Polaron residue and spatial structure in a Fermi gas

TL;DR

This paper investigates the spatial structure and residue of polarons in a Fermi gas, revealing oscillatory correlations and divergence in impurity size, with analytical insights into the effects of impurity mass and interactions.

Contribution

It introduces a truncated Hilbert space approach to analyze polaron properties beyond energy, uncovering oscillatory correlations and divergence phenomena in a Fermi gas.

Findings

Polaron pair correlation function exhibits Friedel-like oscillations.

Polaron residue and rms radius diverge for heavy impurities.

Analytical results in the weakly attractive limit highlight the limitations of the truncation.

Abstract

We study the problem of a mobile impurity of mass $M$ interacting {\sl via} a s-wave broad or narrow Feshbach resonance with a Fermi sea of particles of mass $m$. Truncating the Hilbert space to at most one pair of particle-hole excitations of the Fermi sea, we determine ground state properties of the polaronic branch other than its energy, namely the polaron quasiparticle residue $Z$, and the impurity-to-fermion pair correlation function $G(x)$. We show that $G(x)$ deviates from unity at large distances as $-(A\_4+B\_4 \cos 2 k\_F x)/(k\_F x)^4$, where $k\_F$ is the Fermi momentum; since $A\_4>0$ and $B\_4>0$, the polaron has a diverging rms radius and exhibits Friedel-like oscillations. In the weakly attractive limit, we obtain analytical results, that in particular detect the failure of the Hilbert space truncation for a diverging mass impurity, as expected from Anderson orthogonality catastrophe; at distances between $\sim 1/k\_F$ and the asymptotic distance where the $1/x^4$ law applies, they reveal that $G(x)$ exhibits an intriguing multiscale structure.