Repulsive polarons in two-dimensional Fermi gases

¹ T.C.M. Group, Cavendish Laboratory - JJ Thomson Avenue, Cambridge CB3 0HE, UK
² London Centre for Nanotechnology - Gordon Street, London, WC1H 0AH, UK

Received: 18 March 2012
Accepted: 10 April 2012

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.