Impact of damping on superconducting gap oscillations induced by intense Terahertz pulses

TL;DR

This paper explores how damping influences superconducting gap oscillations triggered by intense Terahertz pulses, introducing a formalism that accounts for quasiparticle interactions and decay processes affecting superconductor dynamics.

Contribution

A semi-phenomenological model incorporating damping effects beyond BCS theory, specifically T1 and T2 processes, applied to superconducting dynamics after Terahertz pulse excitation.

Findings

Damping significantly affects gap oscillations in superconductors.

The T2 process governs the picosecond-scale dynamics post-pulse.

Experimental data on NbN supports the model's relevance.

Abstract

We investigate the interplay between gap oscillations and damping in the dynamics of superconductors taken out of equilibrium by strong optical pulses with sub-gap Terahertz frequencies. A semi-phenomenological formalism is developed to include the damping within the electronic subsystem that arises from effects beyond BCS, such as interactions between Bogoliubov quasiparticles and decay of the Higgs mode. Such processes are conveniently expressed as $T_{1}$ and $T_{2}$ times in the standard pseudospin language for superconductors. Comparing with data on NbN that we report here, we argue that the superconducting dynamics in the picosecond time scale, after the pump is turned off, is governed by the $T_{2}$ process.