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TT: Fachverband Tiefe Temperaturen

TT 32: Postersession Superconductivity: Josephson Junctions, SQUIDs, Heterostructures, Andreev Scattering, Vortex Physics, Cryodetectors, Measuring Devices, Cryotechnique

TT 32.20: Poster

Mittwoch, 25. März 2009, 14:00–18:00, P1A

Decreasing excitation gap in Andreev billiards by disorder scattering — •Florian Libisch¹, Jürgen Möller¹, Stefan Rotter¹, Maxim Vavilov², and Joachim Burgdörfer¹ — ¹TU--Vienna, Austria — ²University of Wisconsin, USA

We investigate the distribution of the lowest-lying energy states in a disordered Andreev billiard by solving the Bogoliubov-de Gennes equation numerically [1]. Contrary to conventional predictions we find a decrease rather than an increase of the excitation gap relative to its clean ballistic limit. We relate this finding to the eigenvalue spectrum of the Wigner-Smith time delay matrix between successive Andreev reflections. We show that the longest rather than the mean time delay determines the size of the excitation gap. With increasing disorder strength the values of the longest delay times increase, thereby, in turn, reducing the excitation gap.

[1] F. Libisch, J. Möller, S. Rotter, M. G. Vavilov, J. Burgdörfer, Europhys. Lett. 82, 47006 (2008).