effective pinning centers.
Cryogenic STM/STS observations of Pb-doped Bi2Sr2CuOy single crystals
Hideki Mashimaa, Go Kinodaa, Hiroshi Ikutab, Tetsuya Hasegawaa
aMaterials and Structures Laboratory, Tokyo Institute of Technology, Midori-ku, Yokohama 226-8503, Japan
bCenter for Integrated Research in Science and Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
Cleaved ab-surfaces of Pb-doped Bi2Sr2CuOy (Bi2201) single crystals were probed by scanning tunning tunneling microscopy/spectroscopy (STM/STS) at cryogenic temperatures below Tc. The obtained STS spectra clearly indicate a d-wave like gap structure superimposed on inverse V-shaped background, similar to previous STS observations on pure Bi2201. Furthermore, we found that the gap value 2D was spatially non-uniform in a nm scale and ranged from 20 to 50 meV.
STM/STS studies on YBa2Cu3O7-d thin films treated with an atomic oxygen beam
Shigehiro Uenoa, Satoshi Kashiwayaa, Norio Teradab, Yukio Tanakac, Masao Koyanagia, Kouzou Obarab
aNanoelectronics Research Institute of AIST, Umezono 1-1-1, Tsukuba, Ibaraki 305-8568, Japan
bDepartment of Electrical and Electronics Eng., Kagoshima University, Kagoshima 890-0065, Japan
cDepartment of Applied Physics, Nagoya University, Nagoya 464-8603, Japan
The surface electronic states of YBa2Cu3O7-d (YBCO) films are studied by using scanning tunneling microscopy/spectroscopy (STM/STS) at low temperature (T8K). In order to improve the surface quality of YBCO, an atomic oxygen beam was utilized as a cleaning technique. The spatial dependences of the work function and the energy gap were measured by STM/STS. The origin of inhomogeneity of electronic states is discussed in the relation with the surface bound states due to d-wave pair potential.
Comparative study of the transport properties of sub-micron bicrystal and ramp junctions
A. Ya Tzalenchuka,b, B Högberga, T Lindströma, E Stepantsova, P Komissinskia, Z Ivanova,
T Claesona
aChalmers University of Technology, Department of Microelectronics and Nanoscience, Fysikgränd 3, SE-412 96 Göteborg, Sweden
bNational Physical Laboratory, Teddington, Middlesex, TW11 0LW, UK
A process has been developed that makes it possible to fabricate high quality sub-micrometer wide YBCO Josephson junctions using bicrystal or ramp junction technology. Junctions fabricated using this process allowed us to make comparative studies of sub-micron bicrystal and ramp junctions. We have especially studied junctions with one or both crystal axes oriented 45 degrees with respect to the barrier.
STM Study of Vacancy Resonances in Bi2Sr2CaCu2O8 + d
E.W. Hudsona, V. Madhavana, K. McElroya, J.E. Hoffmana, K.M. Langa, H. Eisakib, S. Uchidab, J.C. Davisa
aDepartment of Physics, University of California, Berkeley, CA, 94720-7300
bDepartment of Superconductivity, Tokyo University, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan
Low temperature scanning tunneling microscopy (STM) of various samples of the high temperature superconductor Bi2Sr2CaCu2O8 + d consistently reveals the presence of quasi-particle scattering resonances, similar both spectroscopically and spatially to those observed around Zn atoms in Zn-doped BSCCO. As the resonances appear at energies indicative of nearly unitary scattering ( ~ 0.5 meV) and are always accompanied by topographic depression of the surface Bi atom around which they are centered, we postulate that the source of scattering may be Cu vacancies in the CuO2 plane. Such resonances should thus provide a simpler test case for theoretical models than those created by Zn or Ni substitution.
Photoexcited Carrier Relaxation in a-axis Oriented YBa2Cu3O7-d Thin Films Measured by Femtosecond Time-Resolved Spectroscopy
C. W. Luoa, M. H. Chena, K. H. Wua, J. Y. Juanga, T. M. Uena, J.-Y. Linb, Y. S. Goua
aDepartment of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan, R.O.C.
bInstitute of physics, National Chiao Tung University, Hsinchu, Taiwan, R.O.C.
The photoexcited carrier relaxation dynamics in a-axis oriented YBa2Cu3O7-d (YBCO) thin films has been investigated by femtosecond time-resolved spectroscopy. Distinct responses along CuO3 chain and c-axis of YBCO have been separated by the polarization-dependent femtosecond pump-probe measurements. At superconducting state, the transient reflectivity (DR/R) curves in c-axis direction are similar to those at normal state. However, the DR/R curves along CuO3 chain at temperature below Tc become broad and its relaxation time of carriers is longer than one above Tc. The obvious difference of carrier relaxation processes between CuO3 chain and c-axis is discussed.
Anomalous suppression of Tc in an over doped region of TlBa2Ca2Cu3O9-d
A. Iyoa, M. Hiraib, K. Tokiwac, T. Watanabec, M. Tokumotoa, M. Ariyamab, Y. Tanakaa
aAIST and CREST, Tsukuba, Ibaraki 305-8568, Japan
bDep. of Phys.,Tokyo University of Science and CREST, Noda, Chiba 278-8510, Japan
cDep. of Appl. Elec., Tokyo University of Science and CREST, Noda, Chiba 278-8510, Japan
Anomalous suppression of Tc has been found in an over doped region of TlBa2Ca2Cu3O9-d superconductors. A heavily-over doped sample (Tc @ 100 K) was synthesized under high pressure. Tc was measured with decreasing the hole carriers. A dip of Tc was found before the doping state reaches to an optimally doped one (Tc ³ 130 K) i.e. in an over doped one. A dip was also found in La-214 system which is explained by stripe order. The anomalous behavior of Tc is discussed in terms of reconstruction of electric structure accompanied with Tl valence change (Tl3+ to Tl(3-d)+) or effect of inhomogeneous carrier distribution between crystallography different CuO2 layers as well as stripe order.
Symmetry Crossover of the Superconducting Coherent Peak and the Quasiparticle Band in High Tc Superconductors
Shunji Sugai, Haruyuki Suzuki, Yasumasa Takayanagi, Toshihiko Hosokawa, Naoki Hayamizu
Department of Physics, Faculty of Science, Nagoya University, 464-8602 Nagoya, Japan
The carrier density dependence of the superconducting coherent peak (pair breaking peak) was investigated by Raman scattering in YBa2Cu3Oy, La2-xSrxCuO4, Bi2212, and Bi2201. The symmetry of the coherent peak changes from B2g (xy) to B1g (x2-y2) as carrier density increases. The crossover point is the 60 K phase (y=6.63) in YBCO and the optimum carrier density in LSCO and Bi2212. In Bi2201 the clear crossover is not observed, but the B2g (xy) coherent peak appears only at underdoping. It suggests that the pairing symmetry changes from d(xy) to d(x2-y2) as carrier density increases. This crossover is related to the crossover of the low energy intensity suggesting that doped carriers make a quasiparticle band around (p/2, p/2) at low carrier density and move to (p, 0) as carrier density increases.
Nonmonotonic d-wave superconducting order parameter in electron doped cuprates
G. Blumberga, A. Koitzscha, P. Fournierb, R.L. Greeneb
aBell Laboratories, Lucent Technologies, Murray Hill, NJ 07974, USA
bDepartment of Physics, University of Maryland, College Park, MD 20742
We report Raman scattering studies on Nd1.85Ce0.15CuO4. The data is consistent with order parameter of the d-wave symmetry. As distinguished from the convensional monotonic d-wave superconducting gap, the present results require a nonmonotonic d-wave form of the order parameter. We find that in contrast with hole doped cuprates for Nd1.85Ce0.15CuO4 the positions of the gap maxima are located closer to the nodes than to the Brillouin zone boundaries. The gap enhancement in the vicinity of the Fermi surface intersections with antiferromagnetic Brillouin zone emphasizes role of antiferromagnetic fluctuations and similarity in the origin of superconductivity for electron- and hole-doped cuprates.
Four-fold symmetry of 90K-YBCO single crystals in magnetic fields
Seiya Haraguchia, Yuuya Kawabataa, Tomoyuki Naitoa, Hideo Iwasakia, Terukazu Nishizakib, Norio Kobayashib
aSchool of Materials Science, Japan Advanced Institute of Science and Technology(JAIST), Tatsunokuchi 923-1292, Japan
bInstitute for Materials Research, Tohoku University, Sendai 980-8577, Japan
We have measured the angular dependence of the resistivity r(q) in 90K-YBCO single crystals, where q is the angle between the direction of a magnetic field H and the current I. The obtained r(q) shows the four-fold symmetry. On the other hand, Kwok et al. had observed only the two-fold symmetry in 90K-YBCO single crystals. The origin of the difference between the symmetry of each case is still not clear; however, We speculate that it comes from the difference of anisotropy which depends on the concentration of oxygen in CuO-chains.
Difference in Ru ionic state between Ru1212 and Ru1222 from ESR measurements
Koji Yoshida, Masatoshi Nakamura, Hiroki Kojima, Hajime Shimizu
Tokyo University of Science, Yamaguchi, Onoda 756-0884, Japan
RuSr2GdCu2O8 (Ru1212) is expected to give a good opportunity to understand a coexistence of ferromagnetism with superconductivity. However, a detailed magnetic structure in the RuO2 layers is still controversial. In order to investigate the electronic state of Ru ions, we performed ESR measurements using polycrystalline samples of Ru1212 and its analogous RuSr2(Gd1.4Ce0.6)Cu2O10 (Ru1222). A resonance signal which indicates a ferromagnetic correlation between the Ru ions appears below TM = 140K (Ru1212) and 175K (Ru1222). Our most interesting finding is that the signal can clearly be separated into two components only in Ru1212. This suggests that a charge segregation of Ru4+ and Ru5+ in the RuO2 layers occurs in Ru1212, while an ionic valence of Ru5+ occupies in Ru1222.
A Raman Scattering Study of Superconductivity in MgB2
James W. Quiltya,b, Sergey Leeb, Ayako Yamamotob, Setsuko Tajimab, Akio Yamanakac
aDepartment of Complexity Science and Engineering, Tokyo University, Hongo 7-3-1, Bunkyo-ku, Tokyo.
bSRL-ISTEC, 1-10-13 Shinonome, Koto-ku, Tokyo 135-0062, Japan.
cChitose Institute of Science and Technology, Chitose, Hokkaido 066-8655, Japan.
Measurements of the in-plane and out-of-plane electronic Raman continuum in MgB2 single crystals show markedly different behaviour below Tc, indicative of a complex gap structure. In xx and xy polarisation configurations, a sharp pair-breaking peak is seen near 100 cm-1 but no scattering threshold forms directly below the peak. In zz and zx polarisations, a threshold is seen at 30 cm-1 but no pair-breaking peak appears. The gap structure seen in the Raman spectra is consistent with, and sheds light on, results from other techniques. Explanations for the polarisation dependence of the spectra are considered. This work was supported by the New Energy and Industrial Technology Development Organization.
LiBC and related compounds under high pressure
Kazuaki Kobayashi
Computational Materials Science Center, National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki, Japan, 305-0044.
We calculated the electronic and lattice properties of MgB2 under high pressure (hydrostatic, uniaxial, a, b-axis) in the previous studies[1,2]. The electronic and lattice properties of LiBC and related compounds (MgB2, MgC2) under a variety of compression conditions are calculated at present study. The lattice properties are optimized automatically by the first-principles molecular dynamics (FPMD) method. The electronic properties of LiBC and related compounds (MgB2, MgC2) are also calculated. We investigate the change of the band structures under high pressure.
[1] K. Kobayashi and K. Yamamoto: J. Phys. Soc. Jpn. 70 (2001) 1861.
[2] K. Kobayashi and K. Yamamoto: J. Phys. Soc. Jpn. 71 (2002) 397.
Bonding Nature and Wave Function around the Fermi Level of MgB2-related Compounds
Masao Nakao
School of Eng., Tokai University, 1117 Kitakaname, Hiratsuka, Kanagawa 259-1292, Japan
We present first-principle molecular-orbital calculations for the 39-K superconductor MgB2 and related diborides using the DV-Xa method. The electronic structure of a slab cluster embedded in the Madelung potential is determined self-consistently in terms of charge transfer between Mg and B. In contrast with the previous band calculation, the negative charge of B is estimated to be 0.39. Our results, which include total and B 2p partial density of states, overlap population in the neighboring B-B and Mg-B bonds and wave functions around the Fermi energy EF consisting of B 2px,y orbitals in the B planes, indicate the incomplete filling of the s orbitals in MgB2. We discuss possible ways to achieve higher transition temperatures in non-periodic systems such as surfaces and hetero-structures based on this study.
MgB2: superconductivity and effects of pressure
Valery A. Ivanovab, Joseph J. Betourasa, François M. Peetersa
aDepartement Natuurkunde, UIA, Universiteitsplein 1, B-2610 Antwerpen, Belgium
bN. S. Kurnakov IGIC of the Russian Academy of Sciences, Leninskii prospect 31, 117907 Moscow, Russia
The Ginzburg-Landau theory of MgB2 has been constructed taking into account the possibilities of different bands which superconduct: both s- and p-bands or s-alone. Then the microscopic theory of superconducting MgB2 is proposed based on the strongly interacting s-electrons and non-correlated p-electrons of borons. The kinematic and Coulomb interactions between the orbitally degenerated s-electrons provide the superconducting state with the s* -wave symmetry. Tc has a non-monotonic dependence on the distance r between the centers of s- and p-bands. MgB2 on a bell-shaped curve Tc (r) is identified in the overdoped region. The superconducting density of electronic states is in a satisfactory agreement with available experimental and theoretical data. The pressure effects are discussed.
Specific heat of inhomogeneous superconductors as applied to MgB2
A. M. Gabovicha, Mai Suan Lib, M. Pekalac, H. Szymczakb, A.I. Voitenkoa
aCrystal Physics Department, Institute of Physics, prospekt Nauki 46, 03028 Kiev, Ukraine
bInstitute of Physics, Al. Lotnikow 32/46, PL-02-668 Warsaw, Poland
cDepartment of Chemistry, University of Warsaw, Al. Zwirki i Wigury 101, PL-02-089 Warsaw, Poland
Temperature, T, dependences of the electronic specific heat C were calculated for spatially random inhomogeneous superconductor consisting of domains with different critical temperatures. The domain sizes are considered larger than the coherence length. The assumed disorder simultaneously smears the anomaly at Tc and leads to the µ T2 low-T asymptotics of C(T). The latter can be observed at strong enough dispersions, otherwise the validity region of the power-law asymptotics becomes unobservable. In this case the transitional C(T) dependence similar but not identical to the BCS one may be observed for the lowest attainable T. The discovered features reproduce well the variety of data for MgB2.
Physical properties of Be doped magnesium diboride
Y. Zenitani, K. Kadomura, S. Akutagawa, H. Takagiwa, T. Muranaka, J. Akimitsu
Department of Physics, Aoyama-Gakuin University, 6-16-1, Chitosedai, Setagaya-ku, Tokyo, 157-8572, Japan
The intermetallic compound magnesium diboride (MgB2) exhibits the highest superconducting transition temperature(Tc=39K) of all metallic superconductors.
We report on the electrical transport and the magnetic properties for Be doped magnesium diboride. For sample preparation of Mg1-xBexB2, powdered magnesium , boron and powdered beryllium are mixed together and the mixture is press-formed into pellets. Pelletized samples are synthesied at 1623 K under 5.5 GPa with high pressure technique. We estimated the superconducting critical current J c from magnetization curves of flux of Mg1-xBexB2
A Simple Preparation of Superconducting MgB2 Thin Films by Composite -Target Sputtering System
Masahiro Akinaga, Seigo Umeda, Hidetoshi Hasegawa, Toshiro Shirasawa
Departmment of Physics, Fukuoka University of Education, Munakata, Fukuoka 811-4192, Japan
As-grown superconducting MgB2 thin films were prepared by usual simple R.F. sputtering. A two component target comprising of many small slices of B on a Mg disk was used. The films were deposited onto polished single crystal sapphire or SrTiO3 substrates at rather low temperatures ranging from 100 oC to 110 oC. For higher substrate temperature, we could not prepare a superconducting film. Five samples on SrTiO3 (111) substrate and one on sapphire showed zero resisitivity at about 15 K and onset at about 20 K. The overall feature of the transport phenomena was very different from measured feature in the prepared MgB2 bulk sample with much grain boundaries.
Dc and microwave fluctuational conductivity of anisotropic superconductors
Enrico Silvaa, Romolo Marcona, Renato Fastampab, Maurizio Giurab, Stefano Sartib
aDip. di Fisica ``E.Amaldi'' and Unità INFM, Università Roma Tre, 00146, Roma, Italy
bDip. di Fisica and Unità INFM, Università ``La Sapienza'', 00185, Roma, Italy
We present measurements of the dc and microwave excess
conductivity above Tc in anisotropic superconductors, including
cuprates and MgB2. When temperature raises well above Tc,
both the dc and microwave (24 and 48 GHz) excess conductivities drop
much faster than predicted by the well-established gaussian theory.
We introduce a spectral cutoff in the calculation of the
finite-frequency fluctuational conductivity in order to suppress the
contribution of high-momentum modes at high temperatures.
Calculations are presented for 3D, 2D and 1D superconductors at finite
frequencies as well as in dc. We find that our data are well described by the model for appropriate
dimensionalities.
Dendrites flux instability in superconducting MgB2 film
T. H. Johansena, M. Baziljevicha, P. E. Goaa, A. V. Bobyla, F. Barkova, D. V. Shantseva, Y. M. Galperina, S. I. Leeb
a Department of Physics, University of Oslo, P. O. Box 1048 Blindern, N 0316 Oslo, Norway
b National Creative Research Initiative Center for Superconductivity, Department of Physics, Pohang University of Science and Technology, Pigohang 790-784, Republic of Korea
We show, using magneto-optical imaging that below 10 K the flux penetration in MgB2 films is dominated by large dendritic structures abruptly entering the film. The formation of dendrites correlates with the large noise observed in magnetization data, which reduces the apparent Jc by nearly 50%. The instability is of thermo-magnetic origin as supported by computer simulations of vortex dynamics which reproduce the dendritic flux patterns. Dendrites nucleate near the film edge where a local magnetic field exceeds a threshold value of » 12 mT at 4 K. The instability can be suppressed by thermal stabilization.
Determination of critical current density in flux creep state
H. Luo, X. Leng, Y. Liu, L. Qiu, S. Y. Ding
National Laboratory of Solid State Microstructures, department of physics, Nanjing University, Nanjing 210093, China
We propose a new method to determine critical current density (jc) for a superconductor with flux creep from the real part of AC susceptibility (ACS), which facilitates the determination of temperature dependent jc in a wide range. The relationship between jc of MgB2 and temperature at different criterions were determined by means of experimental real part of ACS curves throughout 5 to 38K at different DC fields Bd. Influence of criterion Ec on jc was studied by varying amplitude (Bac) and frequency (f) of AC field, arguing that it is not proper to obtain temperature dependence of jc by measuring only the peak temperature of imaginary part of ACS.
Evidence of Bragg glass phase in high-Tc vortex states with columnar defects
Yoshihiko Nonomuraa,b, Xiao Hub
aLyman Laboratory of Physics, Harvard University, Cambridge, MA 02138, USA
bComputational Materials Science Center, National Inst. for Materials Science, Tsukuba 305-0047, Japan
Although the Bose glass phase in high-Tc vortex states has been intensively studied, most attention has been paid to the region with dense and strong columnar defects so far. We numerically study the complementary region with sparse and weak columnar defects, and find a new phase characterized by a triangular Bragg peak and surrounded by the Bose glass phase. This new phase correnponds to the Bragg glass phase in high-Tc vortex states with point defects, and the phase transition to the Bose glass phase is of first order. In the case with point defects, the melting temperature Tm monotonously decreases as defects increase, while in the present case Tm increases as columnar defects increase up to a certain value. This qualitative difference can be explained by ``partial trap'' of flux lines to columnar defects.
Preparation, scaling behavior of activation energy, and anisotropy of Hg-1212 HTS thin films
Abouelwafa Salem, Gerhard Jakob, Michael Basset, Hermann Adrian
Institut für Physik, Johannes Gutenberg-Universität, 55099 Mainz, Germany
We have successfully prepared high-quality epitaxial (Hg0.9Re0.1) Ba2CaCu2O6+d HTS thin films without special handling during the preparation. The resistive transition have been investigated in magnetic fields up to 6 T parallel and perpendicular to the c-axis. We have determined the scaling behavior of the effective activation energy. Under variation of the angle q between the field direction and the c-axis of the film with high angular resolution ( Dq » 0.1 °) the anisotropic properties of the vortex state and the depinning field of epitaxially grown Hg-1212 films have been studied.The films exhibit sharp superconducting transitions at Tc @ 120 K with DT @ 2 K. Also the films exhibit critical field anisotropy with a factor 7.67 with respect to the c-axis.
Thermal melting and order-disorder transition in high-Tc superconductors
Ernst Helmut Brandta, Grigorii Mikitikb
aMax-Planck-Institut für Metallforschung, D-70506 Stuttgart, Germany
bB. Verkin Institute for Low Temp. Physics & Engineering, Ukr. Acad. of Sci., Kharkov 61103, Ukraine
Using Lindemann criteria and results of collective pinning theory, we investigate thermal melting of the vortex Bragg glass and the order-disorder transition from the Bragg glass to an amorphous vortex state in three-dimensional high-Tc superconductors. Accounting for both pinning-caused and thermal fluctuations of the vortex lattice, we calculate the boundaries separating the regions of single vortex, small bundle, and large bundle pinning in the temperature-magnetic field plane. This enables us to clarify how the melting line and the order-disorder line merge: For weak pinning these lines cross, with the melting line continuing above the crossing point, but for large quenched disorder in the vortex lattice it is quite possible that these two lines transform gradually into each other, forming one single transition line.
Magnetic Relaxation in Y-Ba-Cu-O Thin Films
R. Kondoa, T. Fukamib, K. Makisec, T. Tamegaid
aFaculty of Engineering, Oita University,700 Dannoharu Oita, Japan
bDepartment of Materials Science and Engineering, Himeji Institute of Technology,Himeji, Japan
cDepartment of Physics, Kyushu University, Fukuoka, Japan
dFaculty of Engineering, University of Tokyo, Tokyo, Japan
Distribution of a local field B(x) on the surface of YBCO thin films in the mixed state and its time dependence is measured using a micro Hall-probe array. Analizing these data based on the flux diffusion equation, the model-independent activation energy U is obtained. Since the local current density J is defind to reproduce the field profile B(x), U(B,J) can be plotted in a 3-dimensional space. This 3-dimensional mapping gives us information on U as a function of B and J.
Microwave-Induced Zero-Current Crossings in Bi2Sr2CaCu2O8+y Intrinsic Josephson Junctions
Takasada Shibauchia, Jun Hashimotoa, Ken-ichi Fujitaa, Takao Watanabeb, Azusa Matsudab, Minoru Suzukia
aDepartment of Electronic Science and Engineering, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
bNTT Basic Research Laboratories, 3-1 Morinosato Wakamiya, Atsugi-shi, Kanagawa 243-0198, Japan
Current-voltage characteristics in mesa-structured Bi2Sr2CaCu2O8+y intrinsic junctions under in-plane magnetic fields reveal zero-current crossings (ZCCs) when microwave is applied. From measurements with controlled number of junctions (N=5 ~ 14), we find that the number of ZCCs is just N in total of positive and negative bias sides; half of the 2N branches reported without microwave. Unlike Shapiro steps, the voltage step increases with microwave amplitude. Such features can be explained by considering the charging effect of superconducting layers and the pinning of triangular Josephson vortex lattice.
Interlayer Josephson Coupling for a Gas of Pancake Vortices
Ernst Helmut Brandta, Edouard Soninb
aMax-Planck-Institut für Metallforschung, D-70506 Stuttgart, Germany
bRacah Institute of Physics, Hebrew University of Jerusalem, Jerusalem 91904, Israel
The dependence of the Josephson interlayer coupling in layered superconductors on the magnetic field H is studied numerically in the limit of complete disorder of the positions of pancake vortices (pancake gas). The case is considered where the Josephson length essentially exceeds the intervortex distance (high magnetic field). We find that the spatial average ácosj([r\vec]) ñ is proportional to 1/H1/2, where j is the gauge-invariant phase difference between two layers. From the theory which interprets the magnetoabsorption resonances observed in layered superconductors as Josephson-plasma resonance, the experiment requires that ácosj([r\vec]) ñ should be proportional to 1/Ha with a between 0.7 and 1. The implication of our result for the interpretation of the magnetoabsorption resonances is discussed.
Order parameter and pseudogap in electron doped high-temperature superconductors
Lambert Alff, Bettina Welter, Yoshiharu Krockenberger, Achim Marx, Rudolf Gross
Walther-Meißner-Institut, Walther-Meißner-Str. 8, 85748 Garching, Germany
Recently, renewed interest in electron-doped high-temperature superconductors (HTS) has arisen from the question whether the phase diagram is symmetric with respect to electron/hole doping. The presently contradictory experimental status in favor of d- or s-wave symmetry of the superconducting order parameter for electron doped HTS is discussed. There are only few experimental reports on the pseudogap behavior of electron doped HTS. Here, we report on the observation of two different kinds of a normal state pseudogap in the electron doped HTS La2-xCexCuO4 and Pr2-xCexCuO4, one on the scale of the superconducting gap energy D, and one on the scale of the magnetic interaction energy J. Both gaps decrease resp. vanish with increased doping.
3D Fermi-liquid ground state in a quasi-1D cuprate
Matthew N. McBriena, Nigel E. Husseya, Luis Balicasb, Shigeru Horiic, Hiroshi Ikutad
aH. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol, BS8 1TL
bNational High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306, U.S.A
cDepartment of Applied Chemistry, University of Tokyo, Tokyo 113-8656, Japan
dC.I.R.S.E., Nagoya University, Chikusa-ku, Nagoya, 464-8603, Japan
Interchain magnetotransport measurements have been performed on the quasi-1D cuprate PrBa2Cu4O8 (Pr124). A T2 resistivity in all three crystallographic directions and a large transverse magnetoresistance are observed at low T. Crossovers to states of reduced dimensionality are seen in both directions perpendicular to the CuO chains as field and temperature are increased, from which we are able to estimate the transfer integrals in Pr124 as tb2:ta2:tc2 = 2500:2:1. The results provide compelling evidence for a Fermi liquid ground state in the quarter-filled CuO chains in Pr124.
Magnetic excitations investigated by ultrashort pulse excitation in high-Tc superconductors
L. H. Machtouba, T. Suemotoa, J. Shimoyamab, K. Kishiob
aInstitute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Chiba 277-8581, Japan
bGraduate School of Engineering, University of Tokyo,7-3-1, Hongo,Bunkyo-ku,Tokyo 113-8656, Japan
We have investigated the relaxation of elementary excitations in underdoped Bi2212 by ultrafast Raman spectroscopy. In x'y' symmetry, a broad feature has been observed around 2500 cm-1 in the Stokes side and assigned to B1g two - magnon peak. In investigating the power dependence of the broad feature, we observed a super-linear behavior in B1g symmetry, which is ascribed to the excess magnon population generated through the non-radiative relaxation across the CT gap. We observed a fast relaxation component around 0.4 ps and a long life time component greater than 20 ps for the B1g two-magnon peak.
Normal state resistivity of BSCCO single crystals: description with a two-barreers model
Enrico Silvaa, Renato Fastampab, Maurizio Giurab, Stefano Sartib
aDip. di Fisica ``E.Amaldi'' and Unita' INFM, Universita' Roma Tre, 00146, Roma, Italy
bDip. di Fisica and Unita' INFM,Universita' ``La Sapienza'', 00185, Roma, Italy
We present multiterminal measurements of the resistivity tensor of
BiSrCaCuO single crystal at various oxygen doping level d, ranging from under- (d=0.22)
to slightly over-doped
(d=0.27). Data are analized
in term of a model which assumes two simultaneously present mechanisms
for the out-of-plane conduction, markedly thermal activation and
incoherent tunneling. Within this model we are able to describe data
of normal state resistivity for all samples. Analysis of the parameters
involved in the model is also presented.
c-axis YBCO: mid-infrared ab-plane response as a function of doping and temperature determined by attenuated total reflection
D. George Walmsley, G.A. Farnan, G.F. Cairns, P. Dawson, S. O'Prey, M.P. McCurry
Department of Pure and Applied Physics, Queen's University, Belfast BT7 1NN, United Kingdom
The mid-infrared optical response of c-axis thin films of YBCO has been studied at a wavelength of 3.392microns using Otto-configuration attenuated total reflectance. The results are that the imaginary part of the dielectric function is temperature independent while the absolute value of the real part shows a moderate decrease with increasing temperature. A stronger dependence on doping is found and critical comparison is made with infrared normal reflectance data. In a generalised Drude analysis the scattering rate decreases with temperature and increases with decreased doping; this supports the notion of stronger coupling in the underdoped regime.
Ni Impurity Spin Fluctuations in YBa2(Cu1-xNix)4O8 and YBa2(Cu1-xNix)3O6.95 via Cu NQR
Yutaka Itoh, Takato Machi, Nobuaki Watanabe, Seiji Adachi, Naoki Koshizuka
Superconductivity Research Laboratory, International Superconductivity Technology Center, 1-10-13 Shinonome, Koto-ku, Tokyo 135-0062, Japan
We report a Cu NQR study of Ni impurity spin fluctuations in high Tc cuprate superconductors, YBa2(Cu1-xNix)4O8 and YBa2(Cu1-xNix)3O6.95, from measurement of Ni-induced Cu nuclear spin-lattice relaxation times. We found that the temperature dependence of the Ni spin correlation time is different from that of Kondo impurity in a conventional metal. e.g. Mn or Fe in Cu. Discussion will be made from viewpoints of an underscreening Kondo effect or an impurity in pseudo spin-gap state. This work was supported by New Energy and Industrial Technology Development Organization (NEDO).
Phase fluctuation in pseudogap state of underdoped BSCCO thin film
H. Murakamia, M. Tonouchib, T. Uchiyamac, I. Iguchic, Z. Wangd
aRCSP, Osaka Univ., Suita, Osaka 565-0871, Japan
bRCSP, Osaka Univ. and CREST-JST, Suita, Osaka 565-0871, Japan
cDept. of Phys., Tokyo Inst. of Tech. and CREST-JST, Tokyo 152-8551, Japan
dKARC, Communication Research Laboratory, Kobe 651-2492, Japan
In oder to investigate the fluctuating state above TC in underdoped BSCCO, a combine study by means of time-resolved pump-probe transmissivity measurement using femtosecond optiocal pulses and time-domain terahertz transmission spectroscopy have been carried out. Both experimental data showed the pseudogap opening below ~ 210K, and can well explain a localized domain picture in which localized coherent domains with a pseudogap fluctuate with a lifetime shorter than 1ps and have an important role for the realization of macroscopic superconductivity state.
Defects-Induced Thermal Instability in YBCO Films in Microwave Field
Volodymyr Pana, Constantin Tretiatchenkoa, Victor Flisa, Valentin Komashkoa, Ernst Pashitskiib, Alexander Ivanyutab, Gennadiy Melkovb, Henny Zandbergenc, Vassily Svetchnikovc
aInst. for Metal Physics, Vernadsky Blvd. 36, Kiev 03142, Ukraine
bT.Shevchenko National University, 03127 Kiev, Ukraine
cNational Centre for HREM, TU Delft, Rotterdamseweg 137, AL Delft 2628, The Netherlands
The heat instability induced by linear defects is assumed to enhance the remarkable difference between microwave properties of YBCO single crystals and thin films due to extended strain fields near out-of-plane edge dislocations. We have shown that a single dislocation can not have a strong effect on Rs, but dislocation arrays, which were observed experimentally, can induce the thermal instability, if edge dislocations in the arrays are spaced closer than the heat relaxation length. Ordered dislocation structures provide much higher local temperature perturbation than randomly distributed dislocations.
Specific Heat, Magnetic Susceptibility and Resistivity Of In-Doped Sn0.8Pb0.2Te
Mohammed Tahara, Dmitri Popova, Sergei Nemovb
aDepartment of Physics SUNY College at Brockport, Brockport, NY 14420
bState Technical University, St.-Petersburg, Russia
We report experimental results on In-doped Sn0.8Pb0.2Te solid solutions which are semiconductors with superconducting properties. We carried out simultaneous magnetic susceptibility and resistivity (four points) measurements from room temperature down to 1.5 K, as well as specific heat below 4.2 K, on poly-crystalline samples. All measurements indicate same critical temperature region, above which the specific heat exhibits a T3 behavior, with qD=80K consistent with that of the constituent elements. Application of a magnetic field ( ~ 1 kG) lowers the temperature at which the specific heat anomaly occurs. The results suggest that the transition occurs in the bulk and is enhanced by the In impurities, even at high concentrations. This is understood to support the resonance scattering mechanism.
First finding of reentrant superconductivity driven by hyperfine interaction
Thomas Herrmannsdörfer
Forschungszentrum Rossendorf, High Field Lab, P.O.Box 51 01 19, D-01314 Dresden, Germany
Compared to magnetically doped superconductors described by the theory of Abrikosov and Gorkov, electronic singlet ground state systems can have a much larger critical concentration of magnetic impurities, following the model of Keller and Fulde. The recent study of the superconducting Van Vleck paramagnet La1-xPrxTe revealed a critical Pr3+ concentration x close above 0.50. Surprisingly, in La0.50Pr0.50Te the superconducting state with Tc = 0.20 K appeares not to be stable down to zero temperature. Instead, a reentrant transition to the normal state likely caused by the hyperfine enhanced magnetic moments of the 141Pr nuclei occurs at about 0.02 K. Although these moments are not in a magnetically ordered ground state at T = 0.02 K, their contribution to Cooper pair breaking seems to be even stronger than of ferromagnetically ordered but non enhanced nuclear moments in type-I superconducting AuIn2.
Nonlinear Conductivity in the Slightly Hole-Doped Sr14-xCaxCu24O41 Ladder Compounds
H. Kitanoa, R. Inouea, A. Maedaa, N. Motoyamab, K. Kojimab, S. Uchidab
aDepartment of Basic Science, The University of Tokyo, Japan
bDepartment of Advanced Materials Science, The University of Tokyo, Japan
The slightly hole-doped spin-ladder compound Sr14-xCaxCu24O41 has attracted much attention because a formation of some density wave state was suggested by the observation of the collective mode resonance in the microwave region. We studied the nonlinear dc conductivity along both the ladder and the rung directions, as a function of electric field. For Sr14Cu24O41, we observed a definite nonlinearity even at a low electric field in the ladder direction, similar to observations in the sliding density wave state. Systematic studies with Ca substituted compounds suggest that the observed collective mode is easily destroyed with increasing amount of holes on the ladders, which may be characteristic of this new collective mode.
Single energy scale for magnetism and superconductivity
in the HTSC CaxLa1-xBa1.75-xLa0.25+xCu3Oy.
Amit Kanigel, Amit Keren, Yaakov Eckstein, Arkady Knizhnik
Physics Department, Technion-Israel Institute of Technology, Haifa 32000, Israel.
The pairing mechanism in HTSC is believed to be due to magnetic interactions. Therefore, the critical temperature of superconductivity Tc, and of magnetic freezing Tg, in the superconducting state, should be intimately related. We show that this is indeed the case in (CaxLa1-x)Ba(1.75-xLa0.25+x)Cu3Oy where we determine Tg for various values of x and y using mSR. Both Tc(x,y) and Tg(x,y) collapses into a universal curve by making the coordinate transformation Tc® Tc/Tcmax(x), and y ® K(x)Dy, where Dy is chemical doping measured from optimum, and K is a scaling parameter which relates chemical to charge doping. This indicates that a single energy scale controls both magnetic and superconducting transitions.
Fast time-resolved measurements of c-axis quasiparticle conductivity in intrinsic Josephson junctions of 2212-BSCCO
Jonathan C. Fenton, Guang Yang, Colin E. Gough
Superconductivity Research Group, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
We present time-resolved four-point VI-characteristic measurements on 2212-BSCCO mesa structures, using a wide-band cryogenic amplifier measurement system. The measurements demonstrate the importance of self-heating on 50 ns time scales. Such heating is likely to have been very significant in many previously published measurements, where the reported nonlinear VI characteristics have been used to derive superconducting energy gaps. Our technique also allows us to investigate the relative importance of simple heating and nonequilibrium effects.
Critical current of Na doped YBa2Cu3O7-y
X. Lenga, H. Luoa, S.Y. Dinga, J.W. Linb, Y. Liua
aNational Laboratory of Solid State Microstructures, department of physics, Nanjing University, Nanjing 210093, China
bCollege of Science, Hohai University, Nanjing 210098, China
Na-doped sample YBa1.9Na0.1Cu3Oy +40molYBa2Cu3Oy (YBCO) were fabricated by the Melt-Textured Growth (MTG) method to study the effect of Na ion on critical current density of YBCO. The field and temperature dependence of critical current density,effective pinning energy U(T,Hdc,J) and irreversibility line Hirr(T) were determined by measurements of ac susceptibility (acs) for the samples. It is found that the doping Na ion plays a negative rule on flux pinning effect in YBCO sample. We argue that the appearance of the second peak in jc(Hdc) relation and the enhancement of anisotropy in the Na doped sample reported elsewhere is a further support to our conclusion.
Stripes and superconductivity in the HTSC copper oxides
S. Titovaa, V. Balakireva, J. T. S. Irvineb, I. Bryntsec, P. P. Pal-Vald, L. N. P. Pal-Vald, D. Kochubeye
aInstitute of Metallurgy, UrD RAS, Russia;
bSt Andrews University, St Andrews, UK
cStockholm University, Stockholm, Sweden
dVerkin Institute for Low Temperature Physics, Kharkov, Ukraine
eInstitute of Catalysis, SibD RAS, Novosibirsk, Russia
Structural anomalies, at T2 ~ 240K and T1 ~ 160K, have been investigated for HTSC copper oxides by X-ray and neutron powder diffraction study. T2 anomaly is attributed to formation of the stripe structure. T1 anomaly is attributed to relaxation process during exchange of the electric charge between (Ba/Sr)0-layer and CuO2-planes in the materials. The measurements of the ultrasonic sound attenuation at T1 and T2 confirm this conclusion.
Field- and Temperature-Dependent Magnetic Hysteresis in GBCO Ceramics
Akihiko Nishida, Shigeto Teshima, Chihiro Taka
Department of Applied Physics, Fukuoka University, 8-19-1, Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan
Magnetic hysteresis measurements have been performed in GBCO ceramics, and effects of magnetic field, temperature and substitution were investigated. The hysteresis DM has been found to obey thermal activation type: DM µ exp[-T/T0]. The activation temperature T0 varied around 20 K, which seemed to depend on the magnetic field as H-1/n. Substitution tended to increase DM. These results have been examined in relation to flux pinning models along with the critical current densities.
Field Penetration and the Effect of Prehistory on the HTSC Demagnetization
Kh. R. Rostami
Institute of Radioengineering and Electronics RAS, 141190 Fryazino Moscow dist., Russia
For correct investigating of the characteristics of HTSC critical state with large demagnetization, high bound barrier and volume pinning the technique of selective study of demagnetization, volume and bound pinning is developed. It is based on the sample volume scanning by external field with sample thickness changing. In YBaCuO and BiSrCaCuO monocrystal and polycrystal HTSC using Hall transducer(moving it along sample radius and axis) we found out the distinction in effect of demagnetization, bound barrier and volume pinning on processes of field penetration and distributing and on magnetic flux trapping. It was found that the effective demagnetization coefficient N passes the maximum when trapped magnetic field (TMF) increases. It was shown that if sample thickness is decreased TMF effect on the N is enlarged. Empirical model describing of TMF effect on N is developed.
Millimeter Wave and Microwave Electrodynamic Spectroscopy of
YBa2(Cu1-xZnx)3Oy in the Meissner and Mixed State
K. Kinoshitaa, Y. Inouea, Y. Tsuchiyaa, T. Umetsua, H. Kitanoa, A. Maedaa, T. Hanagurib, T. Nishizakic, T. Satoc, K. Shibatac, N. Kobayashic
aDept. of Basic Science, The Univ. of Tokyo, Komaba, Meguro-ku, Tokyo, 153-8902, Japan
bDept. of Advanced Material Science, The Univ. of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan
cInstitute for Materials Research, Tohoku, Univ., Katahira, Aoba-ku, Sendai, 980-8577, Japan
Study of the vortex core in high-Tc cuprates is quite interesting because new phenomena may be expected. Previously, we measured the magnetic-field dependence of the microwave surface impedance ZS and revealed that the vortex core in pure YBa2Cu3Oy (YBCO) is moderately clean. In this paper, we investigate ZS for widely Zn-doped YBCO at various frequencies (0.5-100 GHz) and discuss the scattering mechanism of the quasiparticle in the vortex core by combining several different methods.
i-soliton, fractional flux and breakdown of time reversal symmetry in multi-band superconductor
Y. Tanakaabc, A. Iyoac, K. Tokiwabc, T. Watanabebc
aNational Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan
bDepartment of Applied Electronics, Tokyo University of Science, Noda, Chiba, Japan
cCREST, JST, Kawaguchi, Saitama, Japan
We pointed out a soliton can be present in a multi-band superconductor [Phys. Rev. Lett. 88 (2002) 017002]. We named it i-soliton. It connects two different coherent states having different phases. The i-soliton traps a fractional flux inside a superconducting loop. These properties may realize a fractional flux quantum (FFQ) device beyond a single flux quantum(SFQ) decive. The i-soliton would be found in the multi-layer cuprate superconductor having crystallographically nonequivalent CuO2 planes in one unit cell of which representative is CuxBa2Ca3Cu4Oy (Cu-1234).
Flux Quantization in Superconducting Micro Disks
Yoshiaki Hataa, Jun-ichi Suzukia, Itsuhiro Kakeyab, Kazuo Kadowakib, Akikazu Odawarac, Atsushi Nagatac, Satoshi Nakayamac, Kazuo Chinonec
aAdvanced Science Research Center, Japan Atomic Energy Research Institute, Ibaraki 319-1195, Japan
bInstitute of Materials Science, University of Tsukuba, Ibaraki 305-8573, Japan
cSeiko Instruments Inc., Matsudo, Chiba 270-2222, Japan
Recently a novel vortex state appearing in a superconducting micro disk has been investigated and it is found theoretically that magnetic flux distribution in such a disk is determined by the boundary conditions (shape and size). In order to study the phenomena experimentally, we have observed the magentic flux distribution of a micro YBCO disk with 50 mm in diameter by a scanning SQUID microscope. Single quantanized vortices are observed in the disk and the number of vortices increases on increasing the applied magnetic field. These results suggest that the multi-vortex state appears in the disk.
Vortex pinning enhancement in a magnetic-superconducting heterostructure
Antoni García-Santiagoa, Florencio Sánchezb, Manuel Varelab, Javier Tejadaa
aDept. Física Fonamental, Universitat de Barcelona, Diagonal 647, Plta. 3, 08028 Barcelona, Spain
bDept. Física Aplicada i Óptica, Universitat de Barcelona, Diagonal 647, Plta. 4, 08028 Barcelona, Spain
Pinning of vortices in a high-temperature superconductor by the magnetic domain structure of a highly anisotropic ferromagnet is investigated by means of magnetic measurements in nanoscale period superconductor/ferromagnet (SC/FM) heterostructures. Two different samples consisting of highly epitaxial films of YBa2Cu3O7 (SC) and BaFe12O19 (FM) are analyzed relative to a pure superconducting YBa2Cu3O7 film. The irreversibility line obtained in the magnetic-field vs reduced-temperature phase diagram for each heterostructure is found to shift upwards when compared to the line corresponding to the pure superconducting sample. This effect is interpreted as an evidence for the enhancement of pinning of vortices in the SC layer by the magnetic domain structure in the FM layer.
Effect of Thermal Neutron Irradiation on the Pinning Properties of TSMG Sm-123
Ugur Topala, Lev Dorosinskiia, Husnu Ozkanb, Hasbi Yavuzc
aTUBITAK-UME, National Metrology Institute, P.K. 54, 41470, Gebze-KOCAELI/Turkey
bDepartment of Physics, Middle East Technical University, 06280, Ankara/Turkey
cITU, Institute for Nuclear Energy, 80626, Maslak-Istanbul/Turkey
It was well studied by many groups that thermal neutron irradiation has an important role to improve the pinning properties and critical current densities of different types of superconductors. On the other hand, according to our knowledge, effect of thermal neutron irradiation on the pinning properties of Sm-123 samples was not studied before. In this report, we present the results of the effect of thermal neutron irradiation on the pinning properties and critical current densities of TSMG processed Sm-123 sample.
Phase diagram in highly anisotropic layered superconductors: crossing lattice melting transitions
Kazuo Kadowakia, Jovan Mirkovi\'cb, Sergey Savel'evc
aInstitute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan
bFaculty of Sciences, University of Montenegro, PO Box 211, Podgorica, Yugoslavia
cFrontier Research System, The Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-0198, Japan
Recently, the crossing vortex lattice state in highly layered superconductors such as Bi2Sr2CaCu2O8+d has been explored both theoretically and experimentally by intensive studies in magnetic fields parallel to the superconducting CuO2 plane. We discuss it to establish the vortex phase diagram with emphasis on the spatial symmetry breaking. A possibility of the novel phase transition in the vortex liquid state will be argued and demonstrated experimentally.
Nature of the Vortex-Glass Order in the Type-II Limit
Hikaru Kawamura
Faculty of Science, Osaka University, Toyonaka 560-0043, Japan
In spite of extensive studies for a decade, the question of nature of the thermodynamic phase diagram of random high-Tc superconductors in magnetic fields remains unsettled. Here, I wish to address the question of the nature of the possible vortex-glass order in random type-II superconductors with point disorder in the unscreened limit. Extensive Monte Carlo simulations are performed for a three-dimensional lattice XY model which is more realistic than the gauge-glass model in that a uniform field threads the system and that the quenched randomness appears in the pinning energy. The existence of a stable vortex-glass order is established in the absence of screening. Various critical estimates assoicated wuth a continuous vortex-glass transition are estimated and are compared with those of the gauge-glass model. Destructive effects of screening on the vortex-glass order is also discussed.
Antivortices in the mixed paramagnetic-orbital pair breaking regime
Ulf Klein
Institute for Theoretical Physics, University of Linz, Altenbergerstrasse 69, A-4040 Linz, Austria
We consider a thin superconducing layer with a magnetic field direction slightly tilted from the plane-parallel orientation. In such a situation, which generalizes the FFLO state, both paramagnetic and orbital pair-breaking effects must be taken into account. We minimize the quasiclassical free energy to obtain the stable order parameter stucture near the upper critical field, extending previous work [U.Klein et al. J. Low Temp. Phys. vol.118 91 (2000)] with regard to magnetic field contributions. We find two-dimensional periodic states, characterized by Landau quantum numbers n > 1 showing antivortices, e.g. a unit-cell with three order parameter zeros (two vortices and an antivortex) carrying totally a single flux quantum. The underlying physical mechanism is different from a recent prediction of antivortices in mesoscopic samples of triangular shape [L. F. Chibotaru et al. Phys. Rev. Lett. vol.86 1323 (2001)].
Vortex States just below the Vortex-Glass Phase Probed by Voltage Noise
M. Kamada, S. Okuma
Research Center for Low Temperature Physics, Tokyo Institute of Technology, Ohokayama, Meguro-ku, Tokyo 152-8551, Japan
We have measured the current-induced voltage noise in various fields H to study the vortex states of a thick amorphous MoxSi1-x film. We focus on the field region between the Meissner and vortex-glass (VG) phase, where vortex states have not yet been clarified. Noise is largest in the Meissner phase (H < Hc1). With increasing H, noise falls near or below the background level; it then starts to rise at H0, taking a broad peak in the VG phase, and falls again below the background level at a VG-to-liquid transition. We interpret H0 as a characteristic field where order of VG starts to form. In the temperature T range studied the field region (Hc1 < H < H0) just prior to VG order grows monotonically on cooling. This is in contrast to the theory for clean systems which predicts H0® Hc1 in the limit of T=0.
Crystallisation and melting of the vortex system with a periodic pinning
Igor Rudnev, Mikhail Zubin, Vladimir Kashurnikov
Moscow State Engineering Physics Institute (Technical University), Moscow, 115409 Russia
We present the results of the numerical simulations of the vortex system configurations in a quasi two-dimensional HTSC plate with different types of periodic pinninng. The simulation has been performed be means of a modified Monte-Carlo technique for the cases of square, triangular, rectangle, non-centered hexagonal, centered square and Kagome defects lattices. We have observed the systematic appearances of ordered vortex configurations (OVC) for every type of the defect lattices. Various structure and superstructure transitions of the vortex system have been observed at the increase and decrease of the applied magnetic field as well as at the changes of temperature. The appearances of OVC are accompanied by the peaks on the magnetization curves. But we have observed that some peaks are the results of shielding of the vortex entrance to the superconducting plate instead of the structure ordering transitions.
On the vortex mass in superconductors
Robert Vardanian, Armen Kteyan
Solid State Division, Institute of Radiophysics and Electronics, Armenian National Academy of Sciences, Ashtarak-2, ARMENIA e-mail: rvard@irphe.am
Vortex motion in a superconductor is considered at absolute zero temperature. Due to existence of collective modes of condensate oscillation, the vortex is shown to be a "relativistic-like" object, with a limiting velocity equal to the collective mode propagation velocity. Kinetic energy of this object is formed by the energy of superfluid condensate existing around the singularity line, and is due to creation of longitudinal electric fields. The rest mass of vortex obtained from the "relativistic" expression for condensate energy, is shown to exceed the mass of the vortex core.
Vortex fluctuations in the crossing lattice structure
S. Savel'eva, J. Mirkovi\'cb, F. Noria,c
aFrontier Research System, The Institute of Physical and Chemical Research (RIKEN), Wako-shi 351-0198, Japan
bInstitute of the Materials Science, University of Tsukuba, Japan
cDepartment of Physics, University of Michigan, Ann Arbor, MI 48109-1120, USA
For the first time, we have derived the elastic free energy of the crossing vortex lattice, considering displacements of both pancake vortex stacks and Josephson vortices. The developed elastic theory has been applied to both, the equilibrium vortex configuration and also the vortex fluctuations. By using the Lindemann criterion the Hc-Hab phase diagram of the vortex lattice melting transition has been calculated. The results are in reasonable agreement with recent experimental data.
Vortex state of a 2D Josephson junction array at irrational frustration
In-Cheol Baek, Young-Je Yun, Mu-Yong Choi
BK21 Physics Division and Institute of Basic Science, Sungkyunkwan University, Suwon 440-746, Korea
IV characteristics of a 2D Josephson junction array are studied experimentally at frustrations f=(3-Ö5)/2, 3/8, 8/21, 2/5, and 5/12, with a focus on the irrational frustration for which possible glassy natures without any intrinsic randomness have drawn particular interests for many years. For all five frustrations, the IV characteristics exhibit a scaling behavior, indicating a finite-temperature continuous superconducting transition. Scaling analyses show that the critical exponents for f=(3-Ö5)/2 are identical, within experimental errors, with those of f= 8/21 and 2/5. The similarity in critical behaviors for three adjacent frustrations suggests that the vortex state at the irrational frustration is neither a vortex glass nor a high-order commensurate domains separated by domain walls as expected by some, but possibly a quasi-ordered state with the f= 2/5 structure as the principal structure.
New Hall voltages in a planar pinning potential
Valerij A. Shklovskij
Institute for Theoretical Physics, National Science Center -
Kharkov Institute of Physics and Technology,
1 Akademicheskaya St., 61108,
Kharkov, Ukraine and Kharkov National University,
Physical Department, 4 Svobody Sq., 61077, Kharkov, Ukraine
Two-dimensional vortex dynamics in a planar pinning potential (PPP) created by uniaxial or bianisotropic pinning planes in the presence of thermal fluctuations is considered on the basis of a Fokker-Planck equation. Explicit expressions for two new nonlinear anisotropic Hall voltages (longitudinal and transverse with respect to the current direction) are derived and analyzed. The physical origin of these odd (with respect to magnetic field reversal) voltages is caused by the subtle interplay between even effect of vortex guiding along the PPP and the odd Hall effect. As new odd voltages arise due to the Hall effect their characteristic scale is proportional to the Hall constant.
Pinning Induced Instability of the Abrikosov Lattice Motion
Alexander Yu. Galkina, Boris A. Ivanovb
aInstitute of Metal Physics, 36 Vernadsky Blvd.,03142, Kiev, Ukraine
bInstitute of Magnetism, 36 "B" Vernadsky Blvd.,03142, Kiev, Ukraine
Abrikosov vortex lattice dynamics in a type-II superconductor with weak defects is studied taking into account gyroscopic (Hall) properties. It is demonstrated that the interaction of the moving lattice with weak defects results in the additional drag force with a nonmonotonic velocity dependence. It leads to a nonlinear I-V characteristic of the superconductor. The condition dV/dF < 0, F is the total drag force, is shown to be only the necessary condition of the instability of the lattice translational motion with the velocity V under the action of the external force, Fext. The inequality dV/dFext < 0 is more strict requirement than dV/dF < 0, but the instability with respect to some non-uniform perturbations appears even at the positive differential mobility dV/dFext > 0.
The Antiferromagnetic Spin Fluctuation in Sr2RuO4
Mariko Urataa, Takashi Nagatab, Hazuki Kawano-Furukawab,c, Hideki Yoshizawad, Hiroaki Kadowakie
aGraduate School of Humanities and Sciences, Ochanomizu Univ., Bunkyo-ku, Tokyo, 112-8610, Japan
bDepartment of Physics, Ochanomizu Univ., Bunkyo-ku, Tokyo, 112-8610, Japan
cPrecursory Research for Embryonic Science and Technology, Kawaguchi-shi, Saitama, 332-0012, Japan
dInstitute for Solid State Physics, University of Tokyo, Kashiwa-shi, Chiba, 277-8581, Japan
eDepartment of Physics, Tokyo Metropolitan University, Hachioji-shi, Tokyo, 192-0397, Japan
Although Sr2RuO4 is suggested to be a spin triplet superconductor, neutron scattering experiments have not detected any evidence of FM spin fluctuations so far. Recently, I.I.Mazin et al. predicted that a magnetic response may appear at ([(2p)/3],[(2p)/3],0), and it was confirmed by neutron scattering measurement by Y.side et al. In the present paper, we report the energy and temperature dependences of the AFM fluctuations in detail, and discuss the role of the spin fluctuations to the spin triplet superconductivity.
Field-Temperature Phase Diagram of the 3-K Phase of Sr2RuO4
Hiroshi Yaguchia, Masahiko Wadaa, Yoshiteru Maenob, Takehiko Ishiguroa
aDepartment of Physics, Kyoto University, Kyoto 606-8502, Japan
bInternational Innovation Center and Department of Physics, Kyoto University, Kyoto 606-8501, Japan
The eutectic system Sr2RuO4-Ru is referred to as the 3-K phase of the spin-triplet superconductor Sr2RuO4 (Tc = 1.5 K) since the eutectic system has an enhanced Tc of ~ 3 K. We have established the field-temperature phase diagram of the 3-K phase for two field directions (H//ab and H//c) using resistivity data. We have found an upturn curvature in the Hc2(T) curve for H//c and rather gradual temperature dependence of Hc2 close to Tc. We propose that these charecteric features are explained, at least in a qualitative fashion, on the basis of theory that assumes surface superconductivity with a two-component order parameter at the interface between Sr2RuO4 and Ru inclusions.
Gap-like behavior of the c-axis dynamic conductivity in Sr2Ru1-xTixO4
Klaus Puchera, Alois Loidla, Naoki Kikugawab, Yoshiteru Maenob
aExperimentalphysik V, EKM, Institut für Physik, Universität Augsburg, D-86135 Augsburg, Germany
bDepartment of Physics, Kyoto University, Kyoto 606-8502, Japan
We report measurements of the out-of-plane reflectivity of pure and Ti-doped Sr2RuO4 single crystals investigated by infrared spectroscopy. The electronic part of the dynamic conductivity can be well described by a two-component model. In the superconducting samples (x < 0.0015) a sharp plasma edge with a small spectral weight develops below 140 K. The scattering rate g shows a gap-like T-dependence, while higher doped samples (where superconductivity is suppressed) reveal an almost constant g in the investigated temperature range 5 K < T < 300 K. We compare the observed charge gap, which still exists far above Tc (e.g. Tc=1.43 K for x=0), with investigations of the spin dynamics in the ruthenates and discuss them in the context of the pseudogap behavior in the cuprates.
Shubnikov-de Haas Oscillations in the Superconducting Fluctuation Region of k-(BEDT-TTF)2Cu(NCS)2
Hiroshi Itoa, Yasuhisa Hasegawaa, Jun-ichi Yamadab, Gunzi Saitoc
aDepartment of Applied Physics, Nagoya University, Chikusa, Nagoya 464-8603, Japan
bDepartment of Material Science, Himeji Institute of Technology, Kamigori, Hyogo 678-1297, Japan
cDepartment of Chemistry, Kyoto University, Sakyo, Kyoto 606-8502, Japan
Shubnikov-de Haas oscillations in an organic superconductor k-(BEDT-TTF)2Cu(NCS)2 are studied near the upper critical field of Hc2 @ 5 T. Below 7.3 T, the oscillations suffer additional damping which is ascribable to the superconducting fluctuation effects. The damping is not observed in a pressure of 2 kbar. In this pressure, the superconductivity is suppressed and the Hc2 becomes as low as 1 T. This clearly demonstrates that the additional damping observed at ambient pressure is relevant to the superconductivity.
Electronic Heat Capacity of k-(BEDT-TTF) 4Hg3-dX (X=Br, Cl)
A. Naitoa, Y. Nakazawaa, H. Taniguchib, K. Kanodac, K. Saitoa, M. Soraia
aResearch Center for Molecular Thermodynamics, Osaka Univ., Machikaneyama, Osaka 560-0043, JAPAN
bDepartment of Physics, Saitama Univ., Saitama 338-8570, JAPAN
cDepartment of Appl. Physics, the Univ. of Tokyo, Hongo, Tokyo 171-8588, JAPAN
Low-temperature heat capacity measurements for single crystals of k-(BEDT-TTF)4Hg3-dX8 (X=Br, Cl) which are known as a strongly correlated organic system are performed. We observed interesting behavior in lattice heat capacity associated with the chain structure of mercury atoms in the anion layers. The electronic heat capacity coefficient, g was found to be 3-4 times larger than those of well known 10 K class superconductors k-(BEDT-TTF)2Y. (Y=Cu(NCS)2, Cu[N(CN)2]Br). Large antiferromagnetic spin fluctuations which observed at low temperatures is considered as a reason for this large electron mass enhancement.
Pressure effects in the Field-Induced Superconducting State of l-(BETS)2FeCl4
L. Balicasa, J. S. Brooksa, S. Ujib, M. Tokumotoc, H. Tanakad, H. Kobayashid
aNational High Magnetic Field Laboratory, Florida State University, Tallahassee-FL 32310, USA.
bNational Research Institute for Metals, Tsukuba, Ibaraki 305-0003, Japan
cNanotechnology Research Institute, Tsukuba, Ibaraki 305-8568, Japan
dInstitute for Molecular Science, Okazaki, Aichi 444-8585, Japan
We investigate, by electrical transport, the field-induced superconducting state (FISC) in the organic conductor l-(BETS)2FeCl4 at 1 Bar and 1.4 kBar of hydrostatic pressure. At 1 Bar and below 4 K, antiferromagnetic-insulator (AFI), metallic, and eventually superconducting (FISC) ground states are observed with increasing in-plane magnetic field. In the other hand, pressure stabilizes superconductivity (SC) which is followed by a SC to AFI transition upon cooling. Pressure also decreases the compensation field and considerably broadens the field dependence of the FISC state.
Atomic size Josephson Junctions in field effect doped organic crystals
Samuel Wehrli, Christian Helm, Manfred Sigrist, Maurice T. Rice, G. Blatter, B. Batlogg
ETH Hönggerberg, Institute of Theoretical Physics, Zürich, Switzerland
The recent observation of a Fraunhofer pattern in the magnetic field dependence of the critical current Ic (B) by H. Schön, B. Batlogg et al. is a crucial evidence for superconductivity in the surface of field effect doped organic crystals. We propose a microscopic origin for the Josephson junction due to steps in the interface layer, where the external electric field is shielded by a charge dipole and the local depletion of the charge density forms an atomic size weak link. In the light of this experiment, we show that for junctions between type II superconducting films the length l determining the period of Ic(B) is significantly smaller than the penetration depth lL in the Meissner state due to flux penetration. In equilibrium the intervortex distance a(B) enters, while in critical flux states induced by surface or bulk pinning l is independent of B. Further, the local magnetic field at the junction is affected by the geometry.
Penetration depth measurements of the borocarbides LuNi2B2C and YNi2B2C
P. Rodièrea, J. Fletchera, A. Carringtona, R Prozorovb, R.W. Giannettab, S.L. Bud'koc, P.C. Canfieldc
aUniversity of Bristol, England.
bUniversity of Illinois at Urbana-Champaign, USA
cAmes Laboratory, Iowa States University, USA
Recent work on the non-magnetic borocarbide superconductors has shown the presence of low energy excitations in the vortex state, suggesting a possible anisotropic superconducting gap. We present measurements of the temperature dependence of the London penetration depth in the Meissner state of single crystals of LuNi2B2C and YNi2B2C down to 1.3K using a high resolution radio frequency technique. Our results on samples with clean, prepared surfaces are in excellent agreement with a simple, isotropic, BCS weak-coupling, s-wave superconducting gap.
Measurement of an Anisotropic Superconducting Gap Parameter Resolved to a Single Fermi Surface Sheet: The de Haas-van Alphen Effect in YNi2B2C
Daniel Bintley, Phil J. Meeson
H.H.Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL U.K.
We have used the de Haas-van Alphen technique in the normal and superconducting states of YNi2B2C to measure the (angularly resolved) orbitally averaged superconducting gap parameter. The results show that the gap parameter is fourfold symmetric and highly anisotropic. This is the first time that superconducting gap anisotropies have been explored and resolved to individual sheets of the Fermi surface. Our results are not inconsistent with the suggestions of `s+g' symmetry in this material by Maki, Thalmeier and Won. In addition we have observed for the first time an excess damping due to screening by vortex motion in the peak effect region.
Vortex Lattice Evolution and Low-Field Reorientation Transition in LuNi2B2C
L. Ya. Vinnikova, T. L. Barkova, P. C. Canfieldb, S. L. Bud'kob, J. E. Ostensonb, F. D. Laabsb, V. G. Koganb
aInstitute of Solid State Physics, RAS, 142432 Chernogolovka, Moscow district, Russia
bAmes Laboratory, DOE and Department of Physics, Iowa State University, Ames, Iowa 50011
We present the results on VL evolution in as grown and annealed LuNi2B2C single crystals by the decoration technique at a broad region of magnetic fields. We have observed the reorientation transition at magnetic field H1 ~ 250 Gs in the annealed samples. The transition to square lattice in the annealed samples occurs at the lower value of magnetic field H2 ~ 600 Gs. We have also found a strong anisotropy in the long-range VL orientational order in the vicinity of the transition field H2. The observed VL behavior is discussed in frames of nonlocal London theory.
Growth and study of Ba1-xKxBiO3-y single crystals: crystal structure and cation composition correlation
A. G. Soldatova, S. N. Bariloa, S. V. Shiryaeva, S. N. Ustinovicha, L. D. Iskhakovab, V. P. Sokolc
aInstitute of Physics of Solids and Semiconductors, Acad. of Sci., Minsk 220072, Belarus
bFiber Optics Center at Institute of General Physics, Russian Acad. of Sci., Moscow 117942, Russia
cInstitute of Physical and Organic Chemistry, Acad. of Sci., Minsk 220072, Belarus
Newly done results on the BKBO (0.06 £ x £ 0.67) single crystals growth of precise homogeneity composition, full cation analysis data, and structural aspects are reported. Structural studies have established a new low temperature phase for the superconducting BKBO compounds. The XRD data on BKBO crystals (0.39 £ x £ 0.55) demonstrate that superstructure reflections for the crystals exist already at room temperature, which stay constant down to 18K. The dependence of the pseudo-cubic lattice constant on both average bismuth valence and potassium content has been defined as an approximate function.
Field Effect Doping to SrTiO3
Isao H Inouea, K Miyadaia, K Miyadaib, H Satoa, T Yamadaa, H Takagia, H Takagic, H Akoha, Y Tokuraa, Y Tokurad
aCorrelated Electron Research Center (CERC), AIST Tsukuba Central 4, Tsukuba 305-8562, Japan
bKanagawa Institute of Technology, Japan
cDepartment of Advanced Materials Science, University of Tokyo, Japan
dDepartment of Applied Physics, University of Tokyo, Japan
Temperature and electric-field dependence of the current-voltage characteristics and charge-carrier mobility of an interface between SrTiO3 and Al2O3 are reported. The measurements were performed on field-effect transistor (FET) structures, which were prepared on top of a SrTiO3 single crystal by the deposition of aluminium source and drain contacts, a sputtered Al2O3 gate dielectric, and a gold gate electrode.