Attractive Fermi polarons at nonzero temperature with finite impurityconcentration

TL;DR

This paper studies how temperature and impurity concentration influence the properties of attractive Fermi polarons, revealing significant effects near the unitary limit and improving agreement with experimental measurements.

Contribution

It provides a detailed theoretical analysis of temperature and impurity concentration effects on Fermi polarons using T-matrix theories, especially near the unitary limit.

Findings

Effective mass approaches bare mass with increasing temperature.

Residue is significantly enhanced at higher temperatures.

Polaron energy shifts downward due to attractive polaron-polaron interactions.

Abstract

We theoretically investigate how quasi-particle properties of an attractive Fermi polaron are affected by nonzero temperature and finite impurity concentration. By applying both non-self-consistent and self-consistent many-body $T$-matrix theories, we calculate the polaron energy (including decay rate), effective mass, and residue, as functions of temperature and impurity concentration. The temperature and concentration dependences are weak on the BCS side with a negative impurity-medium scattering length. Toward the strong attraction regime across the unitary limit, we find sizable dependences. In particular, with increasing temperature the effective mass quickly approaches the bare mass and the residue is significantly enhanced. At the temperature $T\sim0.1T_{F}$, where $T_{F}$ is the Fermi temperature of the background Fermi sea, the residual polaron-polaron interaction seems to become attractive. This leads to a notable down-shift in the polaron energy. We show that, by taking into account the temperature and impurity concentration effects, the measured polaron energy in the first Fermi polaron experiment {[}A. Schirotzek \textit{et al.}, Phys. Rev. Lett. \textbf{102}, 230402 (2009){]} can be better theoretically explained.