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arXiv · 2105.09820

Excitation Spectrum and Superfluid Gap of an Ultracold Fermi Gas

Hauke Biss·Lennart Sobirey·Niclas Luick·Markus Bohlen·Jami J. Kinnunen·Georg M. Bruun·Thomas Lompe·Henning Moritz
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Abstract

Ultracold atomic gases are a powerful tool to experimentally study strongly correlated quantum many-body systems. In particular, ultracold Fermi gases with tunable interactions have allowed to realize the famous BEC-BCS crossover from a Bose-Einstein condensate (BEC) of molecules to a Bardeen-Cooper-Schrieffer (BCS) superfluid of weakly bound Cooper pairs. However, large parts of the excitation spectrum of fermionic superfluids in the BEC-BCS crossover are still unexplored. In this work, we use Bragg spectroscopy to measure the full momentum-resolved low-energy excitation spectrum of strongly interacting ultracold Fermi gases. This enables us to directly observe the smooth transformation from a bosonic to a fermionic superfluid that takes place in the BEC-BCS crossover. We also use our spectra to determine the evolution of the superfluid gap and find excellent agreement with previous experiments and self-consistent T-matrix calculations both in the BEC and crossover regime. However, towards the BCS regime a calculation that includes the effects of particle-hole correlations shows better agreement with our data.

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Hauke Biss, Lennart Sobirey, Niclas Luick, Markus Bohlen, Jami J. Kinnunen, Georg M. Bruun, Thomas Lompe, Henning Moritz. 2021-05-20. Excitation Spectrum and Superfluid Gap of an Ultracold Fermi Gas. https://doi.org/10.1103/physrevlett.128.100401

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