Phase-dependent magnetoconductance fluctuations in a chaotic Josephson junction

Abstract

Motivated by recent experiments by Den Hartog et al., we present a random-matrix theory for the magnetoconductance fluctuations of a chaotic quantum dot which is coupled by point contacts to two superconductors and one or two normal metals. There are aperiodic conductance fluctuations as a function of the magnetic field through the quantum dot and $2π$-periodic fluctuations as a function of the phase difference $ϕ$ of the superconductors. If the coupling to the superconductors is weak compared to the coupling to the normal metals, the $ϕ$-dependence of the conductance is harmonic, as observed in the experiment. In the opposite regime, the conductance becomes a random $2π$-periodic function of $ϕ$, in agreement with the theory of Altshuler and Spivak. The theoretical method employs an extension of the circular ensemble which can describe the magnetic field dependence of the scattering matrix.