Nonadiabatic transitions between adiabatic surfaces: phase diffusion in superconducting atomic point contacts

TL;DR

This paper investigates nonadiabatic transitions in superconducting atomic point contacts, revealing how phase diffusion on Andreev levels explains experimental results beyond conventional theories.

Contribution

It introduces an approximate evolution equation for adiabatic surface populations considering strong dissipation, advancing understanding of nonadiabatic effects in superconducting contacts.

Findings

Agreement with experimental observations not explained by traditional models

Identification of curve crossings importance at high transmissions

Development of a master equation approach for phase dynamics

Abstract

Motivated by experiments with current biased superconducting atomic point contacts the general problem of nonadiabatic transitions between adiabatic surfaces in presence of strong dissipation is studied. For a single channel device the supercurrent is determined by the diffusive motion of the superconducting phase difference on two Andreev levels. These surfaces are uncoupled only in the adiabatic limit of low to moderate transmissions, while for high transmissions curve crossings are important. Starting from a general master equation of the full density matrix an approximate time evolution equation for the populations on the adiabatic surfaces in the overdamped limit is derived from which the relevant observables can be obtained. Specific results for the case of atomic point contacts are in agreement with experimental observations that cannot be explained by conventional theory.