Probing the excitation spectrum of a Fermi gas in the BCS-BEC crossover regime

TL;DR

This paper presents a novel spectroscopy method to measure excitation spectra of ultracold fermionic gases in the BCS-BEC crossover, revealing pairing and collective excitations and providing insights into the pairing gap.

Contribution

It introduces a new modulation-based spectroscopy technique to probe excitation spectra in strongly interacting Fermi gases.

Findings

Observation of collective excitations.

Detection of fermion pair dissociation.

Measurement of pairing gap in the crossover regime.

Abstract

We measure excitation spectra of an ultracold gas of fermionic $^{40}$K atoms in the BCS-BEC crossover regime. The measurements are performed with a novel spectroscopy that employs a small modulation of the B-field close to a Feshbach resonance to give rise to a modulation of the interaction strength. With this method we observe both a collective excitation as well as the dissociation of fermionic atom pairs in the strongly interacting regime. The excitation spectra reveal the binding energy / excitation gap for pairs in the crossover region.