Excitation spectra and rf-response near the polaron-to-molecule transition from the functional renormalization group

TL;DR

This paper introduces a novel functional renormalization group method to analyze the excitation spectra and rf-response of polarons and molecules in a Fermi gas near the transition, providing detailed spectral and decay information.

Contribution

It develops a unified framework with full self-energy feedback to compute spectral functions of polarons and molecules, advancing understanding of their transition and decay properties.

Findings

Confirmed scaling of excited state decay rate near the transition

Analyzed energy spectra and decay widths of polaron and molecule

Proposed experimental rf-spectroscopy procedure for Li6 Fermi gas

Abstract

A light impurity in a Fermi sea undergoes a transition from a polaron to a molecule for increasing interaction. We develop a new method to compute the spectral functions of the polaron and molecule in a unified framework based on the functional renormalization group with full self-energy feedback. We discuss the energy spectra and decay widths of the attractive and repulsive polaron branches as well as the molecular bound state and confirm the scaling of the excited state decay rate near the transition. The quasi-particle weight of the polaron shifts from the attractive to the repulsive branch across the transition, while the molecular bound state has a very small residue characteristic for a composite particle. We propose an experimental procedure to measure the repulsive branch in a Li6 Fermi gas using rf-spectroscopy and calculate the corresponding spectra.