Observation of pseudogap behavior in a strongly interacting Fermi gas

Abstract

Ultracold atomic Fermi gases present an opportunity to study strongly interacting Fermi systems in a controlled and uncomplicated setting. The ability to tune attractive interactions has led to the discovery of superfluidity in these systems with an extremely high transition temperature, near T/T_F = 0.2. This superfluidity is the electrically neutral analog of superconductivity; however, superfluidity in atomic Fermi gases occurs in the limit of strong interactions and defies a conventional BCS description. For these strong interactions, it is predicted that the onset of pairing and superfluidity can occur at different temperatures. This gives rise to a pseudogap region where, for a range of temperatures, the system retains some of the characteristics of the superfluid phase, such as a BCS-like dispersion and a partially gapped density of states, but does not exhibit superfluidity. By making two independent measurements: the direct observation of pair condensation in momentum space and a measurement of the single-particle spectral function using an analog to photoemission spectroscopy, we directly probe the pseudogap phase. Our measurements reveal a BCS-like dispersion with back-bending near the Fermi wave vector k_F that persists well above the transition temperature for pair condensation.

References in corpus (10)

• Vortices and Superfluidity in a Strongly Interacting Fermi Gas
• Observation of the Pairing Gap in a Strongly Interacting Fermi Gas
• Using photoemission spectroscopy to probe a strongly interacting Fermi gas
• Verification of universal relations in a strongly interacting Fermi gas
• Determination of the Superfluid Gap in Atomic Fermi Gases by Quasiparticle Spectroscopy
• The potential energy of a ${}^{40}$K Fermi gas in the BCS-BEC crossover
• Bragg Spectroscopy of Cold Atomic Fermi Gases
• Extracting the condensate density from projection experiments with Fermi gases
• Probing Fermionic Condensates by Fast-Sweep Projection onto Feshbach Molecules
• Superfluid to insulator phase transition in a unitary Fermi gas

Cited by in corpus (8)

• Evolution of the Normal State of a Strongly Interacting Fermi Gas from a Pseudogap Phase to a Molecular Bose Gas
• Momentum Distribution and Contact of the Unitary Fermi gas
• Temperature and coupling dependence of the universal contact intensity for an ultracold Fermi gas
• Quantitative comparison between theoretical predictions and experimental results for Bragg spectroscopy of a strongly interacting Fermi superfluid
• Virial expansion for a strongly correlated Fermi gas with imbalanced spin populations
• Anisotropic Superfluidity in the Two-Species Polar Fermi Gas
• Effects of a particle-hole asymmetric pseudogap on Bogoliubov quasiparticles
• Dynamics of a quantum quench in an ultra-cold atomic BCS superfluid