Dipole-Mode Spectrum and Hydrodynamic Crossover in a Resonantly Interacting Two-Species Fermion Mixture

Abstract

Ultracold quantum-gas mixtures of fermionic atoms with resonant control of interactions offer a unique test-bed to explore few- and many-body quantum states with unconventional properties. The emergence of such strongly correlated systems, as for instance symmetry-broken superfluids, is usually accompanied by hydrodynamic collective behavior. Thus, experimental progress in this field naturally requires a deep understanding of hydrodynamic regimes. Here, we report on experiments employing a tunable Fermi-Fermi mixture of ${}^{161}$Dy and ${}^{40}$K near quantum degeneracy. We investigate the full spectrum of dipole modes across a Feshbach resonance and characterize the crossover from collisionless to deep hydrodynamic behavior in measurements of frequencies and damping rates. We compare our results with a theoretical model that considers the motion of the mass centers of the two species and we identify the contributions of friction and mean-field interaction. We show that one oscillating mode exists over the whole range of interactions, exhibiting striking changes of frequency and damping in the deep hydrodynamic regime. We observe the second oscillating mode to split into two purely exponential damping modes. One of these exponential modes shows very fast damping, faster than any other relevant timescale, and is largely insensitive against experimental imperfections. It provides an accurate measure for the interspecies drag effect, which generalizes the concept of spin drag explored in other experiments. We characterize the interspecies drag locally in terms of a microscopic friction coefficient and we discuss its unitarity-limited universal behavior on top of the resonance.

20 pages, 11 figures

References in corpus (23)

• Theory of ultracold Fermi gases
• Collective excitations of a degenerate gas at the BEC-BCS crossover
• Quantum degenerate dipolar Fermi gas
• Exploring an ultracold Fermi-Fermi mixture: Interspecies Feshbach resonances and scattering properties of 6Li and 40K
• Quantum degenerate two-species Fermi-Fermi mixture coexisting with a Bose-Einstein condensate
• Ultracold Heteronuclear Fermi-Fermi Molecules
• Two-species fermion mixtures with population imbalance
• Low-energy three-body dynamics in binary quantum gases
• Universal Fermi gases in mixed dimensions
• Trimers, molecules and polarons in imbalanced atomic Fermi gases
• Finite-Temperature Collective Dynamics of a Fermi Gas in the BEC-BCS Crossover
• Polarized Fermi condensates with unequal masses: Tuning the tricritical point
• Dynamics of a strongly interacting Fermi gas: the radial quadrupole mode
• Heavy-Light Fermion Mixtures at Unitarity
• Collective Modes in a Unitary Fermi Gas across the Superfluid Phase Transition
• Five-Body Efimov Effect and Universal Pentamer in Fermionic Mixtures
• Superfluid pairing between fermions with unequal masses
• Coupled Dipole Oscillations of a Mass-Imbalanced Bose and Fermi Superfluid Mixture
• Beyond-mean-field description of a trapped unitary Fermi gas with mass and population imbalance
• Double-degenerate Fermi mixtures of ${}^6$Li and ${}^{53}$Cr atoms
• Observation of low-field Feshbach resonances between ${}^{161}$Dy and ${}^{40}$K
• Observation of Feshbach resonances in an ${}^{167}$Er-${}^6$Li Fermi-Fermi mixture
• Spin-dipole mode in a trapped Fermi gas near unitarity

Cited by in corpus (2)

• Optically trapped Feshbach molecules of fermionic ${}^{161}$Dy and ${}^{40}$K: Role of light-induced and collisional losses
• Particle-hole origin of thermal beating in dipole-compression modes of a 1D Bose gas