Delayed response of a fermion-pair condensate to a modulation of the interaction strength

TL;DR

This paper analytically investigates how a fermion-pair condensate responds with delay to sinusoidal modulation of interaction strength, revealing nonadiabatic effects, disequilibrium, and relaxation dynamics that explain recent experimental observations.

Contribution

It introduces an analytical model for the delayed response of a fermion-pair condensate under time-dependent interactions, incorporating relaxation effects and explaining experimental delays.

Findings

Nonadiabatic modulation causes disequilibrium in quasiparticle populations.

The delay in response is linked to the condensate's relaxation time.

Analytical gap dynamics describe the system's out-of-equilibrium behavior.

Abstract

The effect of a sinusoidal modulation of the interaction strength on a fermion-pair condensate is analytically studied. The system is described by a generalization of the coupled fermion-boson model that incorporates a time-dependent intermode coupling induced via a magnetic Feshbach resonance. Nontrivial effects are shown to emerge depending on the relative magnitude of the modulation period and the relaxation time of the condensate. Specifically, a nonadiabatic modulation drives the system out of thermal equilibrium: the external field induces a variation of the quasiparticle energies, and, in turn, a disequilibrium of the associated populations. The subsequent relaxation process is studied and an analytical description of the gap dynamics is obtained. Recent experimental findings are explained: the delay observed in the response to the applied field is understood as a temperature effect linked to the condensate relaxation time.