High Frequency Sound in a Unitary Fermi Gas

Abstract

We present an experimental and theoretical study of the phonon mode in a unitary Fermi gas. Using two-photon Bragg spectroscopy, we measure excitation spectra at a momentum of approximately half the Fermi momentum, both above and below the superfluid critical temperature $T_{\mathrm{c}}$. Below $T_{\mathrm{c}}$, the dominant excitation is the Bogoliubov-Anderson (BA) phonon mode, driven by gradients in the phase of the superfluid order parameter. The temperature dependence of the BA phonon is consistent with a theoretical model based on the quasiparticle random phase approximation in which the dominant damping mechanism is via collisions with thermally excited quasiparticles. As the temperature is increased above $T_{\mathrm{c}}$, the phonon evolves into a strongly damped collisional mode, accompanied by an abrupt increase in spectral width. Our study reveals strong similarities between sound propagation in the unitary Fermi gas and liquid helium.

arXiv comment6 pages, 3 figures

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Cited by in corpus (14)

• Excitation Spectrum and Superfluid Gap of an Ultracold Fermi Gas
• Tunneling transport of unitary fermions across the superfluid transition
• Thermography of the superfluid transition in a strongly interacting Fermi gas
• Quantum critical thermal transport in the unitary Fermi gas
• Collective excitations of superfluid Fermi gases near the transition temperature
• Second sound with ultracold atoms: A brief historical account
• On the Gravitational Wave to Matter Coupling of Superfluid Fermi Gases Near Unitarity
• Emergence of Sound in a Tunable Fermi Fluid
• Dispersion of first sound in a weakly interacting ultracold Fermi liquid
• Inclusion of pairing fluctuations in a semiclassical approach: The case of study of the Josephson effect
• Two-band atomic superfluidity in the presence of an orbital Feshbach resonance
• Quasiparticle disintegration in fermionic superfluids
• A model study on superfluidity of a unitary Fermi gas of atoms interacting with a finite-ranged potential
• Extreme dynamics and relaxation of quantum gases: A hydrodynamic approach