Peaks and widths of radio-frequency spectra: An analysis of the phase diagram of ultra-cold Fermi gases

TL;DR

This paper offers a detailed theoretical analysis of radio-frequency spectra in ultra-cold Fermi gases, revealing how spectral features relate to pairing phenomena across the BCS-BEC crossover in the normal phase.

Contribution

It introduces a two-peak analysis of rf spectra in the normal phase, extending the correlation between spectral widths and pair size beyond the superfluid regime.

Findings

Identification of two characteristic peaks in rf spectra across the crossover.

Extension of pair size and spectral width correlation to the normal phase.

Partitioning of the phase diagram into distinct physical sectors based on spectral analysis.

Abstract

We provide a comprehensive theoretical study of the radio-frequency (rf) spectra of a two-component Fermi gas with balanced populations in the normal region of the temperature-vs-coupling phase diagram. In particular, rf spectra are analyzed in terms of two characteristic peaks, which can be either distinct or overlapping. On the BEC side of the crossover, these two contributions are associated with a fermionic quasi-particle peak and a bosonic-like contribution due to pairing. On the BCS side of the crossover, the two peaks are instead associated with interactions between particles occurring, respectively, at high or low relative momenta. Through this two-peak analysis, we show how and to what extent the correlation between the widths of the rf spectra and the pair size, previously identified in the superfluid phase at low temperature, can be extended to the normal phase, as well as how the temperature-vs-coupling phase diagram of the BCS-BEC crossover can be partitioned in a number of distinct physical sectors. Several analytic results for the shape and widths of the rf spectra are also derived in appropriate temperature and coupling limits.