Vertex corrections to nonlinear photoinduced currents in 2D superconductors

TL;DR

This paper investigates the nonlinear photoinduced supercurrent in 2D superconductors, emphasizing vertex corrections to ensure gauge invariance and proposing a spectroscopic method to analyze relaxation times.

Contribution

It introduces a gauge-invariant theoretical framework with impurity-sensitive vertex corrections for analyzing photoinduced supercurrents in 2D superconductors.

Findings

Derived impurity-sensitive vertex corrections within BCS theory.

Demonstrated the supercurrent's potential for spectroscopic analysis.

Provided a self-consistent Keldysh Green's function approach.

Abstract

The emergence of a rectified steady-state supercurrent as a response to the photoexcited current of the quasiparticles constitutes the concept of a superconducting photodiode. This phenomenon occurs in a two-dimensional thin superconducting film with a built-in DC supercurrent that is exposed to a circularly polarized external electromagnetic field. The flow of a Cooper-pair condensate, resulting as a second-order photo-response in a direction transverse to the initially built-in supercurrent, represents a superconducting counterpart to the photogalvanic effect. In this paper, we examine the photodiode supercurrent by restoring gauge invariance within the mean-field BCS framework. To achieve this, we derive an impurity-sensitive BCS-interaction-induced correction to the vertex function by performing self-consistent calculations within the Keldysh Green's function technique. The resulting photodiode current can be utilized for spectroscopic analysis of typical relaxation times in superconducting films.