Fermions in 3D Optical Lattices: Cooling Protocol to Obtain Antiferromagnetism

TL;DR

This paper demonstrates that in 3D optical lattices, increasing fermion repulsion within a trap can induce cooling and facilitate the formation of antiferromagnetic phases, overcoming challenges in achieving such states.

Contribution

The study provides a detailed equation of state for the 3D Fermi-Hubbard model and shows how trap-induced entropy redistribution enables antiferromagnetism.

Findings

Increasing repulsion causes cooling in a trap due to entropy redistribution.

Trap allows AF Mott phase formation even at higher average entropy.

Unbiased quantum Monte Carlo methods accurately model the system.

Abstract

A major challenge in realizing antiferromagnetic (AF) and superfluid phases in optical lattices is the ability to cool fermions. We determine the equation of state for the 3D repulsive Fermi-Hubbard model as a function of the chemical potential, temperature and repulsion using unbiased determinantal quantum Monte Carlo methods, and we then use the local density approximation to model a harmonic trap. We show that increasing repulsion leads to cooling, but only in a trap, due to the redistribution of entropy from the center to the metallic wings. Thus, even when the average entropy per particle is larger than that required for antiferromagnetism in the homogeneous system, the trap enables the formation of an AF Mott phase.