Polaron residue and spatial structure in a Fermi gas

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$k_F$istheFermimomentum;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 $\sim 1\mathrm{/}k\mathrm{\_}F$ and the asymptotic distance where the $1\mathrm{/}{x}^4$ law applies, they reveal that $G(x)$ exhibits an intriguing multiscale structure.