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

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.

arXiv comment17 pages, 5 figures

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• Verification of universal relations in a strongly interacting Fermi gas
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• Fermi polarons in two dimensions
• Boiling a Unitary Fermi Liquid
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• Short-Time Operator Product Expansion for rf Spectroscopy of a Strongly-interacting Fermi Gas
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• Contact and Momentum Distribution of the Unitary Fermi Gas
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• Temperature dependence of the pair coherence and healing lengths for a fermionic superfluid throughout the BCS-BEC crossover
• The contact in the unitary Fermi gas across the superfluid phase transition
• Emergence of a pseudogap in the BCS-BEC crossover
• Diagrammatic Monte Carlo algorithm for the resonant Fermi gas
• Systematic investigation of the effects of disorder at the lowest order throughout the BCS-BEC crossover
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• Breakdown of the Fermi polaron description near Fermi degeneracy at unitarity
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• Evolution of Cooper pairs with zero-center-of-mass momentum and their first-order correlation function in a two-dimensional ultracold Fermi gas near the observed Berezinskii-Kosterlitz-Thouless transition
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• A Universal Energy Functional for Trapped Fermi Gases with Large Scattering Length
• Spectroscopic Bogoliubov features near the unitary limit
• Effective control of chemical potentials by Rabi coupling with rf-fields in ultracold mixtures
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• Radio-frequency driving of an attractive Fermi gas in a one-dimensional optical lattice