Nonequilibrium Electron Dynamics in a Solid with a Changing Nodal Excitation Gap

TL;DR

This paper introduces a computationally efficient model to study nonequilibrium electron relaxation in solids, focusing on the effects of a changing nodal excitation gap in superconductors and its impact on relaxation dynamics.

Contribution

It presents a novel model that captures the coupled dynamics of electron relaxation and gap evolution in nodal superconductors, highlighting phase-space restrictions.

Findings

Electron populations remain thermal in metals despite relaxation.

Presence of a fixed nodal gap reduces relaxation rates.

Dynamic gap opening significantly affects electron relaxation behavior.

Abstract

We develop a computationally inexpensive model to examine the dynamics of boson-assisted electron relaxation in solids, studying nonequilibrium dynamics in a metal, in a nodal superconductor with a stationary density of states, and in a nodal superconductor where the gap dynamically opens. In the metallic system, the electron population resembles a thermal population at all times, but the presence of even a fixed nodal gap both invalidates a purely thermal treatment and sharply curtails relaxation rates. For a gap that is allowed to open as electron relaxation proceeds, effects are even more pronounced, and gap dynamics become coupled to the dynamics of the electron population. Comparisons to experiments reveal that phase-space restrictions in the presence of a gap are likely to play a significant role in the widespread observation of coexisting femtosecond and picosecond dynamics in the cuprate high-temperature superconductors.