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TT: Tiefe Temperaturen

TT 12: Tunnelsysteme und Symmetrien in HTSL

TT 12.1: Hauptvortrag

Dienstag, 23. März 1999, 15:00–15:30, F2

Junctions and interfaces in d-wave superconductors — •J. Annett¹, J.J. Hogan O’Neill¹, and A.M. Martin² — ¹University of Bristol, HH Wills Physics Laboratory, Bristol BS8 1TL, UK — ²Université de Genève, Départment de Physique Théorique, 1211 Genèeve 4, Switzerland

The d-wave pairing state in the cuprates has been confirmed by many experiments, including the junction experiments of Wollman et al. and Tsuei et al. which have been especially decisive. These experiments make use of the Josephson effect in junctions between high Tc (HTS) and low Tc superconductors or in grain boundaries in HTS. However a detailed microscopic theory of these junctions is needed. We have carried out self-consistent numerical solutions of the Bogoliubov de Gennes equations for interfaces between d wave and s wave superconductors and for grain boundaries on d-wave superconductors. In particular we have investigated the supercurrent in HTS grain boundaries using a simple geometrical model of the atomic structure at the boundary. This allows us to contrast the behaviour of grain boundaries in s-wave and d-wave superconductors. We calculate the supercurrent, I, in the junction as a function of the order parameter phase shift across the junction, φ, finding that I(φ) is a sawtooth function due to Andreev states at the interface. We also calculate the junction critical current as a function of the grain boundary angle. We compare these results to the Sigrist-Rice formula for d-wave grain boundaries and with the critical currents found in experiments for cuprate grain boundaries. We discuss implications of our results for the properties of realistic cuprate grain boundaries.