Heterogeneous High Temperature Cuprate Superconductors
Masahiko Hayashi, Hiromichi Ebisawa
Graduate School of Information Sciences, Tohoku University, Aramaki Aoba-ku, Sendai 980-8579, Japan
An intriguing possibility to observe superconductivity in the cuprate superconductors above the transition temperature of the optimally doped sample is pointed out within the framework of the t-J model. The system we consider is a heterogeneous structure made of a cuprate superconductor consisting of several regions with different doping rates. This new superconductivity appears when there is a boundary between two non-superconducting regions of over- and under-doping. At such boundary, the singlet resonating valence bond order and the holon condensate can exist simultaneously because of the proximity effect, thus giving rise to the superconductivity. We discuss several realistic situations where this boundary superconductivity can be observed experimentally. The relevance of this phenomenon to the inhomogeneous superconducting phenomena observed in actual cuprates is also addressed.
Monte Carlo Study of Pseudo-Gap Temperature T* within JJA Model
C. Kawabataa, M. Takeuchia, N. Hayashib, F. Onoc, S. R. Shenoyd, A. R. Bishope
aFaculty of Environmental Science and Technology, Okayama University, Okayama 700-8530, Japan
bComputer Center, Okayama University, Okayama 700-8530, Japan
cDepartment of Physics, Okayama University, Okayama 700-8530, Japan
dCondensed Matter Group, Abdus Salam ICTP, Trieste 34100, Italy
eTheoretical Division, Los Alamos National Laboratory, Los Alamos, NM87545, U.S.A.
We study pseudo-gap temperature T* of high-Tc superconductors by a Monte Carlo simulation of anisotropic 3D Josephson Junction Array (JJA) model based on the Ginzburg-Landau theory. We investigate T* both in the cases of zero external current and finite external current I in the JJA. It is found that the external current I depresses the pseudo-gap temperature T* and T* exhibits little dependence on the anisotropy between inter- and intra-layers of the 3D JJA.
Electronic states of high-Tc cuprate in the anomalous metallic regime
Hiroaki Matsueda, Kenji Takanaka
Department of Applied Physics, Tohoku University, Sendai 980-8579
By use of the d-p model for cuprate, we investigate the density of states. The retarded propagator matrix we use is defined by several composite particles, for example, pure fermion, dressed fermion with local spin fluctuation, and one with global spin fluctuation between nearest neighbour Cu sites. The shapes of the density of states rapidly change by doping and temperature because the matrix includes some mean fields which easily change by external parameters. In this paper, we discuss metal-insulator transition near the half-filling, evolution of the coherent peak, and close relationship between spin fluctuation and the spin gap phemomena.
Role of antiferromagnetic fluctuations on charge ordering and superconductivity as viewed through quantal phases
Akihiro Tanaka, Xiao Hu
Computational Materials Science Center, National Institute for Materials Science, Tsukuba 305-0047 Japan
With the use of nonperturbative methods which invoke the notion of quantal (Berry) phases, we investigate the role played by antiferromagnetic fluctuations on charge ordering and superconductivity for both quasi-1d and 2d electron systems. In both cases we find it essential to incorporate the full SU(2) symmetry of the spin degree of freedom. For the 2d case we arrive at an interesting duality between superconductivity and stripe order similar to that proposed by Zaanen but from a quite independent route. Experiments are interpreted in this light.
Perturbation Analysis of Superconductivity in Hubbard Model
Hirono Fukazawa, Hiroaki Ikeda, Kosaku Yamada
Department of Physics, Kyoto University, Kyoto 606-8502, Japan
We study the possible pairing states in the two- and three-dimensional single-band Hubbard models, which are the strongly correlated systems. The lattice structures are the square, simple cubic, bcc and fcc lattices. We analyze the dominant superconducting state on the basis of the third order perturbation theory with respect to Coulomb interaction. The pairing effective interaction is divided into the vertex correction term and the RPA-like term induced by the spin fluctuation. We investigate the roles of the two terms promoting the p-, d- and f-wave pairing states. We give the result that the vertex correction plays an important role for the triplet superconductivity.
The Electron-Hole Asymmetry in the Cuprate Superconductors
Akito Kobayashi, Atsushi Tsuruta, Tamifusa Matsuura, Yoshihiro Kuroda
Department of Physics, Nagoya University, Nagoya 464-8602, Japan
We investigate the phase diagram in the d-p model by taking the antiferromagnetic fluctuations in the fluctuation-exchange (FLEX) approximation and taking the superconducting fluctuations in the self-consistent t-matrix approximation. Obtained phase diagrams in the hole-doped rigion and in the electron-doped region have common features, i. e. the antiferromagnetic state, the superconducting state and the pseudgap phenomenon. However, the antiferromagnetic state in the electron-doped region exists approximately in 3 times wider doping-range than that in the hole-doped region. It is due to the intrinsic nature of the ingap state which is the quasi-particle state in the vicinity of the charge-transfer-type Mott insulator (cond-mat/0202116). We will show the electron-hole asymmetry in several quantities, e. g. w-dependent quasi-particle damping.
Superconductivity in a boson- fermion mixture with weak interaction
Tofik Mamedov, Tofik Mamedov
Engineering Department, Baskent University, Baglica 06530, Ankara, Turkey
A superconductivity in a mixture of fermions coexisting and interacting with the Cooper pairs, treated as real composite bosons, is examined. The equations for the fermion chemical potential, for the number of pairable but unpaired fermions and for the total number of bosons are obtained. Two temperatures are classified: First, a pseudogap temperature, Tp, determined as a one at which nonzero averages of the composite boson creation and annihilation operators are firstly manifested while the density of condensed bosons, n0(T), (i.e. bosons in a state with total zero momentum) remains negligible. Second, temperature of condensation, Tc, below which n0(T) just ceases to be zero. Tp depends as on the interaction parameter V responsible for the electron- boson transformations, as well on the boson formation energy, giving rise to the decrease of Tp with growth of V. The Tc vs V dependence reveals a non-monotonic behavior.
Quantum Melting of Stripes in Two Dimensions
Tsutomu Momoi
Institute of Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan
Quantum fluctuations of striped domain walls in two-dimensional incommensurate states are investigated. Both stripes with short-range and long-range interactions are considered. Mapping the quantum stripes to 3D XY model, we show that stripes melt and become a stripe liquid due to dislocations created by quantum fluctuation. This quantum melting transition is second order and characterized by the 3D XY universality class. We find that, in the case of short-range interaction, stripes melt in a large-wall-spacing (low density) region, whereas stripes with long-range interactions that fall off as power laws become a liquid in a short-wall-spacing (high density) region. These results are applied to incommensurate domain walls in two-dimensional adsorbed atoms on substrate and doped antiferromagnets, e.g. Cupper oxides.
Electron-hole asymmetry in the electronic states of high-TC superconductors: a variational quantum Monte Carlo study
Seiji Yunoki, Sandro Sorella
International School for Advanced Studies, via Beirut 4, 34014 Trieste, Italy
Motivated by recent photoemission experiments for n-type high-TC cuprates, providing a clear microscopic evidence for the electron-hole asymmetry in the electronic structures, here we study the origin of this asymmetry and the consequences theoretically using recently developed variational quantum Monte Carlo method1. We first show the existence of the antiferromagnetic long range order extending away from zero doping and the asymmetry of the regions in the phase diagrams. Next we will present the momentum distribution functions as a function of doping to examine the evolution of the shape of Fermi surface. Our results will be compared with the photoemission experiments.
Low field DC SQUID Nuclear Magnetic Resonance on single crystal UPt3
R. Körbera, A. Caseya, B.P. Cowana, M.E. Digbya, Junyun Lia, J. Luoa, C.P. Lushera, J. Saundersa, D. Drungb, T. Schurigb, J.B. Kyciac, J.I. Hongc, D.N. Siedmanc, W.P. Halperinc
aDepartment of Physics, Royal Holloway University of London, Egham, Surrey, TW20 0EX, UK
bPhysikalisch-Technische Bundesanstalt, Berlin, Germany
cNorthwestern University, Evanson, IL 60208, USA
A SQUID spectrometer is being used to study high-quality single-crystals of UPt3 in low magnetic fields by performing pulsed NMR on 195Pt. The system uses a multiloop DC SQUID with Additional Positive Feedback (APF) and operates in flux-locked loop mode from DC to 3 MHz. It has an overall coupled energy sensitivity of 800 h and a dead time of ~ 5 ms. NMR signals from UPt3 have been observed in both the superconducting mixed state and in the normal state. A bulk platinum marker is used to determine the magnetic field. Measurements of 195Pt Knight shifts in UPt3 are reported.
Superconductivity in a Ferromagnet UGe2 -Heat Capacity measurement under High Pressure-
Naoyuki Tateiwaa, Tatsuo C. Kobayashib, Kiichi Amayaa, Yoshinori Hagac, Rikio Settaid, Yoshichika Onukid
aGraduate School of Engineering Science, Osaka University, Osaka 560-8531, Japan
bKYOKUGEN, Osaka University, Toyonaka, Osaka 560-8531, Japan
cJapan Atomic Energy Research Institute, Tokai-mura, Naka-Gun, Ibaraki, 319-1195, Japan
dGraduate School of Science, Osaka University, Osaka 560-8531, Japan
Recently co-existence of the superconductivity and the ferromagnetism was reported under high pressure phase (1.0-1.6 GPa) of UGe2. In this presentation, we will show the result of our heat capacity measurements under high pressure.It was found that the superconducting peak was observed in the narrow pressure range around the critical pressure PC* where the another transition T* disappeared.
Specific Heat of CeRhIn5 Under Pressure to 21 kbar: Pressure-Driven Transition from Antiferromagnetism to Heavy-Fermion Superconductivity
R. A. Fishera, F. Bouqueta, N. E. Phillipsa, M. F. Hundleyb, P. G. Pagliusob, J. L. Sarrob, Z. Fiskb, J. D. Thompsonb
aLawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720 USA
bLos Alamos National Laboratory, Los Alamos, NM 87545 USA
CeRhIn5 has an unusual transition at a critical pressure Pc » 15 kbar. Specific-heat data show a gradual change in the zero-field "magnetic" specific-heat anomaly from one typical of antiferromagnetic ordering at ambient P to one more characteristic of a Kondo singlet ground state at 21 kbar. At 15 kbar there is a discontinuous change from an antiferromagnetic to a superconducting ground state, and evidence of a weak first-order transition. Above Pc the low-energy excitations are characteristic of superconductivity with line nodes in the energy gap, and, at intermediate P, of extended gaplessness.
Gap Structure and Anomalous Superconducting state of Quasi 2D Heavy-Fermion CeCoIn5
Koichi Izawaa, Hidemasa Yamaguchia, Yuji Matsudaa, Hiroaki Shishidob, Rikio Settaib, Yoshichika Onukib
aInstitute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8581, Japan
bGraduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
To specify the direction of the nodes in the superconducting gap, we measured the thermal conductivity of quasi 2-D heavy ferimon CeCoIn5 in a magnetic field rotating within the 2D planes. A clear fourfold symmetry of the thermal conductivity which is characteristic of a superconducting gap with nodes along the (±p,±p)-directions is resolved. The thermal conductivity also reveals a first order phase transition at Hc2. The results indicate that the symmetry most likely belongs to dx2-y2, implying that the anisotropic antiferromagnetic fluctuation is relevant to the superconductivity.
Specific Heat Study on Heavy-Fermion Superconductor PrOs4Sb12
Yuji Aoki, Takahiro Namiki, Shuji Ohsaki, Shanta R. Saha, Hitoshi Sugawara, Hideyuki Sato
Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan
Thermal properties of the filled skutterudite PrOs4Sb12, the first Pr-based heavy-fermion superconductor with a superconducting (SC) transition temperature Tc=1.8 K [1], have been studied using high-quality single crystals. At ~ 0.9Tc in the SC phase, specific heat shows a kink structure, which may reflect a possible multiphase superconductivity. Obtained GL parameter k2 diverges with decreasing temperature indicating no paramagnetic effect being dominant. The upper critical field is slightly anisotropic (of the order of 2%). Outside of the SC phase, distinct anomaly evidencing a field-driven phase transition is found above 4 T. This phase might be due to a field-induced antiferromagnetic ordering as those in quadrupole-ordered CeB6 and TmTe or magnetically frustrated Gadolinium Gallium Garnet.
[1] E.D. Bauer et al.: Phys. Rev. B 65 (2002) 100506(R).
Superconductivity of YBCO/(Sr,Ca)-Cu-O/YBCO system
Shinichiro Koba a, Masahiro Saitob, Zon Moria, Toshiya Doib, Yoshinori Hakurakub
aYatsushiro National College of Tech., 2627 Hirayama-shinmachi, Yatsushiro, Kumamoto 866-8501, Japan
bFaculty of Engineering, Kagoshima University, 1-21-40 Koorimoto, Kagoshima 890-8232, Japan
The superconductivity and the dependence of Tc to oxygen and compound ratios (x) of SrxCa0.1-xCuOz films (thickness=2200Å) sandwiched with YBa2Cu3O7-d (YBCO) films (1500Å) has been examined. The trilayer films were fabricated on a SrTiO3 substrate by using DC magnetron sputtering in the oxygen gas (0.1 - 1.0Torr). The Tc on the resistivity of YBCO/Sr0.1CuOz/YBCO ranged from 55K to 91K concerning the variation of oxygen pressure. On the optimized oxygen (0.3Torr), the characteristics to (x) of SrxCa0.1-xCuOz were examined. Then YBCO electrode by the substrate and that of top layer had Tc=72K and 19K, respectively. The dependence of Tc to (x) ranged over that of YBCO electrodes and had the optimized Tc (Tc-on=95K, Tc-end=91K) at x=0.05.
Oxygen Ordering and Superconductivity in RBa2Cu3Oy=6.4 (R=Er, Yb)
James R. O'Briena, Hong S. Kimb, Hans Oesterreicherb
aQuantum Design, 11578 Sorrento Valley Road, San Diego, CA 92121
bDepartment of Chemistry, University of California, San Diego, La Jolla, CA 92093-0506
Shot quenched orthorhombic non-superconducting samples are found to transform at room temperature into bulk superconductors by means of a thermally activated oxygen rearrangement mechanism. The influence of rare earth size on the rate of the transformation is examined. The development of superconductivity is monitored in a Quantum Design MPMS SQUID magnetometer by controlled time exposure at elevated temperatures. Within one hour at 300 K in the MPMS, the materials have obtained a transition temperature Tc of 30 K. The smaller rare earth size and corresponding increased lattice pressure cause a faster transformation from an initial orthorhombic 3-fold coordinate Cu chain site into a 4-fold coordinate Cu chain site.
Intrinsic Josephson Effect on Bi-2212 LPE Films
T. Yasudaa, T. Kawaeb, T. Yamashitac, C. Takad, A. Nishidad, S. Takanoa
aDept. Computer Science and Electronics, Kyushu Institute of Technology, Fukuoka 820-8502, Japan
bRIEC, Tohoku University, Sendai 980-8577, Japan
cNICHe, Tohoku University, Sendai 980-8579, Japan, and CREST, JST, Japan
dDepartment of Applied Physics, Fukuoka University, Fukuoka 814-0180, Japan
We fabricated stacks of the intrinsic Josephson junctions (IJJs) on the single-crystalline Bi2Sr2CaCu2Ox (Bi-2212) films prepared by liquid phase epitaxy (LPE). In addition to the 3-dimensional stack design similar to the conventional whisker IJJs, we realized the planar IJJs on the LPE films grown on the step-patterned substrates. Both stacks displayed multibranched current-voltage characteristics inherent in the Bi-2212 single crystals. In order to control the critical temperature and the critical current of the films, we studied the effects of oxygen annealing and yttrium doping.
Critical Current Density for Melt-Processed Filamentary Monolithic RE123 (RE=Nd, Sm, Eu, Gd) Superconductors
Tomoko Gotoa, Kazuo Watanabeb, Eriko Banc
a Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 Japan
bInstitute of Materials Research, Tohoku University, 2-1-1Katahira, Aoba-ku, Sendai, 980-8577 Japan
cMeijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya 468-8502 Japan
The filamentary monolithic RE123 (RE=Nd, Sm, Eu, Gd) precursor was prepared by a solution spinning method. The precursor was partially melted under various conditions and then oxygenated. The influence of field dependence of Jc on the initial different RE elements in the filamentary RE1123 superconductors was examined. The highest Jc values was attained for the Nd123 and Eu 123 samples partially melted in flowing 0.1%O2+Ar and for the Sm123 and Gd123 samples partially melted in flowing 1%O2+Ar. The field dependence of Jc for the Eu123 sample was superior to that for the other samples.
Josephson Plasma Resonance in Partially Irradiated Bi2Sr2CaCu2O8+y
Naoto Kamedaa, Masashi Tokunagaa, Tsuyoshi Tamegaia, Marcin Konczykowskib, Satoru Okayasuc
aDepartment of Applied Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
bCNRS, URA 1380, Laboratoire des Solides Irradiés, École Polytechnique, 91128 Palaiseau, France
cJAERI, 2-4, Shirakata Shirane, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan
We study the Josephson plasma resonance in Bi2Sr2CaCu2O8+y (BSCCO) with inhomogeneous phase coherence caused by partial introduction of columnar defects. In these BSCCO, we observe several resonance peaks which are different from the superposition of each constituent parts. At 50K in half irradiated BSCCO, we observe a sudden change in resonance behavior at wcr = 55 GHz, from irradiated part dominating resonance below wcr to pristine part dominating resonance above wcr The sine-Gordon equation with characteristic length scale of lc can reproduce this behavior. The sample size and temperature dependence of wcr can also be qualitatively understood in the same scheme.
Current distribution in the welded YBCO bulk material
Noriko Chikumotoa, Mayu Oishia, Junko Yoshiokab, Kazumasa Iidab, Masato Murakamia
a Superconductivity Res. Lab., ISTEC, 1-16-25 Shibaura, Minato-ku, Tokyo 105-0023, Japan
bSuperconductivity Res. Lab., ISTEC, 3-35-2 Iioka-Shinden, Morioka, Iwate 020-0852, Japan
Recently we have succeeded in joining the two monoloths of single grain YBCO superconductors by means of welding technique. We found the microstructure at the joint is largely influenced by the alignment of the sample. We got better joint for (110)/(110) than for (100)/(100) joint. Detailed measurement of the magnetic penetration was performed by mean of the magneto-optical technique. The field and current distrubution revealed larger Jc for (110)/(110) joint.
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.
Effect of Chemical Pressure on Superconductivity of Nd(Sr2-xBax)(Cu2.7Mo0.3)Oz system
H.K. Leea, H.J. Trodahlb
aDepartment of Physics,Kangwon National University Chunchon 200-701,Republic of Korea
bSchool of Chemical and Physical Sciences, Victoria University of Wellington, New Zealand
Nd(Sr2-xBax)(Cu2.7Mo0.3)Oz(x=0-1.0) samples were synthesized and examined with respect to the chemical pressure effect. It is found that the non-superconducting phase NdSr2(Cu2.7Mo0.3)Oz can be made superconducting by substitution Ba at the Sr site. Raman measurements indicate that the movement of the apical oxygen toward the CuO2 planes induced by the chemical pressure is similar to that observed in Y(Ba2-xSrx)Cu3Oz system. Thermoelectric power measurements show that all the samples are underdoped and hole density on the CuO2 planes decreases as the Sr:Ba ratio raised.These results are discussed in relation to the local structural changes induced by the chemical pressure
Annealing Effects on [BaCuO2]m/[CaCuO2]n Superlattice Thin Film
Yasuharu Kodamaa, Jia Cai Nieb, Athynarayanan Sundaresanb, Yasumoto Tanakaa
aNanoelectronics research Institute, AIST, 1-1-1 Umezono, Tsukuba 305-8568, Japan
bCREST, Kawaguchi 332-0012,Japan
Layer by layer deposition of thin film fabrication is very attractive technique, and it is suitable for [BaCuO2]m/[CaCuO2]n superlattice which possess CuBa2Can-1CunOx superconductor based structure. But it is difficult to obtaine superconducting superlattice thin film made by sputtering process. One reason of non-superconductivity is a lack of oxygen because of relative low oxygen partial pressure duraing sputtering process. Then we investigated several annealing on superlattice thin film in order to intruduce oxygen into superlattice structure. We try to realaize superconductivety on superlattice thin film.
Generalized Method of Image and the tunneling spectroscopy in High-Tc Superconductors
Chung-Yu Mou, Shin-Tza Wu
Department of Physics, National Tsing Hua University, Hsinchu 30043, Taiwan
A generalized method of image is developed to deal with the tight-binding nature involved in the tunneling problem. In particular, we investigate the zero-bias conductance peaks (ZBCPs) that occur in the metal-d-wave superconductor junctions. The evolution of ZBCPs versus dopings is obtained. In addition, the splitting of ZBCPs in magnetic fields is found in good agreement with experiments. Finally, a conductance peak at the bias of chemical potential for tunneling into the (110) direction of the d-density wave state is predicted, providing a signature to look for in experiments.
Quasiparticle Spectra and Their Spatial Variation on YBa2Cu3Oy by Scanning Tunneling Spectroscopy
Kenji Shibataa, Makoto Makia, Terukazu Nishizakia, Norio Kobayashib
aInstitute for Materials Research (IMR), Tohoku University, Sendai 980-8577, Japan
bIMR and Center for Low Temperature Science, Tohoku University, Sendai 980-8577, Japan
Low-temperature scanning tunneling spectroscopy studies have been performed on YBa2Cu3Oy in magnetic fields. In zero field, spatially homogeneous superconducting gap spectra are observed over 100 nm square range, in contrast to the spatially inhomogeneous feature reported in Bi2Sr2CaCu2O8+d. In magnetic fields, two types of spectra are observed. One has superconducting gap almost the same as that observed in zero field. In another type of spectrum, superconducting coherence peak is suppressed and the spectrum shows localized states at Vtip @ ±5 mV, representing quasiparticle density of state inside a vortex core. The spectrum form and spatial structure of low energy excitation around vortex is discussed.
I-V Characteristics of YBCO Thin Film with a Periodic Array of Ni Dots
W. J. Yeha, Bo Chenga, B. L. Justusb
aDepartment of Physics, University of Idaho, Moscow, Idaho 83844, U.S.A.
bOptical Sciences Division, Naval Research Laboratory, Washington, D.C. 20375-5338, U.S.A.
Enhancing the pinning force in cuprates can be achieved by externally introduced magnetic dots. We use a novel nanochannel glass technique to create metal replica masks with submicron-size holes that have a triangular lattice pattern. With this replica mask, Ni dots with a periodic array are deposited onto the surface of YBCO thin films. The I-V characteristics of YBCO thin film strips with Ni dots are measured. They are compared with that of a bare YBCO strip without Ni dots. The results show that as the magnetic field increases the critical current value of the strip with Ni dots reduces with a much slower pace in comparison with the values obtained from the bare sample. This effect becomes more profound at temperatures close to Tc.
LT-STM observation of YBa2(Cu1-xZnx)3O7-d single crystals
Makoto Makia, Terukazu Nishizakia, Norio Kobayashia,b
aInstitute for Materials Research, Tohoku University, Sendai 980-8577, Japan
bCenter for Low Temperature Science, Tohoku University, Sendai 980-8577, Japan
We present low-temperature scanning tunneling microscopy measurements of the BaO layer in cold-cleaved YBa2(Cu1-xZnx)3O7-d single crystals, showing the one-dimensional charge modulations at lower bias voltage. Such modulations were not observed on Zn-free samples. We consider that the observed charge modulations are closely related to the electronic local density of states in the CuO2 plane right under the BaO layer. Spatial electronic inhomogeneity induced by Zn impurities in the CuO2 plane seems to give the most probable interpretation for our experimental results. One-dimensional character of the charge modulations suggests that the CuO-chain layer effects on the electronic states of the CuO2 plane.
Tunneling Studies of Electronic State in High Tc Bi(2212)-System
Morio Suzuki, Atsushi Suzuki, Kenta Kainuma
Department of Physics, Faculty of Science and Engineering, Saga University, Saga 840-8502, Japan
The critical temperature Tc in Bi2Sr2Ca1-xYx(Cu1-yZny)O8+z (referred to BSCYCZO) has been reported to be strongly suppressed near x = 0.3 and y = 0.03 (Phys. Rev. B 57(1998)7491). To elucidate the relation between the suppression of Tc and the electronic state, the tunnel conductance G(V) was measured various temperatures for the planar junction fabricated on cleaved single crystal BSCYCZO. The G(V) for x = 0 and y = 0.03 was highly symmetric around V = 0 at a temperature above and below Tc = 83 K, while the G(V) for x = 0.02 and y = 0.03 was symmetric around V = 0 at a temperature above Tc = 65 K but strongly asymmetric below Tc = 65 K, where the electron excitation band was strongly enhanced in comparison with the hole band. This confirms that the destruction of symmetry in the electron and hole excitation bands strongly suppresses Tc.
Destruction of Stripe Order by Zn-Doping and Formation of a New Phase by Ni-Doping in La1.875Ba0.125Cu1-yMyO4 (M=Zn or Ni)
Yoshitoshi Okajimaa, Osamu Anegawab, Satoshi Tandac, Kazuhiko Yamayac
aAsahikawa National College of Technology, Asahikawa 071-8142, Japan
bFujitsu Quantum Devices Limited, Fourth Technological Division, Yamanashi 409-3883, Japan
cDepartment of Applied Physics, Hokkaido University, Sapporo 060-8628, Japan
Effects of spin substitution on the stripe order have been investigated in La1.875Ba0.125Cu1-yMyO4 (M=Zn or Ni). Spin S=1/2 at the Cu site is substituted to S=0 by Zn-doping and to S=1 by Ni-doping. The substitution dependence of the electronic coefficient of specific heat g in La1.875Ba0.125Cu1-yMyO4 (M=Zn or Ni) demonstrates directly destruction of stripe order by Zn (S=0) and formation of a new phase by Ni (S=1). We discuss the destruction process of the stripe order by Zn-doping and the formation process of the new phase by Ni-doping.
Temperature Dependence of the Hall Angle in Disordered Y1-xPrxBa2Cu3O7-d Thin Films
K. Makisea, Y. Yadoguchia, F. Ichikawab, T. Aominea, Z. Haoc, B. Zhuc, B. Xuc, B.R. Zhaoc
aDepartment of Physics, Kyushu University, Fukuoka 812-8581, Japan
bDepartment of Physics, Kumamoto University, Kumamoto 860-8555, Japan
cChinese Academy of Sciences, Beijing 100080, China
We have studied the behavior of carriers near the field-induced superconductor-insulator transition for different disordered Y1-xPrxBa2Cu3O7-d thin films. The measurement of longitudinal and Hall resistivities was carried out in the magnetic fields. For the lower disordered film the superconducting transition appeared even at 10 T, and the temperature T dependence of Hall angle cotqH was positive above Tc. While, the insulating behavior was observed for the higher disordered film, and the T dependence of cotqH was negative. We discuss the behavior of carriers on the viewpoint of the localized state.
Microwave surface impedance anisotropy of YBa2Cu3Ox single crystals with different oxygen content
Yuri Nefyodov, Mikhail Trunin
Institute of Solid State Physics, Russian Acad. of Sci., 142432, Chernogolovka, Moscow distr., Russia
The linear microwave response of ultra high-quality YBa2Cu3Ox single crystals grown in BaZrO3 crucibles is measured at 9.4 GHz in rf magnetic fields parallel and perpendicular to the ab-plane in the temperature range 5 £ T £ 200 K. Having found the analytic solution for the magnetic field distribution on the sample surface we determine both the surface impedance Zab=Rab+iXab in the ab-plane and Zc=Rc+iXc along c-axis of the crystals. For the first time the evolution of the Zab(T) and Zc(T) dependences on the same sample and in a wide range of oxygen content is obtained. For x=6.95 (optimum oxigen content) the temperature dependence of the c-axis superfluid density, nsc(T), is found to be strikingly similar to nsab(T) and becomes more convex with x lowering.
Anomalous Behavior of Low- and High-Temperature Antiferromagnetic Superconductors at the vicinity of TN
Krzysztof Rogacki
Institute of Low Temperature, Polish Academy of Sciences, 50-950 Wroclaw, Poland
Recent discovery of the presence of long-range magnetic order and superconductivity in rare earth nickel borocarbides and Ru-based compounds has triggered a new series of experiments and inspired a return to the so-called coexistence phenomenon. In high temperature superconductors REBa2Cu3O7 (RE= magnetic rare earth), screening currents are strong enough to hide an interaction between superconducting electrons and localized magnetic moments of RE ions and no sign of mutual influence has been observed at or below the antiferromagnetic ordering temperature. For these compounds, however, RE(RE-Ba)2Cu3O7+d solid solution can be obtained, where superconductivity is weakened and magnetism strengthened, and pair-breaking effects may expose.
In-plane and out-of-plane temperature dependencies of the resistivity in single crystals and films of Nd2CuO4
T. Charikovaa, A. Ignatenkova, A. Ponomareva, A. Ivanovb, T. Klimchukc, W. Sadowskic
aInstitute of Metal Physics RAS, 620219 Ekaterinburg, Russia
bMoscow Engineering Physics Institute, 115409 Moscow,Russia
cDepartment of Physics, Technical University of Gdansk,80-952 Gdansk, Poland
The temperature dependencies of the in-plane rab(T) and out-of-plane rc(T) resistivities of two groups of Nd2CuO4 single crystals (films and bulk single crystals) are investigated in a temperature range 20-300 K. The aim of the present work is to study the effect of modified heated treatment and annealing conditions on transport properties of the pra-crystals Nd2CuO4. It was found that nonstoichionometric disorder leads to different dependencies of the resistivity both in rab(T) and rc(T).
This work was supported by the Competition of Ural Branch of RAS for young scientists, grant No. 10.
Coherent-to-Incoherent Crossover in Optical Conductivity of
Bad-Metallic
La2-xSrxCuO4
Koshi Takenaka, Ryozo Shiozaki, Shunsuke Okuyama, Jiro Nohara, Shunji Sugai
Department of Physics, Nagoya University, 464-8602 Nagoya, Japan
We have investigated the in-plane charge dynamics of lightly doped La1.92Sr0.08CuO4. The in-plane resistivity rab(T) exhibits a typical behavior of a bad metal; it is metallic (dr/dT > 0) over the entire temperature range up to 1000 K without saturation at the Mott criterion. On the other hand, the in-plane optical conductivity sab(w) deviates from a simple Drude response; it shows a slowly decaying ( µ w-1) quasi-Drude behavior below a certain temperature T*, above which it is characterized by a finite-energy peak instead of a Drude-like term. The relationship between the shift of the Drude peak and the Mott criterion indicates that the charge carriers are dynamically" localized above T*. The universality of the observation with respect to other compositions and other bad metals are also discussed.
Direct measurement of the critical magnetic fields in MgB2 crystals
G. K. Perkins Posdoc, J. Moore Young, Yu. V. Bugoslavsky Posdoc, L. F. Cohen Lecturer, A. D. Caplin Professor
Blackett Lab, Imperial College, Prince Consort Road, London, UK SW7 2BZ
Using novel techniques we have directly measured the lower and upper critical fields (Hc1(T) and Hc2(T) respectively) and the anisotropy gamma in MgB2 single crystals. Our results suggest that Hc1 is much higher than previous estimates and that consequently the Ginzburg Landau parameter kappa is very low (around 3). We also find gamma 2, independent of temperature and magnetic field.
Fundamental mixed state parameters of superconducting MgB2
M. Zehetmayera, M. Eisterera, H. W. Webera, J. Junb, S.M. Kazakovb, J. Karpinskib, A. Wisniewskic
aAtominstitut der Österreichischen Universitäten, A-1020 Vienna, Austria
bSolid State Physics Laboratory, ETH, CH-8093 Zürich, Switzerland
cInstitute of Physics, Polish Academy of Sciences, PL-02-668 Warsaw, Poland
We report on measurements of the magnetic moment in superconducting MgB2 single crystals by SQUID, vector VSM and torque techniques. The results indicate that MgB2 is a clean limit superconductor of intermediate coupling strength with very pronounced anisotropy effects (g = 4.6 at T = 0 K). Furthermore, neutron irradiation is employed to modify the defect structure of the crystals. We will show that the mixed state parameters are primarily modified by the change in the mean free path of the charge carriers.
Similarity of thermal expansion anomalies in MgB2 and HTS oxides
N. V. Anshukovaa, B. M. Bulichevb, A. I. Golovashkina, L. I. Ivanovac, I. B. Krinetskiib, A. P. Rusakovc
aP.N.Lebedev Physical Institute RAS, Moscow, Russia
bMoscow State University, Moscow, Russia
cMoscow Steel and Alloys Institute, Moscow, Russia
The measurements of thermal expansion a(T) of MgB2 were carried out at low temperatures both in zero magnetic field H and at H » 4T. As for oxide high-temperature superconductors (HTS) the anomalous (negative) thermal expansion was observed for MgB2. It was found also the strong magnetic field influence on the a(T). Qualitative explanation of both effects on the basis of known charge density wave properties was given. The results indicate on the similarity of the anomalous properties of MgB2 and oxide HTS.
STM at very low temperatures in the borocarbides and in MgB2
H. Suderowa, P. Martinez-Sampera, G. Rubio-Bollingera, S. Vieiraa, J. P. Brisonb, P. Lejayb, P. C. Canfieldc
a Laboratorio de Bajas Temperaturas, UAM, E-28049 Cantoblanco, Spain
b CRTBT-CNRS, BP 166, 38042 Grenoble Cedex 9, France
c Ames Lab. and Dpt. of Physics and Astronomy, Iowa State Univ., Ames, Iowa 50011, USA
We discuss very low temperature (0.4K) STM measurements in single crystals of several borocarbide materials. The magnetic superconductor TmNi2B2C (Tc=10.5K and TN=1.5K) shows clean, s-wave like spectra. But the apparently more simple, non-magnetic compounds YNi2B2C and LuNi2B2C show, surprisingly, the presence of an anomalously anisotropic superconducting gap. The consequences of our tunneling measurements concerning the pairing interaction will be discussed. We compare these results with the tunneling spectroscopy of MgB2, where we find a clear s-wave density of states.
Critical Current Density and Flux Pinning Characteristics of Powdered MgB2 Specimens
Y. Matsumotoa, I. Shigetab, T. Abiruaa, Y. Terasakia, T. Akunec, N. Sakamotoc
aDepart. Elec. Engi., Fukuoka University, 8-19-1 Nanakuma, Fukuoka 814-0180 Japan
bAdvanced Mate. Insti., Fukuoka University, 8-19-1 Nanakuma, Fukuoka 814-0180 Japan
cDepart. Elec. Engi., Kyushu Sangyo University, 2-3-1 Matsukadai, Fukuoka 813-8503, Japan
Field and temperature dependence of magnetization and also time dependent magnetization (flux creep) of powdered MgB2 specimens have been measured by using SQUID magnetometer. Scaling plots of normalized pinning force density Fp/Fpmax as a function of normalized flux density B/Bmax in the temperature range of 25 £ T £ 37K showed that a two dimensional pinning is dominant for the flux pinning. Another distinct feature is that a linear reduction of Jc with increasing temperature at temperatures lower than 30K and a quadratic decrease at higher temperatures than 30K have been observed.
Far-Infrared Optical Reflectance Spectra in Sintered MgB2 Ceramics
Hajime Shibataa, Shinji Kimuraa, Satoshi Kashiwayaa, Akira Iyoa, Takashi Yanagisawaa, Kunihiko Okaa, Yoshikazu Mitsugia, Yukio Tanakab
aNational Institute of Advanced Industrial Science and Technology, Tsukuba Central 2, Tsukuba, Ibaraki 305-8568, Japan
bNagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
Far-infrared optical reflectivity studies in sintered MgB2 ceramics with a superconducting transition temperature Tc = 38 K were performed at temperatures from 5 to 47 K. A significant raise was observed in the reflectance spectra below 110 cm-1, which can be attributed to the evolution of the superconducting energy gap. However, we could not observe the evolution of significant reflectance edge which is expected to be observed in the conventional isotropic s-wave superconductors. The observed results are consistent with the theoretical calculation of optical reflectance spectra for the anisotropic s-wave superconductors.
The nonphonon superconducivity of the flat borons
Rogdai O. Zaitsev
Russian Research Center "Kurchatov Institute", Kurchatov Sq. 1, Moscow 123 182, Russia
On the basis of concept of strong interaction in the same elementary cell the possibility of Cooper's instability existence in the system with hopping between cautions and anions nonetransition elements is established. The phase diagram of cooper's pairing existence depending on the degree of filling (np) 2p- and (ns) 3s- shells of nonetransition elements is constructed. Eventually the solvability conditions can be written as the BSC-relation Tc » t* exp(-1/gr), where r is the density of states on the Fermi surface and g- is the function from es, ep, ns, np and the scattering amplitudes gs, gp. If one takes g=0 then it gives the condition for appearance of superconductivity. Together with the equation of state this condition defines the superconductive domains in the ns,np- variables.
Temperature and Field Dependence of MgB2 Energy Gaps from Tunneling Spectra
Mohamed Badr, K.-W. Ng
Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506-0055, U. S. A.
We have synthesized MgB2/Pb planar junctions to study the temperature and field dependence of the superconducting energy gap of MgB2. The major peak occurs at D of about 2 meV, and this corresponds to a 2D/kBTcvalue of 1.18. While this is significantly smaller than the BCS weak coupling value, there are features in the tunneling spectra indicating the possibility of another larger gaps. By fitting the dI/dV curves with a simple model, the larger gap is estimated to be about 4.5 times the smaller gap. Temperature dependence of both gaps are near BCS like, and start to open up at temperatures just below Tc ( 39K). This confirms that these gaps are indeed bulk properties of MgB2. The junction is stable only up to a field of 3.l9T. By extrapolation, we can estimate the Hc to be about 6.2T.
Dynamic Jahn-Teller Effect and Superconductivity in MgB2
Jaejun Yu, Young Woo Son, Jisoon Ihm
School of Physics, Seoul National University, Seoul 151-747, Korea
Recent experimental observations of anomalous temperature- and magnetic field-dependence in specific heat and tunneling spectra of the newly discovered high Tc MgB2 superconductor have suggested a possible multiple-gap nature of the superconducting state of MgB2. We propose a novel mechanism of superconductivity in MgB2 based on the dynamic Jahn-Teller effect of the interplay between the doubly degenerate ps electronic states and the E2g phonon modes. The hopping motion of holes in the ps states of the 2D B layers is constrained by the accompanying phonons, and thereby a non-trivial superconducting state with multiple order parameters is found to arise from conventional electron-phonon interactions due to the presence of additional pairing channels. Important experimental observations including high Tc and the anomalous specific heat are explained using this theory.
Electron Transport in MgB2, NbB2, TiB2, TaB2, ZrB2 and ZrB12
Vitaly A. Gasparov a, N.S. Sidorova, M.P. Kulakova, I.I. Zver'kovaa, Hong-Ying Zhaib, H.M. Christenb, M.P. Paranthamanb, D.H. Lowndesb
aInstitute of Solid State Physics RAS, 142432, Chernogolovka, Moscow District, Russia
bOak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6100, USA
We report on syntheses and electron transport properties of ceramics and thin films of MgB2 and diborides (AB2) with (A=Zr,Nb,Ta,Ti), as well as of ZrB12. We conclude that these diborides as well as MgB2 samples behaves like a simple metals in the normal state, with usual Bloch-Grüneisen temperature dependence of resistivity and with Debye temperatures (270 K, 480 K,760 K, 700 K and 720 K, for ZrB12, ZrB2, NbB2, TiB2 and MgB2, respectively). A clear exponential temperature dependence of l(T) in MgB2 thin films (Tc = 39 K) was observed at T < Tc/2, with an energy gap 2D(0)/Tc = 1.6. At the same time a linear l(T) and Hc2(T) dependencies (Hc2(0) = 0.16 T) were observed for ZrB12.
Critical currents of Bi: 2212 doped by Er, Fe and Ni
Gheorghe Iloncaa, Tzuen Rong Yangb, Aurel Popa, Gabriela Stiufiuca, Rares Stiufiuca, Claudiu Lunga
aBabes-Bolyai University, 3400, Cluj Napoca, Romania
bNational Taiwan Norma University, Department of Physics, Taipei, Taiwan, ROC
Measurements of the irreversible magnetization, AC susceptibility and electrical resistivity of Bi2Sr2Ca1-xErx(Cu1-yMy)2O8+d bulk are reported. The samples were prepared by the conventional solid state reaction. Low concentration of the doping elements increase the pinning force density and shift the magnetic irreversibility line towards higher fields. The intergranular critical current density was determined from ac susceptibility data by varying the field amplitude Hac in the range from 0.4 A/m to 1000 A/m and from the irreversible part of magnetization using Bean's model. The results were discussed in terms of SIS-and SNS-type models for granular superconductors.
Magnetic Torque in the Vortex State of Bi2Sr2CaCu2O8+d Single Crystal below 30K
Kouta Maeda, Takahiro Suzuki, Michinori Kim, Yoshiko Fujii
Department of Applied Physics, Okayama University of Science, 1-1 Ridai-cho, Okayama 700-0005, Japan
The magnetic torque originating from the intrinsic pinning parallel to the CuO2 plane and the flux pinning perpendicular to the CuO2 plane has been measured as a function of the angle q between the CuO2 plane and the applied magnetic field. The amount of flux running parallel to the CuO2 plane (Josephson vortex) was calculated from the magnetic torque as a function of q (0 £ q £ 90)at 4.5K, 6K and 12K. The amount of flux pinned perpendicular to the CuO2 plane showed saturation at about 0.5T. The depinning of the flux pinned perpendicular to the CuO2 plane at 4.5K was studied as a function of the temperature and the applied magnetic field parallel to the CuO2 plane.
Critical Current Density in HTS Films with Growth-Induced Linear Defects
Volodymyr Pana, Yuri Fedotovb, Sergey Ryabchenkob, Ernst Pashitskiib, Alexei Semenovb, Yuri Cherpaka, Valentin Komashkoa, Victor Flisa, Vassily Svetchnikovc, Henny Zandbergenc
aInstitute for Metal Physics, Vernadsky Blvd. 36, Kiev 03142, Ukraine
bInstitute of Physics, Nauki Ave. 46, Kiev 03028, Ukraine
cNational Centre for HREM, TU Delft, Rotterdamseweg 137, AL Delft 2628, The Netherlands
Jc magnetic field dependencies are measured in YBCO films by AC susceptibility and transport current technique. Out-of-plane edge dislocations are shown to play a crucial role in Jc-behavior due to strong vortex pinning on their normal cores. In the field applied along the c-axis Jc(H) is shown to have a plateau Jc = const at H < Hmin and to be approximated well at H > Hmin by Jc(H)/Jc(0) = alog(H*/H). The fitting parameter a is almost temperature independent and H* is proportional to 1 - T/Tc. A model of pinning by out-of-plane edge dislocation and by mosaic domain low angle boundaries is developed.
Effect of Thermal Neutron Irradiation in Boron-Doped Melt-Textured YBCO
Ugur Topala, Lev Dorosinskiia, Husnu Ozkanb, Hasbi Yavuzc
aTUBITAK-UME, National Metrology Institute, P.K. 54, 41470, Gebze-KOCAELI/Turkey
bDepartment of Physics, Middle East Technical University, 06280, Ankara/Turkey
cITU, Institute for Nuclear Energy, 80626, Maslak-Istanbul/Turkey
Y1.6Ba2.3Cu3.3Ox superconductors with different amounts of boron-doping have been synthesized using the MPMG technique. Undoped and boron doped samples were irradiated with thermal neutrons to study the effects of defects produced by the fission reaction, B (n,a) Li, on the pinning properties and the critical current densities. We observed that pinning properties and critical current densities were improved with thermal neutron irradiation. This improvement was stronger on boron-doped samples compared to undoped one.
Relaxation study of RE-123 materials with different types of pinning defects.
Milos Jirsaa, Vitalii Zablotskiia, Terukazu Nishizakib, Norio Kobayashib, Miryala Muralidharc, Masato Murakamic
aInstitute of Physics, ASCR, Na Slovance 2, CZ-182 21 Praha 8, Czech Republic
bInstitute for Material Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan
cSuperconductivity Research Laboratory, ISTEC, 1-16-25 Shibaura, Minato-ku, Tokyo 105, Japan
Total magnetic moment relaxation study is made on RE-123 samples with large-particle, point-like-disorder, and twin-boundary pinning structures. The correlation of relaxation data with M-H loop shape via S=-dlnM/dlnt=gE (kE - dlnM/dlnB) (gE and kE being constants) derived by Perkins et al. [PRB 51 (1995) 8513] is documented in a wide range of temperatures and on different types of samples. Potentials and limitations of the total magnetic moment relaxation studies is discussed from the point of view to what extent different pinning mechanisms can be characterized and distinguished on this basis.
Vortex lattice melting transition under the influence of the c-axis current
S. Savel'evba, J. Mirkovi\'ca, K. Kadowakia
aInstitute of the Materials Science, University of Tsukuba, Japan
bFrontier Research System, The Institute of Physical and Chemical Research (RIKEN), Wako-shi 351-0198, Japan
We have studied theoretically and experimentally how the c-axis current influence on the vortex lattice melting transition. Considering the renormalization of the elastic matrix by the c-axis current the mean square displacements of pancake vortices has been calculated. Using the Lindemann criterion we get the Hc-J phase diagram of the vortex lattice melting transition. The experimental date have been analyzed in the frame of the developed model.
From Mott Insulator to Superconductor : An ARPES Study of the Cuprates
Kyle Shena, Hidenori Takagib, Zhi-Xun Shena
aDepartment of Applied Physics, Stanford University
bDepartment of Advanced Materials Science, University of Tokyo
We have studied the heavily underdoped region of the cuprate phase diagram by angle-resolved photoemission (ARPES), focusing on the doping dependence of the newly synthesized compound Ca2-xNaxCuO2Cl2. We find that upon light doping, the chemical potential shifts to the top of the lower Hubbard band. In addition, by x = 0.10, we observe well-defined low-energy excitations which emerge near (p/2, p/2) and lie along a small arc-like contour. These results are compared and contrasted to results from both La2-xSrxCuO4, where the low-lying excitations appear to be formed within the gap, as well as the electron-doped cuprate, Nd2-xCexCuO4.
Stripes and a two-component interpretation of NMR in cuprates
Alpo Kallio, Johannes Hissa, Vinski Bräysy
Department of Physical Sciences, POB 3000, FIN-90014 University of Oulu, Finland
Based on the experimental fact that the susceptibilities ca (T) and the corresponding Knight shifts Ka (T) (a = c,ab) are linearly related above certain temperature Tc* ( > Tc), one normally draws a conclusion that a single Fermi component is operative. We show that this may not be generally valid. As a counter example we propose a two-component system were the susceptibilities are determined by a universal function f(T). The model consist of a Fermi component h+ and a Bose component B++ with triplet spin localized in CuO5 sites, in chemical equilibrium with respect to reaction B++\rightleftharpoons 2 h+, where f(T) gives fraction of bosons and 1-f(T) the fraction fermions. The susceptibilities above T*c are given by adding the fermion and boson contributions in the form ca (T) = ca0 + Aa [1-f(T)]+Ba f(T), where ca0, Aa and Ba are T-independent. Elimination of f(T) shows that cc(T) and cab(T) are linearly dependent.
Superconducting condensation energy in the pseudogap regime of La2-xSrxCuO4
Masayuki Ido, Naoki Momono, Toshiaki Matsuzaki, Migaku Oda
Division of Physics, Graduate School, Hokkaido University, sapporo 060-0810, Japan
We measured the electronic specific heat Cel of La214 over a wide doping-level p and T range and evaluated the superconducting (SC) condensation energy Uo from the result of Cel. The Cel was obtained by using the phonon term Cph which was obtained on Ni-doped non-superconducting samples. We reconfirmed that the Uo agrees with the BCS value in highly-doped samples which exhibit no pseudogap, but it is markedly suppressed in the pseudogap regime (x < 0.2) as well as the DOS at EF, N(0). The reduction of Uo is too large to be explained by taking into account the reduction of N(0) only. To explain the experimental values of Uo in the pseudogap region, we had to introduce a new energy scale De(=bpDo), which play an effective SC gap, instead of Do. We propose that the energy gap formed over the nodal Fermi arcs near (p/2,p/2) will play a role of the effective SC gap.
Charge Ordering and Anomalous Elastic Properties of Cuprates Superconductors
Vasilii Gusakov
Institute of Solid State and Semiconductor Physics, P. Brovki str. 17, 220072 Minsk , Belarus
In cuprates superconductors an unusual (hysteretic) temperature behavior of elastic properties is frequently observed. In this work the detailed analysis of the hysteretic temperature behavior of elastic properties is given. It is shown that the hysteretic temperature dependencies of elastic properties of YBa2Cu3O7-d crystals are strongly anisotropic and connected to the hysteretic behavior of the module C3333 only. The analysis of the elastic constant tensor on the basis of a microscopic model has allowed to draw the conclusion, that the hysteretic behavior of the C3333 module of YBa2Cu3O7-d crystal is caused by temperature dependent renormalization of interaction constants of apex oxygen atoms with copper atoms and are connected to the formation of charge ordering.
The normal state scattering rate in high-Tc cuprates
Nigel E. Hussey
H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol, BS8 1TL, U. K.
I present a new phenomenological model for the normal state transport properties of high-Tc cuprates. In particular, I identify a form of scattering rate that shows surprisingly good qualitative and quantitative agreement with all the normal state (magneto)-transport properties of the single-band single-layer cuprate Tl2Ba2CuO6+d from optimal doping through to the overdoped side of the phase diagram. The form of the scattering rate is also consistent with features seen in photoemission spectroscopy in Bi2Sr2CaCu2O8+d and offers a new intuitive way to understand the evolution of the temperature dependence of the inverse Hall angle with disorder and with carrier concentration.
Raman-active c-axis plasma modes in multilayer cuprate superconductors
Dominik Munzar*
Institute of Condensed Matter Physics, Masaryk University, Kotlárská 2, 611 37 Brno, Czech Republic
The additional absorption peak
that appears at low temperature (T)
in the spectra of the c-axis conductivity
of bilayer cuprate superconductors
has been assigned [1,2]
to the out-of-phase c-axis plasma mode (PM) [3].
Is there any Raman-active (RA) counterpart of this PM?
We demonstrate that RA PMs
can be expected to occur in n-layer cuprates with n > 2
and present compelling evidence that
the peak in the low-T A1g electronic continuum
of the four-layer superconductor Hg-1234 [4] corresponds
to such a RA PM.
The related spectacular phonon anomalies [4]
are explained along the lines of Ref. [1].
* In collaboration with M. Cardona (MPI Stuttgart).
[1] D. Munzar et al., Solid State. Commun. 112, 365 (1999).
[2] M. Grüninger et al., Phys. Rev. Lett. 84, 1575 (2000).
[3] D. van der Marel and A. Tsvetkov, Czech. J. Phys. 46,
3165 (1996).
[4] V. G. Hadjiev et al., Phys. Rev. B 58, 1043 (1998).
Magnetotransport Properties of Y1-xPrxBa2Cu3O7-d (0.13 £ x £ 0.42)
V. Sandua, E. Cimpoiasua, Shi Lib, M. B. Mapleb, C. C. Almasana
aDepartment of Physics, Kent State University, Kent, OH 44242, USA
bDepartment of Physics, University of California, San Diego, La Jolla, CA 92093, USA
With decreasing temperature T, the in-plane resistivity of Y1-xPrxBa2Cu3O7-d (0.2 £ x £ 0.42) exhibits a crossover at Tcr from sublinear to overlinear. The sublinear T dependence is attributed to the increasing contribution of hot spots as the Fermi surface FS approaches the magnetic Brillouin zone when T approaches Tcr. For T > Tcr, the orbital magnetoconductivity Dsab µ T- a, where a = 4 in x=0.13 and continuously decreases to a = 3.5 in x=0.42. This change in a is also consistent with the change in FS. The magnetoresistivity Dr(q) µ sin2 q (the angle between H and the c-axis) for T > Tcr, while a second contribution sin4 q appears for T < Tcr and becomes dominant close to Tc. This contribution is consistent with the reduction in the spin fluctuations and the increase in the superconducting fluctuations.
Zn-Induced Wipeout Effect on Cu NQR Spectra in La2-xSrxCu1-yZnyO4
Hideki Yamagata, Hiroyuki Miyamoto, Koiichi Nakamura, Masahiro Matsumura, Yutaka Itoh
Department of Material Science, Faculty of Science, Kochi University, Kochi 780-8520, Japan
We report a systematic study of Zn-substitution effect on Cu NQR spectrum for high Tc superconductors La2-xSrxCu1-yZnyO4 from carrier-underdoped to -overdoped regimes (polycrystalline samples, x =0.10, 0.15, and 0.20). We observed no appreciable wipeout effect for the overdoped samples, a gradual and partial wipeout effect below about 80 K for the optimally doped ones, and very abrupt and full wipeout effect below about 40 K for the underdoped ones. The wipeout effect indicates a highly enhanced spectral weight of Cu spin fluctuations at a low frequency. We associate the wipeout effect with a Zn-induced local magnetism enhanced near the magnetic and electric instability.
Magnetic Field Dependence of the Low-temperature Specific Heat of MgCNi3
J.-Y. Lina, P. L. Hob, H. L. Huangb, P. H. Lina, Y.-L. Zhangc, R.-C. Yuc, C.-Q. Jinc, H. D. Yangb
aInstitute of Physics, National Chiao Tung University, Hsinchu 300, Taiwan ROC
bDepartment of Physics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan ROC
cInstitute of Physics, Center for Condensed Matter Physics and Beijing High Pressure Research center, Chinese Academy of Sciences, P. O. Box 603, Beijing 100080, PRC
The specific heat of a superconductor carries crucial signature of its order parameter. For example, The magnetic field dependence of g(H) is sensitive to the symmetry of the order parameter. The newly discovered superconductor MgCNi3is predicted to be unstable to ferromagnetism, and its order parameter symmetry is of current interest. To shed light on this issue, we have measured the low-temperature specific heat of MgCNi3 in H. Careful analysis of the data reveals a g(H) µ H. Together with other physical properties, the results strongly indicate that MgCNi3 is a moderate-coupling BCS superconductor.
First observation of superconductivity in LaCu6 and possible applications
Thomas Herrmannsdörfera, Frank Pobella, Josef Sebekb, Pavel Svobodab
aForschungszentrum Rossendorf, High Field Lab, P.O.Box 51 01 19, D-01314 Dresden, Germany
bAcad. of Sciences and Charles Univ., Joint Lab for Magnetic Studies, CZ-18000 Prague, Czech Republic
We have measured the ac susceptibility and resistivity of highly pure samples of the intermetallic compound LaCu6 down to ultralow temperatures. We have prepared the samples by arc melting of stoichiometric amounts of 99.99% La and 99.9999% Cu in a water-cooled copper crucible under Ar protective atmosphere and analysed them by x-ray diffraction and SQUID magnetometry. At T £ Tc = 0.16 K we observe a sharp superconducting transition. Due to the manifold physical properties of isostructural ReCu6 compounds (e.g. RE = Ce: heavy fermion system, RE = Pr: hyperfine enhanced nuclear spin system, RE = Nd: electronic antiferromagnet), numerous studies of interplay phenomena may become possible in the quasibinary compounds RE1-xLaxCu6, respectively.
Dynamic Screening and Superconductivity in Layered Intercalated Chloronitrides
Vladimir Kresina, Andreas Billb, Hans Morawitzc
aLawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720, USA
bPaul Scherrer Institute, Condensed Matter Theory, 5232 Villigen PSI, Switzerland
cIBM Almaden Research Center, San Jose, CA 95120, USA
Experiments done on nitride chloride (Hf,Zr)NCl and related layered materials have shown that intercalation of metallic ions (Na, Li) leads to a strong enhancement of the superconducting critical temperature Tc( ~ 25K). It is known that the electron-phonon interaction alone is unable to explain such high Tcs. We show that the strong increase in Tc is due to the pairing induced by the dynamic screened Coulomb interaction, via exchange of low energy electronic collective modes (äcoustic" plasmons). This additional coupling is specific to layered systems. We describe quantitatively the experimental findings.
Possible Superconductivity in Langmuir-Blodgett Films based on Alkylammonium-metal(dmit)2
Yasuhiro F. Miuraa, Masato Hedob, Yoshiya Uwatokob, Shin-ichi Moritaa, Shin-hachiro Saitoa,
Michio Sugia
aDepartment of Functional Chemistry, Faculty of Engineering, Toin University of Yokohama, Kurogane-cho, Aoba, Yokohama 225-8502, Japan
bInstitute for Solid State Physics, University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
We report on the possible superconducting transition of the Langmuir-Blodgett (LB) film of ditetradecyl-dimethylammonium-Au(dmit)2. The evidence has been observed as a sharp diamagnetic drop of the ac magnetic susceptibility at 3.9 K and it shifts to the lower temperature side for 0.6 K with superposing a dc magnetic field of 60 mT. The lateral resistance shows a blunt decrease with decreasing temperature below 3.9 K. The effects of stronger magnetic fields and hydrostatic pressure will be also presented.
Antiferromagnetic vortex core of Tl2Ba2CuO6 studied by 205 Tl-NMR
Kosuke Kakuyanagia, Ken-ich Kumagaia, Yuji Matsudab, Tadashi Hasegawac
aDivision of Physics, Graduate School of Science, Hokkaido University, Sapporo 060-0180, Japan
bInstitute for Solid State Physics, University of Tokyo, Kashiwa, 277-8581, Japan
cInstitute for Materials Research, Tohoku University, Sendai, 980-8577, Japan
Unlike conventional BCS superconductors, HTSC have strong antiferromagnetic correlations, and thus the microscopic electronic structure of HTSC is quite different from that of the conventional ones. Recently physics of vortex core of HTSC attracts great interest. Here, we report spatially-resolved NMR studies on the magnetic properties of vortex core of HTSC. The extremely large enhancement of the nuclear spin-lattice relaxation time, T1, of the Tl site of Tl2Ba2CuO6 is observed in the vicinity of the vortex core. The broadening of the 205Tl-NMR spectrum is observed at low temperature. Based on our NMR results, we will give a clear evidence of the antiferromagnetic vortex core in Tl2Ba2CuO6.
Ultrafast optical response of TBCCO(2212) thin films
H. Murakamia, Y. Tominaria, M. Tonouchib, H. Waldc, P. Seidelc, H. Schneidewindd
aRCSP, Osaka Univ., Suita, Osaka 565-0871, Japan
bRCSP, Osaka Univ. and CREST-JST, Suita, Osaka 565-0871, Japan
cFriedrich-Schiller Univ., Helmholtzweg 5, D-07743 Jena, Germany
dInstitute for Physical High Technology, P. O. Box 100239, D-07702 Jena, Germany
Ultrafast optical response of TBCCO(2212) thin films has been investigated by means of a pump-probe technique using femtosecond optical pulse. The time-resolved pump-probe data showed a relaxation time of optically excited quasi-particles as long as 3.6ps at 4.6K. This value is an intermediate value between those for YBCO(123) and BSCCO(2212), and well explains the difference in the radiation properties of terahertz-wave pulse emitted by FOP illumination to these HTSC materials. These experimental details will be presented.
La214 phase diagram features as a consequense of percolation over -U centers
Mitsen Kirill, Ivanenko Olga
Lebedev Physical Institute, 119991 Moscow, Russia.
The mechanism of -U center formation in high-Tc superconductors (HTS) with doping is considered. It is shown that the transition of HTS from insulator to metal passes through the particular dopant concentration range where local transfer of singlet electron pairs from oxygen ions to pairs of neighboring cations (-U centers) are allowed while the single-electron transitions are still forbidden. The arising singlet hole pairs are localized in the nearest vicinity of -U center and the hole conductivity starts up at the dopant concentration exceeding the percolation threshold for chain of -U centers. In the framework of the proposed approach taking into account the partial dopant ordering the phase diagram of Ln-214 compounds is constructed. Also the mechanism of ßtripe" structure formation is considered as a consequence of the spiral ordering of AFM microdomains in spin glass phase.
Negative Magnetoresistance in Granular HTSC with Trapped Magnetic Flux
A. A Sukhanov, V. I. Omelchenko
Institute of Radioengineering and Electronics RAS, 141190 Fryazino Moscow dist., Russia
Magnetoresistive properties of Bi-based ceramic and film HTSC with trapped magnetic flux are investigated in the temperature region near superconducting transition. The effect of trapped field and transport current values and orientations on the field dependence of magnetoresistance DR(H) is studied. It was found that for the magnetic field parallel and the current perpendicular to trapping inducing field the dependence DR(H) is nonmonotonic and magnetoresistance turns out to be negative for small fields, H < Hi. The magnetoresistance sign inversion field Hi and the maximum value of negative magnetoresistance increase linearly with the trapped magnetic field and slightly decrease with transport current. The results are explained in the framework of model of magnetic flux trapping in grains or superconductive loops embedded in weak links matrix.
Cross Field Vortex Interactions in Bi2212 Studied by Microwave Absorption
Ahmad Gufran, Hashizume Akinori, Iwasaki Shin-ichi, Endo Tamio
Faculty of Engineering, Mie University, Tsu, Mie 514-8507, Japan
We have succeeded to detect vortex reentrant phase (RP) by field (H) swept microwave absorption (MA) on Bi2212 crystal. Microwave power (P) dependence of the spectrum was investigated for H//c-axis. The broad peak (solid phase) shifts rapidly to lower H with increasing P for P < 10 mW due to sample-temperature rise (by 4 K) by the stronger MA. Then it shifts gradually for higher P due to a competing effect; higher field shift of the solid phase due to stronger pinning nature of Abrikosov vortex (AV) by the microwave-field induced Josephson vortex (JVm). When H is applied along 45 deg (cross field), the dip (RP) is enhanced and the broad peak is shifted to "higher" field with increasing P. The reentrant melting is promoted owing to decoupling of 2D pancakes by JVm at the low H. Though the pinning is enhanced at the higher H because the thread-like AV is more pinned in two-dimensions by JVm and H-induced JV.
An anomalous dip in thermoelectric power of Nd1-xPrxBa2Cu3O7-d
S. R. Ghorbani, Ö. Rapp
Solid State Physics, Department of Microelectronics and Information Technology, KTH Electrum 229, SE-164 40 Kista, Sweden
The thermoelectric power, S, has been studied for sintered samples of Nd1-xPrxBa2Cu3O7-d with 0 £ x £ 0.30 in the temperature range from the superconducting Tc to room temperature. S increases with decreasing temperature, and has a broad maximum at Tmax in the region around 120 K before decresing strongly when Tc is approached. Transport properties indicate a decrease of charge concentration with decreasing doping, x, from S(x, 290 K), Tmax(x), and the resistivity r(x, 290 K). An anomaly has been observed in S(T) for x ³ 0.20 in the form of a dip at 78 K of order 15% of S. The origin of this feature is not known.
Crossing Lattices State Probed by c-axis Resistance
Shuuichi Ooi, Takashi Mochiku, El Hadi Sadki, Kazuto Hirata
National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan
In highly anisotropic layered superconductors like Bi2Sr2CaCu2O8+y (BSCCO), the existence of crossing lattices (CL) in the vortex phase has been recently known in fields tilted from c-axis. To investigate the properties of CL state, we have measured the c-axis resistance Rc(H) as a function of field in BSCCO intrinsic Josephson junctions fabricated by focused ion beam. When the field is tilted from the c-axis, Josephson-vortex flow resistance appears at low c-axis fields in the so-called lock-in state. Although the vortex flow stops when pancake vortices start to penetrate, the c-axis resistance gradually reappears in CL state with increasing field. In this regime, we observe specific features originated from CL state.
Phase Diagram and Dynamical Matching of Josephson Vortices in Mesoscopic Layered High-Tc Superconductors
Masahiko Machida
CCSE, Japan Atomic Energy Research Institute, Ueno Sumitomo Bldg.8, 6-9 Higashi-Ueno, Taito-ku, Tokyo, 110-0015 Japan
We study Josephson vortex lattice structures and their dynamics in mesoscopic layered High-Tc superconductors. Although superconducting vortices generally form the triangular lattice due to their repulsive interaction, the behavior drastically changes for Josephson vortices in mesoscopic sample of layered High-Tc superconductors by influences from sample edges. Moreover, Josephson vortices show a unique dynamical effect due to dynamical matching with sample edges. In this paper, we clarify both their static structures and dynamical effects in mesoscopic scale by performing computer simulations on the coupled sine-Gordon equation.
The Fluctuations of a local magnetic field in underdoped cuprates
Ikuzo Kanazawa
Department of Physics, Tokyo Gakugei University, Koganei, Tokyo 184-8501, Japan
Nuclear magnetic-nuclear resonance and muon spin resonance experiments show that in underdoped cuprates, on cooling from Tc, divergent behaviour of the relaxation rates(glassy spin-freezing) occurs [1]. Recently the rpresent author [2] has proposed the chiral-like spin-glass mechanism in underdoped cuprates. More recently Mooke et. al. [3] by means of inelastic neutron scattering measurements in underdoped superconducting(YBCO) detected longitudinal with respect to c-axis magnetic moments of unkown origin, with the fluctuation of a local magnetic field. In this study, we will propose the origin of the fluctuations of a local magnetic field due to the chiral-like spin-glass mechanism.
[1] M.H.Julien et.al. Phys.Rev.B63,144508(2001). [2] I.Kanazawa, Physica C 357-360,149(2001). [3] H.A.Mook et.al. Phys.Rev.B64,012502(2001).
Apparent non-scaling of pinning force data in Bi-based high-Tc superconductors
Michael R. Koblischka
Institute of Experimental Physics, P.O. Box 151150, D-66041 Saarbrücken, Germany
The scaling of the normalized volume pinning forces, Fp/Fp,max, versus a reduced field h=Ha/Hscale has proven to be a very informative tool to study the origin of the flux pinning in superconductors. Remarkably, on (Pb,Bi)2Sr2Ca2Cu3O10+d (Bi-2223) and Bi2Sr2CaCu2O8+d (Bi-2212) data were mostly analyzed only in a narrow temperature range around 77 K). Here, we present a study of the pinning forces in various Bi-2223 samples at temperatures between 18 K and 80 K. The measurements clearly reveal that there is an apparent non-scaling of the pinning force data; instead, two different temperature regimes can be recognized, which are in direct relation to the second step in the m(T) curves as reported earlier.
Vortex solid-to-liquid transition in underdoped YBa2Cu3O7-d single crystals with B ||ab
Magnus Andersson, Björn Lundqvist, Östen Rapp
Solid State Physics, IMIT, KTH, Electrum 229, SE-164 40 Kista, Sweden
From studies of ab-plane and c-axis resistivity in underdoped single crystals of YBa2Cu3O7-d, a nearly magnetic field independent vortex solid-to-liquid transition is found at high magnetic fields B ||ab. Experimentally, the vortex solid-to-liquid transition appears to occur almost simultaneously for the two orientations despite the fact that the Lorentz force is directed along the ab-planes for the c-axis resistivity and across the layers for the ab-plane resistivity. Thus, in moderately anisotropic layered materials, the intrinsic pinning due to the layering does not lead to a total decoupling of the layers. Instead it suggests a collectively pinned vortex lattice with suppressed thermal fluctuations along the c-axis.
Dislocation Mechanisms in Crystalline and Flux-Line Lattices
Valery P. Kisel, Theodor L. Barkov
Institute of Solid State Physics, RAS, 142432 Chernogolovka,Moscow distr., Russia
The remarkable finding of this work is the strict identity of dislocation dynamics in crystalline lattices (CL) and the kinetics of flux penetration into low- and high-temperature superconducting films. This is confirmed by every detail of their common features: surface and size effects, the same sigmoidal form of temperature-, stress and stress-field sweep rate dependences of the mean paths of dislocations and magnetic structures, the same scaling of Hc1 and Hc2 for FLL and for the starting and yield stresses in CL [1] etc. This corroborates the strict correlation between the properties of CL and their FLL, the vital role of deformation work-hardening in the origin of superconductivity [1].
1. V.P. Kisel et al., Proc. Symp. Micro-Nanocryogenics, Aug. 1-3, 1999, Finland, Res.Rep. 3/99,pp 48-51; cond-mat/0009648; Uzbek J. of Physics, 2, No 1., 89 (2000).
Critical fields and flux-flow resistances in strongly disordered ultra-thin superconducting films
K. Das Gupta, Swati S. Soman, N. Chandrasekhar
Department of Physics, Indian Institute of Science, Bangalore 560012, India.
Strongly disordered ultra-thin films of Bi and Sn, ( < 100Å) produced by quench-condensation, are well known systems that show Insulator-Superconductor transition. Some aspects of the transition and the nature of the superconducting state are weakly dependent on the material and substrate, but we find that the critical field (Hc2) of Bi and Sn films of comparable resistance show different temperature dependences. For Sn the mean field Hc2 is seen to vary with tempearature as Hc2(T) = Hc2(0)(1 - ([ T/(Tc)])2), whereas for Bi it is found to be Hc2(T) = Hc2(0)(1 - [ T/(Tc)])a with a » 1.14. In films with low sheet resistance we find a dissipationless vortex solid regime. The flux-flow resistance calculated from the I-V traces taken in several magnetic fields show a much faster field-dependence than existing theories predict.
Guided vortex motion in Nb films on facetted substrate surfaces
Oleksiy K. Sorokaa, Michael Hutha, Valerij A. Shklovskijb, Jens Ostera, Hermann Adriana
aInstitute of Physics, Johannes Gutenberg-Universitaet, Staudinger Weg 7, 55099 Mainz, Germany
bKharkov State University, Physical Department, 4 Svobody Sq., 61077, Kharkov, Ukraine
Anisotropy of the pinning force in superconductor can cause a guiding effect on the vortices, which leads to the appearance of new components in the galvanomagnetic properties of the sample. In this case one can observe an additional odd magnetoresistive component with respect to magnetic field reversal. Furthermore, an even contribution to the Hall voltage is observed. Guided motion of vortices in Nb films on facetted a-Al2O3 (10[`1]0) was found by measuring the longitudinal and transversal resistivities of three films with transport current directed parallel, perpendicular and at an angle 450 with respect to the facet ridges. Field inversion was used to separate the even and odd components of the measured magnetoresistivities to obtain contributions caused by the guided vortex motion.
A Critical-Current Jump Triggered by Vortex-Lattice Screw Dislocations
Ken Sugawara
Ibaraki Polytechnic College, 864-4 Suifu-cho, Mito, Ibaraki 310-0005, Japan
The energy of vortex-lattice screw dislocations is computed numerically by basing upon the isotropic London approximation, where the Burgers vectors of two adjacent slip planes are antiparallel. The results of computation are applied to the Larkin-Ovchinnikov pinning theory. The present modified pinning model predicts that, for sufficiently strong pinning, a vortex lattice stably possesses screw dislocations with the slip-plane spacing nearly equal to the vortex-lattice constant. In a superconducting film, penetration of such screw dislocations triggers vortex-line bending accompanying a discontinuous jump of the critical current. This prediction is compared with the critical-current jump observed in amorphous NbxGe films.
Transformation from flux tube array to labyrinthine pattern in the intermediate state of superconducting Indium
V. Jeudya, C. Gourdona, Tu Le Anhb, G. Karczewskic
aGroupe de Physique des Solides Tour 23, UPMC, 4 Place Jussieu 75251 Paris Cedex 05, France
bInstitute of Material Sciences - NCST, Nghia Do, Cau Giay, Hanoï, Vietnam
cInstitute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland
Magnetic flux structures in Type I superconductors are observed by the magneto-optical imaging technique using a CdMnTe semimagnetic quantum well heterostructure as a probe. A superconducting 10 micrometer thick Indium plate is submitted to a perpendicular applied magnetic field. At low field, the flux is arranged in flux tubes. There size, corresponding to 500 flux quanta, is observed to remain constant when the field is increased. At higher field, the tubes merge to form a labyrinthine pattern. This transformation seem not to be predicted by conventional intermediate state models.
STM Imaging of Vortex Structures in NbN Thin Films
Terukazu Nishizaki, Alexei Troyanovski, Gertjan van Baarle, Jan Aarts, Peter Kes
Kamerlingh Onnes Laboratory, Leiden University, POB 9504, 2300 RA Leiden, The Netherlands
We report on imaging of the vortex structure in NbN thin films ( ~ 50 nm) by using low temperature scanning tunnelling microscopy and spectroscopy (LT-STM/STS) technique at 4.2 K. The NbN thin films were prepared by rf-sputtering method. In order to avoid oxidation and to obtain the smooth surface, very thin films of amorphous (a)- Mo3Ge and Au were covered immediately after deposition of NbN thin film. The top surface is a superconducting everywhere in zero fields and vortices are imaged up to 1.2 T. The vortices show a disordered structure in all the field region measured, indicating the strong pinning effects in the NbN thin films. The field dependence of the vortex structure and the pinning properties are discussed comparing the results of the weak pinning material such as a-Mo3Ge thin films.
Zero-bias conductance peak in disordered ferromagnetic metal/dx2-y2 wave superconductor junction
Nobukatsu Yoshidaa, Hiroyoshi Itohb, Yasuhiro Asanoc, Yukio Tanakad, Jun-ichiro Inoued, Satoshi Kashiwayae
aToyota Physical and Chemical Reseach Institute, Nagakute-cho,Aichi,480-1192,Japan
bDepartment of Quantum Engineering, Nagoya University, Nagoya, 464-8603, Japan
cDepartment of Applied Physics, Hokkaido University, Sappro, 060-8628, Japan
dDepartment of Applied Physics, Nagoya University, Nagoya, 464-8603, Japan
eNational Institute of Advanced Industrial Science and Technology, Tsukuba, 305-0045, Japan
We investigate numarically the spin-polarized tunnleing effect in ferromagneic metal / insulator / dx2-y2-wave superconductor (FM/I/d-wave SC) junctions.
Mean field approach to dynamical melting and transverse pinning of moving vortex lattices interacting with periodic pinning
Clécio Silvaa, Gilson Carneirob
aDepartamento de Fisica, Universidade Federal de Pernambuco, 50670-901, Recife-PE, Brasil
bInstituto de Fisica, Universidade Federal do Rio de Janeiro, C.P. 68528, 21945-970, Rio de Janeiro-RJ, Brasil
Dynamical melting and transverse pinning of moving vortex-lattices in clean superconducting films with periodic pinning are studied by a mean-field treatment of Langevin's equations for the whole vortex-lattice, assuming elastic flow. Vortex displacements due thermal fluctuations and to the periodic pinning force are calculated by a perturbative solution of the mean-field equations of motion. The dynamical melting temperature is obtained using Lindemann's criterion. Transverse pinning is demonstrated for motion along the periodic pinning high-symmetry directions and the critical force is estimated.
Scanning Tunneling Spectroscopy of Sr2RuO4
H. Kambaraa, T. Matsuia, I. Uedaa, T. Shishidoa, N. Kikugawab,c, Y. Maenob,c, Hiroshi Fukuyamaa
aDepartment of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
bDepartment of Physics, Kyoto University, Kyoto 606-8502, Japan
cCREST, Japan Science and Technology Corporation, Kawaguchi, Saitama 332-0012, Japan
We will present preliminary results of scanning tunneling spectroscopy studies of the spin-triplet superconductor Sr2RuO4 with an ultra-low temperature scanning tunneling microscope which operates at temperatures below 100 mK and in magnetic fields up to 6 T. Single crystals of Sr2RuO4 are cleaved along the ab plane at 8 K in an ultra-high vacuum (UHV) chamber, and then transferred to the STM chamber without braking the UHV environment. We found that the resultant surfaces are clean and flat from the low energy electron diffraction studies. Spatial information of the quasiparticle density of states, i.e., the superconducting gap structure, near the quantized vortices in magnetic fields will be reported.
Nuclear Magnetic Relaxation Rate in the Vortex State of a Chiral p-Wave Superconductor
Nobuhiko Hayashia, Yusuke Katob
aComputer Center, Okayama University, Okayama 700-8530, Japan
bDepartment of Basic Science, University of Tokyo, Tokyo 153-8902, Japan
Recently the site-selective NMR method for vortex cores in type-II superconductors was revealed to be a powerful experimental tool for investigating the electronic structure inside vortex cores related to the pairing symmetry. We theoretically study the site-selective relaxation rate T1-1 inside a vortex core in a chiral p-wave superconductor within the framework of the quasiclassical theory of superconductivity. We find that T1-1 inside the vortex core depends on whether the vorticity and chirality are parallel or antiparallel, i.e., on the sense of the chirality of the Cooper pair. Numerical results for T1-1 are presented to show typical features of the difference in T1-1 between the two chiral states [^k]x ±i [^k]y.
Josephson Effect in s-wave / p-wave / s-wave superconductor junction
Takashi Hiraia, Yukio Tanakaa, Jun-ichiro Inouea, Kashiwaya Satoshib
CREST, Japan Science and Technology Corporation (JST)
aDepartment of Applied Physics, Nagoya University, Nagoya
bNational Institute of Advanced Industrial Science and Technology (AIST)
Anomalous behavior of Josephson current in Pb/Sr2RuO4/Pb was studied both theoretically and experimentally. The calculated results of temperature dependence of Josephson current in s-wave / p-wave / s-wave superconductor junction show nonmonotonic behavior depending on the thickness of the p-wave superconductor. This behavior was also observed by experiment of Pb/Sr2RuO4/Pb junction, and obtained results are one of the evidence of triplet superconductivity on Sr2RuO4. However, in the previous theoretical study, the effects of barrier potential at the interface and spin-orbit coupling are not considered. In this paper, we calculate the Josephson current including these effects.
Two dimensional superconductivity with strong spin-orbit interaction
S. K. Yip
Institute of Physics, Academia Sinica, Nankang, Taipei 11529, Taiwan
We consider superconductivity confined at a two-dimensional interface with a strong surface spin-orbit (Rashba) interaction. This system is special in that the superconducting order parameter can no longer be classified by singlet or triplet. We evaluate the spin susceptibility and consider the magneto-electric effects of this sytem, using simple arguments. We explain physically the results previously obtained by Edelstein, and by Gorkov and Rashba. Furthermore, we show the existence of an additional magneto-electric effect, that an in-plane Zeeman field can induce a supercurrent flow.
Quantum Vortex Liquid State in the Quasi Two Dimensional Organic Superconductor k-(BEDT-TTF)2Cu(NCS)2
T. Sasaki, T. Fukuda, T. Fujita, T. Nishizaki, N. Yoneyama, N. Kobayashi
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
We report the transport properties in the quantum vortex liquid (QVL) state of the layered organic superconductor k-(BEDT-TTF)2Cu(NCS)2. In QVL the low resistance state appears below about 1 K. The finite resistivity remains in the low resistance state even at T ~ 0. It is noted that a weak non-linear behavior is found in the low resistance state. Such non-linearity is not observed in the high resistance state and the thermal vortex liquid region above 1 K. These transport properties are similar to the short range vortex order state discussed as the vortex slush phase in the High-Tc oxide. We will also mention about an insulating behavior in QVL near the upper critical field at T ~ 0.
Phase diagram of partially deuterated k-(BEDT-TTF)2Cu[N(CN)2]Br
N. Matsunaga, K. Yamashita, M. Yamashita, A. Kawamoto, K. Nomura
Division of Physics, Hokkaido University, Sapporo 060-0810, Japan
The phase diagram of k-(BEDT-TTF)2Cu[N(CN)2]Br around the metal-insulator (MI) boundary controlled by partially deuteration and by cooling rate through the 80 K anomaly has been investigated by resistivity measurements under magnetic fields. According to approach to the critical region of MI transition from the metallic side by the progressive deuteration and by the increase of cooling rate, a) in addition to the deuteration and the cooling rate dependence of the resistance maximum, the hump structure of resistance, observed at 33 K in the partially deuterated sample for slowly cooled, is shifted towards a lower temperature, b) the temperature of the resistance jump with the hysteresis of resistance increases. Our results suggest that these anomalies are related to the phase separation of the metallic and insulator phase around the MI boundary.
Thermal conductivity of the antiferromagnetic conductor k-(BETS)2FeBr4 in the low-field and field-induced superconducting states
M. A.. Tanatara, M. Suzukia, T. Ishiguroa, H. Fujiwarab, H. Kobayashib
aDepartment of Physics, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan
bInstitute for Molecular Science, Myodaiji-cho, Okazaki 444-8585, Japan
The thermal conductivity study of the low-field and field-induced superconducting states of the antiferromagnetic organic conductor k-(BETS)2FeBr4 is presented. Both the antiferromagnetic state with TN = 2.3 K and the superconducting state with Tc= 1.1 K are shown to be of bulk nature. The magnetic pair-breaking is shown to be responsible for field and orientation dependence of thermal conductivity and for unusual anisotropy of the upper critical fields in the low-field state. In the parallel fields above 10 T the thermal conductivity shows formation of a re-entrant superconducting state due to a Jaccarino-Peter effect.
Mechanism of High Temperature Superconductivity in Intercalated Fullerides
Andreas Billa, Vladimir Z. Kresinb, Rene Windiksa, Bernard Delleya
aPaul Scherrer Institute, Condensed Matter Theory, 5232 Villigen PSI, Switzerland
bLawrence Berkeley National Laboratory, University of California, Berkeley 94720, USA
Intercalation of polyatomic molecules into a superconductor can strongly affect the properties of the compound. The recent observation of high Tcs in hole-doped C60 fullerides intercalated with CHX3 (X=Cl,Br) molecules is explained by the additional contribution to the pairing arising from the interaction of holes with the vibrational manifold of the intercalated molecules. The observed large shift in Tc upon Cl®Br substitution (80K® 117K) is described by the ßoftening" of the molecule's vibrational spectrum and is calculated in good agreement with the experiment. We suggest to observe site-selective isotope effect and that intercalation of CHI3 molecules will increase the critical temperature to Tc @ 140K [ A.B., V.Z.K., Eur.Phys.J.B 26, 3 (2002).] We also present band structure calculations within DFT using DMol3.
Effect of Pressure on the Superconducting Properties of Y0.5Ho0.5Ni2B2C
Gendo Oomia, Issei Minamitakea, Daisuke Masaokab, Tomoko Kagayamab, Noritaka Kurodab, B.K. Cho2c, P.C. Canfieldc
aDepartment of Physics, Kyushu University, Ropponmatsu, Fukuoka 810-8560, Japan
bDepartment of Mechanical Engineering and Materials Science, Kumamoto University, Kumamoto ,Japan
cAmes Laboratory and Department Physics and Astromy,Iowa State University, Ames, Iowa 50011, USA
In the rare earth borocarbide RNi2B2C, the antiferromagnetism is well known to coexist with superconductivity. In the present work, we attempted to measure the electrical resistance and lattice spacings under high pressure to make clear the interplay of antiferromagnetism and superconductivity under high pressure. It is found that the superconducting transition temperature TC decreases with increasing pressure and the tetragonal ThCr2Si2 structure is stable up to 10 GPa at room temperature.
Specific Heat Study of Magnetic Superconductor ErNi2B2C Single Crystal under Magnetic Fields
S. Nakaoa, T. Hanagurib, K. Hashimotob, M. Noharab, H. Takagib, K. Kitazawab
aDepartment of Superconductivity, The University of Tokyo, Tokyo 7-3-1, Japan
bDepartment of Advanced Materials Science, The University of Tokyo, Tokyo 7-3-1, Japan
The low temperature specific heat Cp was measured in a borocarbide magnetic superconductor ErNi2B2C single crystal. In the absence of magnetic fields, both antiferromagnetic and weak ferromagnetic transitions were clearly observed as peaks in Cp at TN and TWF, respectively. Under magnetic fields parallel to the [110] direction, TN monotonically decreases with increasing field, while TWF increases at low fields and decreases above 1 T. This reentrant behavior of TWF is reasonably explained by assuming the competition between crystalline magnetic anisotropy and the weak ferromagnetism arising from the magnetic moment at the antiferromagnetic domain wall.
Supercondutivity and Thermal Conductivity of LuNi2B2C under Apllied Magnatic Fields
Cao Shixuna, Zhang Jincanga, Qin Xiaolinga, Nishimura Katsuhikob, Mori Katsunorib
aDepartment of Physics, Shanghai University, Shangda Road 99, Shanghai 200436, P. R. China
bFaculty of Engineering, Toyama University, 3190 Gofuku, Toyama 930-8555, Japan
The superconductivity and thermal conductivity of the nickel borocarbide compounds LuNi2B2C system has been systematically studied, together with other systems of RNi2B2C (R=Y or rare earth). Temperature and applied magnetic field dependences of the superconductivity and thermal conductivity have been measured in the temperature range from 4.2 K to 25 K, under the applied magnetic field range from 0 to 80 kOe. The thermal conductivity in zero magnetic field showed clear changes at its superconducting transition temperature, and the magnetic field dependence of the thermal conductivity showed characteristic changes at the lower and the upper critical fields at temperatures below Tc.
Synthesis of the Electron-Doped Bismuth Oxide Ba0.6Bi0.4BiO3-x
Yoshinori Imaia, Masatsune Katoa, Yoji Koikea, Arthur W. Sleightb
aDepertment of Applied Physics, Tohoku University, Sendai 980-8579, Japan
bDepartment of Chemistry, Oregon State University, Corvallis OR 97331, USA
The electron-doped bismuth oxide Ba0.6Bi0.4BiO3-x has been successfully synthesized by the two-step heating method. Stoichiometric mixed powders of BaO2 and Bi2O3 were heated in a flowing gas of N2 at 800°C for 12 hours. The reacted samples were heated at 400°C first in a flowing gas of O2 for 24 hours and then under O2 of high pressures at 400°C for 96 hours. It crystallized in the pseudo-cubic symmetry. From the XRD and ICP analyses, the substitution of Bi for Ba has been confirmed. From the iodometric titration, the oxygen content 3-x has been estimated as 2.92. The product has been found to remain an insulator. This may be due to the oxygen vacancy and/or the tilt of the BiO6 octahedron.
Phase state diagram of high-Tc Ba-K-Bi-O
L. N. Zherikhinaa, A. I. Golovashkina, A. V. Gudenkoa, G. V. Kuleshovaa, M. L. Nortonb, A. M. Tskhovrebova
aP. N. Lebedev Physical Institute of RAS, Leninsky Pr. 53, Moscow, 119991, Russia
bDepartment of Chemistry, Marshal University, Huntington, WV 25755, USA
The magnetic behavior of Ba-K-Bi-O single crystals below Tc was investigated. The magnetic moment hysteresis loop were examined with the help of a small Hall detector. The complex analysis of data on temperature dependencies of the residual magnetic moment and Hc1, obtained from the magnetic experiments, and the resistive superconducting transition curves give rise to the following picture: at Tc=30 K the transition to the continuos superconducting phase takes place, while at T*=17 K one more transition happens - to spatially inhomogeneous superconductor- insulator state, that also could be destroyed either by temperature or by magnetic field.
1S. Sorella, Phys. Rev. B 64, 024512 (2001); cond-mat/0201388.
2present address: Department of Materials Science & Engineering, K-JIST 500-712, South Korea