Universal Relations for Fermions with Large Scattering Length

TL;DR

This paper reviews the universal relations governing fermions with large scattering lengths, focusing on the contact parameter that links microscopic pair correlations to macroscopic thermodynamics and dynamic properties.

Contribution

It summarizes the theoretical framework and experimental evidence for universal relations involving the contact in strongly interacting fermionic systems.

Findings

Universal relations connect the contact to thermodynamics and correlation functions.

The contact determines the high-momentum and high-frequency behavior of the system.

Current experimental measurements support the theoretical predictions.

Abstract

The behavior of fermions with two spin states that interact with a large scattering length is constrained by universal relations that hold for any state of the system. These relations involve a central property of the system called the contact, which measures the number of pairs of fermions with different spins that have small separations. The contact controls the thermodynamics of the system as well as the large-momentum and high-frequency tails of correlation functions. This review summarizes the current theoretical and experimental status of these universal relations.