Fulde-Ferrell-Larkin-Ovchinnikov pairing states between $s$- and $p$-orbital fermions

TL;DR

This paper investigates FFLO pairing states in an imbalanced two-component Fermi gas with s- and p_x-orbital bands in an anisotropic 2D optical lattice, revealing stable finite-momentum pairing and a nested π-FFLO phase.

Contribution

It demonstrates the emergence of stable FFLO states due to band structure inversion and nesting effects in s- and p_x-orbital fermions, mapping phase diagrams and BKT transition temperatures.

Findings

Stable FFLO states are favored due to band structure inversion.

A nested π-FFLO phase with spatial modulation is stabilized.

Phase diagrams and BKT transition temperatures are mapped.

Abstract

We study pairing states in an largely imbalanced two-component Fermi gas loaded in an anisotropic two-dimensional optical lattice, where the spin up and spin down fermions filled to the $s$- and $p_x$-orbital bands, respectively. We show that due to the relative inversion of band structures of the $s$ and $p_x$ orbitals, the system favors pairing between two fermions on the same side of the Brillouin zone, leading to a large stable regime for states with finite center-of-mass momentum, i.e., the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. In particular, when the two Fermi surfaces are close in momentum space, a nesting effect stabilizes a special kind of $\pi$-FFLO phase with spatial modulation of $\pi$ along the easily tunneled $x$-direction. We map out the zero temperature phase diagrams within mean-field approach for various aspect ratio within the two-dimensional plane, and calculate the Berezinskii-Kosterlitz-Thouless (BKT) transition temperatures $T_{\rm BKT}$ for different phases.