Low Energy Excitations of a 1D Fermi Gas with Attractive Interactions

TL;DR

This paper investigates the low-energy excitations of a 1D Fermi gas with attractive interactions, revealing an inversion of spin-charge separation and effects of pairing using Bragg spectroscopy.

Contribution

It provides experimental evidence of the Luther-Emery liquid behavior in a 1D Fermi gas with attractive interactions, including spin-charge dynamics and pairing phenomena.

Findings

Spin wave propagates faster than charge density wave with attraction

Small spin polarization suppresses the spin gap

Evidence of pairing from reduced spin correlations and RF spectra

Abstract

The low-energy excitations of a two-component repulsive Fermi gas confined to one dimension are linear dispersing spin- and charge-density waves whose respective propagation velocities depend on the strength and sign of their interaction. Quasi-1D fermions with attractive interaction realize the Luther-Emery liquid, which exhibits a rich array of phenomena, many of which are qualitatively different from those exhibited by their repulsive counterpart. We use a Feshbach resonance to access attractive interactions with $^6$Li atoms. We measured the spin and charge dynamic structure factors using Bragg spectroscopy and find that, contrary to repulsive interactions, the spin wave propagates faster than the charge density wave, thus producing an inversion of the classic spin-charge separation. We also find that a small spin polarization strongly suppresses the spin gap in the measured Bragg spectra. Evidence for pairing are a reduction in spin correlations with increasing attraction and RF spectra consistent with an atom/molecule mixture.