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arXiv:1103.5725 · Physical Review A

Repulsive fermions in optical lattices: Phase separation versus coexistence of antiferromagnetism and d -wave superfluidity

S. Y. Chang, Sandeep Pathak, Nandini Trivedi

Published Jan 18, 2012• 1 citation

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. Using a variational formalism, we show that the energy density of a hole ${e}_{\mathrm{hole}}(x)$ 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 t-J model.

DOI: 10.1103/physreva.85.013625

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d

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has a minimum at doping

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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 t-J model.

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We studied the superfluidity of strongly repulsive fermionic atoms in optical lattices. Atoms are paired through a correlated tunneling mechanism, which induces superfluidity when repulsive nearest-neighbor interactions are included in the Hubbard model. This paired superfluid is a metastable state, which persists for a long time as the pair-broken process is severely suppressed. The mean-field phase diagram and low-energy excitations are investigated in a square lattice system. Intriguingly, spontaneous superflows may appear in the ground state of a triangular optical lattice system due to antiferromagnetic frustration.

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We examine antiferromagnetic and

d

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We show that the Hubbard Hamiltonian with particle-assisted tunneling rates---recently proposed to model a fermionic mixture near a broad Feshbach resonance---displays a ground-state phase diagram with superfluid, insulating, and phase-separated regimes. In the latter case, when the populations are balanced the two phases coexist in microscopic antiferromagnetic domains. Macroscopic phase segregation into a high-density superfluid of molecules and a low-density Fermi liquid of single atoms appears in the density profile above a critical polarization

{p}_{c}

.