Quantum Monte Carlo simulations of two-dimensional repulsive Fermi gases with population imbalance

TL;DR

This study uses quantum Monte Carlo simulations to explore the properties of two-dimensional repulsive Fermi gases with population imbalance, revealing the stability of partially ferromagnetic phases and characterizing polaron behavior.

Contribution

It provides new insights into the ground-state properties and phase stability of 2D repulsive Fermi gases, including polaron effective mass and coupling, using advanced Monte Carlo methods.

Findings

Partially ferromagnetic phase is stable in a narrow interaction range.

Polaron effective mass and coupling are quantitatively characterized.

Magnetic susceptibility closely matches mean-field predictions.

Abstract

The ground-state properties of two-component repulsive Fermi gases in two dimensions are investigated by means of fixed-node diffusion Monte Carlo simulations. The energy per particle is determined as a function of the intercomponent interaction strength and of the population imbalance. The regime of universality in terms of the s-wave scattering length is identified by comparing results for hard-disk and for soft-disk potentials. In the large imbalance regime, the equation of state turns out to be well described by a Landau-Pomeranchuk functional for two-dimensional polarons. To fully characterize this expansion, we determine the polarons' effective mass and their coupling parameter, complementing previous studies on their chemical potential. Furthermore, we extract the magnetic susceptibility from low-imbalance data, finding only small deviations from the mean-field prediction. While the mean-field theory predicts a direct transition from a paramagnetic to a fully ferromagnetic phase, our diffusion Monte Carlo results suggest that the partially ferromagnetic phase is stable in a narrow interval of the interaction parameter. This finding calls for further analyses on the effects due to the fixed-node constraint.