Can mesoscopic fluctuations reverse the supercurrent through a disordered Josephson junction?

Abstract

We calculate the Josephson coupling energy $U_J(\varphi )$ (related to the supercurrent $I=(2e/\hslash )d{U}_J/d\varphi$) for a disordered normal metal between two superconductors with a phase difference $\varphi$. We demonstrate that the symmetry of the scattering matrix of non-interacting quasiparticles in zero magnetic field implies that $U_J(\varphi )$ has a minimum at $\varphi =0$. A maximum (that would lead to a $\pi$-junction or negative superfluid density) is excluded for any realization of the disorder.

2 pages