Density instabilities in a two-dimensional dipolar Fermi gas

TL;DR

This paper investigates density instabilities in a two-dimensional dipolar Fermi gas, revealing that beyond-RPA correlations lead to novel stripe phases and collapse instabilities, challenging previous assumptions about the system's behavior.

Contribution

The study introduces an improved correlation scheme beyond RPA, uncovering new density-wave and stripe instabilities in 2D dipolar Fermi gases.

Findings

Identification of density-wave and collapse instabilities.

Discovery of spontaneous stripe phase formation.

Demonstration that RPA is insufficient for this system.

Abstract

We study the density instabilities of a two-dimensional gas of dipolar fermions with aligned dipole moments. We show that the Random Phase Approximation (RPA) for the density-density response function is never accurate for the dipolar gas. We incorporate correlations beyond RPA via an improved version of the Singwi-Tosi-Land-Sjolander scheme. In addition to density-wave instabilities, our formalism captures the collapse instability that is expected from Hartree-Fock calculations but is absent from RPA. Crucially, we find that when the dipoles are perpendicular to the layer, the system spontaneously breaks rotational symmetry and forms a stripe phase, in defiance of conventional wisdom.