Correlator Projection Theory of Single-Particle Dynamics in High-Tc Cuprates
Shigeki Onodaa, Masatoshi Imadab
aTokura Spin Superstructure Project, ERATO, Japan Science and Technology Corporation, Department of Applied Physics, University of Tokyo, Hongo 7-3-1, Tokyo 113-8656, Japan
bInstitute for Solid State Physics, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba 277-8581, Japan
Single-particle dynamics around the Mott insulating phase in the 2D Hubbard model is studied with a new nonperturbative theory of correlator projection. Upon decreasing holes towards the Mott insulator from the metal, a phase separation occurs near half filling at finite temperatures, in agreement with experimental results in high-Tc cuprates. Then, strong correlation effects beyond the band picture emerge; at the first-order transition characterized by the phase separation, a large hole-like Fermi surface disappears with a downward jump of the lower Hubbard dispersion around (p,p) across the chemical potential.
Formation of Extended Coherent Hole States in Cuprates up to T = 1200 K
Alexander V. Mitin
P.L.Kapitza Institute for Physical Problems, RAS,
Kosygin Str. 2, Moscow 117334, Russian Federation;
International Laboratory of High Magnetic Fields and Low
Temperatures, 95 Gajowicka Str., 53-421 Wroc aw, Poland
The proposed microscopic model purports to explain a genesis of pseudogap manifestations in underdoped cuprates. It implies the formation of quasi-one-dimensional superconducting structure fragments with a broad distribution of local critical temperatures Tci £ 1200 K due to the condensation and subsequent pairing of oxygen holes under a spatially modulated Coulomb extra-potential. An analysis is based on a concept of ``polymerization'' of pseudo-atoms with quantized hole ``orbitals'' into spin-charge stripes by means of strong electron correlations and self-organization effects. The doping dependences of calculated electronic spectra composed mainly of extended coherent states are consistent with experimental data.
Effect of the hole-phonon interaction on the single-hole spectral function in the t-J model
A.S. Mishchenkoa, N. Nagaosaa, N.V. Prokof`evb, B.V. Svistunovc
aCorrelated Electron Research Center, AIST, Tsukuba Central 4, Tsukuba 305-8562 Japan
bDeapartment of Physics, University of Massachusetts, Amherst, Massachusetts 01003
cRussian Research Centre ``Kurchatov Institute'', 123182 Moscow, Russia
Spectral functions of the coupled to optic phonons single hole in the t-J model are calculated using exact Diagrammatic Monte Carlo technique and subsequent analytic continuation to the real frequencies. It is shown that coupling to magnons increases the influence of the hole-phonon interaction on the hole properties: for the same parameters of the hole-phonon coupling the free hole properties are weekly renormalized while the spectral function of the hole in t-J model is drastically changed. The properties of ARPES spectra are calculated and discussed.
Cuprate of Two-Gap Superconductivity on a Vibronicly Renormalized Spectrum Formed by doping
N. Kristoffela, P. Rubina, T. Ördb
aInstitute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia
bInstitute of Theoretical Physics, University of Tartu, Tähe 4, 51010 Tartu, Estonia
A two-band model of cuprate superconductivity with interband transfer of intraband pairs between vibronicly coupled electronic components is developed. A midgap band created by doped holes evolves above the valence band. Bands overlap reached by progressive doping corresponds to the end of underdoping. At this concentration the vibronic effect is maximal and also the behaviour of the electron liquid changes. The two superconductivity gaps are vibronicly renormalized. Two normal phase pseudogaps are present at underdoping (electronic and vibronic) and there is one of vibronic nature at higher dopings. Various cuprate properties are discussed in the framework of the model.
Pseudogap phenomenon and density waves in Cuprates
Angsula Ghosh
Departamento de Física Geral, Instituto de Física, Universidade de São Paulo, Caixa Postal 66318 05315-970, S.P Brazil .
Recently, there has been a great interest in the study of the pseudogap phase in high temperature cuprate superconductors. The angle resolved photo emission spectrum gives evidence of the fact that the pseudogap also exhibits a d-wave symmetry. Various theoretical scenarios have been proposed to understand the above phenomenon. We consider the charge-density waves as a possible explanation for the pseudogap.The phase diagrams for the order parameter and temperature with doping and also The temperature dependence of the order parameter and specific heat is also demonstrated.
Multiple-superconducting Amplitudes in Multi-layer High-Tc Cuprates
Michiyasu Mori, Takami Tohyama, Sadamichi Maekawa
Institute for Materials Research, Tohoku University Sendai 980-8577, Japan
We study the superconducting (SC) amplitudes in multi-layer cuprates by calculating the current in a break junction with bias voltage. The tunneling Hamiltonian is adopted between the two superconductors which have the multiple-SC amplitudes and the inter-layer hopping among the CuO2 layers. In the lowest order of the tunneling matrix element, the conductance as a function of the voltage has several peaks, which depend on the SC amplitudes, the inter-layer hopping and the number of CuO2 layers. By studying these dependencies, we find the way to estimate the SC amplitudes in the multi-layer cuprates. By including higher order terms of the tunneling matrix element, we obtain the sub-harmonic gap (SHG) structure in the multi-layer compounds. We discuss the peak positions and their intensities in the SHG structure in connection with the recent experimental studies.
Electron-Phonon Coupling in High Temperature Superconducting Cuprates
Takeshi Egami, Przemek Piekarz
LRSM, University of Pennsylvania, Philadelphia, PA 19104, USA
Phonons are widely regarded as irrelevant to high-temperature superconductivity. However, recent experimental results indicate that such a belief may be ill-founded. We argue that the electron-phonon coupling in the cuprates is fundamentally different from that in simple metals because of the phonon-induced Cu-O charge transfer. With the Hubbard model we show that the strong softening around the (p, 0) zone-boundary and inversion of the LO/TO dispersions of the Cu-O bond-stretching phonons we recently observed by neutron inelastic scattering can be explained in terms of the sign-reversed Born effective charge due to the intersite charge transfer and a negative dynamic dielectric function. This mechanism allows strong electron-phonon coupling without structural instability, and can contribute significantly to the d-wave superconductivity of the cuprates.
Electronic contribution to thermal conductivity of CDW superconductors
M. Ausloosa, A. M. Gabovichb, M. Pekalac, A.I. Voitenkob
aSUPRAS, Institut de Physique B5, Universit\' e de Liege, Sart Tilman, B-4000 Liege, Belgium
bCrystal Physics Department, Institute of Physics, prospekt Nauki 46, 03028 Kiev, Ukraine
cDepartment of Chemistry, University of Warsaw, Al. Zwirki i Wigury 101, PL-02-089 Warsaw, Poland
Electronic contribution kel to thermal conductivity k of superconductors partially-gapped by charge density wave (CDW) was calculated. A dielectric gap | S| is assumed to exist above and below a superconducting critical temperature Tc. It is shown that the coherence factor for kel in the pure CDW state (above Tc) is constructive, in contrast to the BCS superconductor. In the mixed state (below Tc) there is an interplay between two order parameters. Thus, the dependence kel(T) may become nonmonotonic with a maximum below Tc. This is exactly the picture observed for cuprates if one identifies the nonsuperconducting gap (pseudogap) with the CDW one.
Superconductivity with Nonzero Chern Numbers
Shuichi Murakami, Naoto Nagaosa
Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
In strongly correlated electron systems it often happens that electronic bands acquire nonzero Chern numbers, either by spin chirality or by spin-orbit coupling. It implies that the phase of the wavefunctions cannot be defined uniquely all over the Brillouin zone, and one should be careful in defining order parameters. In this presentation, we will develop a theory of condensation happening in bands with nonzero Chern numbers. We take the Haldane model (Phys.Rev.Lett.61(1988)2015.) on the honeycomb lattice as an example, and explain what will happen when excitonic order or superconductivity occurs in a band with a nonzero Chern number. It can also be related to quantization of Hall conductivity or spin Hall conductivity.
Bi- and Tri-layer splittings in a new formulation for the t-J model of cuprates
Stewart Barnesa,b, Sadamichi Maekawab
aPhysics Department, University of Miami, Coral Gables, FL33124 USA
bInstitute for Materials Research, Tohoku University, Sendai 980-8577, Japan
A new Jordan-Wigner transformation approach for multilayer two dimensional t-J-models has been developed. The effective spinon hoping ~ [(J/2) - xt] and implies a quantum critical point (QCP) for xc ~ J/2t, but which is suppressed by superconductivity. In this formulation the superconductive peaks are Kondo resonances while the quasi-particle bands reflect charge fluctuations effects relative to Kondo ground state. Simulations of the ARPES data for strongly overdoped Bi2212 agree well with experiment and explain a mysterious slitting of the superconductive coherence peaks. Using the same parameters as for the bi-layers, simulations of the tri-layer ARPES agree well with experiment for the normal state. Predictions are made for the splitting of the superconductive peaks in strong over doped tri-layer samples.
AC magnetic susceptibility measurements on UGe2
Hiroyuki Nakane, Gaku Motoyama, Setsushi Nakamura, Takashi Nishioka, Noriaki K. Sato
Department of Physics, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan.
We have measured the ac magnetic susceptibility of the pressure induced ferromagnetic superconductor UGe2 at pressures up to ~ 18 kbar using a dilution refrigerator. The superconductivity (SC) appears between ~ 10 kbar and ~ 16 kbar, as reported in the literature. However, we have found that the magnitude of the SC diamagnetic susceptibility strongly depends on the pressure ; it exhibits a maximum at Px ~ 13 kbar at which the SC transition temperature is maximal. On the other hand, the Px corresponds to a pressure at which an unknown anomaly observed in the electrical resistivity and the magnetization vanishes. From these results, we will argue that the SC state in UGe2 is inhomogeneous and the unknown anomaly is possibly related to the appearance of the SC.
Thermal expansion measurement under high pressure of UGe2
Yasuhisa Ushida, Takashi Nishioka, Gaku Motoyama, Setsushi Nakamura, Noriaki. K Sato
Department of Physics, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan
The linear thermal expansion coefficients ai(T) (i=a, b, c) of single crystalline UGe2 samples have been measured in the temperature range 0.34 K < T < 60 K and at pressures up to ~ 1.8 GPa. The coefficients ai(T) at ambient pressure show a sharp transition at TCurie=52 K and a broad hump at around Tx @ 30 K. At around P @ 0.9 GPa, above which the superconductivity appears, we found that the anomaly at Tx becomes sharp; it looks like a phase transition discontinuity. The temperature dependence of volume at this pressure also shows a distinct change at Tx as well as at TCurie. We will report these experimental results together with those of the ac magnetic susceptibility that was measured at the same time.
Electrical resistivity of CeTIn5 (T=Rh,Ir) under high pressure
Takaki Muramatsua, Tatsuo C Kobayashia, Katsuya Shimizub, Kichi Amayab, Dai Aokic, Hiroaki Shishidoc, Yoshinori Hagad, Yoshichika Onukic
aKYOKUGEN, Osaka Univ., Toyonaka, Osaka 560-8531, Japan
bGraduated School of Engeneering Science, Osaka Univ., Toyonaka, Osaka 560-8531, Japan
cGraduated School of Science, Osaka Univ., Toyonaka, Osaka 560-8531, Japan
dAdvanced Science Research Center, Japan Atomic Enegy Research Institute, Tokai, Ibaraki 319-1195, Japan
We have researched the superconducting natures of CeTIn5 (T=Rh,Ir) under high pressure in terms of electrical resistivitiy and superconducting phase in pressure-temperature phase diagram were determined for both samples and those exist in a wide pressure range (1.5 GPa < P < 6.5 GPa :CeRhIn5, 0 GPa < P < 5.2 GPa :CeIrIn5).
Perturbation Theory of the Superconductivities in Heavy Fermion Systems
Yunori Nisikawa, Hiroaki Ikeda, Kosaku Yamada
Department of Physics, Kyoto University, Kyoto 606-8502
We reformulate the Éliashberg's equation for the superconducting transition within the quasi-particle description, which takes account of the heavy electron mass. We discuss the superconductivity of heavy fermion systems by using such a renormalized formula. Both normal and anomalous self-energies are calculated up to third order with respect to the repulsive interaction. Superconducting transition temperatures (Tc) are obtained by solving the Éliashberg's equation. We point out that it is reasonable to treat the electron correlation by perturbation theory based on Fermi liquid theory, in calculating Tc of typical heavy fermion superconductors.
Effect of Magnetic Ion Ni-doping for Cu in the CuO2 Plane on Electronic Structure and Superconductivity on Y123 Cuprate
Cao Shixuna, Zhang Jincanga, Deng Dongmeib, Li Xiguib
aDepartment of Physics, Shanghai University, Shangda Road 99, Shanghai 200436, P. R. China
bDepartment of Physics, Henan Normal University, Xinxiang 453002, P. R. China
As an effective probe of local electron density, positron experiment was used for YBa2Cu3-xNixO7-y system with x=0.0 to 0.4. The results indicate that at small doping region lifetime t1 decreases monotonically. For larger doping concentrations, t1 has a small increase, follows an flat section. Considering the change of Tc, the results may prove that the localization of carriers in CuO2 planes may have enormous influence on superconductivity. The small increase of t1 may prove that with the increase of Ni concentration, more electrons are localized around the dopant site, resulting in the decrease of hole density. In large doping concentrations, there exits the weakening of electron localization.
High-field magnetotransport in strained La2-xSrxCuO4 films
Tsuyoshi Sekitania, Michio Naitob, Hisashi Satob, Noboru Miuraa
aISSP, University of Tokyo, Kashiwanoha, Kashiwa-shi, Chiba, 277-8581, Japan
bNTT Basic Research Laboratories, Morinosato-Wakamiya, Atsugi-shi, Kanagawa, 243-0198, Japan
We present the low-temperature normal-state transport properties of strained La2-xSrxCuO4 films achieved by suppressing superconductivity with high magnetic fields up to the megagauss range. Systematic measurements were performed on six MBE grown films with under-, optimum-, and over-doping levels (x = 0.11, 0.15, and 0.19) and also with either compressive or tensile epitaxial strain produced by two different substrates (LaSrAlO4 and SrTiO3). We observed that the low-temperature upturn in resistivity as seen in bulk single crystals of under- or optimum-doped La2-xSrxCuO4 is significantly suppressed by in-plane compressive strain. By interpreting the upturn as due to the Kondo effect by Cu2+ spins, our results indicate that the Kondo interaction is regulated by epitaxial strain.
Lanthanoid Substitution in Sr2YCu2FeO6+d System
Takashi Mochikua, Yu Nakanob, Yasumasa Miharab, Yoshiaki Hatac, Jun-ichi Suzukic, Kazuo Kadowakib, Kazuto Hirataa
aNational Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
bUniversity of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan
cJapan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan
The Sr2YCu2FeO6+d compound exhibits superconductivity around 50 K. We have obtained the single phase of Sr2LnCu2FeO6+d (Ln=Nd, Er) which substituted Ln for Y in Sr2YCu2FeO6+d. While Sr2ErCu2FeO6+d exhibits superconductivity, Sr2NdCu2FeO6+d does not exhibit superconductivity. We have analyzed the crystal structure of Sr2LnCu2FeO6+d to be compared with that of Sr2YCu2FeO6+d using X-ray and neutron powder diffraction. These studies indicate that it is easy to substitute Cu for Fe and Sr for Ln in Sr2NdCu2FeO6+d than other componds.
Intra- and inter-grain critical current density in (Cu,C):1234 superconductors
A. Crisana, P. Badicaa, M. Hiraib, H. Kitoc, A. Iyoc, Y. Tanakac
aNeRI, AIST, Tsukuba, 305-8568 Japan and Nat. Inst. Mat. Phys., POB MG-7, Bucharest, Romania
bNeRI, AIST, Tsukuba, 305-8568 Japan and Science Univ. of Tokyo, 2641 Yamazaki, Noda, Chiba, Japan
cNeRI, AIST, Tsukuba, 305-8568 Japan and CREST, JST, Kawaguchi, Saitama, 332-0012 Japan
Using DC magnetization and AC susceptibility we estimated the inter- and intra-grain critical current density Jc of high-pressure synthesized (Cu,C):1234 high-Tc superconductors, for T between 20 and 105 K and DC fields up to 14 T. Inter-grain Jc was estimated from the difference in magnetization between the as-grown sample and the finely ground one. Both Jc's resulting from magnetization studies are compared with the ones deduced from susceptibility measurements. Finally, we investigated the intra-grain Jc of neutron and heavy-ion irradiated (Cu,C):1234, which showed an impressive increase, one order of magnitude for neutron irradiation and two orders of magnitude for heavy-ion irradiation.
Magnetic Flux Trapping in Granular HTSC near Superconducting Transition
A. A Sukhanov, V. I. Omelchenko, G. A. Orlova
Institute of Radioengineering and Electronics RAS,141190 Fryazino Moscow dist., Russia
The temperature and field dependences of the trapped magnetic fields and of the frozen magnetoresistance of (Pb)Bi-Sr-Cu-0 ceramics and Bi-based magnetron films are investigated. It is found that in the resistive transition region of granular Bi-HTSC the trapped magnetic fields became highly inhomogeneous and alternating in sign on scale of less than 50 mm. Unlike ceramic the films have critical temperature of trapping lower than the upper temperature of magnetoresistance disappearance. The experimental results are explained by a model in which the magnetic flux is trapped in superconducting loops embedded in Josephson weak links medium. The loops nature which is essentially different for films and ceramics is discussed. Observed temperature and field dependences of trapped field are in good agreement with those calculated for normal law of the loops distribution on critical fields.
Non-ohmic resistance due to nanostructural inhomogeneity in RPrBaCuO
Katsukuni Yoshidaa, Katsuya Otaa, Takamasa Hayasakaa, Takuya Haradaa, Sizumasa Uedab
aDepartment of Fundamental Energy Science, Kyoto University, Uji, Kyoto, 611-0011 Japan
bInstitute of Advanced Energy, Kyoto University, Uji, Kyoto, 611-0011 Japan
Non-ohmic resistance observed for complex cuprates R1-xPrxBa2Cu3Oy (RPBCO, R=Gd, Nd, Y) with Pr-concentration x ranging from 0 to 0.8 has been investigated in reference to the nanostructural inhomogeneity. At Pr-concentration above the percolation threshold xpc, where the overall superconductivity vanishes, the resistance has been found to considerably depend on the supplied current I. The dependence is classified into three types according to the range of x; firstly the resistance at around xpc increases with increasing I, subsequently it becomes independent of I, and eventually the resistance at x much higher than xpc changes into a decreasing function of I. A model has been given of this non-ohmic resistance in terms of a breaking process of the percolation network and a local rise in temperature due to Joule heat.
EFFECT OF Ti SUBSTITUTIONS ON SUPERCONDUCTIVITY OF TlSr1212 CERAMICS
A. Kamal Yahyaa, Faizah M. Salleha, Norazila Ibrahima, Roslan Abd-Shukorb
a Faculty of Applied Sciences,Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia
b School of Applied Physics, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia
Effect of Ti substitutions on superconductivity of (Tl0.8Pb0.2)(Sr2-xTix)(Ca0.9Y0.1)Cu2O7 (x = 0-0.7) and Tl(Sr2-xTix)CaCu2O7 (x = 0-0.6) ceramics have been investigated. (Tl0.8Pb0.2)(Sr2-xTix)(Ca0.9Y0.1)Cu2O7 (x=0) was observed to superconduct with Tc onset of 90 K and Tc zero of 21 K. Substitution of Ti with x=0.1-0.5 observed an increase in Tc zero to 56-62 K with Tc onset remain the same at around 90 K. Tl(Sr2-xTix)CaCu2O7 (x = 0 to 0.2) was not superconducting above 20 K but for x = 0.3 superconductivity was observed with Tc onset of 66 K and Tc zero of 34 K.
Synthesis and Properties of TiSr2(RE1-xCex)2Cu2Oz
Toru Ishigaki, Yutaka Ogasawara
Department of Materials Science and Engineering, Muroran Institute for Technology, Muroran 050-8585, Japan
The result of the synthesis for TiSr2(RE1-xCex)2Cu2Oz (Ti-1222) (RE=Gd,Eu,Sm) are reported. The single phase of Ti-1222 were not synthesized under ambient and high pressure (3.5 GPa), but two phased samples with Ti-1222 and TiSr2RECu2Oz (Ti-1212) were obtained. The crystal structures were analyzed using X-ray diffraction for both Ti-1222 and Ti-1212 phases. Resistivity measurements for the all samples showed insulating behaviors.
Phonon Structure in the Tunneling Conductance of Bi2Sr2CaCu2O8
Daisuke Shimadaa, Makoto Saitohb, Nobuo Tsudab
aDepartment of Physics, Shizuoka University, 836 Ohya, Shizuoka 422-8529, Japan
bDepartment of Applied Physics, Science University of Tokyo, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
The spectral function of the electron-phonon interaction a2F has been determined for Bi2Sr2CaCu2O8 (Bi2212)-GaAs junction. However, it is only one clear example of a2F, and it has been desired to confirm its reproducibility.
In this study the tunneling conductance of a mechanical Bi2212-Au junction in which a barrier is formed in Bi2212 itself. The gap edge peak is as narrow as for the GaAs junction but the phonon structures are more faint. The differences between the Au and GaAs junctions are discussed by taking into account an inhomogeneity in the gap and the scattering effect at the contact.
Temperature and Field Dependence of the Gap Structure in Bi2Sr2CaCu2O8+d Studied by Short-Pulse Interlayer Tunneling Spectroscopy
Kenkichi Anagawaa, Takashi Hamatania, Takao Watanabeb, Takasada Shibauchia, Minoru Suzukia
aDepartment of Electronic Science and Engineering, Kyoto University, Kyoto 606-8501, Japan
bNTT Basic Research Laboratories, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan
We measure tunneling characteristics of Bi2Sr2CaCu2O8+d intrinsic junctions by a sub-microsecond pulse technique to investigate temperature and field dependence of the bulk gap structure without excess Joule heating. The conductance curve shows a peak at the superconducting gap voltage (Vp) at low temperatures, and the peak becomes broader when we increase either temperature or magnetic field that is a pair breaking parameter. However, Vp has a non-monotonic T dependence with a dip near Tc, while Vp increases monotonically with field. This difference indicates that Vp (T) cannot be explained by a simple pair breaking effect, and implies the existence of two distinct superconducting and pseudo gaps.
Observation of Large Superconducting Gaps in Bi-Based Cuprates by Tunneling Spectroscopy
Iduru Shigetaa, Fusao Ichikawab, Takeshi Fukamic, Takafumi Aomined
aAdvanced Materials Institute, Fukuoka University, Fukuoka 814-0180, Japan
bDept. of Physics, Kumamoto University, Kumamoto 860-8555, Japan
cDept. of Materials Science and Engineering, Himeji Institute of Technology, Himeji 671-2201, Japan
dDept. of Chemistry and Physics of Condensed Matter, Kyushu University, Fukuoka 812-8581, Japan
Large superconducting gaps were observed in some tunneling spectra of Bi2Sr2CaCu2O8+d (Bi2212) single crystals. This gap magnitude is about twice as much as that of the resent studies of Bi2212. Magnetic susceptibility was also measured and the results showed that the crystals retained a single phase of Bi2212. The experimental results suggest that the large gaps arise by way of Josephson effect due to the interfaces of the crystal boundary, and this indicates a possibility of device applications of Josephson junction.
STM Spectroscopy Study of High-Tc Superconductivity under Spin-Injection
John Y.T. Weia, Yu-Chih Tsenga, Joseph Ngaia, Frank Chenb, Doug D. Perovicb
aDepartment of Physics, University of Toronto, Toronto, ON M5S1A7 Canada
bDepartment of Materials Science and Engineering, University of Toronto, Toronto, ON M5S3E4 Canada
To study how the high-Tc order parameter (OP) evolves under the injection of spin-polarized quasiparticles, a novel STM spectroscopy technique has been performed on superconductor/ferromagnet heterostructures comprising YBa2Cu3O7-x (YBCO) and La0.7Ca0.3MnO3 (LCMO) at 4.2K. Quasiparticle-tunneling and Andreev-reflection characteristics measured on the YBCO under spin-injection from the LCMO were analyzed with the d-wave Blonder-Tinkham-Klapwijk theory, to reveal a spectral evolution which gives direct evidence for dynamic magnetic pair-breaking. The spectral analysis also shows the d-wave OP to remain time-reversal invariant as it is suppressed by the spin-injection. These results are discussed in terms of the general search for quantum critical-points in the high-Tc phase-diagram.
Magnetic properties of square Josephson arrays with SIS and SNS junctions
Salavat M. Ishikaeva, Edward V. Matizena, Valerii V. Ryazanovb, Vladimir A. Oboznovb
aInstitute of Inorganic Chemistry SB RAS, 630090, Novosibirsk, Russia
bInstitute of Solid State Physics RAS, Chernogolovka, Moskow region, Russia
Field dependence of magnetic moment of 100×100 SIS and SNS Josephson arrays was investigated by SQUID-magnetometer. It was found, that magnetic flux penetrated into SIS array by means of randomly distributed avalanches of tens and hundreds of flux quanta. The distribution of jumps by their size is a power function, which gives an evidence of self-organised criticality in regular Josephson structures. On SNS array the similar jumps were not observed, but penetration of a magnetic field in array was considerably asymmetric. Periodic peaks at external field, corresponding to integer and semi-integer of flux quanta per cell, were observed only while absolute field was increased, and was not observed if the field is decreased. At partial destruction of border cells the asymmetry does not changed appreciably.
Formation of Vortex State Induced by a Small Iron Tip in YBaCuO Thin Films
Lance Hornga, J. C. Weib, P. C. Kanga, W. H. Jua, J. L. Chena, C. W. Chena
aDepartment of Physics, National Changhua University of Education, Changhua 500, Taiwan.
bDep. Computer Science & Information Engi., Hungkuang Institute of Technology, Taichung 433, Taiwan.
Screening effect and flux penetration of YBaCuO superconducting thin films induced by a iron coil tip have been carrier out using an x-y scanning Hall probe. The characteristics of flux distribution on the surface of thin films can provide the evidence for the flux pinning effect between the vortex and defects. Changing the applied current of the iron coil and the distance between the iron coil and the film, we obtain the magnetic field dependence of flux profile of the vortex state, which can point out the surface energy barrier for formation of vortex-antivortex pairs in the local mixed state.
Raman scattering study of electronic and magnetic excitations in La2-xSrxCuO4
Masayuki Udagawaa, Norio Ogitaa, Shigenobu Sakitab, Jun'ya Horib, Fumihiko Nakamurac, Takeshi Suzukic, Toshizo Fujitac
aFaculty of Integrated Arts & Sciences, Hiroshima University, Higashi-Hiroshima, 739-8521, Japan
bVenture Business Laboratory of Hiroshima University, Higashi-Hiroshima, 739-8527, Japan
cGraduate School of ADSM, Hiroshima University, Higashi-Hiroshima, 739-8526, Japan
Electronic and magnetic excitations in La2-xSrxCuO4 (x=0, 0.1, 0.113, 0.15, 0.22) have been investigated by the polarized Raman scattering in the energy region between 0 and 4000cm-1. In the (a,a) polarization both magnetic and electronic excitations are allowed, while only electronic excitation for (c,c). In x £ 0.15, the intensity of (a,a) is larger than that of (c,c) due to the additional existence of the magnetic excitation, however, both spectra become the same for x=0.22. This result is the experimental evidence that dynamical magnetic fluctuation disappears in the over-doped region in La2-xSrxCuO4.
Formation of Static Stripes in Lightly-Doped La2-xSrxCuO4 as Manifested in Magnetic and Transport Properties of Untwinned Single Crystals.
Alexander N. Lavrov, Seiki Komiya, Yoichi Ando
Central Research Institute of Electric Power Industry, 2-11-1 Iwado-kita, Komae, Tokyo 201-8511, Japan
The doped holes in cuprates may self-organize in a stripe manner. Here we report on the anisotropy in the magnetic susceptibility c and magnetoresistance of untwinned LSCO crystals, which is a manifestation of such hole ordering. The in-plane anisotropy of c, found in the ``paramagnetic'' and ``spin-glass'' regions of the phase diagram, implies that antiferromagnetic domains, separated by antiphase boundaries (stripes), persist after the Néel order is destroyed by hole doping. Interestingly, upon the field-induced stripe rearrangement, the in-plane resistivity changes by as large as a factor of two, indicating that stripes can significantly affect the hole motion. Furthermore, the hysteretic behavior is observed in both resistivity and magnetic susceptibility at low temperatures, which signals the freezing of stripes upon cooling.
AC resistivity in s-wave and d-wave superconductors
Mai Suan Lia, Hoang Zungb, D Domínguezc
aInstitute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland
bVietnam National University, Ho Chi Minh City, 227 Nguyen Van Cu Str., Ho Chi Minh, Vietnam
cCentro Atomico Bariloche, 8400 S. C. de Bariloche, Rio Negro, Argentina
We model s- and d-wave disordered granular superconductors with a three-dimensional Josephson junction lattice with finite self-inductance. The current amplitude dependence of the nonlinear ac resistivity at the peak position is calculated using Langevin dynamical equations and found to be power law characterized by exponent a. The later depends on the self-inductance and current regimes. In the weak current regime a is independent of the self-inductance and a = 0.5 ±0.1 for both of s- and d-wave materials. For the strong current regime the values of a become to depend on the screening. We find a » 1 for some interval of inductance and it agrees with the experimental finding for d-wave ceramic superconductors.
Peculiarity in heat capacity of 90 K samples of YBa2Cu3O6+x above Tc
Victor N. Naumova, Anatoly I. Romanenkoa, Galina I. Frolovaa, Veronika V. Nogtevaa, Olga B. Anikeevaa, Tooru Atakeb
aInstitute of Inorganic Chemistry, Siberian Branch of Russian Academy of Science, Novosibirsk, Russia
bTokyo Institute of Technology, Yokohama, 226, Japan
The temperature dependence of heat capacity for the 90 K samples of YBa2Cu3O6+x with x = 0.85, 0.90 and 0.95 was investigated above Tc. For separating the heat capacity into regular and anomalous contributions the special technique was used. For all the samples the anomalies in intervals 100-200 K (Tlow), 205-230 K (Tm) and 260-290 K (Th) were detected. The nature of the discovered anomalies is discussed. The analysis shows, that one may consider some anomalies as a characteristic property of the 90 K samples of YBa2Cu3O6+x.
Nonlinear conductivity in Bi2Sr2CuOy single crystal
and possible
relation to stripe ordering
Katsuhiko Inagaki, Satoshi Tanda, Kazuhiko Yamaya
Department of Applied Physics, Hokkaido University, Sapporo 060-8268, Japan
Nonlinear conductivity of a Bi2Sr2CuOy single crystal is observed. The authors reported this nonlinear conductance in terms of weakly localized regime of Anderson localization, however, this attempt resulted that interlayer coupling between CuO2 should be concerned to interpret the observed logarithmic behaviors (logT, logH, and logV). We discuss the nonlinear conductivity of Bi2Sr2CuOy with a new approach in which a scaling relation is assumed. With this scaling relation, current-voltage characteristics of various temperatures below the transition fall into a single curve. The scaling relation is similar to those appear in Luttinger-Liquid behavior (Fisher's scaling theory). One plausible interpretation might be based on one dimensional current transport in relation to the formation of the charge stripe ordering.
Electrochemical synthesis of superconductive MgB2 from molten salts
Kenji Yoshiia, Hideki Abeb
aJapan Atomic Energy Research Institute, Mikazuki, Hyogo 679-5148, Japan
bNational Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
Superconducting bulk material of MgB2 has been prepared by means of electrolysis on the molten salts composed of MgCl2, KCl, NaCl and MgB2O4 [1,2]. In this paper, we report the effects of substitution of NaCl by the other alkali halides such as LiF. Superconducting properties of the samples have been evaluated from both magnetic and transport measurements.
[1] H. Abe and K. Yoshii, cond-mat/0204169; Jpn. J. Appl. Phys (2002) in press. [2] K. Yoshii and H. Abe, cond-mat/0204208; submitted to Supercond. Sci. Technol.
Persistent Supercurrents in MgB2
Jurgen P. Franck, John J. Jung
Department of Physics, University of Alberta, Edmonton, Alberta, T6G 2J1, Canada
Persistent currents were measured in rings of superconducting granular MgB2 through observation of the self-field using a travelling Hall probe. This method is therefore contact-less. We obtained both the temperature dependence of the critical current Jc from 15 K to Tc (39 K), and the time-decay for up to 105 sec. The temperature dependence is similar to that observed in granular YBCO rings. The time-decay of the persistent current from the critical level is less than 1% for a time interval of 105 sec at temperatures between 15 and 35 K. This decay rate is much smaller than that observed in high critical current rings of YBCO films, where we find a drop of 10% at 15 K.
Infrared studies of superconducting MgB2 thin films
Vladimír Zeleznýa, Dagmar Chvostováa, Libuse Pajasováa, Andrej Plecenikb, Peter Kúsb, Leonid Satrapinskyb
aInstitute of Physics, ASCR, Na Slovance 2, 18221 Prague, Czech Republic
bInstitute of Electrical Engineering, SAS, 84239 Bratislava, Slovak Republic
Reflectance of superconducting MgB2 thin films (Tc » 35 K) has been measured in a broad spectral range from 30 to 110 000 cm-1. A typical plasma edge with a minimum at about has been found at 15000 cm-1. In the far-infrared region we observe a pronounced rise of the reflectance below 60 cm-1, which appears below Tc and can be associated with superconducting state. The temperature-dependent complex conductivity at infrared frequencies has been determined using the Kramers-Kronig analysis. The real and imaginary parts of the conductivity below Tc also show a temperature evolution, which is characteristic for superconducting gap opening (decrease in s1 and rise in s2).
Properties of MgB2 in a two-gap superconductivity model
T. Örda, N. Kristoffelb, K. Rägoa
aInstitute of Theoretical Physics, University of Tartu, Tähe 4, 51010 Tartu, Estonia
bInstitute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia
For MgB2 where coexist two coupled superconductivity gaps a two-band scheme has been developed. Three interaction channels have been taken into account: a pair-transfer type s-p-interband repulsion, a s-intraband effective attraction of electron-phonon nature, and a s-intraband Coulomb interaction. By means of simultaneous fitting of Tc, heat capacity jump and zero-temperature gaps ratio the optimal values of interaction constants have been found. The Tc isotope effect exponent, the temperature dependencies of gaps and the thermodynamic characteristics (heat capacity, Hc2 etc.) calculated without any additional free parameters agree with the experimental findings. The theoretical curve of Tc vs chemical potential reproduces qualitatively the influence of doping on superconductivity phase transition in MgB2.
MgB2 thin film fabrication by rf-magnetron sputtering
Zon Mori a, Koji Eitoku b, Toshiya Doi b, Shinichiro Koba a, Yoshinori Hakuraku b
a Yatsushiro National College of Tech., 2627 Hirayama-shinmachi, Yatsushiro, Kumamoto 866-8051, JAPAN
b Faculty of Engineering, Kagoshima University, 1-21-40 Korimoto, Kagoshima, 890-0065 JAPAN
Superconducting MgB2 thin films on MgO and Al2O3 substrate were fabricated by rf magnetron sputtering. Sputtering was preformed in 50mTorr Ar atmosphere at room temperature using pure B and Mg metal target. Sputtering deposition was followed by the in-situ annealing at 923K for 5 minutes in high vacuum, to prevent the oxidizing of Mg atoms. This is essential for obtaining the high quality MgB2 thin film. To compensate for lack of B in the sputtered thin film, we examined the arrangement of target metals. The film grown on MgO had superconducting transition temperature of 30K.
Evidence for Superconductivity in the Boron Layers of MgB2
Ken'ichi Takahashia, Mingxiang Xub, Hideaki Kitazawab, Takekazu Ishidaa
aDepartment of Physics and Electronics, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
bNanomaterials Laboratory, National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan
Single crystals of MgB2 have been synthesized by the vapor transport method. We examine the superconducting anisotropy g = Ö{mc/mab} of a metallic high-Tc superconductor MgB2 by measuring the magnetic torque of a single crystal. The anisotropy g does not depend sensitively on the applied magnetic field at 10 K. We obtain the anisotropy parameter g = 4.31 ±0.14. The torque curve shows the sharp hysteresis peak when the field is applied parallel to the boron layers. We consider that this comes from the intrinsic pinning and is direct evidence for the occurrence of superconductivity in the boron layers. This is consistent with what the band calculations predict in the electronic states.
Quasi-Two-Dimensional Nucleation of Superconductivity in MgB2
A.S. Sidorenkoa, V.V. Ryazanovb, A.N. Rossolenkob, L.R. Tagirova, R. Tidecksa
aInstitut für Physik, Universität Augsburg, 86159 Augsburg, Germany
bInstitute of Solid State Physics, 142432 Chernogolovka, Russia
The crystal structure of MgB2 and band structure calculations suggest that quasi-2D boron planes are responsible for superconductivity. We report on the critical fields and resistance measurements of 5.6 mm thick MgB2 films grown on a supphire single crystalline substrate. The temperature dependence of the upper critical fields revealed 3D character of magnetic field penetration into the film. Alternatively, the resistivity measurements showed that temperature dependence of fluctuation conductivity above Tc agrees with the Aslamazov-Larkin-Maki-Thompson theory for layered superconductors. We consider this finding as an experimental evidence of quasi-two-dimensional nucleation of superconductivity in MgB2. This work was partially supported by INTAS grant No. 99-00585 and BRHE grant No. REC-007.
Temperature Dependence of Magnetic Torque for a Single Crystal MgB2 in 10 kG
Toshiyuki Atsumia, Mitsuyuki Tsujia, Mingxiang Xub, Hideaki Kitazawab, Takekazu Ishidaa
aDepartment of Physics and Electronics, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
bNanomaterials Laboratory, National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan
A new torque magnetometer has been constructed by using a 4-K closed cycle refrigerator and a variable field permanent magnet. The temperature of a top-loading space can be controlled from 300 K down to 1.5 K. The torque sensor consists of the four piezoresistors on a silicon cantilever. The torque can be measured as an off-balance signal of the Wheatstone bridge. Single crystals of MgB2 have been synthesized by the vapor transport method. We examine the mass anisotropy g = Ö{mc/mab} by using the London model. We discuss the temperature dependence of g for MgB2 in a constant field 10 kG.
Superconductivity and Electronic Structure of MgCNi3
Günter Fuchsa, Andreas Wältea, Stefan-L. Drechslera, Sergey Shulgaa, Karl-H. Müllera, Axel Handsteina, Jens Freudenbergera, Ludwig Schultza, Helge Rosnerb, Michelle Johannesb, Warren Pickettb
aInstitute für Festkörper- und Werkstofforschung Dresden, P.O. Box 270116, D-01171 Dresden, Germany
bUniversity of California, Davis, CA, 95616, USA
Polycrystalline samples of MgCNi3 and RNi2B2C (R=Y,Lu) were investigated by resistivity, ac susceptibility, dc magnetization and specific heat measurements. MgCNi3 can be considered as the 3-D analogue of RNi2B2C. A WHH-like shape of Hc2(T) is observed for MgCNi3 which contrasts with the positive curvature of Hc2(T) near Tc observed for RNi2B2C. The Hc2(T) and specific heat data of of MgCNi3 are discussed in terms of effective single- and multiband models as well as in terms of the symmetry of the gaps. Our analysis is based on an orbital assignment of the disjoint Fermi surface sheets.
MgB2 Superconducting Tip for Scanning Tunneling Microscopy Study
Mingxiang Xu, Yoshihiko Takano, Takeshi Hatano, Masayo Kitahara, Daisuke Fujita
National Institute for Materials Science, 1-2-1, Sengen, Tsukuba 305-0047, Japan
We demonstrate a simple method for the fabrication of sharp and stable MgB2 superconducting tips. The quality of these tips have been verified by imaging the surface of a Au(111) sample using a low temperature STM operated in UHV. With the MgB2 superconducting tip, the I-V characteristics of the Au(111) sample have been measured in the temperature range 4.2 - 45 K. The observed I-V characteristics of the sample have been discussed in this paper.
Pressure Dependence of Chiral-Glass Transition in Y-Ba-Cu-O Ceramics
Kuniyuki Koyamaa, Hiroyuki Deguchib, Seishi Takagib, Kiyoshi Mizunoa
aFaculty of Integrated Arts and Sciences, The University of Tokushima, Tokushima 770-8502, Japan
bFaculty of Engineering, Kyusyu Institute of Technology, Kitakyusyu 804-8550, Japan
Ceramic high-TC superconductors may be viewed as a weakly coupled random Josephson network containing the so-called p-junctions, and a chiral-glass transition is predicted to be occured in d-wave ceramics. In the present work, pressure dependence of the chiral-glass transition have been investigated on YBa2Cu3O7-y and YBa2Cu4O8 ceramics. With decreasing temperature, a superconducting order occurs at first inside each grain at TC1 and furthermore among the grains at TC2 ( < TC1). The TC2 increases with increase of pressure, however, the sharpness of the transition at TC2 does not change. In spite of differences in not only TC2's but also TC1's, the increasing rates of TC2 by pressure are nearly the same.
Magneto optical observation of ''super-cooled'' disorder vortex state in Bi2Sr2CaCu2O8+d
B. Kalisky, A. Shaulov, Y. Yeshurun
Institute of Superconductivity, Bar-Ilan University, Ramat-Gan 52900, Israel
Magnetic induction profiles across the surface of a Bi2Sr2CaCu2O8+d crystal were measured during field descent from above the vortex solid-solid phase transition field, Bss, to zero. These profiles indicate dynamic coexistence of two vortex phases: a disordered phase in the sample interior and a quasi-ordered phase near the sample edges. The border between these two phases, marked by an abrupt change in the slope of the profiles, moves with time towards the sample's center. The break in the profiles always appears at the same induction, Bf, below the value of Bss. We interpret this phenomenon in terms of the field dependence of the nucleation and growth of the quasi-ordered phase, and relate Bf to the transition field.
Magnetostriction and Magnetoacoustic Measurements on YBCO Crystals
Christian Curaa, Josef Pala, Rainer Schuberta, Siegfried Ewerta, Günter Fuchsb, Gernot Krabbesb
aInstitute of Physics, University of Cottbus, 03013 Cottbus, Germany
bIFW Dresden, 01069 Dresden, Germany
Magnetostriction hysteresis data reveal the presence of the fishtail effect in isothermal scans. Thermal cycles in magnetic fields show the behaviour of pinning of flux lines in the different phases Bragg glass, vortex glass and vortex liquid. Ultrasonic attenuation and the relative change of sound velocity for various magnetic fields were measured. The aim is to examine the elastic behaviour of the flux line lattice. In the framework of the thermally assisted flux flow model (TAFF) the depinning temperature and the activation energy were been deduced. The measurements on pure YBCO crystals are discussed and compared with investigations on Zn doped YBCO crystals. The magnetostrictive effects are verified by supplementary AC- and DC-magnetization measurements.
Dynamical Scaling Analysis of Susceptibility in Ceramic YBCO Superconductors
Hiroyuki Deguchia, Miyoko Yasunakaa, Ryo Onikia, Seishi Takagia, Kuniyuki Koyamab, Kiyoshi Mizunob
aFaculty of Engineering, Kyushu Institute of Technology, Kitakyushu 804-8550, Japan
bFaculty of Integrated Arts and Scence, The University of Tokushima, Tokushima 770-8502, Japan
Dynamical properties of the ceramic YBa2Cu3O7-d have been investigated by magnetic measurements in order to clarify the inter-grain ordering. Kawamura and Li proposed that a chiral-glass ordering might occur in d-wave ceramic superconductors. We measured the ac-susceptibilities at various frequency under zero external field and carried out a dynamic scaling analysis of the susceptibility near the inter-grain transition temperature. The results exhibit scaling behavior for the critical exponents zn=8 and b=0.5. These values are fairly close to the ones for the chiral-glass estimated by Monte Carlo simulations.
Flux Flow Excited by Ultrasonic Deformation of Flux Line Lattice in High Temperature Superconducting Ceramics
Yuuji Horie, Kenji Yamasaki, Teruaki Nomiyama, Tomoyuki Miyazaki
Dept. of Electrical and Electronics Engineering, Kagoshima University, Kagoshima 890-0065, Japan
To investigate the flux pinning properties in HTSC against various kinds of deformation of flux line lattice(FLL), the flux flow excited by ultrasonic deformation of FLL was measured for bulk sintered samples of Bi2Sr2Ca2Cu3Oy. The longitudinal, tilt and shear ultrasonic deformations, which are associated with the elastic moduli of C11, C44 and C66 of FLL in isotopic superconductors, were applied to FLL. A peak of the flux flow resistivity was observed at a temperature Tp at which the dissipation of ultrasonic energy became the maximum. The differences in Tp and the peak height among the deformations were small differently from the theoretical prediction with the model of thermally assisted flux flow. The results suggest that most flux lines are bent by the pinning at insulating layers and/or grain boundaries.
A new phase in the vortex solid region in Bi2Sr2CaCuO8
Mitsuru Uehara, Shigeki Nimori, Takashi Mochiku, Takenori Numazawa
National Institute for Materials Science, 3-13 Sakura, Tsukuba, 305-0003 Japan
The time decay of the zero field cooled diamagnetic magnetization of Bi2212 can be explained in terms of a characteristic relaxation time t0, and a mean activation energy E which is proportional to the reciprocal magnetic field. We find that t0 becomes extremely longer to be around 10 sec at low temperatures below 15K. This low-temperature phase in the vortex solid region is directly observed by the ac susceptibility measurements in the ultra low frequency range.
Transport Measurements in YBaCaCuO
Hector F. Castro, Guy Deutscher
School of Physics and Astronomy, Tel Aviv University, 69978 Tel Aviv, ISRAEL
Hall and longitudinal resistivities have been measured in Ca-doped YBCO thin films with different oxygen concentrations. Oxygen content has been controlled by annealing so that the same sample is modified from overdoped (as grown) to underdoped. Room temperature is sufficient to reduce the overdoping level over a few days. Our data is discussed on the frame of the nearly antiferromagnetic Fermi liquid model as presented by Stojkovic and Pines. The emphasis being on the range from overdoped to optimally doped where data and discussion is scarce.
Zeeman Splitting of the 63/65 Cu NQR Line in optimally doped HgBaCaCuO below T c
H. Breitzkea, K. Lüdersa, K. A. Lokshinb, E. V. Antipovb
aPhysics Department, Free University Berlin, Arnimallee 14, D-14195 Berlin, Germany
bDept. of Chemistry, Moscow State University, 119899 Moscow, Russia
We report pure zero field nuclear magnetic resonance (NQR) measurements on the optimally doped three layer compound HgBaCaCuO with Tc 134 K. Above Tc two Cu line pairs are observed in the spectrum corresponding to the two inequivalent Cu lattice sites. Below Tc the Cu NQR spectrum shows a splitting of these two line pairs into six line pairs. From a multi exponential spin lattice relaxation with a dependency on the initial conditions, we find a formation of magnetic moments in the CuO layers as the origin of the line splitting. Furthermore, the magnetic moments are oriented parallel to the symmetry axis of the electrical field gradient tensor with magnitudes of the order of 1000 G.
The normal state magnetic susceptibility of La2CuO4+d with excess oxygen
Junko Shimizu, Mengyuan Chen, Masahito Nakagawa, Yasukage Oda
Department of Material Science, Graduate School and Faculty of Science, Himeji Institute of Technology, Ako-gun, Hyogo 678-1297, Japan
We have studied the superconducting and magnetic properties of the ceramic La2CuO4+d with excess oxygen, which were prepared by the electrochemical oxidation. Hirayama et al. reported that the ceramic La2CuO4+d with excess oxygen has two superconducting phases, whose Tc's are 32K (36K) of the low Tc phase and 45K of the high Tc phase, respectively. In this paper, we have measured the magnetic susceptibility of the two phases in the normal states. The temperature dependence of the magnetic susceptibility of the high Tc's phase was found to be very similar to that of the optimum doped (LaSr)2CuO4+d. However, the temperature dependence of the magnetic susceptibility of the low Tc's phase was found to include the antiferromagnetic phase and paramagnetic phase.
Coexistence of ferromagnetism and superconductivity in Cu-rich lanthanum Cu-oxides
Bai-Ru Zhao, Xiao-Li Dong, Peng-Shun Luo, Zhong-Xian Zhao, Yong-Ming Ni, Bo Xu, Fei Wu
National Laboratory for Superconductivity, Institute of Physics and Center for Condensed Matter Physics, Chinese Academy of Sciences, PO Box 603, Beijing 100080, PR China
The magnetization of the lightly oxygen doped Cu-rich La2CuO4+d is measured in zero field and field cooling and in a wide temperature range (5K to 350K). The data together with the evolution of the magnetic hysteresis loop suggest that the ferromagnetism with Curie temperature of 280K coexists with superconductivity below the transition temperature ~ 34K. Such coexistence occurs in the hole-rich clusters of size small than 150nm, which are electronic phase separated from the hole-poor antiferromagnetic background.
Tl, Cu-NMR study on high-TC cuprate TlBa2(Y1-xCax)Cu2O7
Yuuji Kuniia, Takao Suzukia, Aya Kakishimaa, Takayuki Gotoa, Satoru Nakajimab
aFaculty of Science and Technology, Sophia University, 102-8554 Japan
bAkita National College of Technology 1-1, Bunkyo-cho, Iijima, Akita, 011-8511, Japan
Hole doped high TC cuprate TlBa2(Y1-xCax)Cu2O7 has wide range solution limit from the antiferromagnetic (Ca=0) to the slightly overdoped (Ca=1.0). The superconducting transition temperature TC is raised adruptry from zero to 100K at Ca=0.6 and almost constant to Ca=1.0. The local spin susceptibility (KS) at Cu-site (Ca=0.8) shows spin-gap-like behavior from room temperature, suggesting that Ca=0.8 is in the underdoped region. The sample of Ca=1.0, believed to be slightly overdoped, does not show any spin-gap-like behavior. (T1T)-1 at Tl-site for every superconducting sample shows the Curie-Weiss behavior at high temperature limit. As decreasing temperature, a clear spin gap is observed from far higher temperature than TC even in the slightly overdoped sample (Ca=1.0).
Neutron Scattering Studies of In-Plane Longitudinal Phonons of YBa2Cu3Oy
M. Itoa, H. Harashinaa, Y. Yasuia, M. Satoa, K. Kakuraib
aDepartment of Physics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602 Japan
bAdvanced Science Research Center, JAERI, Tokai, Ibaraki 319-1105 Japan
In plane longitudinal phonon of YBa2Cu3Ox(YBCO or YBCOx;x=6.5, 6.7 and ~ 7.0) with B2u/B3u symmetry has been measured by neutron inelastic scattering to study whether effects of dynamical ``stripes" can be observed in the mode of YBCO. Along Q=(3+h,0,0), we have observed two branches with the energy dispersions between 20 ~ 34 meV, corresponding to the B2u and B3u modes, which are perpendicular and parallel to the CuO chains. No anomaly has been observed in their dispersion curves. Rather strong smearing has been found in the former mode with larger chain oxygen motion than that of the latter. Because the degree of the smearing depends neither on x or on the temperature T, it may not be considered as an efect of the ``stripes" but due to the oxygen deficiency at the chain sites.
THz imaging of supercurrent distribution in Meisner state of LPE-BSCCO film
H. Murakamia, T. Kiwaa, M. Tonouchib, T. Yasudac
aRCSP, Osaka Univ., Suita, Osaka 565-0871, Japan
bRCSP, Osaka Univ. and CREST-JST, Suita, Osaka 565-0871, Japan
cDept. Computer Science and Electronics, Kyushu Inst. Tech., Iizuka, Fukuoka 820-8502, Japan
Previously, we reported terahertz (THz) imaging for supercurrent distribution in high temperature superconductor thin film. In this method, THz pulse is emitted by ultrafast supercurrent modulation caused by femtosecond optical pulse excitation, and the intensity of the THz pulse transmitted through the sample is detected to visualize the supercurrent distribution. In the present study, in order to apply this technique to thick film, we observed the THz pulse reflected from the front side of LPE-BSCCO film, and investigated the Meisner current distribution under magnetic field.
Observation of Spin-Gap in Bi2+xSr1.6-xLa0.4CuO6+d by Transport Measurements
S. NishiZakia, S. Motooib, R. Yoshizakib
aCryogenics Center, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan
bInstitute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan
We have measured the in-plane resistivity rab of Bi2+xSr1.6-xLa0.4CuO6+d which is the single layered high-Tc superconductor. We observed the spin-gap temperature T*, where rab derives from the temperature linear dependence. Furthermore, we found that T* decreases with increasing the carrier density controlling by the annealing under various oxygen partial pressure. This systematic variation of T* is the same tendency as the other high-Tc superconductors. However the scaling of relation between T* and Tc which M. Oda et al. [Physica C 341-348 (2000) 847.] experimentally suggest is completely different from that in the others. In the presentation, we discuss the relation between T* and Tc.
Thermodynamic properties of MgCNi3 superconductor
C. Q. Jin, Y. L. Zhang, Z. X. Liu, F. Y. Li, W. Yu, R. C. Yu
Institute of Physics, Chinese academy of Sciences, P. O. Box 603, Beijing 100080, P. R. China
We have measured the magnetic properties on the high quality polycrystal sample of the recently discovered ternary carbide superconductor MgCNi3[1], which shows sharp superconducting transition around 8 K. The lower critical field Hc1 has been estimated through the non-linear deviation of the initial magnetization curve, and the upper critical field Hc2 measured via the superconducting transition at different applied magnetic field. Consequently the coherence length, penetration depth, and the Ginzburg-Landau parameter were calculated, respectively. The difference of the penetration depth was analyzed in an isotropic s-wave BCS description.
Superconductivity in Electrochemically Li-intercalated Niobates with Layered Perovskite Structure
Masatsune Katoa, Akira Inouea, Ichiro Nagaib, Masato Kakihanab, Arthur W. Sleightc, Yoji Koikea
aDepartment of Applied Physics, Tohoku University, Sendai 980-8579 Japan
bMaterials and Structures Lab., Tokyo Institute of Technology, Yokohama 226-8503 Japan
cDepartment of Chemistry, Oregon State University, Corvallis OR 97331 USA
Li-intercalated layered perovskites LixAB2Nan-3NbnO3n+1 with n =3 and 4 (A = K, Rb, Cs; B=Ca, Sr, Ba) have been prepared by an electrochemical technique. For the LixAB2Nb3O10 superconducting materials with a triple-layered NbO6 octahedron, there is a relation between Tc and a-axis length, where Tc tends to increase up to about 6 K as the a-axis length increases. For LixCsBa2Nb3O10 with the largest a-axis length, however, superconductivity does not appear. The non-superconductivity may be due to the transition from metal to insulator. In addtion, LixKCa2NaNb4O13 shows no superconductivity.
Inelastic light scattering studies of superconducting Ru-based double perovskites
Hsiang-Lin Liua, Chang-Chung Chena, Fan-Z Chienb, Mow-Kuen Wuc
aDepartment of Physics, National Taiwan Normal University, Taipei 116, Taiwan
bDepartment of Physics, Tamkang University, Tamsui 251, Taiwan
cInstitute of Physics, Academia Sinica, Nankang 115, Taiwan
We report an inelastic light scattering study of double perovskite structure Sr2Y(Ru1-xCux)O6 systems as a function of temperature and doping (x = 0.0, 0.05, and 0.1). As the temperature is lowered, for x = 0.0, the 770 cm-1 A1g apical oxygen phonon mode exhibits a softening and an enhancement of the linewidth in the antiferromagnetic phase. Similar anomalies are also observed for x = 0.1 when the superconducting gap opens. This suggests that a strong lattice-spin-charge coupling plays an important role in the magnetic and superconducting properties observed in these materials.
Microwave Josephson's absorption in high-temperature superconductors
J. Niewolskia, A. Koodziejczyka, T. Zajaca, K. Przybylskib, T. Brylewskib, G. Gritznerc, M. Ederc, M. Enenglc, W. Königc, O. Heimlc
aUniversity of Mining and Metallurgy, Faculty of Physics and Nuclear Technique and
bFaculty of Material Engineering and Ceramics, 30-059 Cracow, Poland
cKepler Universität, Institut für Chemische Technologie Anorganischer Stoffe, A-4040 Linz, Austria
Magnetic field dependence of Direct (DMA) and Magnetically Modulated (MMMA) Microwave Absorption of a number of Y-, Bi- and Tl- based high-temperature superconductors were measured at 4.2 K and 77 K by reconstructed X-band microwave spectrometer. It was found correlation between value of the low field maximum (LFM) of the absorption and the inter-grain critical currents of the Josephson junction system for these families of superconductors. Some results were analyzed and compared to the theoretical models of magnetoabsorption available in the literature yielding a fairly good agreement.
Elastic constant of the vortex lattice in La1.875Ba0.065Sr0.060CuO4
Takao Suzukia, Takayuki Gotoa, Hideto Gokab, Masaki Fujitab, Kazuyoshi Yamadab
aDepartment of Physics, Sophia University, 7-1 Kioi-cho, Chiyoda-ku Tokyo, 102-8554, Japan
bInstitute for Chemical Research, Kyoto University, Uji Kyoto, 610-0011, Japan
In the stripe phase observed in La-214 system around the hole concentration of x=0.12, whether or not the superconductivity coexists with the stripe order is a controversial problem. In order to estimate the superconducting volume fraction, we measured the elastic constant under high magnetic fields by the ultrasonic technique in the stripe phase La1.875Ba0.065Sr0.060CuO4 single crystal which undergoes the structural phase transition to the low-temperature orthorhombic (Pccn) phase. The elastic constant of c44 mode of the vortex lattice shows the step like change below Tc=5K and the saturated value is 68% of the theoretical result. Probing with the vortex lattice, the superconducting volume fraction seems to be about two over three in the stripe phase of Pccn phase.
Spin and Charge Inhomogeneity in the Cuprates characterized by NMR
Juergen Haase
Max Planck Institute for the Chemical Physics of Solids, 01187 Dresden, Germany
We prove the existence of correlated spin and charge variations in the cuprates and characterize these structures with NMR. Charge density variations are found to induce modulations of the spin susceptibility depending on the doping at two different wave vectors. The longer wave component disappears near Tc, the other, near the antiferromagnetic wave vector, grows as T is lowered and exists in the superconducting state.
The glue is the clue: mesoscopic charge and spin ordering in HTSC
Annette Bussman-Holder
Max-Planck-Institute for Solid State Research, D-70569 Stuttgart, Germany
In high temperature superconducting copper oxides (HTSC) there is accumulating evidence that mesoscale charge ordering precedes the spin ordering and persists into the superconducting phase. This scenario implies that a spatial segregation of holes takes place which reflects itself in a granularity in the local density of states. It will be described here how the charge ordering is driven by highly anharmonic lattice effects which induce polaronic level shifts on the doped holes and induce incommensurate dynamical modulations in the spatial hole distribution. The effect of the spatially modulated electron-lattice interaction driven level shift is to form the glue between the two components, spin and charge, by adjusting the spin and charge related energy levels through their mixing and substantially enhancing the superconducting transition temperature.
Checkerboard of Quasi-Particle States Around Vortices in Bi2Sr2CaCu2O8+d
J. E. Hoffmana, K. P. McElroya, D. H. Leea, K. M. Langa, H. Eisakib, S. Uchidab, J. C. Davisa
aDepartment of Physics, University of California, Berkeley, CA 94720-7300, USA.
bDepartment of Superconductivity, University of Tokyo, Tokyo 113-8656, Japan.
We use scanning tunneling spectroscopy to image the spatial and energetic structure of the quasiparticle states surrounding quantized vortices in the high-Tc superconductor Bi2Sr2CaCu2O8+d. These states exhibit a four unit cell periodic ``checkerboard'' pattern, oriented along the copper-oxygen bond directions, with a decay length of ~ 30 Å. Speculation on the possible charge density wave origin of this phenomenon has raised questions about its register to the atomic lattice, its energy dependence, and its temperature dependence. Here we report new results with high spatial and energy resolution, and we analyze the ``checkerboard'' phenomenon as a function of distance from the vortex core.
Point-Defects-Induced Vortex Phase Diagram in High-Tc Superconductors: Monte Carlo Simulation Study
Ryoko Suganoa, Toshiyuki Onogia, Kazuto Hiratab, Masashi Tachikib
aAdvanced Research Laboratory, Hitachi, Ltd., Hatoyama, Saitama 350-0395, Japan
bNational Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan
We investigated the field-temperature vortex phase diagram of high-Tc copper-oxide superconductors in the presence of dense point defects, by using a Monte Carlo simulation based on the Lawrence-Doniach model. We found a temperature-driven depinning line within the Bragg and vortex glass phases, well below the melting line. We also found a field-driven transition line from the Bragg-to-vortex glass at low temperatures, accompanied by an abrupt reduction in the interlayer vortex correlation. The complex phase boundaries are drastically controlled by the vortex pinning force of the defects, defect density, and anisotropy. These computational results explain the experimental results on BSCCO and YBCO.
Anomalous oscillation of ac susceptibility in low temperature for Bi2Sr2CaCu2O8+y
Shigeki Nimori, Mitsuru Uehara, Takashi Mochiku, Takenori Numazawa
Tsukuba Magnet Laboratory, National Institute for Materials Science, 3-13 Sakura, Tsukuba, 305-0003 Japan
We studied magnetizations of over-doped Bi2Sr2CaCu2O8+y single crystals. The thermoremanent magnetization shows an anomalous random oscillation in low frequency modulation field below 20K. The result indicates a random motion of the vortices, which suggest there exists a new magnetic phase in the vortex solid phase.
Extreme Smallness of the Transverse Force on Moving Vortices in Bi2Sr2CaCu2O8
Koki Mochizukia, Jae-Hyuk Choia, John T. Markerta, Yoichi Andob, K. Nakamurab
aDepartment of Physics, University of Texas, Austin, TX 78712 USA
bCRIEPI, 2-11-1 Iwato-kita, Komae, Tokyo 201-8511, Japan
We report the results of direct force measurements of the longitudinal (pinning and viscous) forces and the transverse (``Magnus") force on vortices along the c direction in Bi2Sr2CaCu2O8 single crystals. The magnetic flux is applied locally to the center of a crystal using a micro-electromagnet, thus avoiding edge-pinning and geometrical-pinning effects. The pinning and viscous forces measured by two different high-Q mechanical oscillator techniques are in good agreement, and agree with theoretical predictions. The measured transverse force on moving vortices is extremely small, in sharp contrast to recent ``universal" theories, which predict the full hydrodynamic value. The data indicate that the transverse force on a moving vortex is smaller than the hydrodynamic value by a factor a £ 0.015.
Josephson vortex flow and pinning probed by c axis transport measurements
Itsuhiro Kakeyaa, Sanshiro Amana, Katsumi Suzukib, Kazuo Kadowakia
aInstitute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573 Japan
bSuperconducting Research Laboratory, ISTEC, Tokyo 105-0023, Japan
We have investigated dynamical properties of Josephson vortex (JV) system probed by the c axis transport properties of Bi2Sr2CaCu2O8+d mesa structures with magnetic field alignments very close to the ab plane (|q| < 0.1°). In I-V characteristics, zero-resistance and single branch regions were obtained in addition to a multiple branch region which is a distinctive feature of intrinsic Josephson junctions. The zero-resistance and single branch are considered to be realized by JV pinning and JV flow, respectively. Temperature dependence of the starting current of the single branch, which is given by the pinning force of JVs, shows a peak effect at around 10 K below Tc at 5 kOe. This peak effect cannot be explained with the random pinning but requires peculiar pinning mechanisms based on the crossing lattice model.
Purely viscous motion of the vortices in semiclassical d-wave superconductor
Y. Matsudaa, K. Izawaa, H. Ikutab, M. Hasegawac, Y. Katod
aInstitute for Solid State physics, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa 277-8581, Japan
bCenter for Integrated Research in Science and Engineering, Nagoya University, Nagoya 464-8603, Japan
cInstitute for Materials Research, Tohoku University, Sendai 980-8577, Japan
dDepartment of Basic Science, University of Tokyo, Komaba 3-8-1, Meguro-ku, Tokyo 153-8902, Japan
We report the free flux flow (FFF) resistivity associated with a purely viscous motion of the vortices in clean d-wave superconductor Bi:2201 in the strongly overdoped regime (Tc=16 K) in the vortex state. It is found that the FFF resistivity is remarkably different from that of conventional s-wave superconductors. At low fields the FFF resistivity increases linearly with H, while at higher fields the FFF resistivity increases in proportion to ÖH up to Hc2. On the basis of these results, the energy dissipation mechanism associated with the viscous vortex motion in ßemiclassical" d-wave superconductors is discussed.
Heavy-ion Irradiation dependence of the Superconducting properties of
(Cu,C)Ba2Ca3Cu4O10.5-d
Hijiri Kitoa, Akira Iyoa, A Crisanb, Manabu Hiraic, Madoka Tokumotoa, Satoru Okayasud, Masahito Sasased, Yasumoto Tanakaa, Hideo Iharaa
aA.I.S.T, Tsukuba, 305-8568 Japan and CREST, JST, Kawaguchi, 332-0012 Japan
bA.I.S.T, Tsukuba, 305-8568 Japan and Nat. Inst. Mat. Phys., POB MG-7, Bucharest, Romania
cA.I.S.T, Tsukuba, 305-8568 Japan and Tokyo Univ. of Science, Noda, 278-8510 Japan
dJ.A.E.R.I, Tokai, Ibaraki 319-1195 Japan
For further enhancement of critical currents density Jc and irreversibility field Hirr of (Cu,C)-1234 (Tc=117K), we have investigated heavy-ion irradiation dependence. The polycrystalline samples were irradiated with Au15+ ions (240 MeV energy) at a fluence of 1×1011, 2.5×1011 and 5×1011 ions/cm2, respectibly. Jc and Hirr were estimated from magnetic measurement.
Effect of variation of facets size on fractional flux vortices at asymmetric grain boundaries in YBCO films
Roman Mints, Ilya Papiashvili
School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
We consider numerically Josephson vortices at asymmetric grain boundaries in YBCO films. The study is focused on the effect of random variations of facets size on the values of fractional flux carried by these vortices. The grain boundaries are treated as Josephson junctions with a critical current density alternating along the junctions with a typical length-scale of order of the facets size. Our numerical simulations demonstrate that the flux of the vortices varies along the junction. The values of the fractional flux are defined by the local Josephson properties of the grain boundaries.
Universality of ultra-fast flux penetration into superconducting films
U. Bolza, D. Schmidta, B. Biehlera, B.-U. Rungea, R.G. Mintsb, K. Numssenc, H. Kinderc, P. Leiderera
aUniversity of Konstanz, 78457 Konstanz, Germany
bTel Aviv University, Tel Aviv 69978, Israel
cTechnical University of Munich, 85748 Garching, Germany
We report on universalities of ultra-fast flux penetration into a YBCO superconducting film exposed to a transverse magnetic field of few mT. Using a fs pump-probe magneto-optic technique we are able to investigate the magnetic flux penetration on a subnanosecond timescale. The laser pulse is focussed with a cylindrical lens onto the film, hereby heating a line above Tc. Depending on H and T we observe two different regimes how magnetic flux penetrates from this line into the superconductor: at low field gradients homogeneously propagating flux fronts are observed, whereas at high gradients dendritic flux avalanches develop.
Current-voltage characteristics of three-dimensional vortex glass
Hoang Zunga, Mai Suan Lib
aVietnam National University, Ho Chi Minh City, 227 Nguyen Van Cu Str., Ho Chi Minh, Vietnam
bInstitute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland
The current-voltage characteristics of the three-dimensional vortex-glass model of disordered type-II superconductors with a uniformly field threading the system are studied by the Lagevin dynamics technique. In agreement with static simulations, the vortex glass phase is found to be spoiled by the screening effect. We obtained correlation length exponent n » 3.5. This value is considerably higher than that for the gauge-glass model.
Vortex motion noise in amorphous Nb0.7Ge0.3 microbridges
D. Babi\'ca, C. Strunka, T. Nussbaumera, C. Schönenbergera, C. Sürgersb
aInstitute of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
bPhysikalisches Institut, University of Karlsruhe, D-76128 Karlsruhe, Germany
We investigated the voltage noise in amorphous Nb0.7Ge0.3 microbridges, which is induced by vortex motion in the mixed state. There is a remarkable difference between the noise below and above the irreversibility field Birr. Below Birr, in the presence of measurable pinning, the noise at small applied currents resembles shot noise, and in the regime of flux flow at larger currents decreases with increasing voltage due to a progressive ordering of the vortex motion. At magnetic fields B between Birr and the upper critical field Bc2 flux flow is present already at vanishingly small currents. In this regime the noise scales with (1-B/Bc2)2 V2 and has a frequency (f) spectrum of 1/f type. We interpret this noise in terms of the fluctuation properties of strongly driven depinned vortex systems at high vortex density.
Vortex dynamics and upper critical fields in ultrathin Bi films
N Chandrasekhar, G Sambandamurthy, K Das Gupta, Swati S Soman
Department of Physics, Indian Institute Science, Bangalore 560 012, INDIA
Current-voltage (I-V) characteristics of quench condensed, superconducting, ultrathin Bi films in a magnetic field are reported. Films close to superconductor-insulator transition (SIT), show a peak in the critical current as a function of magnetic field, as well as temperature, indicating a structural transformation of the vortex solid (VS). This is contrary to the recently reported results of a absence of VS phase near SIT. Underlayers of Ge/Sb, used to make the films more homogeneous, are found to be more effective in pinning the vortices. The upper critical fields (Bc2) of these films are determined from the resistive transitions in perpendicular magnetic field, and are found to differ significantly from Ginzburg-Landau theory.
Vortices in Bulk and Mesoscopic Superconductors: Variational Calculations
Walter V. Pogosova, Alexander L. Rakhmanovb, Kliment I. Kugelb
aMoscow Institute of Physics and Technology, Dolgoprudnyi, Moscow region, 141700 Russia
bInstitute for Theoretical and Applied Electrodynamics, Russian Academy of Sciences, Izhorskaya Str. 13/19, 127412 Moscow, Russia
A variational method is used for the analysis of the vortex structures in bulk and mesoscopic type-II superconductors. The approach is based on various trial functions for the order parameter and minimization of the Ginzburg-Landau free energy. The magnetization of bulk superconductor is calculated in the whole field range between Hc1 and Hc2 in the Wigner-Seitz cell approximation. The vortex phase diagram for long mesoscopic cylinders with suppressed surface superconductivity is determined under general boundary conditions. The comparison of our results with known exact solutions and asymptotics demonstrates a good accuracy of the proposed method.
Interaction effects in non-Hermitian models of vortex physics
Kihong Kima, David R. Nelsonb
aDepartment of Molecular Science and Technology, Ajou University, Suwon 442-749, Korea
bLyman Laboratory of Physics, Harvard University, Cambridge, Massachusetts 02138, U.S.A.
Vortex lines in superconductors in an external magnetic field slightly tilted from randomly-distributed parallel columnar defects can be modeled by a system of interacting bosons in a non-Hermitian vector potential and a random scalar potential. We develop a theory of the strongly-disordered non-Hermitian boson Hubbard model using the Hartree-Bogoliubov approximation and apply it to calculate the complex energy spectra, the vortex tilt angle and the tilt modulus of both (1+1)- and (2+1)-dimensional directed flux line systems. We construct the phase diagram associated with the flux-liquid to Bose-glass transition and discuss the effects of interaction on the nature of this transition.
Vortex Structures in the Ferromagnet-Superconnductor Bilayer
Konstantin Traitoa, Reino Laihoa, Erkki L[(a)\ddot]hderantaa, Edouard Soninb
aWihuri Physical Laboratory, University of Turku, FIN-20014 Turku, Finland
bRacah Institute of Physics, Hebrew University of Jerusalem, Jerusalem 91904, Israel
Vortex structures in ferromagnet/type-II superconductor bilayer are investigated for the case when the ferromagnetic layer has domain structure and magnetic anisotropy perpendicular to the bilayer. It is found that two equilibrium vortex states can be realized: (i) Straight vortices with alternating directions corresponding to the direction of the magnetization in the ferromagnetic domains. The vortices appear near the domain centers. (ii) Vortex semi-loops, which appear near the domain walls and connect the ferromagnetic domains with opposite direction of the magnetization. These two states are separated by an energy barrier of geometrical origin. The values of the critical magnetization for the formation of these vortex structures are determined.
Study of vortex configuration in the mixed state of a-W/Si multilayers
Ryuta Honmaa, Yoshinori Kuwasawaa, Kazunuki Yamamotob, Tsutomu Nojimac
aDepartment of Physics, Faculty of Science, Chiba University, Chiba 263-8522, Japan
bDepartment of Materials Technology, Faculty of Engineering, Chiba University, Chiba 263-8522, Japan
cCenter for Low Temperature Science, Tohoku University, Katahira, Sendai, 980-8577, Japan
Configuration and motion of vortices have been studied on amorphous W/Si multilayers with strong (3D) and weak (quasi-2D) layer coupling through the simultaneous measurements of two components of electric fields in the film plane, Ex and Ey, as a function of current in magnetic fields of the form (H, H, aH), where |a| < 0.15 and x || the current direction. The analysis of Ex and Ey shows that in the 3D sample a change in the vortex structure from the kinked line to the correlated straight one occurs at the vortex glass transition. In the quasi-2D sample, only the dynamics of 2D pancake vortices including the velocity drift due the Magnus force has been observed in all the temperature range measured even at a = 0.
Nonlinear Thermomagnetic Shock Waves in Type II Superconductors
N. A. Taylanov
Theoretical Physics Department, Institute of Applied Physics, National University of Uzbekistan, Vuzgorodok, 700174, Tashkent, Uzbekistan
In this work the structure of the thermomagnetic shock waves in superconductors is analyzed with an account of dissipation and dispersion effects. The effect of the dependence jc(H) on the structures of the nonlinear thermomagnetic wave propagation is studied. It is shown that taking into account the nonlinear dependency of the critical current density jc on the external magnetic field H the latter would not qualitatively change the main results, therefore the character of the equilibrium state at the phase plane remains essentially the same
Search for Spontaneous Magnetization in Sr2RuO4
Tsuyoshi Tamegaia, Kohei Yamazakia, Masashi Tokunagaa, Zhiqiang Maob,c, Yoshiteru Maenob,c
aDepartment of Applied Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
b Department of Physics, Kyoto University, Kyoto 606-8502, Japan
c CREST, Japan Science and Technology Corporation, Kawaguchi, Saitama 332-0012, Japan
mSR measurements in Sr2RuO4 indicate that an internal magnetic field is established below Tc, suggesting that the superconducting state breaks time-reversal symmetry. We used a micro-Hall probe (5×5 mm2) to search for spontaneous magnetic field at the edge of chiral domains in the time-reversal symmetry breaking state. We did not detect magnetic signal larger than 0.02 G at zero field. This value is one order of magnitude smaller than the theoretical estimate, and suggests that either the spontaneous magnetization is absence or the chiral domain is smaller than 5 mm. In the latter case, history dependent measurements of the vortex pinning force strongly suggest that the chiral domains can be easily flipped.
Search for the chiral state in Sr2RuO4-Ru eutectic
Masaki Yoshiokaa, Hiroshi Yaguchia, Masahiko Wadaa, Yoshiteru Maenob
aDepartment of Physics, Kyoto University, Kyoto 606-8502, Japan
bInternational Innovation Center and Department of Physics, Kyoto University, Kyoto 606-8501, Japan
Sr2RuO4 is a spin-triplet superconductor (Tc = 1.5 K ) with a two-component order parameter (chiral state). Its eutectic system Sr2RuO4-Ru shows a superconducting transition with an enhanced onset of ~ 3 K, though pure Ru is a superconductor with Tc = 0.5 K. In the Sr2RuO4-Ru eutectic, the interface between Sr2RuO4 and Ru is considered to be responsible for the enhanced superconductivity, with its order parameter represented by only one component parallel to the interface near 3 K. Consequently, it is predicted that a second transition to a chiral state occurs at a temperature between 1.5 and 3 K. In order to probe the chiral state, we have measured the ac-susceptibility of Sr2RuO4-Ru eutectic between 2 and 1000 Hz using a homemade ac SQUID magnetometer.
Magnetic excitations in Ca2-xSrxRuO4 near the quantum critical point
O. Friedta, M. Bradenb, P. Pfeutya, S. Nakatsujic, Y. Maenoc
aLaboratoire Léon Brillouin, CEA/CNRS, F-91191 Gif-sur-Yvette Cedex, France
bII. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany
cDepartement of Physics, Kyoto University, Kyoto 606-8502 Japan
We have carried out inelastic neutron scattering experiments on two single crystals of Ca2-xSrxRuO4 in order to investigate the magnetic inelastic response of this system near the ferromagnetic ordering observed for x=0.5. The excitation spectrum in both samples strongly differs from that found in the spin-triplet superconductor Sr2RuO4 which is dominated by incommensurate peaks near (0.3,0.3,0). In Ca2-xSrxRuO4, with x=0.38 and 0.52, we find still incommensurate scattering but situated much closer to the zone-center. These excitations most likely reflect the general tendency of the g-band towards ferromagnetism and are, hence, related to the proposed mechanism for superconductivity in Sr2RuO4.
Electronic and structural properties of organic
superconductor
k-(BEDT-TTF)2Cu[N(CN)2]I
V. S. Yefanova, S. Kagoshimaa, M. A. Tanatarb, T. Ishigurob, V. A. Bondarenkoc, N. D. Kushchd, E. B. Yagubskiid
aDepartment of Basic Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
bDepartment of Physics, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan
cInstitute of Semiconductor Physics, NAS of Ukraine, 41 Prospect Nauki, Kyiv 03028, Ukraine
dInstitute of Problems of Chemical Physics, RAS, Chernogolovka, Moscow Region 142432, Russia
Thermopower and X-ray diffuse scattering were measured in k-(BEDT-TTF)2Cu[N(CN)2]I. Two stage superstructural transformation was shown to be responsible for the formation of the insulating state at ambient pressure as seen in thermopower measurements. The superconducting state was studied by resistance measurements under the uniaxial strain applied along the main crystallographic directions.
Vortex dynamics of organic superconductor k-(ET)2Cu[N(CN)2]Br observed by ultasonic mesurements
Takayuki Simizu, Masahito Yoshizawa, Yoshiki Nakanishi, Mitsuteru Nakamura, Noriyuki Yoshimoto
Department of Materials Science and Engineering , Iwate University, Morioka 020-8551, Japan
Organic superconductors k-(ET)2X (X = Cu(NCS)2, Cu[N(CN)2]Br) show anomalous elastic properties both in the nornal and superconducting states 1. In superconducting state, these salts shows remarkable elastic anomalies in the magnetic field, which mainly come from the interplay between the vortices and the elastic wave. We have measured the vound velocity of Cu[N(CN)2]Br saltwith different experimental configurations. We will discuss the vortex dynamics of this salt by comparing with the previous work 2
Transport properties of q-ET2CsM(SCN)4 (M=Zn,Co) under ultra-high pressure
Masashi Miyashitaa, Hiromi Taniguchia, Kazuhiko Satoha, Masato Hedob, Yoshiya Uwatokob, Kazuya Miyagawac, Kazushi Kanodac
aDepartment of Physics, Saitama University, Saitama, Saitama 338-8570, Japan
bThe Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
cDepartment of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
In order to investigate the electronic states of the organic conductors, q-ET2CsM(SCN)4 (M=Zn,Co), under ultra-high pressure, we performed the resistance measurements up to 8GPa with the cubic anvil press. The insulating states of these salts were suppressed in this pressure range but remained at low temperatures even in 8GPa. The results were discussed in terms of anisotropic pressure dependence of transfer integrals.
Possible change of the superconducting symmetry in the vicinity of the SC-AF transition in NH3A3C60
Yoshihiro Asai
Research Institute for Computational Sciences (RICS), National Institute of Advanced Industrial Science and Technology (AIST), Central 2, Umezono 1-1-1, Tsukuba, Ibaraki 305-8568, Japan and Department of Chemical System Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan
We have studied vertex corrections to both the intraband and interband electron-phonon couplings in the doped C60. The corrections to the Migdal approximation was studied for the self energy of the anomalous Green function. On the basis of our results, we suggest a possible change of the symmetry of the superconductivity in the vicinity of the phase boundary between the superconducting and antiferromagnetic phases of NH3A3C60.
Observation of the Vortex Pinning in YNi2B2C by LT-STS
Hideaki Sakataa, Morimi Oosawab, Nobuhiko Nishidab, Hiroyuki Takeyac, Kazuto Hiratac
aTokyo University of Science, Kagurazaka, Tokyo 162-8601, Japan
bTokyo Institute of Technology, Ookayama, Tokyo 152-8551, Japan
cNational Institute for materials Science, Sengen, Ibaraki 305-0047, Japan
We have performed scanning tunneling spectroscopy measurements on the cut or cracked surface of YNi2B2C. Three distinct regions which are superconducting, metallic and semiconducting were observed. The metallic and semiconducting regions are precipitates which have slightly different compositions from YNi2B2C. Under the magnetic field applied above Tc, the vortices were imaged in the superconducting regions as the increase in the local density of states(LDOS) at Fermi energy. When the applied magnetic field is increased at 4.2K, the LDOS was enhanced along the boundary of the semiconducting precipitates. This enhancement of the LDOS is attributed to a number of pinned vortices at the boundary.
11B NMR study of vortex dynamics in LuNi1.8Pt0.2B2C
Moohee Leea, K. H. Leea, K. H. Kanga, B. J. Meana, K. H. Hahna, K. S. Hahna, S. H. Kima, Moohee Leea, B. K. Chob
aDepartment of Physics, Konkuk University, Seoul 143-701, South Korea
bDepartment of Material Science and Technology, KJ-IST, Kwangju 500-712, South Korea
11B pulsed nuclear magnetic resonance(NMR) measurements have been performed on LuNi1.8Pt0.2B2C superconductor to investigate vortex dynamics. The spectra and the peak point in the superconducting state exhibit a typical local field distribution for a vortex lattice at magnetic field parallel to the c-axis. However, the linewidth of the spectrum is much smaller than expected and the transverse relaxation rate indicates significant thermal fluctuation of vortices. Temperature dependence of 11B NMR spectrum, saddle-point field, linewidth, and transverse relaxation rate are measured to study the change in vortex dynamics originating from the pinning centers of Pt dopants.
Unconventional Superconductivity in YNi2B2C and LuNi2B2C
Peter Thalmeiera, Kazumi Makib
aMax-Planck-Institute for Chemical Physics of Solids, D-01187 Dresden, Germany
bMax-Planck-Institute for the Physics of Complex Systems, D-01187 Dresden, Germany and Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089-0484
The superconductivity in borocarbides is considered to be of strongly anisotropic s-wave type. However both ÖH dependence of the specific heat and H-linear thermal conductivity in the vortex state indicate it belongs to nodal superconductors. We have proposed recently the s+g-wave model, which can account these features. As to the precise location of the nodal points in D(k), the angular dependent magnetothermal conductivity (ADMC) is extremely useful. Also ADMC can distinguish s+g- wave from d-wave superconductivity.
Specific heat and transport measurements in irradiated (K,Ba)BiO3
S. Blancharda, C. Marcenatb, T. Kleina, L.M. Pauliusb, J. Marcusa, K. van der Beekc, M. Konczykowskic
aLEPES/CNRS BP166, 38042 Grenoble Cedex 9, France
bCEA/DRFMC/SPSMS, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France
cSESI/CNRS-UMR 7642, Ecole Polytechnique, 91128 Palaiseau, France
The magnetic field dependence of the thermodynamic transition line in heavy ion irradiated (K,Ba)BiO3 single crystals has been investigated by specific heat measurements. As predicted for the Bose-Glass transition line, we show that the superconducting transition line (HCp(T)) strongly depends on the irradiation dose and angle between the external field and the columnar tracks. In pristine sample, HCp(T) presents an anomalous positive curvature and is progressively shifted towards higher temperature as the irradiation dose is increased. HCp(T) shifts back to the position of the virgin sample for H ^ tracks.
Numerical Study of Phonon Spectra in Strongly Correlated Electron Systems
Kenji Tsutsui, Takami Tohyama, Sadamichi Maekawa
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
Many of the experimental observations such as inelastic neutron scattering data indicate that the phonons may play an important role in the electronic properties of superconducting cuprates. It is well known that there are anomalous behaviors in longitudinal optical oxygen bond-stretching phonon in the CuO2 plane. In this study we examine the phonon dynamics in the electron-phonon-coupled systems. The model Hamiltonians are one-dimensional Hubbard model coupled with phonon system. We perform numerically the exact diagonalization of the Hamiltonians with truncations of phonon Hilbert space. We calculate the phonon excitation spectra and find the broad feature in the spectra in the metallic region. We also calculate the charge and spin excitation spectra and find that the feature in the phonon spectra is caused by the low energy electronic excitations.
1T. Simizu et al., Physica B 281 & 282 (2000) 896.
2M. Yoshizawa et al., J. Low Temp. Phys. 105 (1996) 1745.