Density of states below the Thouless gap in a mesoscopic SNS junction - art. no. 027002

Quasiclassical theory predicts an existence of a sharp energy gap E-g simil ar to (h) over barD/L-2 in the excitation spectrum of a long diffusive supe rconductor-normal metal-superconductor (SNS) junction. We show that mesosco pic fluctuations remove the sharp edge of the spectrum, leading to a nonzer o density of states (DOS) for all energies. Physically, this effect origina tes from the quasilocalized states in the normal metal. Technically, we use an extension of Efetov's supermatrix sigma model for mixed NS systems. A n onzero DOS at energies E < E-g is provided by the instanton solution with b roken supersymmetry.