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Density of States below the Thouless Gap in a Mesoscopic SNS Junction

P. M. Ostrovsky·M. A. Skvortsov·M. V. Feigel'man
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Abstract

Quasiclassical theory predicts an existence of a sharp energy gap E_g \sim D/L^2 in the excitation spectrum of a long diffusive superconductor--normal metal--superconductor (SNS) junction. We show that mesoscopic fluctuations remove the sharp edge of the spectrum, leading to a nonzero DoS for all energies. Physically, this effect originates from the quasi-localized states in the normal metal. Technically, we use an extension of Efetov's supermatrix sigma-model for mixed NS systems. We demonstrate the equivalence of the supersymmetric saddle-point solution to the standard quasiclassical Usadel solution, and show that the instanton solution with broken supersymmetry provides a non-zero DoS at energies E < E_g.

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P. M. Ostrovsky, M. A. Skvortsov, M. V. Feigel'man. 2001-01-04. Density of States below the Thouless Gap in a Mesoscopic SNS Junction. https://doi.org/10.1103/physrevlett.87.027002

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