Enhanced paraconductivity-like fluctuations in the radio frequency spectra of ultracold Fermi atoms

TL;DR

This paper investigates enhanced paraconductivity-like fluctuations in RF spectra of ultracold Fermi gases near the superfluid transition, revealing significant fluctuation effects and linking spectral features to universal pairing energy scales.

Contribution

It introduces a detailed theoretical analysis of paraconductivity fluctuations in RF spectra of ultracold Fermi gases, highlighting their increased role compared to superconductors.

Findings

Fluctuations significantly influence RF spectra above T_c

Enhanced paraconductivity-like effects compared to superconductors

Identification of a universal pairing-related energy scale

Abstract

Ultracold Fermi atoms allow the realization of the crossover from Bardeen-Cooper-Schrieffer (BCS) superconductivity to Bose- Einstein condensation (BEC), by varying with continuity the attraction between fermions of different species. In this context, radio frequency (RF) spectroscopy provides a microscopic probe to infer the nature of fermionic pairing. In the strongly-interacting regime, this pairing affects a wide temperature range comprising the critical temperature T_c, in analogy to the pseudogap physics for high-temperature superconductors. By including what are known in superconductors as "paraconductivity" fluctuations, here we calculate the RF spectra above T_c for fermions with balanced populations and compare them with available experimental data, thus revealing that the role of these fluctuations is considerably enhanced with respect to superconductors. In addition, we extract from the spectra an energy scale associated with pairing and relate it to a universal quantity recently introduced for Fermi gases.