Periodic dynamics in superconductors induced by an impulsive optical quench

TL;DR

This paper explains long-lived oscillations in photoexcited superconductors as a result of parametric generation of plasmon pairs, providing a new framework to understand light-induced superconducting phenomena beyond static explanations.

Contribution

It introduces a Floquet-based theory for bi-plasmon oscillations induced by impulsive optical quenches in superconductors, highlighting their persistence above the transition temperature.

Findings

Long-lived oscillations arise from parametric plasmon pair generation.

Bi-plasmon response can persist above the superconducting transition.

Predicted oscillations are detectable with current experimental techniques.

Abstract

A number of experiments have evidenced signatures of enhanced superconducting correlations after photoexcitation. Initially, these experiments were interpreted as resulting from quasi-static changes in the Hamiltonian parameters, for example, due to lattice deformations or melting of competing phases. Yet, several recent observations indicate that these conjectures are either incorrect or do not capture all the observed phenomena, which include reflectivity exceeding unity, large shifts of Josephson plasmon edges, and appearance of new peaks in terahertz reflectivity. These observations can be explained from the perspective of a Floquet theory involving a periodic drive of system parameters, but the origin of the underlying oscillations remains unclear. In this paper, we demonstrate that following incoherent photoexcitation, long-lived oscillations are generally expected in superconductors with low-energy Josephson plasmons, such as in cuprates or fullerene superconductor K$_3$C$_{60}$. These oscillations arise from the parametric generation of plasmon pairs due to pump-induced perturbation of the superconducting order parameter. We show that this bi-plasmon response can persist even above the transition temperature as long as strong superconducting fluctuations are present. Our analysis offers a robust framework to understand light-induced superconducting behavior, and the predicted bi-plasmon oscillations can be directly detected using available experimental techniques.