Repulsive polarons in two-dimensional Fermi gases

TL;DR

This paper investigates the properties of repulsive polarons in two-dimensional Fermi gases, revealing their metastability, finite momentum, and implications for ferromagnetism in 2D systems.

Contribution

It introduces the concept of repulsive polarons in 2D Fermi gases and analyzes their energy, momentum, and stability, extending understanding from 3D systems.

Findings

Repulsive polarons can form metastable states with energies above non-interacting impurities.

Repulsive polarons can acquire finite momentum under weak attractive interactions.

Saturated ferromagnetism is unlikely in 2D due to polaron lifetime and quasiparticle weight.

Abstract

We consider a single spin-down impurity atom interacting via an attractive, short-range potential with a spin-up Fermi sea in two dimensions (2D). Similarly to 3D, we show how the impurity can form a metastable state (the "repulsive polaron") with energy greater than that of the non-interacting impurity. Moreover, we find that the repulsive polaron can acquire a finite momentum for sufficiently weak attractive interactions. Even though the energy of the repulsive polaron can become sizeable, we argue that saturated ferromagnetism is unfavorable in 2D because of the polaron's finite lifetime and small quasiparticle weight.