Spectra of heavy polarons and molecules coupled to a Fermi sea

TL;DR

This paper investigates the spectral properties of impurities strongly coupled to a Fermi sea, revealing the nature of polarons and molecules, and introducing a diagrammatic approach that accounts for finite impurity mass and Fermi edge effects.

Contribution

It presents a novel diagrammatic scheme for analyzing impurity spectra that captures finite mass effects and Fermi edge singularities, extending previous models.

Findings

Large binding energies lead to a semi-coherent repulsive polaron and an incoherent molecule-hole continuum.

The attractive polaron is unlikely to exist under strong binding conditions.

The spectrum features are characterized by the interplay between polaron and molecule-hole states.

Abstract

We study the spectrum of an impurity coupled to a Fermi sea (e.g., minority atom in an ultracold gas, exciton in a solid) by attraction strong enough to form a molecule/trion. We introduce a diagrammatic scheme which allows treating a finite mass impurity while reproducing the Fermi edge singularity in the immobile limit. For large binding energies the spectrum is characterized by a semi-coherent repulsive polaron and an incoherent molecule-hole continuum, which is the lowest-energy feature in the single-particle spectrum. The previously predicted attractive polaron seems not to exist for strong binding.