Chirped amplitude mode in photo-excited superconductors

TL;DR

This paper demonstrates that the Higgs mode in photo-excited superconductors exhibits chirped oscillations and decay, providing a new way to probe the effective potential and order parameter dynamics through pump-probe experiments.

Contribution

It introduces a numerical scheme to analyze the chirped Higgs mode in superconductors, revealing novel dynamics distinct from conventional theories, and extends computational methods for long-time nonequilibrium states.

Findings

Chirped oscillations and exponential decay of the Higgs mode observed.

Photoinduced current can serve as a proxy for order parameter dynamics.

Extended hierarchical low-rank compression method for long-time nonequilibrium Green's functions.

Abstract

Using a state-of-the-art numerical scheme, we show that the Higgs mode under excitation exhibits chirped oscillations and exponential decay when fluctuations are included. This is in stark contrast to conventional BCS collisionless dynamics which predict power-law decay and the absence of chirping. The chirped amplitude mode enables us to determine the local modification of the effective potential even when the system is in a long-lived prethermal state. We then show that this chirped amplitude mode is an experimentally observable quantity since the photoinduced (super)current in pump-probe experiments serves as an efficient proxy for the order parameter dynamics, including the chirped dynamics. Our result is based on the attractive Hubbard model using dynamical mean-field theory within the symmetry-broken state after a excitation across the superconducting gap. Since the collective response involves long timescales, we extend the hierarchical low-rank compression method for nonequilibrium Green's functions to symmetry-broken states and show that it serves as an efficient representation despite long-lived memory kernels.