Repulsive fermions and shell effects on the surface of a sphere

TL;DR

This paper explores how the curvature of a spherical surface influences the behavior of a two-component repulsive Fermi gas, revealing shell effects and stability criteria at finite temperature.

Contribution

It introduces a theoretical framework for analyzing repulsive Fermi gases on curved surfaces, incorporating shell effects and deriving a finite-temperature Stoner criterion.

Findings

Shell structure modifies low-temperature thermodynamics on a sphere.

Effective Hartree-Fock approach enables analysis of interactions and stability.

Finite-temperature Stoner criterion highlights interplay between interactions and geometry.

Abstract

In recent years, ultracold atomic gases confined in curved geometries have attracted considerable theoretical interest. This is motivated by recent realizations of bubble traps in microgravity conditions, which open the possibility of investigating quantum many-body physics beyond the conventional flat-space paradigm. The theoretical interest up to now was mainly focused on Bose gases and their phenomenology, and has left the study of Fermi gases behind. In this paper, we investigate a two-component repulsive Fermi gas constrained to the surface of a sphere at finite temperature. We first analyze the non-interacting case, showing how the intrinsic geometrical features of the spherical surface give rise to a shell structure and modify the low-temperature thermodynamics compared to the flat two-dimensional gas. Repulsive interactions are then considered through an effective path-integral approach within a Hartree-Fock mean-field approximation, enabling us to derive the grand canonical potential and to regularize the associated Matsubara summation. We then investigate the stability of the spin-balanced state and obtain the finite-temperature Stoner criterion for fermions on a sphere, highlighting the interplay between the repulsive interactions and shell effects.