Efficient Prediction of Time- and Angle-Resolved Photoemission Spectroscopy Measurements on a Non-Equilibrium BCS Superconductor

TL;DR

This paper develops computationally efficient methods to predict time- and angle-resolved photoemission spectra in non-equilibrium BCS superconductors, aiding the extraction of order parameter dynamics from experimental data.

Contribution

It introduces approximate modeling techniques for tr-ARPES spectra in non-equilibrium superconductors, considering relaxation effects and enabling better interpretation of experimental results.

Findings

The methods successfully model equilibrium and non-equilibrium spectra.

Signatures of different superconducting dynamics are identified.

The approach accounts for relaxation and level-broadening effects.

Abstract

We study how time- and angle-resolved photoemission (tr-ARPES) reveals the dynamics of BCS-type, s-wave superconducting systems with time-varying order parameters. Approximate methods are discussed, based on previous approaches to either optical conductivity or quantum dot transport, in order to enable computationally efficient prediction of photoemission spectra. One use of such predictions is to enable extraction of the underlying order parameter dynamics from experimental data, which is topical given the rapidly growing use of tr-ARPES in studying unconventional superconductivity. The methods considered model the two-time lesser Green's functions with an approximated lesser self-energy that describes relaxation by coupling of the system to two types of baths. The approach primarily used here also takes into consideration the relaxation of the excited states into equilibrium by explicitly including the level-broadening of the retarded and advanced Green's functions. We present equilibrium and non-equilibrium calculations of tr-ARPES spectrum from our model and discuss the signatures of different types of superconducting dynamics.