Evolution of Higgs mode in a Fermion Superfluid with Tunable Interactions

TL;DR

This paper investigates how the Higgs mode in s-wave fermion superfluids evolves from the BCS to BEC regimes, highlighting differences between neutral and charged superfluids and the effects of damping and the Anderson-Higgs mechanism.

Contribution

It provides a unified picture of Higgs mode evolution in both neutral and charged fermion superfluids across the BCS-BEC crossover, including damping effects and the role of the Anderson-Higgs mechanism.

Findings

Higgs mode energy increases and spectral weight decreases in neutral superfluids as interactions strengthen.

Damping causes significant broadening of the Higgs mode across the BEC-BCS crossover.

The Anderson-Higgs mechanism stabilizes the Higgs mode in charged superconductors.

Abstract

In this letter we present a coherent picture for the evolution of Higgs mode in both neutral and charged $s$-wave fermion superfluids, as the strength of attractive interaction between fermions increases from the BCS to the BEC regime. In the case of neutral fermionic superfluid, such as ultracold fermions, the Higgs mode is pushed to higher energy while at the same time, gradually loses its spectral weight as interaction strength increases toward the BEC regime, because the system is further tuned away from Lorentz invariance. On the other hand, when damping is taken into account, Higgs mode is significantly broadened due to coupling to phase mode in the whole BEC-BCS crossover. In the charged case of electron superconductor, the Anderson-Higgs mechanism gaps out the phase mode and suppresses the coupling between the Higgs and the phase modes, and consequently, stabilizes the Higgs mode.