Time-dependent quantum transport with superconducting leads: a discrete basis Kohn-Sham formulation and propagation scheme

TL;DR

This paper develops an exact one-particle framework using a discrete basis and Kohn-Sham formulation to study time-dependent quantum transport in superconducting nano-junctions, enabling efficient simulation of non-equilibrium phenomena.

Contribution

It introduces a novel propagation scheme combining Kohn-Sham and NEGF formalisms for superconducting systems, with numerical solutions for static and dynamic BdG equations.

Findings

Demonstrates time-dependent Andreev reflections in models

Shows zero-bias ac current generated by Andreev bound states

Identifies long-living resonant effects from microwave irradiation

Abstract

In this work we put forward an exact one-particle framework to study nano-scale Josephson junctions out of equilibrium and propose a propagation scheme to calculate the time-dependent current in response to an external applied bias. Using a discrete basis set and Peierls phases for the electromagnetic field we prove that the current and pairing densities in a superconducting system of interacting electrons can be reproduced in a non-interacting Kohn-Sham (KS) system under the influence of different Peierls phases {\em and} of a pairing field. An extended Keldysh formalism for the non-equilibrium Nambu-Green's function (NEGF) is then introduced to calculate the short- and long-time response of the KS system. The equivalence between the NEGF approach and a combination of the static and time-dependent Bogoliubov-deGennes (BdG) equations is shown. For systems consisting of a finite region coupled to ${\cal N}$ superconducting semi-infinite leads we numerically solve the static BdG equations with a generalized wave-guide approach and their time-dependent version with an embedded Crank-Nicholson scheme. To demonstrate the feasibility of the propagation scheme we study two paradigmatic models, the single-level quantum dot and a tight-binding chain, under dc, ac and pulse biases. We provide a time-dependent picture of single and multiple Andreev reflections, show that Andreev bound states can be exploited to generate a zero-bias ac current of tunable frequency, and find a long-living resonant effect induced by microwave irradiation of appropriate frequency.