Regensburg 2004 – scientific programme

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DY: Dynamik und Statistische Physik

DY 46: Poster

DY 46.94: Poster

Thursday, March 11, 2004, 16:00–18:00, Poster D

The Bragg glass - Vortex glass transition — •Roland Schorr, Ludger Santen, and Heiko Rieger — Universität des Saarlandes, FR 7.1 Theoretische Physik, 66041 Saarbrücken

Many phase diagrams of high T_c superconductors obtained experimentally, e.g. in Bi₂Sr₂CaCu₂O_8+y (BSCCO) and YBa₂Cu₃O_7−δ (YBCO), reveal a very complicated landscape of various phases. The most significant modifications applied to a naive idea of a type II superconductor, which discriminates only between Meissner (H<H_c1) and Abrikosov (H_c1<H<H_c2) phase, have to take into account the impact of termal fluctuations and disorder. This leads to a water-like melting phenomenon in the regime of the Abrikosov phase with a melting line terminating at fields that are much lower than H_c2. The phase below the melting line is called Bragg glass whereas above the line one has to distinguish between Vortex glass and Vortex liquid. We focus on the phase transition between Bragg glass and Vortex liquid and Vortex glass, respectively, induced by the disorder at finite temperatures. As a starting point of our simulation we choose an elastic description of fluxlines fluctuating in a random potential. We perform a Monte Carlo Simulation applying cluster updates in order to sample the configuration space. Whereas local updating schemes seem to be problematic due to slowing down and a dynamical critical exponent z=2, our cluster algorithm works well with z≈ 0. This enables us to realize the three phases for system sizes up to L=32.