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

Abstract

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