Theory of Interaction Effects in NS Junctions out of Equilibrium.pdfVIP

Theory of Interaction Effects in N-S Junctions out of Equilibrium B. N. Narozhny and I. L. Aleiner Department of Physics and Astronomy, SUNY Stony Brook, Stony Brook, NY 11794 9 B. L. Altshuler 9 Department of Physics, Princeton University, Princeton, NJ 08544 9 NEC Research Institute, 4 Independence Way, Princeton, NJ 08540 1 r We consider a normal metal - superconductor (N-S) junction in the regime, when electrons in a the normal metal are driven out of equilibrium. We show that the non-equilibrium fluctuations M of the electron density in the N-layer cause the fluctuations of the phase of the order parameter in the S-layer. As a result, the density of states in the superconductor deviates from the BCS 5 form, most notably the density of states in the gap becomes finite. This effect can be viewed as a 1 result of the time reversal symmetry breaking due to the non-equilibrium, and can be described in terms of a low energy collective mode of the junction, which couples normal currents in N-layer and ] l supercurrents. This mode is analogous to the Schmid-Sch¨on mode. To interpret their measurements l a of the tunneling current, Pothier et. al [Phys. Rev. Lett. 79, 3490 (1997)] had to assume that h the energy relaxation rate in the normal metal is surprisingly high. The broadening of the BCS - singularity of the density of