Breakdown of Fermi liquid description for strongly interacting fermions

Abstract

The nature of the normal state of an ultracold Fermi gas in the BCS-BEC crossover regime is an intriguing and controversial topic. While the many-body ground state remains a condensate of paired fermions, the normal state must evolve from a Fermi liquid to a Bose gas of molecules as a function of the interaction strength. How this occurs is still largely unknown. We explore this question with measurements of the distribution of single-particle energies and momenta in a nearly homogeneous gas above $T_c$. The data fit well to a function that includes a narrow, positively dispersing peak that corresponds to quasiparticles and an "incoherent background" that can accommodate broad, asymmetric line shapes. We find that the quasiparticle's spectral weight vanishes abruptly as the strength of interactions is modified, which signals the breakdown of a Fermi liquid description. Such a sharp feature is surprising in a crossover.

21 pages including 4 main figures and a supplementary section with 5 extended data figures

References in corpus (14)

• Observation of Fermi Polarons in a Tunable Fermi Liquid of Ultracold Atoms
• Using photoemission spectroscopy to probe a strongly interacting Fermi gas
• The Equation of State of a Low-Temperature Fermi Gas with Tunable Interactions
• Fermi-Polaron: Diagrammatic Monte Carlo for Divergent Sign-Alternating Series
• Observation of pseudogap behavior in a strongly interacting Fermi gas
• Verification of universal relations in a strongly interacting Fermi gas
• Measurement of the Homogeneous Contact of a Unitary Fermi gas
• Evolution of the Normal State of a Strongly Interacting Fermi Gas from a Pseudogap Phase to a Molecular Bose Gas
• Exact Relations for a Strongly-interacting Fermi Gas near a Feshbach Resonance
• Radio-Frequency Transitions on Weakly-Bound Ultracold Molecules
• Temperature and coupling dependence of the universal contact intensity for an ultracold Fermi gas
• Radio frequency spectroscopy of a strongly imbalanced Feshbach-resonant Fermi gas
• Bragg Spectroscopy of Cold Atomic Fermi Gases
• Direct observation of the Fermi surface in an ultracold atomic gas

Cited by in corpus (16)

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• Non-equilibrium strong-coupling theory for a driven-dissipative ultracold Fermi gas in the BCS-BEC crossover region
• Momentum-resolved spectroscopy of a Fermi liquid
• QCD-like phase diagram with Efimov trimers and Cooper pairs in resonantly interacting SU(3) Fermi gases
• Spin Susceptibility Above the Superfluid Onset in Ultracold Fermi Gases
• Quasiparticle Dispersions and Lifetimes in the Normal State of the BCS-BEC Crossover
• In Situ Momentum Distribution Measurement of a Quantum Degenerate Fermi Gas using Raman Spectroscopy
• Spin susceptibility and effects of a harmonic trap in the BCS-BEC crossover regime of an ultracold Fermi gas
• Protocol to engineer Fulde-Ferrell-Larkin-Ovchinnikov states in a cold Fermi gas
• Low-Dimensional Fluctuations and Pseudogap in Gaudin-Yang Fermi Gases
• Spin-dipole mode in a trapped Fermi gas near unitarity
• Pseudogap regime of a two-dimensional uniform Fermi gas
• Normal-state Properties of a Unitary Bose-Fermi Mixture: A Combined Strong-coupling Approach with Universal Thermodynamics