Cold Attractive Spin Polarized Fermi Lattice Gases and the Doped Positive U Hubbard Model

TL;DR

This paper explores the connection between attractive and repulsive Hubbard models using ultracold fermion gases, revealing how the FFLO state relates to striped phases and discussing implications for high-temperature superconductivity.

Contribution

It demonstrates a reinterpretation of attractive Hubbard model results in the context of doped repulsive models, linking FFLO states to striped phases and analyzing their properties.

Findings

FFLO state corresponds to striped state in doped positive U Hubbard model

Periodicity of FFLO state relates to spin polarization

D-wave superconducting phase relates to d-wave spin density wave

Abstract

Experiments on polarized fermion gases performed by trapping ultracold atoms in optical lattices, allow the study of an attractive Hubbard model for which the strength of the on site interaction is tuned by means of a Feshbach resonance. Using a well-known particle-hole transformation we discuss how results obtained for this system can be reinterpreted in the context of a doped repulsive Hubbard model. In particular we show that the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state corresponds to the striped state of the two-dimensional doped positive U Hubbard model. We then use the results of numerical studies of the striped state to relate the periodicity of the FFLO state to the spin polarization. We also comment on the relationship of the $d_{x^2-y^2}$ superconducting phase of the doped 2D repulsive Hubbard model to a d-wave spin density wave state for the attractive case.