Counterflow of spontaneous mass currents in trapped spin-orbit coupled Fermi gases

TL;DR

This paper investigates how symmetric Rashba spin-orbit coupling in trapped 2D Fermi gases induces spontaneous counterflowing mass currents near the trap edge, even without interactions, with robustness against asymmetry.

Contribution

It reveals the spontaneous generation of counterflowing mass currents due to symmetric spin-orbit coupling in trapped Fermi gases, a novel phenomenon not previously characterized.

Findings

Counterflowing mass currents occur near trap edges in symmetric spin-orbit coupled Fermi gases.

Currents decrease toward the molecular BEC limit with increased spin-orbit coupling or interactions.

Currents are robust against asymmetric spin-orbit couplings but vanish in one-dimensional limits.

Abstract

We use the Bogoliubov-de Gennes formalism and study the ground-state phases of trapped spin-orbit coupled Fermi gases in two dimensions. Our main finding is that the presence of a symmetric (Rashba type) spin-orbit coupling spontaneously induces counterflowing mass currents in the vicinity of the trap edge, i.e. $\uparrow$ and $\downarrow$ particles circulate in opposite directions with equal speed. These currents flow even in noninteracting systems, but their strength decreases toward the molecular BEC limit, which can be achieved either by increasing the spin-orbit coupling or the interaction strength. These currents are also quite robust against the effects of asymmetric spin-orbit couplings in $x$ and $y$ directions, gradually reducing to zero as the spin-orbit coupling becomes one dimensional. We compare our results with those of chiral p-wave superfluids/superconductors.