Polarization Measurements and the Pairing Gap in the Universal Regime

TL;DR

This paper analyzes cold-atom experiments on imbalanced Fermi systems, using a minimal model to extract the zero-temperature pairing gap, revealing it is significantly larger than in other strongly-paired fermion systems.

Contribution

The study provides a new estimate of the T=0 pairing gap in the universal regime, showing it exceeds previous measurements in similar systems.

Findings

Pairing gap is greater than 0.4 E_F, with a preferred value of 0.45 ± 0.05 E_F.

Density profiles agree with universal quantum Monte Carlo predictions.

The pairing gap ratio is larger than in other strongly-paired fermion systems.

Abstract

We analyze recent cold-atom experiments on imbalanced Fermi systems using a minimal model with a BCS-like superfluid phase coexisting with a normal phase. This model is used to extract the T=0 pairing gap in the fully paired superfluid state. The recently measured particle density profiles are in good agreement with the theoretical predictions obtained from the universal parameters from previous Quantum Monte Carlo calculations. We find that the T=0 pairing gap is greater than 0.4 times the Fermi energy $E_F$, with a preferred value of $0.45 \pm 0.05$ $E_F$. The ratio of the pairing gap $\Delta$ to the Fermi Energy $E_F$ is larger here than in any other system of strongly-paired fermions in which individual pairs are unbound.