Repulsive Fermions in Optical Lattices: Phase separation versus Coexistence of Antiferromagnetism and d-Superfluidity

TL;DR

This paper studies strongly repulsive fermions in 2D optical lattices, revealing phase separation between antiferromagnetic and d-wave superfluid phases, while also examining coexistence and energetic competition.

Contribution

It provides a detailed comparison of phase separation and coexistence of orders in repulsive fermion systems, including effects of interaction strength and hopping terms.

Findings

Energy density minimum at critical doping indicates phase separation.

Homogeneous coexistence state has energy close to phase-separated state.

Dependence of energy on interaction strength and hopping terms analyzed.

Abstract

We investigate a system of fermions on a two-dimensional optical square lattice in the strongly repulsive coupling regime. In this case, the interactions can be controlled by laser intensity as well as by Feshbach resonance. We compare the energetics of states with resonating valence bond d-wave superfluidity, antiferromagnetic long range order and a homogeneous state with coexistence of superfluidity and antiferromagnetism. We show that the energy density of a hole $e_{hole}(x)$ has a minimum at doping $x=x_c$ that signals phase separation between the antiferromagnetic and d-wave paired superfluid phases. The energy of the phase-separated ground state is however found to be very close to that of a homogeneous state with coexisting antiferromagnetic and superfluid orders. We explore the dependence of the energy on the interaction strength and on the three-site hopping terms and compare with the nearest neighbor hopping {\it t-J} model.