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arXiv:2311.00479 · Results in Physics

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

L. Pisani, Michele Pini, P. Pieri, Giancarlo Calvanese Strinati

Published Jan 20, 2024• 2 citations

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.

DOI: 10.1016/j.rinp.2024.107358

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We present a theoretical interpretation of radio frequency (RF) pairing gap experiments in trapped atomic Fermi gases, over the entire range of the BCS--Bose-Einstein condensation (BEC) crossover, for temperatures above and below

{T}_{c}

. Our calculated RF excitation spectra, as well as the density profiles on which they are based, are in semiquantitative agreement with experiment. We provide a detailed analysis of the physical origin of the two different peak features seen in RF spectra, one associated with nearly free atoms at the edge of the trap, and the other with (quasi-)bound fermion pairs.

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T_c

).These issues have a counterpart in the cold Fermi gases and it would be most useful in future to use these atomic systems to address these and the more sweeping question of how to describe that anomalous superfluid phase which forms in the presence of a normal state excitation gap.

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