Excitation of the Higgs Mode in a Superfluid Fermi Gas in the BCS-BEC Crossover

TL;DR

This paper investigates Higgs amplitude oscillations in a superfluid Fermi gas across the BCS-BEC crossover using time-dependent equations, revealing the relationship between Higgs mode energy, decay, and scattering length changes.

Contribution

It provides a detailed analysis of Higgs mode behavior in a Fermi gas during scattering length ramps, highlighting the decay dynamics and optimal conditions for observation.

Findings

Higgs mode energy matches the pair-breaking threshold.

Decay exponent varies from -1/2 to -3/2 across the crossover.

Optimal ramp speed for clear Higgs oscillations is proposed.

Abstract

In quantum many-body systems with spontaneous breaking of continuous symmetries, Higgs modes emerge as collective amplitude oscillations of order parameters. Recently, Higgs mode has been observed in the ultracold Fermi gas. In the present paper, we use the time-dependent Bogoliubov-de Gennes equations to investigate Higgs amplitude oscillations of the superfluid order parameter in a Fermi gas induced by a rapid change of the ${\it s}$-wave scattering length. In particular, we investigate the Higgs mode with different values of the initial scattering length. We find that the energy of the Higgs mode coincides with the threshold energy of the pair-breaking excitation, and exponent of the power-low decay of the Higgs mode $\gamma$ continuously changes between $\gamma=-1/2$ and $\gamma=-3/2$ through the Bardeen-Cooper-Schrieffer-Bose-Einstein condensation (BCS-BEC) crossover. Moreover, we propose the optimal ramp speed of the scattering length for observing the clearest Higgs oscillations.