Ferromagnetism of a Repulsive Atomic Fermi Gas in an Optical Lattice: a Quantum Monte Carlo Study

TL;DR

This study uses quantum Monte Carlo simulations to explore how a repulsive atomic Fermi gas in an optical lattice transitions to ferromagnetism, revealing conditions that could facilitate experimental observation.

Contribution

It provides the first detailed quantum Monte Carlo analysis of ferromagnetism in a Fermi gas within an optical lattice, including effects of imbalance and impurity.

Findings

Ferromagnetic transition occurs at weaker interactions with increased lattice intensity.

Transitions between paramagnetic and ferromagnetic phases are identified at specific densities.

Results align with and extend previous density functional theory and tight-binding model predictions.

Abstract

Using continuous-space quantum Monte Carlo methods we investigate the zero-temperature ferromagnetic behavior of a two-component repulsive Fermi gas under the influence of periodic potentials that describe the effect of a simple-cubic optical lattice. Simulations are performed with balanced and with imbalanced components, including the case of a single impurity immersed in a polarized Fermi sea (repulsive polaron). For an intermediate density below half filling, we locate the transitions between the paramagnetic, and the partially and the fully ferromagnetic phases. As the intensity of the optical lattice increases, the ferromagnetic instability takes place at weaker interactions, indicating a possible route to observe ferromagnetism in experiments performed with ultracold atoms. We compare our findings with previous predictions based on the standard computational method used in material science, namely density functional theory, and with results based on tight-binding models.