Sarma phase in relativistic and non-relativistic systems

TL;DR

This paper compares relativistic and non-relativistic two-component fermion systems using a Functional Renormalization Group approach to analyze the stability of the Sarma phase, revealing conditions under which it can exist.

Contribution

It demonstrates that fluctuations induce a Sarma phase in relativistic systems at zero temperature and identifies the limited stability region in non-relativistic systems, proposing a cold atom setup for experimental realization.

Findings

Fluctuations induce a Sarma phase in relativistic systems at zero temperature.

The Sarma phase stability is limited to the BEC side in non-relativistic systems.

A proposed ultracold atom setup could realize the Sarma phase experimentally.

Abstract

We investigate the stability of the Sarma phase in two-component fermion systems in three spatial dimensions. For this purpose we compare strongly-correlated systems with either relativistic or non-relativistic dispersion relation: relativistic quarks and mesons at finite isospin density and spin-imbalanced ultracold Fermi gases. Using a Functional Renormalization Group approach, we resolve fluctuation effects onto the corresponding phase diagrams beyond the mean-field approximation. We find that fluctuations induce a second order phase transition at zero temperature, and thus a Sarma phase, in the relativistic setup for large isospin chemical potential. This motivates the investigation of the cold atoms setup with comparable mean-field phase structure, where the Sarma phase could then be realized in experiment. However, for the non-relativistic system we find the stability region of the Sarma phase to be smaller than the one predicted from mean-field theory. It is limited to the BEC side of the phase diagram, and the unitary Fermi gas does not support a Sarma phase at zero temperature. Finally, we propose an ultracold quantum gas with four fermion species that has a good chance to realize a zero-temperature Sarma phase.