Inhomogeneous d-wave state and lattice instability in the three-band Hubbard model for high-Tc cuprates
Takashi Yanagisawa, Shigeru Koikegami, Mitake Miyazaki, Kunihiko Yamaji
Nanoelectronics Research Institute, National Institute of Industrial Science and Technology, Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
The inhomogeneous ground state of the three-band Hubbard model for high-Tc cuprates is investigated by using the variational Monte Carlo method. We evaluate the energy expectation values of the wave function with stripes, d-wave order parameter and lattice deformation in the underdoped region. It is shown that the striped state is stabilized due to the lattice deformation. It is also shown that the superconducting order parameter oscillates in accord with the non-uniform spin and charge distributions and that the superconducting condensation energy is reduced due to the inhomogeneity.
Spin-phonon coupling near the metal-insulator transition in doped HgBa2CuO4.
T. Jarlborg
DPMC, University of Geneva, 24 Quai Ernest-Ansermet, CH-1211 Genève 4, Switzerland
Effects of spin and lattice modulations on the band structure of the high-TC oxide HgBa2CuO4 are studied. Self-consistent band calculations are made for stripe-like modulations due to phonon- or spin-waves in elongated supercells. The virtual crystal approximation is used to study the effect of doping. Modulations of the potential with long-range Fourier components lead to gaps or pseudo gaps depending on the strength of the potential perturbation. The gaps appear at one band below the electron filling of the undoped supercell. The longer the wavelength is, the closer will the gap be to the position of EF in the undoped case. There is a correlation between doping and wavelength of the modulations, since the gain in energy is optimal if the gap is at EF for the doped system. The interaction between spin and phonon waves leads to enhanced coupling l. The pseudogap is a consequence of the stripe modulation.
Possible High Temperature Superconductivity in Systems with Nested Fermi Surfaces Pockets
Kazuhiko Kurokia, Ryotaro Aritab
aDept. of Applied Phys. & Chem., Univ. of Electro-Communications, Chofu-shi,Tokyo 182-8585, Japan
bDepartment of Physics, University of Tokyo, Hongo, Tokyo 113-0033, Japan
We propose that high Tc superconductivity can be achieved in repulsively interacting systems having nested Fermi surface pockets. The idea is that the sign change in the gap function, which is inevitable in superconductivity arising from repulsive interactions, can take place across the pockets, so that the gap is fully open on each pocket, resulting in a high Tc. As an example, we show using fluctuation exchange approximation that the Hubbard model on a series of dimerized lattices can exhibit Tc ~ 0.1t (t is the hopping integral), which is almost an order of magnitude larger than that in the Hubbard model on a square lattice, a model for the high Tc cuprates.
Effects of two-site correlations in the two-dimensional Hubbard model
Satoru Odashima, Adolfo Avella, Ferdinando Mancini
Dipartimento di Fisica Ë.R.Caianiello" - Unitá INFM di Salerno, Universitá degli Studi di Salerno, Baronissi(SA), I-84081, Italy
Electronic states of the two dimensional Hubbard model are investigated by use of the Composite Operator Method. In this paper, we present the way to incorporate the effects of two-site composite excitations as dynamical corrections to the electronic propagator. The used approximation goes well beyond the conventional two-pole approximations. The electronic structure is discussed in detail and the results are compared with those obtained by numerical simulations.
Electron-Phonon Interaction in HTcS: Tunneling and Andreeving Experiments on HTcS oxides at High Pressure
Vladimir M. Svistunov
Donetsk A.Galkin Institute for Physics & Technnology, Academy of Sciences, Donetsk 83114, Ukraine
A short review is presented of the work, that done in collaboration with Japanese colleagues, on tunneling (superconducting and normal state) and Andreev transfer of charge in high-temperature layered cuprates. The distinctive feature of our experimental investigations is the use of High Pressure. The well distinguished phonon structure in TDOS was observed and softing of the high-frequency modes has been found also, that explains the observed rise in 2D/Tc ratio in the framework of the strong EPI model. Attention is directed mainly toward a critical analysis for EPI spectral function that was obtained from tunneling measurements in normal (self-energy corrections) and superconducting states.
Dirac Monopole and Spin Hall Conductance for Anisotropic Superconductivities
Yasuhiro Hatsugaia, Shinsei Ryub
a Dept. of Applied Physics Univ. of Tokyo and PRESTO, JST, 7-3-1 Hongo, Bunkyo-ku, Tokyo, JAPAN
b Dept. of Applied Physics Univ. of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, JAPAN
Concept of the topological order is useful to characterize anisotropic superconductivities. The spin Hall conductance distinguishes superconductivities with the same symmetry. It is given by several different but equivalent topological expressions by the Berry's parametrization. They are covering degree of a surface around the Dirac' monopole, an intersection number of the Dirac's string with the surface and total vorticity of relative phase of a quasiparticle wavefunction. We have calculated the topological numbers for various anisotropic superconductivities with singlet and triplet order parameter. Quantum phase transitions for the various superconductivities are also demonstrated by these topological objects.
Transistor Doping Experiments indicate that Phenomenological Bond Order Rules are common to high Tc Superconductivity
H. Oesterreicher
Dept. of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 920193-0506.
Aspects of transistor doping in CaCuO2 and C60 are in line with expectations from bond ordering [BO] principles. A universal sequence of Tc development with hole doping is apparent, including linear portions up to an optimal BO with a slope corresponding to a radical formalism [RF], which extrapolate to Tc=0 at h=o, and a sharp peak with another linear decrease thereafter. The hallmarks of the BO filling sequence further include Tc onset at a critical BO, where an adverse BO is cooperatively transformed to a beneficial one with twice the RF slope. Mechanisms of the bond order filling are extracted from the slopes. Within the RF slope a region exists with tendencies to electonic freezing [e.g. 1/8 in CaCuO2].
Relation between d-density wave of electron and staggered flux of spinon
Koichi Hamada, Daijiro Yoshioka
Department of Basic Science, University of Tokyo, Komaba 3-8-1, Japan
A d-density wave(ddw) order of electron in 2-dimensional t-J model is analyzed in saddle point level using the U(1) slave boson formalism. We considered not only the staggered flux(s-flux) order of spinon but also the s-flux order of holon. This analysis provides the relation between the s-flux order of spinon and the ddw order of electron. We discovered a new phase in the phase diagram. In this phase, there is a s-flux order of spinon, but no ddw order of electron.
Our results are 1) a region of electron d-density wave exists, 2) there is no coexistence of ddw and d-wave pairing(singlet-RVB), in all region of phase diagram (finite T and T=0 ), and 3) the ground state is a purely superconducting state.
Difference of Electronic States between Hole- and Electron-Doped Cuprtaes
Takami Tohyama, Sadamich Maekawa
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
In electron-doped high-Tc cuprates, the antiferromagnetic phase remains up to electron concentration x ~ 0.15, while a small amount of holes is enough to kill the antiferromagnetic phase in hole-doped high-Tc cuprates. Such asymmetry causes differences in physical properties between the two types of cuprates. We study the electronic states of the electron-doped cuprates and compare them with those of hole-doped cuprates, by using numerically exact diagonalization technique for a t-J model with long-range hoppings, t¢ and t¢¢. Examining the optical conductivity, spectral function, and chemical potential shift, we find remarkable differences of the electronic states between the electron- and hole-doped cuprates. The calculated results are consistent with experimental data reported recentely.
Anisotropic superconductive transition on CeRu3B2
Toshifumi Taniguchi, Keiji Hashimoto, Toyohisa Takaishi, Yoshikazu Tabata, Shuzo Kawarazaki
Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
The superconductivity on the valence fluctuation compound CeRu3B2 (the space group is P6/mmm, Tc=1.0 K) is meaningful, especially when it is compared with the superconductivity on CeRu2. However, all of the previous experiments were done on the polycrystalline samples. We made the single crystal of CeRu3B2 and measured its resistivity and ac susceptibility for a and c axes. The measurements show the superconductivity at Tc=1.0 K as the previous experiments, but the anisotropic behavior has been observed between 1.1 K and Tc.
Effect of anisotropic strain on the electronic properties of the pressure induced superconductor CePd2Si2
Albin Demuer, Alexander T. Holmes, Didier Jaccard
DPMC, University of Geneva, 24 Quai E-Ansermet, 1211 Geneva 4, Switzerland
We report resistivity and calorimetric measurements on two single crystals of CePd2Si2 pressurised up to 7.4 GPa. A weak uniaxial stress induced in the pressure cell demonstrates the sensitivity of the physics to anisotropy. Stress applied along the c-axis extends the whole phase diagram to higher pressures and enhances the superconducting phase emerging around the magnetic instability, with a 40% increase of the maximum superconducting temperature, Tc, and a doubled pressure range. Calorimetric measurements demonstrate for the first time the bulk nature of the superconductivity. Analysis of both the initial slope of the upper critical field and the normal state resistivity behaviour provides evidence about the nature of quasi-particles involved in superconductivity.
Effect of Substitution in the (Gd1-xCax)Ba2Cu3Oy and Gd(Ba2-xAx)Cu3Oy (A = Ca, Sr) Superconducting Compounds
C. H. Chin, H.-C. I. Kao
Department of Chemistry, Tamkang University, Tamsui251, Taiwan
Introducing Ca or Sr ion into GdBa2Cu3Oy, Ca acting as a hole dopant at the R site and a hole filler at the Ba site. Tc is linearly dependent on the orthorhombicity of the unit cell for all three series and it is also correlated to the Ð O(1)-Ba-O(1) along the unit cell a-axis, which is the relative positions of the Ba and the epical O(1) sites.
Nature of Vortex Solid to Liquid Transition in Irradiated Samples of BSCCO
Satyajit S. Banerjeea, Eli Zeldova, Marcin Konczykowskib
aDept. of Condensed Matter Physics, Weizmann Institute of Science, Rehovot-76100, Israel
bLaboratoire des Solides Irradies, CNRS UMR 7642, Ecole Polytechnique, 91128 Palaiseau, France
Using the Differential Magneto-Optical technique, we have imaged the melting process of the vortex matter in the presence of columnar pins in Bi2Sr2CaCu2O8. We find that the columnar defects produce and upward shift in the melting line. The shift increases not only as one goes to lower temperatures but also with the increasing density of columns. In irradiated regions of the sample despite strong pinning, we find that the first order melting transition persists and terminates at a critical point. This critical point moves to a higher temperatures with increasing density of pins. We have discovered an sharp inflection in the curvature of the vortex solid to liquid transition line in the irradiated regions of the sample. The results are summarized in a new vortex matter phase diagram in the presence of columnar defects.
Growth of Nd1-xCexBa2Cu3Oy single crystals by travelling solvent floating zone method
Y. Fujita, H. Sugisaki, H. Iwasaki
School of Materials Science, JAIST, Asahidai 1-1, Tatsunokuchi, Ishikawa, 923-1292, Japan
Superconducting characteristics have been studied from the viewpoint of the annealing condition on single crystals of the Nd1-xCexBa2Cu3Oy system grown by the travelling solvent floating zone (TSFZ) method. As for single crystal, it was proved that there were no impurities by the powder X-rays analysis. The rate of RE was 1.3:2:3 by EDX analysis, and the concentration of Ce was about 10 - 12%. The samples which were annealed at 850 °C in an Ar atmosphere, following an anneal at 300° C in an O2 atmosphere showed a drastic improvement of the superconducting character in the crystals, that is, Tc is quite high and the transition width DTc becomes sharp. This result suggests the possibility that Ce replaces at the Re site in the ReBa2Cu3Oy structure.
Preparation of Tl-1223 and 2212 superconductor thin film and their microwave properties
A Sundaresana, H Asadaa, H Kitoa, A Iyoa, Y Tanakaa, M Kusunokib, S Ohshimab
aNanoelectronic Research Institute of AIST, Tsukuba Centra 2, 1-1-1 Umezono, Tsukuba 305 8568 Also JST-CREST, Kawaguchi Center Building, 1-8, Honcho 4-Chome, Kawaguchi 332-0012, Japan
bFaculty of Engineering, Yamagata University, Yonezawa, 992-8510, Japan
The superconductor TlBa2Ca2Cu3Oy (Tl-1223),with Tc(133 K) comparable to Hg-1223 which holds a record of highest Tc, is a best candidate for microwave electronic device appliations. Therefore, we have investigated microwave properties of Tl-1223 films prepared on CeO2 buffered sapphire substrate by an ex situ process. The observed Tc was lower due to partial substiution of Sr for Ba and Jc was 2×106 A/cm2 at 77 K. The surface resistance was measured by dielectric resonator technique with a frequency of 22 GHz. The details of these results along with those of Tl-2212 will be presented.
Annealing effect of the irreversibility fields in (Cu, C)-12(n-1)n (n = 3, 4)
Manabu Hiraia, Akira Iyob, Hijiri Kitob, Yasuharu Kodamab, Adrian Crisanc, Kazuyasu Tokiwad, Tsuneo Watanabed, Juichiro Araia, Yasumoto Tanakab
aDept. of Phys., Tokyo Univ. of Sci, Noda, Chiba, 278-8510 Japan
bAIST and CREST, Tsukuba, Ibaraki 305-8568 Japan
cAIST and CREST, Tsukuba, Ibaraki, 305-8568, Japan and NIMP, POB MG-7, Bucharest Romania
dDept. of Appl. Elec., Tokyo Univ. of Sci., Noda, Chiba, 278-8510 Japan and CREST
(Cu, C)Ba2Can-1CunOy ((Cu,C)-12(n-1)n) is a promising candidate for applications at 77 K, because it shows high-Tc( > 100 K) and high-Hirr due to a metallic charge reservoir layer. Polycrystalline samples (n = 3, 4) prepared under high pressure were annealed on various reduction conditions. In case of n = 4 Jc and Hirr were improved by the annealing while the Tc remained almost the same, which was quite different from n = 3. This difference in behaviour of samples with n = 3 and n = 4 will be discussed.
Addition of LiF to (Cu,C)-1234 bulk superconductor
P. Badicaa, A. Crisana, A. Iyob, H. Kitob, M. Hiraic, Y. Tanakab
aNeRi, AIST Tsukuba Central 2, 305-8568 Japan and NIMP, POB MG-7, Bucharest, Romania
bNeRi, AIST Tsukuba Central 2, 305-8568 Japan and CREST, JST, Kawaguchi, Saitama, 332-0012 Japan
cNeRi, AIST Tsukuba Central 2, 305-8568 Japan and Science Univ. of Tokyo, 2641 Yamazaki, Noda, Chiba, Japan
(Cu,C)-1234 with addition of LiF has been synthesized by high-pressure technique. LiF is decreasing the synthesis temperature of the superconducting phase for the same oxygen content in the starting composition. LiF promotes the formation of the (Cu,C)-12(n-1)n, n higher than 4, and growth of larger (Cu,C)-1234 grains. Morphology and composition was analysed by SEM and EDS. Superconducting transition was measured by both transport and AC susceptibility, and critical current densities were determined by DC magnetization studies in fields up to 14 T, in the frame of critical state models.
Effects of oxygenation processes on (Nd,Gd)1Sr2RuCu2Ox synthesis
Antonio Vecchionea, Marcello Gombosa, Daniela Sistib, Consiglia Tedescob, Sandro Pacea
aI.N.F.M. U.d.R. Salerno and Dipartimento di Fisica Ë. R. Caianiello", Universitá di Salerno, via Salvador Allende, I-84081 Baronissi (Salerno), Italia.
bDipartimento di Chimica, Universitá di Salerno, via S. Allende, I-84081 Baronissi (Salerno), Italia.
In this work we report on the effect of oxygenation processes on the structure and composition of GdSr2RuCu2Ox and NdSr2RuCu2Ox compounds. By x-ray diffraction analysis, evidence of a progressive amelioration of samples composition due to the disappearance of impurities related peaks has been observed. Evolution of crystalline structure after oxygen annealing treatments has been studied too. Magnetisation measurements data in function of oxygenation are also reported.
Magnetic investigations of the high-Tc superconductor Hg-1212
K. Lüdersa, P. Schilbea, M. Baenitzb, D. A. Pavlovc, A. Abakumovc, E. V. Antipovc
aPhysics Dept., Free University Berlin, D-14195 Berlin, Germany
bMax-Planck-Inst. for Chemical Physics of Solids, D-01187 Dresden, Germany
cDept. of Chemistry, Moscow State University, 119899 Moscow, Russia
The magnetic properties of several powder samples of the high-TC superconductor Hg-1212 are investigated by means of ac and dc susceptibility measurements. The temperature dependence of irreversibility fields is determined up to 14 T using different criteria, e.g. the maximum in the imaginary part of the ac susceptibility. In case of Tl substitution the irreversibility line is clearly enhanced. The results are discussed within a depinning model developed by Matsushita. The relation of the real part to the imaginary part of the ac susceptibility shows without any free parameters a good agreement with the simple Bean-model.
Crystal growth of La2-xCexCuO4
Kunihiko Oka, Hajime Shibata, Satoshi Kashiwaya, Hiroshi Eisaki
National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8568, Japan
Single crystals of La2-xCexCuO4 have been successfully grown by the traveling-solvent floating-zone (TSFZ) method. The optimum condition of the atmosphere on the growth was determined. The effect of the annealing atmosphere and temperature was also studied. The characterization of the crystals by scanning electron microscopy-X-ray energy dispersion spectroscopy (SEM-EDS) and magnetic susceptibility measurement is reported.
Anisotropic Properties of RuSr2GdCu2O8 Thin Films Epitaxially Grown on SrTiO3 (100) and (110) Substrates
Daisuke Serita, Takahiro Kato, Kazuki Yamanaka, Yuh Yamada, Shugo Kubo
Department of Materials Science, Shimane University, 1060 Nishikawatsu, Matsue 690-8504, Japan
For the examination of physical property dependence on the crystalline orientation direction in RuSr2GdCu2O8 (Ru1212), in which superconductivity and a magnetic order coexist, we have tried crystalline-orientation-controlled growth of Ru1212 thin films on SrTiO3 (STO) (100) and (110) substrates. 4-circle X-ray diffractometry has confirmed that Ru1212 (001) films grow epitaxially on STO (100) and Ru1212 (103) on STO (110). The results will be reported on the dependence of electrical and magnetic properties on Ru1212 crystalline orientation directions.
Tunneling-Spectroscopic Evidence for Unconventional Pairing Interaction in Bi2Sr2CaCu2O8+d
Minoru Suzukia, Kenkichi Anagawaa, Yoshiharu Yamadaa, Takao Watanabeb
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
The quasiparticle density of states (DOS) is measured as a function of magnetic field up to 9 T by the short-pulse interlayer tunneling spectroscopy for slightly overdoped Bi2Sr2CaCu2O8+d. The tunneling spectrum in the absence of a magnetic field exhibits typically the superconducting coherence peak and the pseudogap peak. From the field dependence, it is found that little DOS is transferred from the Fermi level to the coherence peak by the superconducting condensation, but rather the coherence peak gathers DOS at energies apart from the Fermi level by 70 to 80 mev. This is totally at variance with the DOS transfer of the BCS type, implying that unconventional pairing interaction occurs in this system.
Scanning Tunneling Microscopy Studies of High Jc NEG123 Crystals
Masato Nishiyamaa, Miryala Muralidhara, Naomichi Sakaia, Keiichi Ogawab, Naoki Koshizukaa, Masato Murakamia
aSuperconductivity Research Laboratory, International Superconductivity Technology Center, 1-10-13 Shinonome, Koto-ku, Tokyo 135-0062, Japan
bYokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama, 236-0027, Japan
We have performed scanning tunneling microscope and spectroscopy (STM/STS) measurements on (Nd,Eu,Gd)Ba2Cu3Oy(NEG123) crystals grown by an oxygen-controlled-melt-growth (OCMG) process at room temperature under ultrahigh vacuum (UHV) condition. We observed a modulation structure on a cleaved surface of the samples with high Jc and high irreversible field Hirr more than 10 T at 77 K. This structure may be associated with an element substitution and the good Jc-B property. This work was supported by New Energy and Industrial Technology Development Organization(NEDO).
Energy gap evolution over wide temperature and hole-doping ranges in Bi2212
Migaku Oda, Naoki Momono, Masayuki Ido
Department of Physics, Hokkaido University, Sapporo 060-0810, Japan
On the basis of tunneling experiments on Bi2212/vaccum/Bi2212 junctions fabricated using STM, we report that there exist two kinds of pseudogaps (LPG and SPG) with different characteristic energies. The LPG, which is 3 to 4 times larger than the SC gap (SCG), develops below ~ Tmax, where the magnetic susceptibility starts to decrease because of the development of AF spin fluctuations. On the other hand, the SPG develops progressively below the mean-field characteristic temperature Tco for d-wave superconductors in addition to the LPG, and then evolves into the SCG at Tc, suggesting that it will be some kind of precursor of superconductivity. We also report that in accordance with the SC transition, the high-energy feature of quasiparticle spectrum outside the SCG, relating to the LPG, changes from a broad hump to a clear dip and hump, in addition to the rapid growth of SCG from SPG.
Scaling Behavior of the C-axis I-V Characteristics for Bi-2212 Single Crystal
Saijun Huanga, Guohua Zhanga, Jing Chena, Sheng Luoa, Yusheng Heb
aSchool of Applied Science, University of Science and Technology Beijing, Beijing 100083, China
bNational Laboratory for Superconductivity & Institute of Physics, CAS, Beijing 100080, China
The c-axis isothermal I-V curves of BSCCO-2212 single crystal in different magnetic fields have been investigated. Following the normal scaling procedure of vortex glass theory, all of the isothermal I-V curves in the same c-axis magnetic field collapse onto two curves and the relevant scaling critical exponents are extracted. This strongly suggests the occurrence of a vortex-glass transition of c-axis direction upon decreasing temperature. The system dimensions are of the order of 3 and 2.5 in the applied c-axis magnetic fields of 0.04T and 0.1T respectively. It hints that the 2D behavior shows up at higher applied magnetic fields. This is consistent with the assumption that BSCCO-2212 single crystals are made of a series of stacks weakly coupled by intrinsic Josephson junctions.
Vortex-antivortex annihilation in underdoped
Brian W. Gardnera, Janice C. Wynna, Doug A. Bonnb, Ruixing Liangb, Walter N. Hardyb, Kathryn A. Molera
aGeballe Laboratory for Advanced Materials, Stanford University, Stanford, CA 94305, USA
bDepartment of Physics and Astronomy, University of British Colombia, Vancouver, BC V6T 1Z1, Canada
Locally applied magnetic fields can be used to create vortex-antivortex pairs in superconducting films and thin crystals. These pairs typically annihilate on some timescale which depends on temperature. We use a 21mm diameter field coil integrated onto a scanning Superconducting QUantum Interference Device (SQUID) to create and observe vortex-antivortex pairs. We present measurements of the distribution of annihilation times as a function of temperature, which should allow us to determine the pinning forces for vortices in these highly underdoped samples of .
Incommensurate Properties of high-Tc superconductor YBa2Cu3O6.93
Tetsuya Yokooa, Masatoshi Araia, Chris Frostb, Setsuko Tajimac, Yu Shioharac, Yasuo Endohd
aInstitute of Materials and Structure Science KEK, Oho 1-1, Ibaraki, Tsukuba 305-0801, Japan
bRutherford Appleton Laboratory, Chilton, Didcot, Oxon, United Kingdom
cSuperconductivity Research Laboratory, ISTEC, Koutou-ku, Tokyo 135, Japan
dDepartment of physics, Tohoku University, Aoba, Sendai 980, Japan
The resonance and incommensurate peaks in optimally doped high- Tc superconductor YBa2Cu3O6.93 are observed by means of TOF neutron scattering technique in a wide q-E space. Overall dynamical properties around (p, p) suggest the incommensurability of d @ 0.1 corresponds to the previous triple-axis measurement. Obtained d=0.1 is smaller than that expected from stripe model. In the high frequency region it is also found the same type of resonance and incommensurate peaks at E=53 meV. This work was partly supported by NEDO.
Incommensurate, dispersive, density of states modulations in Bi2Sr2CaCu2O8+d
K. McElroya, J.E. Hoffmana, D.H. Leea, K.M. Langa, H. Eisakib, S. Uchidac, J.C. Davisa
aDepartment of Physics, University of California, Berkeley, CA 94720-7300, USA.
bAIST, 1-1-1 Central 2, Umezono, Tsukuba, Ibaraki 305-8568, Japan.
cDepartment of Superconductivity, University of Tokyo, Tokyo 113-8656, Japan.
Scanning tunneling spectroscopy of Bi2Sr2CaCu2O8+d reveals weak, incommensurate, spatial modulations in the tunneling conductance. When images of these energy-dependent modulations are Fourier analyzed the dispersion of their wavevectors can be determined. Comparison of the dispersions with angle-resolved photoemission indicates that quasiparticle interference, due to elastic scattering between specific regions of the Fermi surface, provides a consistent explanation for the conductance modulations.
Reversible and irreversible behavior in La1.45Nd0.40Sr0.15CuO4 stripe phase superconductor
Kh. A. Ziq, Kh. A. Ziq
Department of Physics, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
Magnetization measurements for La1.45Nd0.40Sr0.15CuO4 single crystal have been performed in order to investigate the effects of spin-charge ordering on the reversible magnetization and the irreversible fields along the ab-plane and the c-axis. Moreover, the maximum pinning forces obtained from the irreversible magnetization along c and in the ab-plane were found to scales with (Hc)b for both crystallographic directions.
Evidence for Spin Density Wave in the Superconducting YBa2Cu4O8
Takekazu Ishidaa, Kazumasa Katayamaa, Nariaki Yamamotoa, Seiji Adachib, Setsuko Tajimab
aDepartment of Physics and Electronics, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
bSRL-ISTEC, 10-13 Shinonome 1-chome, Koto-ku, Tokyo 135-0062, Japan
The torque curves of YBa2Cu4O8 show the multiple peak effects when the field direction is scanned between the c and a axes. Especially, the position of the first peak, which appears at qca @ 90 ±10°, is independent of T and H. However, the first peak does not appear when the field direction is scanned between the c and b axes. This strongly indicates that the first peak at qca @ 90±10° comes from the CuO double chains and/or the induced anisotropy in CuO2 planes. We propose that the electronic spin modulation along the a axis with the long period of 20a0 is responsible for the appearance of the first peak in the superconducting states at temperatures below 40 K. This work is partially supported by New Energy and Industrial Technology Development Organization (NEDO).
Anisotropic electromagnetic in-plane response of weakly doped La2-xSrxCuO4.
Michael Dumma,b, Dimitri N. Basovb, Seiki Komiyac, Yoichi Andoc
a1. Physikalisches Institut, Universität Stuttgart, 70550 Stuttgart, Germany
bDepartment of Physics, University of California, San Diego, La Jolla, CA 92093, USA
cCentral Research Institute of Electric Power Industry, Tokyo, Japan
We report on the anisotropy of both in-plane electronic conductivity and lattice dynamics examined in the weakly doped phase of a prototypal high-Tc system La2-xSrxCuO4 (x = 0.03 and 0.04) with infrared spectroscopy. Evidence for spin stripes in these materials is well documented. Our data for phonon modes indicate that spin stripes are accompanied by quasi-static charge ordering. We also find significant anisotropy of the electronic response within the CuO2 planes with enhancement of the conductivity along the stripe direction in the limit T,w® 0. These results uncover a complex electronic behavior due to stripes that is beyond an idealized picture of strictly 1D charge channels embedded into AFM insulator.
Josephson Plasma in Ru- and Fe-cuprates
Hiroyuki Shibata
NTT Corporation, NTT Basic Research Laboratories, Atsugi-shi, Kanagawa 243-0198, Japan
Recently, much attention has been paid to Ru- and Fe-cuprates, as the coexistence of superconductivity and ferromagnetism has been reported in some of these compounds. Here, we report the Josephson plasma of these compounds to investigate the interlayer coupling between the superconducting layers through the magnetic layers. We found that the Josephson plasma is observed at 8.5 cm-1 and 13 cm-1 for ferromagnetic RuSr2GdCu2O8 and RuSr2Eu2-xCexCu2O10 (x = 0.5), and it largely increases to 35 cm-1 and 31 cm-1 for non-ferromagnetic Ru1-xSr2GdCu2+xO8 (x = 0.3) and FeSr2YCu2Oy, which indicates a large reduction in the Josephson coupling at the ferromagnetic RuO2 block layers. The temperature dependence of the plasma excludes the possibility of the 0 - p phase transition in the ferromagnetic cuprates. We also discuss about the anomalous features of the plasma in the Ru-cuprates.
Effect of heavy-ion irradiation on the pinning properties of MgB2
Noriko Chikumotoa, Ayako Yamamotob, Marcin Konczykowskic, Masato Murakamia
a Superconductivity Res. Lab., ISTEC, 1-16-25 Shibaura, Minato-ku, Tokyo 105-0023, Japan
bSuperconductivity Res. Lab., ISTEC, 1-10-13 Shinonome, Koto-ku, Tokyo 135-0062, Japan
c Lab. des Solides Irradies, Ecole Polytechique, Palaiseau 91128, France
Pinning properties of MgB2 superconductors irradiated with 5.8 GeV Pb-ions are reported. According to the TEM observation, we found that the irradiation introduces spherical amorphous defects, which is different from the case of cuprate superconductors in which columnar defects are introduced. After the irradiation, enhancement of Jc was observed at high magnetic field range. We also found a slight shift of the irreversibility lines to higher temperature. This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) as Collaborative Research and Development of Fundamental Technologies for Superconductivity Applications.
Point-contact spectroscopy of MgB2 in high magnetic fields
P. Szaboa, P. Samuelya, J. Kacmarcika, T. Kleinb, J. Marcusb, D. Fruchartc, S. Miragliac, L. Jansend
aInstitute of Experimental Physics, Slovak Academy of Sciences, SK-04353 Kosice, Slovakia
bLEPES, Centre National de la Recherche Scientifique, B.P. 166, F-38042 Grenoble Cedex 9, France.
cLC, Centre National de la Recherche Scientifique, BP 166, 38042 Grenoble Cedex 9, France.
dGrenoble High Magnetic Field Laboratory, MPI and CNRS, B.P. 166, F-38042 Grenoble Cedex 9, France.
A strong experimental support for the multiband model of the superconductivity in MgB2 is presented. Our point-contact spectroscopy data clearly reveal an existence of two distinct superconducting energy gaps. Our measurements in magnetic fields up to 1 Tesla, published in our previous paper (P.Szabo et al. Phys. Rev. Lett. 87, 137005 (2001)) show directly in the raw data a presence of the two superconducting gaps at all temperatures up to the same bulk transition temperature. The present contribution represents our analysis of the point-contact spectra obtained at higher magnetic fields up to 10 Tesla.
Specific heat of ceramic and single crystal MgB2
Alain Junoda, Yuxing Wanga, Frederic Bouqueta, Pierre Toulemondea, Morten R. Eskildsena, Michael Eistererb, Harald W. Weberb, Sergey Leec, Setsuko Tajimac
aDPMC, University of Geneva, CH-1211 Geneva 4, Switzerland
bAtomic Institute of the Austrian Universities, A-1020 Vienna, Austria
cSuperconductivity Research Laboratory, Shinonome 1-10-13, Koto-ku, Tokyo 135-0062, Japan
The two-gap structure of MgB2 gives rise to unusual thermodynamic properties which depart markedly from the BCS model, both in their temperature- and field-dependence. We report measurements of the specific heat up to 16 T on ceramic and single crystal samples, which demonstrate these effects in bulk. The low-temperature mixed-state specific heat reveals a field-dependent anisotropy, and points to the existence of unusually large vortices, in accord with local density-of-states measurements by scanning tunneling spectroscopy. It is finally shown that a suitable irradiation process nearly doubles Hc2 in bulk.
Mechanical Milling of MgB2
Hideaki Takano, Akihiro Kanno, Michio Takahashi, Shigeyuki Murayama
Department of Materials Science and Engineering, Muroran Institute of Technology, Muroran, Hokkaido 050-8585, Japan
Changes in structure and magnetization of MgB2 by mechanical milling have been examined by means of X-ray diffraction and magnetization measurements. Powder sample we used is commercially available and contains a small amount of MgO. Mechanical milling was done between 0h and 384h. The intensity of the Bragg peaks decreases and the width increases with milling. This means that the crystallite size became smaller and the strain in the crystal structure increases. All samples show the superconductive transition at Tc=39K and Tc does not change by milling. The diamagnetization caused by superconductivity decreases with increasing milling time. This suggests that mechanical milling acts on not changing a superconductive property in MgB2 but only destroying a superconductive state in MgB2.
Harmonic susceptibilities and pinning properties of MgB2 bulk superconductors
Carmine Senatorea, Massimiliano Polichettia, Danilo Zolaa, Sandro Pacea, Giovanni Giunchib
aDipartimento di Fisica, Universita' di Salerno and INFM, Via S. Allende, Baronissi (SA), I-84081, Italy
bEDISON S.p.A., Foro Bonaparte 31, Milano, I-20121, Italy
The fundamental and third harmonics of the ac magnetic susceptibility have been studied on MgB2 bulk superconductors, obtained by reactive liquid infiltration. In particular, measurements have been performed as a function of the temperature, the dc magnetic field, the ac field amplitude and frequency. Moreover, in order to understand the pinning properties characteristic of our samples, the experimental results have been compared to susceptibility curves obtained by means of analytical and numerical calculations for the non-linear magnetic diffusion equation. In this way, information concerning the dynamical regimes which govern the vortex motion have been also evaluated.
Superconducting Properties of B on Mg Bilayer Films Sequentially Deposited at Low Substrate Temperatures
Shinji Yataa, Gen Shimizua, Yuh Yamadaa, Shugo Kuboa, Akiyuki Matsushitab
aDepartment of Materials Science, Shimane University, 1060 Nishikawatsu, Matsue 690-8504, Japan
bNational Research Institute for Metals, 1-2-1 Sengen, Tsukuba 305-0047, Japan
A simple new method for low temperature synthesis of intermetallic compound superconductor MgB2 films is presented. In this method, bilayers are prepared by sequential evaporation of B on Mg film layer which is deposited at substrate temperatures around 523K. The formation of superconducting thin films with Tc of about 30K has been confirmed by means of this simple preparation method. The growth of MgB2 films on various substrates including plastic ones and their superconducting properties will be reported.
Comparative Study on Anisotropic Superconducting Properties of MgB2
Zhixiang Shia, Aswini K. Pradhana, Masashi Tokunagaa, Tsuyoshi Tamegaia, Yoshihiko Takanob, Kazumasa Toganob, Hijiri Kitoc, Hideo Iharac
aDept. of Appl. Phys., The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
bNational Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan
cNational Institute of Advance Industrial Science and Technology, Tsukuba 305-8568, Japan
The anisotropic superconducting properties of MgB2 are still under debate due to the span of the anisotropic parameter g = Habc2/Hcc2 from 1.1 to 13. In this paper, we report our comparative study of g on single crystals and dense poly-crystals by both transport and magnetic measurements. At temperatures near Tc, the g values for single crystals and polycrystals are about 3 and 4.5, respectively. They show weak temperature dependence. The difference may be resulted from different impurity levels in both samples. The anisotropic superconducting properties in ab-plane will also be reported.
Electric Transport Study of Superconducting MgB2 Wire
Qingfei shena, Xu Xieb, Chunguang Lia, Zhengxiang Gaob, Yusheng Hea
aNational Laboratory for Superconductivity & Institute of Physics, CAS, Beijing 100080, China
bPhysics Department, Peking University, Beijing 100871, China
Superconducting MgB2 wires were made by painting mixture of boron fiber and magnesium powder on tungsten core. The superconducting layer of the wire is about 0.5mm in thickness and 1.5×10-6 cm2 in cross-section area. Special steps have been done on the MgB2 wires to achieve good ohmic contact. R-T curves show that Tc of the MgB2 wire is about 39.4 K with transition width of 1.1 K. In order to reduce the self-heating effect, pulse current method has been used to study the I-V characteristics systematically in a large current range. This kind of MgB2 wire shows a much sharp normal state-superconducting (N-S) transition in the resulted R-I curves. The results and the mechanism of vortex dynamics during the N-S transition will be discussed in the light of the existing vortex dynamics models.
Magnetization and Irreversibility Field in Powderd MgB2 Superconductor
Tadahiro Akunea, Hiroyuki Abea, Nobuyoshi Sakamotoa, Yasukuni Matsumotob
aDept. of Electr. Enginr., Kyushu Sangyo University, 2-3-1 Matsukadai, 813-8503 Fukuoka, Japan
bDept. of Electr. Eng., Adv. Mate. Inst., Fukuoka Univ., 8-19-1 Nanakuma, 814-0180 Fukuoka, Japan
Magnetizations and AC susceptibilities were measured on powdered new superconductor MgB2 using a SQUID magnetometer and a PPMS susceptometer at temperature range 4.5-40 K under DC magnetic fields up to 14 T. Particle diameters d of powdered MgB2 specimens are 20 < d < 30 mm (MgB2-20) and 50 < d < 63 mm (MgB2-50). Magnetization curve for MgB2-50 sample is symmetric and larger than that for MgB2-20 sample. Asymmetric curve for MgB2-20 sample may be caused by the effect of surface screening current. Dependence of the irreversibility fields estimated from the width of magnetization curves and the imaginary parts of the AC susceptibilities on temperature is discussed by comparing with those of oxide superconductors.
Thermoelectric power of hot deformed MgB2
M. Schneidera, A. Gladuna, D. Lippa, A. Handsteinb, H. Vinzelbergb, S.-L. Drechslerb, K.-H. Müllerb, A. T. Burkovc
aInstitut für Tieftemperaturphysik, Technische Universität Dresden, D-01062 Dresden, Germany
bInstitut für Festkörper- und Werkstofforschung e. V., D-01171 Dresden, Postfach 270116, Germany
cA. F. Ioffe Physical-Technical Institute, Russian Academy of Sciences, Sankt-Petersburg, Russia
The thermoelectric power and the electrical resistivity have been measured for a MgB2 sample, textured by hot deformation, in the range from 2 K up to 800 K. The thermopower rises from 0.6 mV/K at the superconducting transition at 38.5 K to a maximum value of 7.0 mV/K at 400 K and then decreases to 5 mV/K at 800 K. The electrical resistivity exhibits only a slight negative deviation from the linear behaviour with temperatures above room temperature. The correlation between transport properties and microstructure is discussed.
Investigation of the Interaction, Induced by AC Magnetic Field, of the Vortex Lattice with Microwave in BSCCO
D. Shaltiela, D. Shaltiela, M. Golosovskyb, M. Bezalelc, T. Tamegaid, E. Walkere
aRacah Institute of Physics, Hebrew University of Jerusalem, Jerusalem, Israel
bRacah Institute of Physics, Hebrew University of Jerusalem, Jerusalem, Israel
cRacah Institute of Physics, Hebrew University of Jerusalem, Jerusalem, Israel
dDepartment of Applied Physics, The University of Tokyo, Hongo, Tokyo Japan
ePhysics Department of Condensed Matter, University of Geneva, Geneva
The "vortex shaking" effect where an ac magnetic field b||a-b in high Tc's enhances the vortex lattice relaxation towards the thermodynamic equilibrium, is investigated via the microwave dissipation induced by the ac field in BSCCO. We show, for the first time, that the ac field induces simultaneously collective motion of staircase vortices and collective motion of Josephson vortices.
Singular and Nonsingular Vortices in High-Temperature Superconductors
D. A. Ryzhov, A. S. Bystrov, A. S. Mel'nikov, I. M. Nefedov, I. A. Shereshevskii, P. P. Vysheslavtsev
Institute for Physics of Microstructures RAS, 603950 Nizhny Novgorod, GSP-105, Russia
The single flux line structure in anisotropic (d+s)-wave superconductor is analyzed within the Ginzburg-Landau (GL) theory. The singular vortex structure and the angular dependence of the lower critical field Hc1 are studied as a function of magnetic field orientation for both weak and strong anisotropy limits. The arrangement of s-wave unit vortices induced in the core is shown to strongly depend on the field orientation and in general case possesses twofold symmetry. It is shown that for magnetic field parallel to the c-axis in a certain range of GL parameters the fourfold symmetric singular vortex is unstable against the relative shift of the s- and d- wave unit vortices in the core. The gap in the resulting nonsingular vortex solution is nonzero everywhere in the center of flux line. The structure of nonsingular vortices is studied and the phase diagram of singular and nonsingular vortices is obtained.
Vortex liquid and solid correlation in untwinned YBa2Cu3O7-d
Therese Björnängen, A. Rydh, Ö. Rapp
Solid State Physics, IMIT, Royal Institute of Technology,
KTH Electrum 229, SE-164 40 Stockholm-Kista, Sweden
Longitudinal- and inter-vortex correlation were studied in the liquid and driven solid state of an untwinned YBa2Cu3O7-d single crystal, using a modified pseudo flux-transformer (PFT) method with two contacts attached on each side of a plate-like sample. Pulsed currents up to 100 mA in the ab plane were used to probe the vortex solid. The magnetic field was applied both in the c-direction and parallel to the a axis. For I||b and H||a the longitudinal vortex-correlation length diverges at the melting temperature Tm, as could be expected for a rigid lattice of straight vortices. With H||c, on the other hand, the measurements provide information on the inter-vortex correlation. For this field direction the correlation was finite even at temperatures well below Tm.
The effect of Pr and Ca doping on the flux pinning and superconducting properties in YBa2Cu3O7-d
Takuya Harada, Katsukuni Yoshida
Department of Fundamental Energy Science, Graduate School of Energy Science, Kyoto University, Gokasho, Uji, Kyoto-fu 611-0011, Japan
The effects of Pr and Ca doping on the critical current density Jc and the critical temperature Tc in YBa2Cu3O7-d have been investigated. The Pr doping has been found to enhance the pinning force and the Jc at 70K in magnetic field. This result indicates that the Pr ions in YBCO induce the nanometric inhomogeneities, which act as effective pinning centers in the presence of magnetic field. On the other hand, the additional Ca doping, which is expected to supply the mobile holes, does not lead to further increase in Jc.
New Type of Low-frequency Size Effect and Peak Effect in Magnetization of Anisotropic Hard Superconductors
L. Fishera, A. Kalinova, I. Voloshina, V. Yampol'skiib
aAll-Russian Electrical Engineering Institute, Moscow 111250, Russia
bInstitute for Radiophysics and Electronics NASU, Kharkov 61085, Ukraine
The dependence of the relative ac losses q(h0) vs. the amplitude of ac magnetic field h0 and the dc magnetization M(H) of anisotropic superconducting plate-like samples has been studied using single domain textured crystals of the Y-123 system with the c axis laying in the sample plane and a single crystal with the preferable orientation of twins in the sample plane. Contrary to the isotropic case, two maxima in the dependence of q(h0) were observed. They are found to be related to the sequential penetration of two different components of the magnetic induction to the middle of the sample. Such a behavior leads to the appearance of additional extrema in the dc magnetization curves.
Vortex dynamics in easy flow channels and electronic structure of grain boundaries in high-Tc superconductors
A. Gurevicha, M.S. Rzchowskia, G. Danielsa, S. Patnaika, X. Songa, J.P. Bubanb, N.D. Browningb, D.C. Larbalestiera
aUniversity of Wisconsin, Madison, WI 53706, USA
bUniversity of Illinois, Chicago, IL 60607, USA
We show that low-angle grain boundaries (GB) in high-Tc superconductors exhibit intermediate Abrikosov vortices with Josephson cores. We obtained an exact solution for the nonlinear flux flow resistivity, which describes well our transport experiments on 7° unirradiated and irradiated YBCO bicrystals. This enabled us to measure for the first time the vortex core size, and the intrinsic depairing current density on nanoscales of few GB dislocations. Our method combined with HREM data can be used to elucidate the effect of the GB atomic structure, and GB overdoping on local superconducting properties.
New magnetic field scaling of NMR in cuprates
Alpo Kallio, Johannes Hissa, Vinski Bräysy
Department of Physical Sciences, POB 3000, FIN-90014 University of Oulu, Finland
The magnetic field dependence of the low temperature specific heat coefficient g(T,H) has been shown to obey the scaling law g(T,H)=g0Ö{T2+Ah}, with h=|H|/1T (A. Kallio at al, Physica C 364-365 (2001) 43). This suggests that also other quantities such as the NMR Knight shifts K(T,h) and relaxation rates w(T,h)=(T1T)-1 may be expressed in terms of the scaled variable [`T]=Ö{T 2+A h} in the form K(T,h)=K0([`T]) and w(T,h)=w0([`T]), where the presence of vortexes in the mixed state simply rises the effective temperature [`T]. We have tested this using the NMR-rate data on TlSr2CaCu2O6.8 by G.-q. Zheng et al (Phys. Rev. Lett. 88 (2002) 77003-1) with H||c. The data points for various fields collapse to a single curve corresponding to h=0, with A=80K2. The curve w(T,0) consists of a fermion part with added stripe contribution, which explains microscopicly the spin gap.
Anisotropic Transport Properties of Bi2Sr2-xLaxCuO6+d Single Crystals
S. Ono, Yoichi Ando
Central Research Institute of Electric Power Industry, Komae, Tokyo 201-8511, Japan
In-plane and out-of-plane resistivities (rab and rc) are measured in a series of Bi2Sr2-xLaxCuO6+d single crystals with various La concentration x (x = 0.23 - 1.02), and the anisotropy ratio rc/rab is determined. It is found that for all concentrations rc(T) shows a steeply diverging behavior with lowering T that is associated with the pseudogap opening; the magnitude of the anisotropy ratio rc/rab is observed to be enhanced to as large as 8 × 105, demonstrating that Bi-2201 is the most anisotropic material among cuprates. Detailed analysis of the temperature and doping dependences of rc/rab reveals that not only the charge confinement but also the pseudogap are responsible for the large electrical anisotropy in Bi2Sr2-xLaxCuO6+d.
Re-appearance of antiferromagnetic ordering with Zn and Ni substitution in La2-xSrxCuO4
T. Machia, I. Katob, Y. Itoha, R. Hareyamab, N. Koshizukaa, S. Araib, M. Murakamia
aSuperconductivity Research Lab.-ISTEC, 1-10-13 Shinonome, Koto-ku, Tokyo 135-0062, Japan
bMeiji University, 1-1-1 Higashi-mita, Tama-ku, Kawasaki-shi, Kanagawa 214-0033, Japan
The effects of Zn and Ni substitution for Cu site on spin correlation are studied for lightly doped La2-xSrxCuO4 polycrystalline samples. As for Zn substitution, the Neel ordering which disappeared with x = 0.02 was observed at around 120K again with Zn concentration of 0.08. On the other hand, it was found that the Neel ordering recovered by Ni substitution. Surprisingly TN reached above 300K with Ni concentration of 0.2. The Neel ordering temperature was suppressed with increasing Sr concentration. However, the antiferromagnetic ordering temperature was observed even at x = 0.06 and 0.08 with Ni substitution in superconducting phase. This work was supported by NEDO.
Pressure effect on a ferromagnetic transition temperature of RuSr2GdCu2O8
Jun Shibataa, Hirotsugu Gotoa, Hiroki Takahashia, Yuh Yamadab, Akiyuki Matsushitac
aCollege of Humanities and Sciences, Nihon University,3-25-40 Sakurajousui,Setagaya 156-8550,Japan
bShimane University, 1060 Matsue-shi, Nishikawazu-cyo, 690-0823,Japan
cNIMS, 1-2-1 Sengen Tsukuba-shi, 305-0047,Japan
A number of attention has been paid for RuSr2GdCu2O8 because of the coexistance of ferromagnetic state and superconducting state below about 30K. In order to investigate the character of the superconducting state which coexists with ferromagnetism, the pressure effect on a ferromagnetic transition temperature has been investigated. The enhancement of ferromagnetic transition temperature was observed with increasing pressure. High-pressure x-ray experiments on this material are in progress.
Polarization-Dependent X-ray Absorption Spectroscopy of In-plane Aligned YBa2Cu3O7-d Thin Films
K. H. Wua, C. W. Luoa, S. J. Liua, M. H. Chena, 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.
Polarization-dependent x-ray absorption spectroscopy on the O 1s edge has been measured on a-axis oriented YBa2Cu3O7-d (YBCO) thin films. For normal incidence case, the x-ray absorption spectra for the electric field E of the linearly-polarized synchrotron light is parallel to b-axis or c-axis of YBCO films by rotating the plane of the sample can be obtained precisely. Furthermore, the x-ray absorption spectra for E//a-axis can be calculated from the oblique incidence with different angles. The electronic structure of CuO2 planes and CuO3 chains and hole concentrations on all oxygens can be investigated by the pure in-plane a-axis oriented YBCO thin films as using detwinned YBCO single crystals.
Magnetic and electrical properties of single-crystal La2-xSrxCu1-yNiyO4
Nobuaki Watanabe, Takahiko Masui, Yutaka Itoh, Isao Kato, Takato Machi, Naoki Koshizuka
Superconductivity Research Laboratory, International Superconductivity Technology Center, 1-10-13 Shinonome, Koto-ku, Tokyo 135-0062, Japan
We report on out-of-plane and in-plane magnetic susceptibilities of La2-xSrxCu1-yNiyO4 (x =0.01 and 0.06, 0 £ y £ 0.1) single crystals grown by TSFZ technique. Our data show that in lightly Sr doped compounds, the Néel temperature TN increases with increasing Ni concentration. This work was supported by New Energy and Industrial Technology Development Organization (NEDO).
Anomalous In-plane Anisotropy of the Resistivity on Single Crystalline 60-K YBa2Cu3O7-d in High Magnetic Fields
Tomoyuki Naitoa, Seiya Haraguchia, Hideo Iwasakia, Terukazu Nishizakib, Kenji Shibatab, Norio Kobayashib
aSchool of Materials Science, JAIST, Tatsunokuchi 923-1292, Japan
bInstitute for Materials Research, Tohoku University, Sendai 980-8577, Japan
We have measured the in-plane anisotropy of the in-plane resistivity on 60-K YBa2Cu3O7-d single crystals in magnetic fields. At H= 150 kOe, the temperature dependence of the resistivity r(T) for H ^I shows the jump near the zero-resistivity transition, while r(T) for H ||I the gradual behavior. Furthermore, the transition temperature of the latter is lower than that of the former, which is inconsistent with the vortex dynamics induced by the Lorentz force. We will discuss the observed anomalous behavior in terms of the phase transition of the Josephson vortex system.
Thermal Transport of Pr2Ba4Cu7O15-y Compound under Several Annealing Conditions
H. Ogasawara a, M. Matsukawa a, S. Shirafuji a, Y. Yamada b, N. Kobayashic
aFaculty of Enginnering, Iwate University, Morioka 020-8551, Japan
b Interdisciplinary Faculty of Engineering, Shimane University, Matsue 690,Japan
cInstitute for Materials Research, Tohoku University, Sendai 980-8577,Japan
We have investigated thermoelectric power (S), thermal conductivity and magnetoresistance (MR) of Pr2Ba4Cu7O15-y (Pr247) compound with the alternative repetition of a single-and double chain. The value of S in Pr247 showed a metallic behavior at lower temperatures, accompanying the appearance of MR effect as well as Pr124. This finding is discussed on the basis of the metallic conduction along the CuO double chain.
Synthesis of new Ru-based cuprate with 1232 structure, RuSr2+xSmCe2-xCu2Oz
Y. Akagia, H. Sasakuraa, S. Noguchib, T. Okac, S. Tsukuic, M. Adachic
aDept. of Physics, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka 431-3192, Japan
bGraduate School of Engineering, Osaka Prefefcture University, Sakai, Osaka 599-8531, Japan
cResearch Institute for Advanced Science and Technology, Osaka Prefefcture University, Sakai, Osaka 599-8531, Japan
New Ru-based cuprate RuSr2+xSmCe2-x Cu2Oz (Ru-1232 phase) has been synthesized. Nearly the single phase can be formed in the x composition range from 0.0 to 0.2. This new phase has a tetragonal unit cell with the lattice parameters of about a=0.384 nm and c=1.70 nm. A bulk sample with x=0.2 shows superconductor-like slightly decreases in resistivity at about 12K and 30K. In the M-T dependence, the sample shows a ferromagnetic behavior at about 80K and a diamagnetic signal at about 20K. In conference, we will report the synthesis and characterization for the new Ru-1232 compound.
Possibility of unconventional superconductivity of SrTiO3-d
Martin Jourdan, Hermann Adrian
Institute of Physics, Johannes Gutenberg University, D-55099 Mainz, Germany
SrTiO3-d can show metallic behavior
and superconductivity at T < 200mK. Due to its low carrier
concentration ( @ 1020cm-1) and huge dielectric
polarisability (e @ 300) this compound is
considered as a candidate for a polaronic superconducting pairing
mechanism.
It is demonstrated that by variation of the annealing temperature
in vacuum the transport properties of SrTiO3-d can
be tuned continuously from semiconducting to metallic. We present
measurements of the upper critical field Bc2(T) which
show near Tc a positive curvature. This unusual temperature
dependence is consistent with a model of weakly interacting
charged bosons which condense in the superconducting state (local
pairing). However, measurements of current-voltage curves reveal
very small critical currents of our samples. This observation is
discussed in the framework of doping inhomogeneities.
STM Spectroscopy on Ba8Si46
Koichi Ichimuraa, Nomura Kazushigea, Hiroshi Fukuokab, Shoji Yamanakab
aDivision of Physics, Hokkaido University, Sapporo 060-0810, Japan
bDepartment of Applied Chemistry, Hiroshima University, Higashi-Hiroshima 739-8527, Japan
Superconducting phase of silicon clathrate Ba8Si46 (Tc=8 K) was studied by the electron tunneling spectroscopy using STM. The energy gap structure associated with the superconducting state was observed clearly. The differential tunneling conductance around zero bias voltage is well reduced and flat, suggesting the finite gap. On the other hand, the finite conductance inside the gap suggests the anisotropy of the gap. The functional form of tunneling spectra is explained by the model, in which the gap is assumed to be finite and has an anisotropy. According to the model, in which the gap varies depending on the direction in k-space, we obtain gap parameters as Dmin=0.5 meV and Dmax=1.5 meV. The temperature dependence of tunneling spectra will be discussed in detail.
Electronic Transport in Underdoped High-Tc Nanowires and Nanostructures
Joseph A. Bonetti, Dale J. Van Harlingen, Michael B. Weissman
Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
We have measured the electronic properties of underdoped YBCO nanowires and nanostructures in order to study the nature of the superconducting and pseudogap regimes in the high-Tc cuprates. By investigating the material on a mesoscopic length scale, we can test for the existence of charge stripes, phase fluctuations, and other model-dependent signatures. We have fabricated a series of nanowires with different dimensions, doping levels, and orientations relative to the YBCO lattice, and measured the critical current, resistivity, current-voltage characteristics, and voltage noise, all as a function of temperature. Nanowires with widths 50-300 nm exhibit discrete, increasing and decreasing switches in the resistance as the temperature or current is varied, suggesting the formation of anisotropic conducting domains.
mSR study on multi-layered HgBa2Ca4Cu5Oy (Hg-1245) superconductor
K. Tokiwa a, S. Itoa, H. Okumotoa, W. Higemotob, K. Nishiyamab, A. Iyoc, Y. Tanakac, T. Watanabea
a Dept. of Appl. Electronics, Tokyo University of Science, Noda, Chiba , Japan
bMeson Science Laboratory(KEK-MSL), KEK, Tsukuba, Ibaraki , Japan
cNational Institute of Advanced Industrial Science and Technology(AIST), Tsukuba, Ibaraki, Japan
We report the magnetic properties of multi-layered HgBa2Ca4Cu5Oy (Hg-1245) superconductor below Tc ( ~ 108 K) studied by muon spin relaxation measurements. Hg-1245 has two outer five-fold CuO2 planes(OP) and three inner four-fold CuO2 planes(IP) and the difference of carrier concentration between OP's and IP's has been shown by NMR measurements. We have observed zero field spin precession of positive muons in Hg-1245 below 40 K and this result indicates that there coexist a antiferromagnetic state on IP and a superconducting state of OP in Hg-1245.
This work has been supported by Core Research for Evolution Science and Technology (CREST)
Study on the limiting factor of critical current in Ag-Bi2223 tapes
Y. Liua, H. Luoa, X. Lenga, J.W. Linb, S.Y. Dinga
aNational Laboratory of Solid State Microstructures, department of physics, Nanjing University, Nanjing 210093, China
bCollege of Science, Hohai University, Nanjing 210098, China
We have fabricated the silver sheathed tapes of Ag-Bi2223 by usual process to study the factor limiting the critical current density of the tapes. Electric transport measurement of V-I characteristics was performed for the tapes immersed in liquid nitrogen with and without magnetic fields. Hysteresis loop of V-I curve was observed. A model based on polycrystalline superconductors was proposed to account for this kind of hysteresis. And it is shown that in our Ag-Bi2223 tapes the weak-links are the key factor limiting the global critical current.
Second peak effect in SmBa2Cu3Oy
S. Y Dinga, X. Lenga, Y. L Jiaob, H. Luoa, Y. Liua
aNational Laboratory of Solid State Microstructures, department of physics, Nanjing University, Nanjing 210093, China
bSuperconducting Materials Research Institute Center, Bejing Generar Institute for Non-ferous Metals
Two SmBa1.9Cu3Oy samples (SBCO) with Y211 (Sm1 and Sm2) were fabricated by Melt-Textured Growth (MTG) method to study the effect of heat treatment in argon atmosphere on the second peak effect (SP). Magnetization-temperature (M-T) measurement at 10G field cooling shows that the sample Sm1 is of transition temperature Tc = 76K but the Sm2 has higher Tc ( =90K) and irreversibility fields than Sm1. Magnetization-field function (M-H curves) at various temperatures T in fields up to 7 T was measured for the samples. The SP of the two samples was abserved and compared at a set of temperatures. Discussion of flux pinning and the effect of Ar and 211 is made
''Dynamic fishtail'' and transient vortex phases in HTS
D. Giller, B. Kalisky, I. Shapiro, B. Ya. Shapiro, A. Shaulov, Y. Yeshurun
Institute of Superconductivity, Bar-Ilan University, Ramat-Gan 52900, Israel
We utilize theoretical analysis 1, based on the Landau-Khalatnikov (LK) dynamic equation, to explain the experimentally measured time evolution of the fishtail in the magnetization curves of HTS crystals. We show that the observed time evolution is a manifestation of a dynamic coexistence of transient-disordered and ordered vortex phases. Numerical solutions of the LK equation predict phenomena observed experimentally, e.g. the absence of the fishtail at short times, its appearance at longer times, and the movement of its onset with time toward higher induction fields, approaching the limit of the solid-solid transition field.
Diminished Equilibrium Magnetization in Hg-1223 and Tl-2212 Superconductors with Fission-generated Columnar Defects
J.R. Thompsona, J.G. Ossandonb, D.K. Christena, K.J. Songc, L. Krusin-Elbaumd, J.L. Ullmanne
aOak Ridge National Laboratory, Oak Ridge, TN 37831-6061 USA
bDept of Engineering Sciences, University of Talca, Curico, Chile
cDep't Physics, University of Tennessee, Knoxville, TN 37996-1200 USA
dIBM Research Center, Yorktown Heights, 10598 NY
eLos Alamos National Laboratory, Los Alamos, NM 87545 USA
When randomly oriented columnar defects (CDs) are added to Hg-1223 and Tl-2212 superconductors, their vortex state equilibrium magnetization Meq decreases substantially. Meq progressively deviates from the usual London ln(B) dependence and the curves become S-shaped. Vortex-defect interactions quantitatively account for this behavior. Research at ORNL and LANL was sponsored by the US DOE.
Experimentally Characterized Reentrant Phase in Bi2212 Crystal
Endo Tamio, Hashizume Akinori, Iwasaki Shin-ichi
Faculty of Engineering, Mie University, Tsu, Mie 514-8507, Japan
Vortex liquid reentrant phase (RP) has been proposed theoretically for two dimensional high temperature superconductors. However, it is difficult to detect RP experimentally. We measured field-modulated microwave absorption on Bi2212 single crystals with sweeping field (H) for H//c-axis at various temperatures (T). At low T (77 K), the spectra show only a narrow "first peak" near zero field. With increasing T ( > 78 K), a "dip", and a "broad peak" appear gradually at higher H around 50 - 200 G. The dip and broad peak shift to the lower field with increasing T. The broad peak finally merges into the first peak at 85 K. No structure appears at T > 87 K because of normal transition. The first peak, dip and broad peak correspond to Meissner, reentrant liquid and solid phases, respectively. We can draw experimentally determined reentrant phase, which is extremely similar to the theoretical one reported by Blatter.
CRITICAL STATE and TRANSPORT CRITICAL CURRENT in HTSC CERAMICS
Nikita A. Bogoliubov
Institute of Inorganic Chemistry SB RAS, 630090, Novosibirsk, Russia
The critical current in Y-123, Bi-2212, and Bi-2223 ceramics HTSC samples in zero magnetic fields has been studied as function of temperature, sample cross-section size and form. An analysis of experimental results shows that the expression for critical current can be written as the product of two functions. One of the functions is a function of temperature only. The other is common power function of the sample cross-section area which independents on the cross-section form. This fact makes it possible to determine the critical current density and magnetic field distributions in sample.
Vortex Glass Transition of the Josephson Vortex System in LSCO Crystals
Hideo Iwasakia, Yuuya Kawabataa, Tomoyuki Naitoa, Yukitoshi Fujitaa, Seiya Haraguchia, Takahiko Sasakib, Norio Kobayashib
aJapan Advanced Institute of Science and Technology (JAIST), Asahidai 1-1, Ishikawa 923-1292, Japan
bInstitute for Materials Research (IMR), Tohoku University, Katahira 2-1-1, Sendai 980-8577, Japan
Electrical resistivity has been measured under magnetic fields parallel to the CuO2 planes in LSCO single crystals, where Josephson vortices form in the region between the CuO2 planes. All samples don't show the first order phase transition in the measurement. In the crystals over the wide Sr content from the under-dope to the over-dope the vortex glass melting transition is observed in the field range of 1T-17.5T. The glass transition lines strongly depend on the anisotropy of the system, that is, it is suppressed to the low field in the under-doped crystal with large anisotropic parameter. The Josephson vortex glass transition will be discussed in terms of the anisotropic parameter.
Friedel Oscillation of Charge Profile in Superconducting Vortex
Masahiko Machidaa, Tomio Koyamab
aCCSE, Japan Atomic Energy Research Institute, Ueno Sumitomo Bldg.8, 6-9 Higashi-Ueno, Taito-ku, Tokyo, 110-0015 Japan
bIMR, Tohoku University, 2-1 Katahira Aoba-ku, Sendai 980-8577, Japan
We perform numerical microscopic calcuations on charge distributions around the superconducting vortex core by including the Poisson equation to the conventional BdG formalism. The calculations reveal that the charge distribution shows the Friedel oscillation around the vortex core and the oscillation survives over the coherence length for small kf x. In order to understand the origin of the oscillation and study charge screening properties we calculate the charge density correlation function around the vortex core. It is found that the function is strongly position dependent and remarkably oscillates only inside the vortex core.
Coexisting ordered and disordered vortex phases in Bi2Sr2CaCu2O8+d
B. Kalisky, A. Shaulov, Y. Yeshurun
Institute of Superconductivity, Bar-Ilan University, Ramat-Gan 52900, Israel
A high temporal resolution magneto-optical system was employed to image the induction distribution on the surface of a Bi2Sr2CaCu2O8+d crystal while the external magnetic field was swept at a constant rate. These data reveal coexistence of quasi-ordered and disordered vortex phases, near the order-disorder phase transition line. The coexistence region in the B-T phase diagram narrows down with increasing temperature or decreasing sweep-rate. These observations clarify previous interpretations of phenomena associated with the fishtail, e.g. the shift of the fishtail onset to higher inductions for slower sweep-rate and the absence of the fishtail at low temperatures.
Influence of the columnar defect densities on the current-voltage characteristics in high-Tc superconducters
Tetsuro Sueyoshia, Hiroyuki Yonemuraa, Tomohito Kisakibarua, Takanori Fujiyoshia, Kuniyuki Miyaharaa, Tomoaki Ikegamia, Kenji Ebiharaa, Ryuji Miyagawab, Norito Ishikawac, Akihiro Iwasec
aFaculty of Engineering, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan
bKumamoto Industrial Research Institute, 3-11-8 Higashi, Kumamoto 862-0901, Japan
cJapan Atomic Energy Research Institute, Tokai-mura, Ibaraki 319-1195, Japan
We investigated the influence of columnar defect densities on the critical exponents estimated by the critical scaling analysis of the current-voltage characteristics in high-Tc superconductors. It is found that the dynamic critical exponent z increased with increasing columnar defect densities, systematically. The peak of z was observed near the magnetic field B/BF=1/3. These results are explained by the depinning model considering the distribution of the pinning strength rather than the voltex glass model.
Vortex Liquid-Vortex Glass Transition in Pb-8.23wt In Alloy Films
T. Fukamia, K. Mizusekib, F. Ichikawac, T. Araib, T. Yamasakia, B. Sinozakib, T. Aomineb
a Department of Materials Science and Technology, Himeji Institute of Technology, Himeji 671-2201, Japan
bDepartment of Physics, Kyushu University, Fukuoka 812-8581, Japan
cDepartment of Physics, kumamoto University, kumamoto 860-8555, Japan
In order to confirm occurrence of vortex glass-vortex liquid(VG-VL) transition in the mixed state in metal superconductors, Pb-In alloy is selected. Isothermal current-voltage(J-E) characteristics for thin films evaporated on glass substrates with 8.23wtsuperconductors. A characteristic temperature where log J vs log E is linear, the static and dynamical critical exponents were determined. These exponents have reasonable values expected theoretically for the transition. The VG-VL transition was confirmed for Pb-In alloys.
Scaling and nonstationary V-I curve for superconductor with flux creep
D. V. Shantsev, Y. M. Galperin, T. H. Johansen
Department of Physics, University of Oslo, P. O. Box 1048 Blindern, N 0316 Oslo, Norway
Time-dependent current distributions and voltage across an initially flux-free superconductor slab biased by a current I(t) are considered. The superconductor is locally described by a power-law voltage-current curve, E µ jn, and a power-law Jc(B) dependence. As current increases, magnetic flux penetrates the slab from the edges and for I=I* the flux fronts meet at the center. The integral voltage-current curve V(I) follows a power-law, V µ Ip, with different exponents p for I < I* (partial penetration), and for I >> I*, (full penetration). At I >> I*, when the current distribution is uniform, the exponents for the local and integral voltage-current curves almost coincide. However, at I < I*, i. e. for highly non-uniform current distribution, p is much smaller than n. This conclusion results from exact scaling properties of the flux density, B(x,t)=tB[s(x,t)]. Thus one expects a crossover in the V(I) law at I=I*.
Effects of the moving vortex structure interaction with longitudinal ultrasonic waves
Eugene D. Gutliansky
Institute of Physics, Rostov State University, Stachki ave. 194, 344104, Rostov-on -Don, RUSSIA
The interaction of a longitudinal ultrasonic wave (LUW) with the moving vortex structure is considered. It is shown that if the vortex structure moves this velocity V then the new collective vortex mode arises. This mode has the velocity 2V. It appears in the anomalous attenuation and in velocity of the LUW at V = 1/2cl here cl is the LUW velocity ignoring interaction with the vortex structure. If the velocity of the vortex structure exceeds cl then the attenuation coefficient changes its sign, and the LUW can be amplified. The effect can be observed relatively easy with using surface acoustic waves in the periodic superconducting film structure when the electric current is passed through the film. The currents required for observation of it are estimated for the selected ultrasonic frequencies.
Dynamical Melting and Transverse Pinning of Moving Vortices Interacting with Periodic Pinning
Gilson Carneiro
Instituto de Física, Universidade Federal do Rio de Janeiro, C.P. 68528, 21945-970, Rio de Janeiro-RJ, Brasil
Dynamical phases and phase transitions of moving vortices in clean films driven by an uniform force and interacting with periodic pinning are investigated at low temperatures by numerical simulations of a London model. Three dynamical phases are identified: moving commensurate and incommensurate vortex-lattices and moving vortex-liquid. Two dynamical transitions are reported: dynamical melting of a moving incommensurate vortex-lattice into a moving vortex-liquid and a transition from a moving vortex-liquid into a commensurate vortex-lattice where tranverse pinning occurs. The transition lines are obtained as a function of the driving force magnitude and direction for a typical vortex density.
Hydrodynamic Instability of Flux-antiflux Interface in Hard Superconductors
V.A. Yampol'skiia, A.L. Rakhmanovb, A.A. Levchenkoa, L.M. Fisherc, P.E. Goad, M. Baziljevichd, T.H. Johansend
aInstitute for Radiophysics and Electronics NASU, 12 Acad. Proskura Str., Kharkov 61085, Ukraine
bInstitute for Theoretical and Applied Electrodynamics RAS, 13/19 Izhorskaya Str., Moscow, Russia
cAll-Russian Electrical Engineering Institute, 12 Krasnokazarmennaya Str., Moscow, 111250, Russia
dDepartment of Physics, University of Oslo, P.O. Box 1048, Blindern, 0316 Oslo 3, Norway
The possible mechanism of the macroturbulence instability observed in fluxline systems during remagnetization of superconductors is proposed. It is shown that when a region with flux is invaded by antiflux the interface can become unstable if there is a relative tangential flux motion. This condition occurs at the interface owing to the anisotropy of the CVC and, therefore, of the viscous motion of vortices. The phenomenon is similar to the instability of the tangential discontinuity in classical hydrodynamics.
Controlling the motion of interacting particles: Analytical study via the nonlinear Fokker-Planck equation.
S. Savel'eva, F. Marchesonia,b, F. Noria,c
aFrontier Research System, The Institute of Physical and Chemical Research (RIKEN), Wako-shi 351-0198, Japan
b INFM and Physics Dept., Universita' di Camerino, I-62032 Camerino, Italy
cDepartment of Physics, University of Michigan, Ann Arbor, MI 48109-1120, USA
We study a nonlinear Fokker-Planck equation that takes into account the interactions between particles. This equation has been used in the analytical study of the so-called ``temperature ratchet" (when the temperature of the system is periodically varied) in both the adiabatic and sudden regimes. We have found a double current inversion with increasing particle density for a chosen asymmetric ratchet potential. These results are applicable to a variety of systems, including vortices in superconductors.
Symmetry Classes of Triplet Vortex Lattice Soluitons of the Bololiubov de-Gennes Equation in a Square Lattice
Akira Gotoa, Masa-aki Ozakib, Yoshiki Horia
aKochi National College of Technology, Nankoku 783-8508, Japan
bKumakouji 19-21 Uji City , Kyoto 611-0002, Japan
We give a group theoretical classification of the triplet vortex lattice states of the two-dimensional Hubbard model with a nearest neighbor ferromagnetic exchange interaction in a uniform magnetic field. We obtain ten types of tetragonal vortex lattice states {G1A, G2A, G1B, G2B, G1E ~ G6E} for the magnetic flux f = f0/p2 (f0=ch/2e is the flux quantum, p is an integer) through a unit cell of crystal lattice. We show the configurations of the order parameters corresponding to axial phase, up spin phase, planar phase and bipolar phase. We also discuss the possibility of those phases in the triplet superconductors like Sr2RuO4.
Driven vortex dynamics in superconductors with asymmetric pinning sites
B. Y. Zhu
Frontier Research System, The Institute of Physical and Chemical Research (RIKEN), Wako-shi 351-0198, Japan
We present recent results for a variety of superconducting samples that can rectify the applied alternating current into a net DC motion of the vortices. We theoretically compute the voltage-current curves, the vortex trajectories, and the field dependence of the critical currents. We explore these type of systems for different geometries, and experimentally-relevant parameters.
Transverse Elastic Moduli in Spin-Triplet Superconductor Sr2RuO4
Noriki Okudaa, Takashi Suzukia, Zhiqiang Maob,c, Yoshiteru Maenob,c,d, Toshizo Fujitaa
aDepartment of Quantum Matter, ADSM, Hiroshima University, Higashi-Hiroshima 739-8530, Japan
bDepartment of Physics, Kyoto University, Kyoto 606-8502, Japan
cCore Research for Evolutional Science and Technology, Japan Science and Technology Corporation (CREST-JST), Saitama 332-0012, Japan
dKyoto University International Innovation Center, Kyoto 606-8501, Japan
Ultrasonic measurements have been performed on single crystalline Sr2RuO4 across the superconducting transition temperature Tc ( >> 1.40 K). We found an indication of a jump at Tc in transverse elastic modulus C66, which may arise from the coupling between the exy strain and a superconducting order parameter(OP). It would be the first evidence from ultrasonic experiments for the spin-triplet superconductivity with a two-dimensional OP with broken time-reversal symmetry .
Physics of Vortex Core in Chiral P-wave Superconductor
Yusuke Katoa, Nobuhiko Hayashib
aDepartment of Basic Science, University of Tokyo, Tokyo 153-8902, Japan
bComputer Center, Okayama University, Okayama 700-8530, Japan
When vorticity (the angular momentum of center of mass motion of Cooper pairs ) and chirality (the angular momentum of relative motion of Cooper pairs) have an opposite sign in a chiral p-wave vortex state, total angular momentum with respect to vortex center becomes zero. In this case, self-consitently determined pair-potential reveals locally recovery of time-reversal symmetry near vortex center. Recovery of T-symmetry and cancellation of angular momentum make chiral p-wave vortex core similar to locally realized zero-field s-wave superconducting region. As an evidence for the similarity, we show that the Anderson's theorem holds in chiral p-wave vortex cores; the impurity scattering rate of quasiparticles by nonmagnetic impurities vanishes inside vortex cores.
Microscopic Theory on the D-vector of Triplet Superconductor Sr2RuO4
Youichi Yanase, Masao Ogata
Department of Physics, University of Tokyo, Tokyo 113-0033, Japan
We perform a microscopic calculation to investigate how the chiral state [^d](k) = (kx ±i ky) [^z] is realized in the triplet superconductor Sr2RuO4. Starting from the three band Hubbard model with spin-orbit interaction, the pairing interaction is calculated by the perturbation theory. The p-wave superconductivity is obtained in the weak coupling region. It is shown that the orbital dependent superconductivity robustly appears in Sr2RuO4. The realized state is determined by comparing Tc. The case of the f-wave superconductivity is also investigated by assuming the pairing interaction. We find that the Hund coupling term as well as the spin-orbit interaction is necessary to lift the degeneracy. The main result is that the chiral state is realized when the p-wave superconductivity occurs with the dominant g-band. On the contrary, an inconsistent d-vector with experiments is realized in the other cases.
The 3-K phase of Sr2RuO4: Insights into an unconventional superconductor
Manfred Sigrista, Hartmut Monienb
aTheoretische Physik, ETH-Hönggerberg, 8093 Zürich, Switzerland
bPhysikalisches Institut, Universität Bonn, 53115 Bonn, Germany
The superconducting phase of Sr2RuO4 realizes a chiral p-wave state with Tc = 1.5 K. Recently the onset of an inhomogeneous superconducting phase has been observed close to 3 K in samples with micrometer-size Ru-metal inclusions. This superconducting phase nucleates very likely on the interface between Sr2RuO4 and the Ru-inclusions. We analyze the properties of this phase and compare them with experimental results. One important aspect is related to frustration effects of the order parameter phase and resulting subgap quasiparticle states which are observable in tunneling spectra. Furthermore, we show that the upper critical field for the ``3K-phase'' provides new insights into the order parameter symmetry and may be taken as an important test experiment.
Electronic Band Structure of Sr2MoO4
Izumi Hasea, Shin-Ichi Ikedaa, Naoki Shirakawaa, Takashi Yanagisawaa, Judy Stalicka
National Institute of Standard and Technology, Gaithersberg, MD 20899-8562, USA
aNanoelectronic Research Institute, AIST, Tsukuba, 305-8568, Japan
The electronic energy band structure of Sr2MoO4, which is isostructural with the unconventional spin-triplet superconducting Sr2RuO4, has been calculated by using the scalar-relativistic full-potential linearized augmented plane wave (FLAPW) method within the local-density approximation in the paramagnetic case. The result of the calculation suggests that this compound is a metal and its electronic structure is similar to that of Sr2RuO4, while in Sr2MoO4 one of the Fermi surfaces has a large dispersion along kz axis. The optimization of the position of the apical oxygen suggests that the RuO6 octahedron is more flattened than the reported one.
Pinning Anomalies in Organic Layered Superconductor k-(BEDT-TTF)2X
Shigeru Kasahara, Fumitoshi Tateishi, Hiroyuki Caneko, Takashi Hara, Yutaka Nishio, Koji Kajita
Department of Physics, Toho University Miyama 2-2-1, Funabashi 274-8510, Japan
Vortices in organic superconductor k-(BEDT-TTF)2X {X=Cu(NCS)2, Cu[N(CN)2]Br} is interesting for their anisotropic character. To investigate their dynamical behavior, ac complex susceptibility and dc electrical resistance measurement were done in the presence of vortices introduced by dc magnetic fields. In the course of experiments, we found that the dc field dependence of complex susceptibility changes drastically for moderate ac magnetic fields, i.e. the shielding effect of the system (-c¢) has peak structure and dissipations (c¢¢) shows dip. In addition to the anomalies in the susceptibility, it turned out that the electrical resistance has a dip structure under the same dc magnetic fields. These anomalies imply that the vortices are less mobile. We believe this is the evidence for elastic softening of the vortices that enhances the effective pinning of the system.
CRYSTAL AND BAND STRUCTURES OF ORGANIC SUPERCONDUCTORS UNDER THE UNIAXIAL STRAIN
Ryusuke Kondoa, Seiichi Kagoshimaa, Mitsuhiko Maesatob
aDepartment of Basic Science, Graduate School of Arts and Sciences, University of Tokyo, Tokyo, 153-8902, Japan
bDivisions of Chemistry, Graduate School of Science, Kyoto University, Kyoto, 606-8502 , Japan
The crystal structure of the organic superconductor, a-(BEDT-TTF)2NH4Hg(SCN)4 under the uniaxial strain along each axis was studied with a unique design of X-ray apparatus. The results of the band structure calculations based on the obtained atomic coordinates suggest that the density-of-states at the Fermi level increases under the b*- andc- axial strain, while it decreases under the a-axial strain. These results are consistent with the observed behaviours of the superconducting transition temperature in the framework of the BCS theory.
Field-induced superconductor-insulator transition in layered organics
Hiromi Taniguchia, Atsushi Kawamotob, Kazushi Kanodaa
aDepartment of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
bDivision of Physics, Graduate School of Science, Hokkaido University, Kita-ku, Sapporo 060-0810, Japan
The k-(BEDT-TTF)2Cu[N(CN)2]Br is known to be a quasi-two-dimensional superconductor with Tc of 11.5K. We finely tune the electronic phase of this organics so as to approach the superconductor-insulator phase boundary by combination of physical and chemical methods. Then we demonstrate that thus tuned superconducting phase is switched into the magnetic insulating phase by magnetic field. This superconductor-insulator switching is the first-order transition.
Specific heat in the mixed state of non-magnetic borocarbides
D. Lippa, S.-L. Drechslerb, J. Freudenbergerb, G. Fuchsb, K. Nenkovb, K.-H. Müllerb, M. Schneiderc, A. Gladunc
aInstitut für Halbleiter- und Mikrosystemtechnik, Technische Universität Dresden, D-01062 Dresden, Germany
bInstitut für Festkörper- und Werkstofforschung e. V., D-01171 Dresden, Postfach 270116, Germany
cInstitut für Tieftemperaturphysik, Technische Universität Dresden, D-01062 Dresden, Germany
The temperature and magnetic field dependence of the specific heat superconducting (sc) mixed state has been measured for YxLu1-xNi2B2C and Y(Ni1-yPty)2B2C samples. The deviations from the usual linear-in-H law of the linear-in-T specific heat contribution g(H) ·T can be possibly ascribed to unconventional pairing and are discussed in the unitary d-wave as well as in the intermediate transition region in between dirty and clean s-wave limits. Considering the g(H) data, unconventional pairing cannot be ruled out.
Evidence of Point Nodes in Superconducting Gap of Borocarbide Superconductor YNi2B2C
Konomi Kamataa, Hidemasa Yamaguchia, Koichi Izawaa, Yuji Matsudaa, Minoru Noharab, Hidenori Takagib, Hiroyuki Takeyac, Kazuto Hiratac
aISSP,University of Tokyo,Kashiwa,Chiba 277-8581,Japan
bDept.of Adv.Mat.Sci.University of Tokyo,Hongo,Tokyo 113-0033,Japan
cNational Institute for Materials Science,Tsukuba,Ibaraki 305-0047,Japan
In oder to determine the superconducting gap structure of the borocarbide superconductor YNi2B2C, we have measured the angular dependence of the thermal conductivity by rotating the applied magnetic field within the ab-planes. A clear fourfold symmetry, which is characteristic of a superconducting gap with nodes along the a and b axes of the crystal, is resolved. The angular variation of the thermal conductivity also provides a strong evidence of point nodes.
Magnetic and Superconducting Properties of R1-xNdxNi2B2C (R=Y and Er) Systems
Katsunori Moria, Katsuhiko Nishimuraa, Shixun Caob
aFaculty of Engineering, Toyama University, 3190 Gofuku, Toyama 930-8555, Japan
bDepartment of Physics, Shanghai University, 99 Shanghai Road, Shanghai 200436, P. R. China
The quaternary nickel borocarbides, RNi2B2C (R=Rare earth element), have attracted considerable attention over the past few years, because they provide an excellent opportunity to study the complex interplay of superconducting and antiferromagnetic ground state. We investigated the superconducting transition temperature, Tc, and magnetic transition temperature, TN, for the R1-xNdxNi2B2C (R=Y and Er) systems. Tc and TN curves for the R=Er system cross over at the substitution concentration x= ~ 0.17, for which TN=5 K, but Tc could not be observed. For the R=Y system, they did not cross over. Tc and TN vs Nd concentration x, for the R1-xNdxNi2B2C systems are given and discussed.
SANS Studies of Vortex Lattice Morphology in YNi2B2C
Charles D. Dewhursta, Simon J. Levetta, Don McK. Paulb
aInstitut Laue Langevin, 6 rue Jules Horowitz, Grenoble 38042, France
bDepartment of Physics, University of Warwick, Coventry CV4 7AL, UK
High-resolution small-angle neutron scattering (SANS) studies of the vortex lattice (VL) in YNi2B2C allow us to separate Bragg scattered intensities from the multi-domain VL that exists for B||c. Precise determination of the VL unit cell angle, b, shows that there is a finite transition width associated with the field-driven 45o reorientation of the VL at a field H1. Low- and high-field rhombic VL phases coexist over a finite range of applied field with no continuous distortion between the two phases. The variation in scattered intensity from each phase through the transition indicates a redistribution of domain populations between the low- and high-field vortex structures. Our data supports the notion of a first-order reorientation transition in the VL at H1 in the presence of weak static disorder (vortex-pinning).
Pressure effect on Ba1-xKxBiO3 near the composition of Metal-Semiconductor transition
M. Shizuya, S. Ueda, T. Nishio, H. Uwe
Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki, 305-8573, Japan
The effect of the hydrostatic pressure up to 1 GPa to the resistivity of Ba1-xKxBiO3 was investigated. Specimens were single crystals prepared by the electro-chemical method. Either the superconducting transition temperature Tc or the conductivity increases with pressure in the metallic phase. On the semiconducting sample(x ~ 0.3), which is near the metallic phase, we found that the temperature dependence of the resistivity changes to [(dr)/dT] > 0 below 20 K at above 0.4 GPa. This suggests that the new conducting phase, which may be superconducting, appears in the semiconducting sample under high pressure.
Possibility of Pressure-Induced Superconductivity by Phonon Mechanism in Palladium
Koshiro Yanai, Tomoki Takezawa, Ikutaro Hamada, Naoshi Suzuki
Graduate School of Engineering Science, Osaka University, Toyonaka, 560-8531, Japan
Pressure dependencies of electronic structures and lattice dynamics of Pd which is close to ferromagnetic instability at ambient pressure are investigated on the basis of the first-principles full-potential LMTO method. With increasing pressure no anomalous behavior is seen in both the electronic structure and lattice dynamics, i.e. the band width becomes wider and the phonon frequencies show hardening in the whole BZ. Particular attention is paid to phonon-mediated superconductivity: the transition temperature Tc without taking into account spin fluctuation effects are estimated to be 6.5 - 8.5 K at ambient pressure and 0.5 - 1.5 K at 50 GPa. Possibility of pressure-induced superconductivity by phonon mechanism is discussed by taking into account the spin fluctuation effects.
Superconductivity in Y2PdGe3-xSix: interplay between Debye temperature and coupling constant
Ajay Kumar Ghosh, Hitomi Nakamura, Masashi Tokunaga, Tsuyoshi Tamegai
Department of Applied Physics, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 133-0033, Japan
We have studied Y2PdGe3-xSix superconductor using magnetization and specific heat measurements. The compounds are very sensitive to changes in the honeycomb layers by Si substitution. The critical temperature shows a maximum of Tc = 3.55K near x=0.3 and decreases with further increase in Si concentration. The changes in the Debye frequency and electron-phonon coupling have combined effect to control the critical temperature.