Exotic superfluidity and pairing phenomena in atomic Fermi gases in mixed dimensions

TL;DR

This paper explores how mixed dimensionality in atomic Fermi gases influences superfluidity and pairing, revealing complex phase behavior and new phenomena across the BCS-BEC crossover.

Contribution

It introduces a detailed analysis of superfluid and pairing phenomena in mixed-dimensional Fermi gases, highlighting the evolution of effective dimensionality and novel phase behaviors.

Findings

Effective dimensionality can shift from quasi-3D to quasi-1D, causing Fermi surface mismatch.

The system exhibits effective quasi-2D behavior in the BEC regime.

Critical temperature $T_c$ shows a constant BEC asymptote in mixed dimensions.

Abstract

Atomic Fermi gases have been an ideal platform for simulating conventional and engineering exotic physical systems owing to their multiple tunable control parameters. Here we investigate the effects of mixed dimensionality on the superfluid and pairing phenomena of a two-component ultracold atomic Fermi gas with a short-range pairing interaction, while one component is confined on a one-dimensional (1D) optical lattice whereas the other is in a homogeneous 3D continuum. We study the phase diagram and the pseudogap phenomena throughout the entire BCS-BEC crossover, using a pairing fluctuation theory. We find that the effective dimensionality of the non-interacting lattice component can evolve from quasi-3D to quasi-1D, leading to strong Fermi surface mismatch. Upon pairing, the system becomes effectively quasi-two dimensional in the BEC regime. The behavior of $T_c$ bears similarity to that of a regular 3D population imbalanced Fermi gas, but with a more drastic departure from the regular 3D balanced case, featuring both intermediate temperature superfluidity and possible pair density wave ground state. Unlike a simple 1D optical lattice case, $T_c$ in the mixed dimensions has a constant BEC asymptote.