Correlated Phases of Population Imbalanced Fermi-Fermi Mixtures on an Optical Lattice

TL;DR

This paper investigates a two-species fermion mixture on a square lattice, revealing various correlated phases such as density waves and p-wave pairing, using a functional renormalization group approach to map the phase diagram.

Contribution

It provides the first detailed phase diagram of population-imbalanced fermionic mixtures on a lattice with tunable interactions, highlighting the emergence of multiple correlated phases.

Findings

Identification of spin density wave and charge stripe phases.

Discovery of p-wave BCS pairing states for both species.

Estimation of critical temperatures for the phases.

Abstract

We study a two species fermion mixture with different populations on a square lattice modeled by a Hubbard Hamiltonian with on-site inter-species repulsive interaction. Such a model can be realized in a cold atom system with fermionic atoms in two different hyperfine states loaded on an optical lattice and with tunable inter-species interaction strength via external fields. For a two-dimensional square lattice, when at least one of the fermion species is close to half-filling, the system is highly affected by lattice effects. With the majority species near half-filling and varying densities for the minority species, we find that several correlated phases emerge as the ground state, including a spin density wave state, a charge density wave state with stripe structure, and various p-wave BCS pairing states for both species. We study this system using a functional renormalization group method, determine its phase diagram at weak coupling, discuss the origin and characteristics of each phase, and provide estimates for the critical temperatures.