Thermal Entropy, Density Disorder and Antiferromagnetism of Repulsive Fermions in 3D Optical Lattice

TL;DR

This paper uses quantum Monte Carlo simulations to explain discrepancies in antiferromagnetic phase transition observations in 3D optical lattices, highlighting the roles of entropy and density disorder.

Contribution

It provides an accurate entropy phase diagram for the 3D Hubbard model, explaining experimental discrepancies by entropy increase and density disorder effects.

Findings

Discrepancy in critical interaction strength explained by entropy increase.

Density disorder in experiments affects antiferromagnetic ordering.

Universal behavior predicted for double occupancy as a function of entropy.

Abstract

The celebrated antiferromagnetic phase transition was realized in a most recent optical lattice experiment for 3D fermionic Hubbard model [Shao {\it et al}., Nature {\bf 632}, 267 (2024)]. Despite the great achievement, it was observed that the AFM structure factor (and also the critical entropy) reaches the maximum around the interaction strength $U/t\simeq 11.75$, which is significantly larger than the theoretical prediction as $U/t\simeq 8$. Here we resolve this discrepancy by studying the interplay between the thermal entropy, density disorder and antiferromagnetism of half-filled 3D Hubbard model with numerically exact auxiliary-field quantum Monte Carlo simulations. We have achieved accurate entropy phase diagram, which allows us to simulate arbitrary entropy path on the temperature-interaction plane and to track the experimental parameters. We then find that above discrepancy can be quantitatively explained by the {\it entropy increase} as enhancing the interaction in experiment, and together by the lattice {\it density disorder} existing in the experimental setup. We furthermore investigate the entropy dependence of double occupancy, and predict its universal behaviors which can be used as useful probes in future optical lattice experiments.