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Mutual friction is a fundamental mechanism in finite-temperature superfluids, arising from vortex scattering with thermally excited quasiparticles and directly influencing vortex dynamics. Its microscopic origin is determined by the intrinsic properties of the system and the nature of its excitations. We investigate the two-dimensional motion of a single vortex orbiting a pinned anti-vortex in a unitary Fermi atomic superfluid at varying temperatures. From the observed trajectory, we extract the previously unknown longitudinal and transverse mutual-friction coefficients, which quantify the vortex-mediated coupling between the normal and superfluid components. Our results suggest that vortex dynamics in unitary Fermi superfluids is essentially affected by the interplay between delocalized thermal excitations and vortex-bound quasiparticles localized within the vortex core, the so-called Caroli–de Gennes–Matricon states. Further, from the mutual friction coefficients we determine the vortex Hall angle, which is linked to the relaxation time of the localized quasiparticles occupying Andreev bound states within the vortex core, and to the vortex Reynolds number associated with the transition from laminar to quantum turbulent flows. N. Grani, D. Hernández-Rajkov et al. For details on the data analysis see also: N. Grani, et al. |
Fermions with tunable interactions... In the lithium lab we produce ultracold Fermi gases of 6Li to explore out-of-equilibrium dynamics and transport phenomena in strongly correlated fermionic matter. Atoms are confined into light-imprinted potential structures, simulating the motion of electrons in solid state devices. Our main goal is the study of two-dimensional strongly correlated phases, such as superfluidity across the BCS-BEC crossover and its robustness to disorder.