Josephson dynamics at high transmissions: Perturbation theory

Abstract

We theoretically analyze Josephson dynamics of superconducting weak links with transmissions T not much smaller than unity at subgap bias voltages V. Employing the effective action approach combined with the Keldysh technique, we develop a regular perturbation theory in R=1−T and derive the first-order correction to the current across the weak link, which consists of two different contributions. One of them is negative, effectively corresponding to a decrease of the excess current at small V due to breaking of the multiple Andreev reflection cycle by normal reflection for some subgap quasiparticles. These quasiparticles, in turn, generate the second (Josephson-like) contribution to the current, which increases with decreasing V down to very small voltages, where the perturbation theory in R ceases to be valid. Some of the above features are not reproduced within the physical picture involving Landau-Zener tunneling between subgap Andreev states.

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