Temperature dependence of the contact in a unitary Fermi gas

TL;DR

This paper reports the first experimental measurements of how the contact parameter in a unitary Fermi gas varies with temperature, confirming theoretical predictions and revealing persistent pair correlations above the superfluid transition.

Contribution

First measurement of temperature dependence of contact in a unitary Fermi gas using Bragg spectroscopy, confirming theoretical decay predictions.

Findings

Contact decreases with increasing temperature.

Pair correlations persist above superfluid transition.

Results align with theoretical models.

Abstract

The contact ${\cal I}$, introduced by Tan, has emerged as a key parameter characterizing universal properties of strongly interacting Fermi gases. For ultracold Fermi gases near a Feshbach resonance, the contact depends upon two quantities: the interaction parameter $1/(k_F a)$, where $k_F$ is the Fermi wave-vector and $a$ is the $s$-wave scattering length, and the temperature $T/T_F$, where $T_F$ is the Fermi temperature. We present the first measurements of the temperature dependence of the contact in a unitary Fermi gas using Bragg spectroscopy. The contact is seen to follow the predicted decay with temperature and shows how pair-correlations at high momentum persist well above the superfluid transition temperature.