Asymmetric Fermi superfluid with different atomic species in a harmonic trap

TL;DR

This paper investigates how asymmetric mixtures of different atomic species in a harmonic trap form superfluid shells, revealing dependence on mass ratios and interaction strength, with implications for phase structures in fermionic gases.

Contribution

It introduces a mean field and local density approximation study of asymmetric Fermi superfluids, highlighting shell structures and phase behaviors based on mass ratios and interaction regimes.

Findings

Superfluid shell structures occur at certain mass ratios.

Shell radii are less sensitive to mass ratios in strong coupling.

Lighter fermions mix more easily with the superfluid core.

Abstract

We study the dilute fermion gas with pairing between two species and unequal concentrations in a harmonic trap using the mean field theory and the local density approximation. We found that the system can exhibit a superfluid shell structure sandwiched by the normal fermions. This superfluid shell structure occurs if the mass ratio is larger then certain critical value which increases from the weak-coupling BCS region to the strong-coupling BEC side. In the strong coupling BEC regime, the radii of superfluid phase are less sensitive to the mass ratios and are similar to the case of pairing with equal masses. However, the lighter leftover fermions are easier to mix with the superfluid core than the heavier ones. A partially polarized superfluid can be found if the majority fermions are lighter, whereas phase separation is still found if they are heavier.