Larkin-Ovchinnikov phases in two-dimensional square lattices

TL;DR

This paper investigates the emergence of Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) phases in two-dimensional fermionic optical lattices with population imbalance, demonstrating the LO state as the ground state and aligning mean-field results with Monte Carlo calculations.

Contribution

It provides a detailed mean-field phase diagram for LO phases in 2D lattices and compares their energetic favorability over FF states, aligning with recent Monte Carlo results.

Findings

LO state is energetically more favorable than FF state.

Phase diagram for LO phase is constructed and matches Monte Carlo results.

Atomic density modulations in the LO phase are calculated.

Abstract

We consider a two-component gas of fermions in optical lattices in the presence of a population imbalance within a mean-field theory. We study phase transitions from a normal gas of unpaired fermions to a superfluid phase of Bose-condensed Cooper pairs. The possibility of Cooper pairs with a nonzero center-of-mass momentum is included, which corresponds to a so-called Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state. We find that for population imbalanced systems such states can form the ground state. The FF and LO state are compared and it is shown that actually the LO state is energetically more favorable. We complete the mean-field phase diagram for the LO phase and show that it is qualitatively in excellent agreement with recent diagrammatic Monte Carlo calculations. Subsequently, we calculate the atomic density modulations in the LO phase.