1PO2-120 Solution of the Anisotropic Ginzburg-Landau Theory by the Iterative Method

I.G. de Oliveira 1, M.M. Doria 2, and E.H. Brandt 3. 1 Universidade Iguacu - UNIG, Nova Iguacu 26260-100 RJ, Brazil. 2 Instituto de Fisica, Universidade Federal do Rio de Janeiro, C.P. 68528, Rio de Janiero 22452-970, Brazil. 3 Max Planck Institute fur Metallforschung, Institut fur Physik, D-70506 Stuttgart, Germany.

Presenting Author: I.G. de Oliveira

Recently a new method was used to solve the Ginzburg-Landau for the ideal Abrikosov vortex in case of conventional isotropic superconductors (E.H. Brandt, Phys. Rev. Lett. 78, 2208 (1997)). The method applies to any value of magnetic induction , to arbitrary symmetry of the vortex lattice, and to any superconductor of type II, specified by the Ginzburg-Landau parameter k . Here we generalize this method to treat anisotropic superconductors thus including one extra parameter into the theory, namely, the mass anisotropy ratio. Three iterative equations are obtained which determine the local order parameter and the local magnetic field. The iterative process starts from an initial solution, taken to be the anisotropic Abrikosov solution near the upper critical, and yields very stable and fast convergent results after a few iterations of the equations. The reversible magnetization is obtained using the virial theorem of Doria, Gubernatis and Rainer (Phys. Rev. B 39, 9573 (1989)). The method allows for the calculation of the form factors of magnetic field and of order parameter and also of the shear modulus of the vortex lattice.

1PO2-121 Vortex arrangement and reversible magnetisation in plane magnetic field of Bi2.1Sr1.9Ca1.0Cu2.0Ox single crystal

G.D. Gu 1, R. Puzinik 2, Z.W. Lin 1, K. Nakao 3, T. Tanable 3, and N. Koshizuka 3. 1 Advance Electronic Materials Group, School of Physics, University of New South Wales, Sydney 2052, Australia. 2 Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, PL 02-668 Warszawa, Poland. 3 Superconductivity Research Laboratory, International Superconductivity Research Center 10-13, Shinonome 1-chome, Koto-ku, Tokyo 135, Japan.

Presenting Author: G.D. Gu

One of the most important intrinsic properties of high Tc Bi-system superconducting materials is its extremely high anisotropy. The magnetic properties in the plane of the crystals has not been known for lack of the large size single crystals. The large, high quality single crystals of Bi-2212 phase superconductors have been grown by floating zone method. The field dependence of magnetisation of the Bi-2212 single crystals of 5*3.6*0.4 mm3 and 5.5*5*1.3 mm3 were studied in-plane magnetic field by a 7 tesla SQUID magnetometer( Quantum Design) equipped with the sample rotation system. One unusual phenomenon observed in the experiment is that the absolute value of magnetisation in a wide field range of Hc1£ H£ Hc2 increases with increasing field. We compare the above results with several proposed theory models and find that the results is agreement with the laminar structure approximation theory for the magnetisation distribution inside superconductor. We also discover that the negative susceptibility under a high external field of 7 tesla does not vanish up to temperature as high as the temperature of 140 K, which is significantly higher than the bulk superconducting transition temperature Tc=88K of the crystal. The high field negative susceptibility above the superconducting transition temperature Tc indicates that the superconducting transition temperature in the layered cuprate is affected by a peculiar interplay between doping and pair-breaking scattering.

1PO2-122 Direct observation of the d-wave contributions to the low temperature specific heat of YBa2Cu3O7

Yuxing Wang, Alain Junod, Bernard Revaz, and Andreas Erb, University of Geneva, Departement of Condensed Matter Physics,24 quai Ernest-Ansermet, CH-1211 Geneva 4, Switzerland

Presenting Author: Y. Wang

The direct observation of the characteristic d-wave contributions to the low temperature specific heat of YBa2Cu3O7 has been obscured up to now by the presence of large magnetic Schottky terms of extrinsic origin. For a new high purity single crystal grown in BaZrO3, paramagnetic terms are reduced to a negligible level (<0.005% spin-1/2 per Cu atom), so that the presence of line nodes in the gap is directly seen in the difference C(B,T)-C(0,T) at fixed temperatures (T<5 K) as a function of the magnetic field (B£ 14 T) along the c-axis. These data illustrate the crossover region between the limits Cµ T2 at low fields to Cµ TB1/2 at high fields, as expected from the scaling theory of Volovik et al. However we do not observe the reduction of the specific heat for a given field in the ab-plane when the direction is set parallel to a node. The absence of this predicted effect may be due to orthorhombicity and twinning.

1PO2-123 Two-dimensional fluctuations in the magnetization of the high-temperature superconductor CaLaBaCu3O7

D.A. Landinez Tellez 1, J. Albino Aguiar 2, and J.M. Calero 3. Universidad Industrial de Santander, Escuela de Física, A.A. 678, Bucaramanga, Colombia. 1 Facultad de Ciencias, Universidad de Pamplona, Pamplona, Norte de Santander, Colombia. 2 Departamento de Fisica, Universidade Federal de Pernambuco, 50670-901, Recife, PE, Brasil. 3 Universidad Industrial de Santander, Escuela de Física, A.A. 678, Bucaramanga, Colombia.

Presenting Author: D.A. Landinez Tellez

Magnetization measurements on a polycrystal of CaLaBaCu3O7 in high magnetic fields (20 - 50 KOe) are reported. The sample has a zero-field transition temperature Tc=77 K and a transition width of 2.0 K. The results show large fluctuation effects, which can be explained by Ginzburg-Landau fluctuation theory for a two-dimensional system. The experimental data were fitted by using a theoretical model based in the lowest Landau levels approximation, showing good agreement. The weak-field fluctuation diamagnetic susceptibility above Tc can be fitted well in terms of the 2D Lawrence-Doniach model.

1PO2-124 Spontaneous Creation of Magnetic Flux in Superconducting Ring

Boris Ya. Shapiro, Mark Ghinovker and Irina Shapiro, Physics Dept., Institute of Superconductivity, Bar-Ilan University, Ramat-Gan 52900, Israel

Presenting Author: B.Ya. Shapiro

Kibble-Zurek mechanism of a creation of topological defects of the order parameter during a symmetry breaking phase transition in a supercooled superconducting hollow cylinder ("ring") is investigated. Solving numerically set of the time-dependent Ginzburg-Landau (TDGL) equations coupled with the thermal diffusion equation we exhibit different scenarios of spontaneous creation of the magnetic flux inside the superconducting ring. Evolution of topological charge in the ring during the superconducting relaxation is studied. It is shown that weak links in the superconducting ring modify the process of spontaneous flux creation.

1PO2-125 Onset of Superconductivity: Domain Wall Instability vs. Topological Explosion

Boris Ya. Shapiro, Mark Ghinovker, Irina Shapiro, and Eugeny Pechenek, Institute of Superconductivity, Dept. of Physics, Bar-Ilan University, Ramat-Gan 52900, Israel

Presenting Author: B.Ya. Shapiro

Recovery of superconductivity in the initially heated above the critical temperature superconducting cylinder in arbitrary external magnetic field is considered both analytically and numerically in the framework of the time-dependent Ginzburg-Landau (TDGL) coupled with the thermal diffusion equations. Three different regimes of dynamics were discovered depending on cooling rate. In particular, fast cooled samples exhibit massive spontaneous nucleation of topological vortices and antivortices while slow cooling leads to domain wall instability resulting in appearance of circular Abrikosov vortex chain. In the intermediate case both the vortex chain and bulk topological explosion emerge simultaneously.

1PO2-126 Josephson Vortex Dynamics in Bi2Sr2CaCu2O8+d Instinsic Josephson Junctions under High Magnetic Field

J.H. Lee, Yonuk Chong, Suyoun Lee and, Z.G. Khim, Department of Physics, Seoul National University, Seoul 151-742, Korea

Presenting Author: J.H. Lee

We have investigated vortex dynamics in Bi2Sr2CaCu2O8 intrinsic Josephson junctions subjected to magnetic field parallel and perpendicular to the CuO2 planes. We measured mesas with 40 x 40 m m2 in size containing ~20 intrinsic junctions. The zero field I-V characteristics showed typical hysteretic, multi-branched nature of the intrinsic Josephson effect.

In high parallel magnetic field (H > 1.5 T), I-V characteristics showed the flux flow step. The step voltage agreed well with the value estimated from known junction parameters. The obtained Swihart velocity was about 4.2 x 105 m/s, which corresponds to the velocity of the lowest mode electromagnetic wave of N-coupled stack. The Experimental I-V curves fit well to the model of Cherenkov radiation including Ohmic and non-linear dissipation terms. This suggests that the dissipation mechanism of Josephson vortex in Bi2Sr2CaCu2O8 intrinsic junctions be due to both Cherenkov radiation and quasiparticle tunneling.

In perpendicular magnetic field, we observed that the I-V characteristics changed their shape at high bias current in magnetic field larger than 0.3 T. This may be explained by the decoupling transition of pancake vortices.

1PO2-127 Vortex Pinning and Dynamics in Layered Superconductors with Periodic Pinning Arrays

Charles Reichhardt 1, and Niels Gronbech-Jensen 2. 1 Department of Physics, University of California, Davis CA 95616. 2 Department of Applied Science, University of California, Davis, CA 95616.

Presenting Author: C. Reichhardt

We examine the pinning and dynamics of vortices interacting with periodic pinning using 3D simulations of pancake vortices in which the vortices have a long-range logarithmic in-plane interaction and a between-plane magnetic interaction. As a function of increasing field we observe a series of pronounced matching effects where the vortex lattice locks with the pinning array. We also observe, as a function of pin tilt angle, a series of novel commensuration effects where the vortices undergo various structural transitions which are visible as pronounced peaks in the critical current. These structures include staircase and zig-zag vortex patterns. With an applied driving force we observe several dynamical flow phases which we characterize by changes in the vortex flow patterns and 3D structures. We will also discuss the evolution of these phases for different interlayer coupling strengths.

1PO2-129 Electronical Casimir Force in Sns System

Dmitri O. Ledenyov 1, Viktor O. Ledenyov 2, and Oleg. P. Ledenyov 1. 1 National Scientific Center Kharkov Institute of Physics & Technology, 1 Akademicheskaya Street, Kharkov 310108, Ukraine. 2 Department of Physics, University of Toronto, Toronto, Ontario M5S 1A7, Canada.

Presenting Author: D.O. Ledenyov

We have shown that between the two superconducting layers enclosed by normal metal, a new force exists which attracts them to each other. The nature of this force is close to the Casimir force, which is presented between the metal plates in vacuum. The usual Casimir force arises because the space quantization of the electromagnetic fields is realized in the volume between the metal plates and there is usual electromagnetic spectrum of the infinity space in the surrounding volume. The difference in the free energy of these fields results in a force and a pressure. The new force arises because the space quantization of the spectrum of the electronical excitations is realized in the normal metal layer which is located between the superconducting layers when the excitations are reflected from the NS boundaries according to the Andreev law and usual normal metal spectrum is realized in volume outside of these layers.

We have measured the distance between superconducting layers in the intermediate state in the cylindrical sample of single crystal of the gallium by the ultrasonic method at the temperature of 0.35K. We have found that in the transversal external magnetic field the thickness of the normal metal layers is much less than follows from the Landau theory and it confirms the existence of a new force.