Theory of light-enhanced phonon-mediated superconductivity

TL;DR

This paper explores how dynamically increasing the electronic density of states via a time-dependent ramp enhances superconductivity in a phonon-mediated system, highlighting the roles of electron-phonon coupling and thermalization processes.

Contribution

It introduces a detailed nonequilibrium analysis of superconductivity enhancement through density of states manipulation using Migdal-Eliashberg equations and compares results with BCS mean-field theory.

Findings

Superconductivity is enhanced when the density of states near the Fermi level increases.

Fast single-particle scattering processes and slow order parameter dynamics govern thermalization.

Electron-phonon coupling is crucial for rapid enhancement and thermalization of superconductivity.

Abstract

We investigate the dynamics of a phonon-mediated superconductor driven out of equilibrium. The electronic hopping amplitude is ramped down in time, resulting in an increased electronic density of states. The dynamics of the coupled electron-phonon model is investigated by solving Migdal-Eliashberg equations for the double-time Keldysh Green's functions. The increase of the density of states near the Fermi level leads to an enhancement of superconductivity when the system thermalizes to the new state at the same temperature. We provide a time- and momentum-resolved view on this thermalization process, and show that it involves fast processes associated with single-particle scattering and much slower dynamics associated with the superconducting order parameter. The importance of electron-phonon coupling for the rapid enhancement and the efficient thermalization of superconductivity is demonstrated, and the results are compared to a BCS time-dependent mean-field approximation.