AQP Seminar: Single vortex dynamics and mutual friction in a strongly interacting Fermi superfluid
Host: Dr. Vladimir Eltsov
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Single vortex dynamics and mutual friction in a strongly interacting Fermi superfluid
Nicola Grani (CNR-INO, LENS, and University of Florence, Italy)
Abstract
The motion of a quantized vortex is intimately connected with its microscopic structure and the elementary excitations of the surrounding fluid [1]. Vortex dynamics in fermionic superfluids presents an especially complex problem, as vortices host in-gap Andreev quasiparticles confined inside their cores, which occupy quantized energy levels referred to as Caroli–de Gennes–Matricon (CdGM) states [2, 3]. We investigate the two-dimensional motion of a single vortex orbiting a pinned anti-vortex in a unitary Fermi atomic superfluid at varying temperature [4]. By analyzing its trajectory, we measure the yet-unknown longitudinal and transverse mutual friction coefficients, which quantify the vortex-mediated coupling between the normal and superfluid components. Both coefficients increase while approaching the superfluid transition. They provide access to the vortex Hall angle [5], which is linked to the relaxation time of the localized quasiparticles occupying Andreev bound states within the vortex core [6], as well as the intrinsic superfluid parameter associated with the transition from laminar to quantum turbulent flows [7]. We compare our results with numerical simulations and an analytic model originally formulated for superfluid 3He [8, 9] in the low-temperature limit, finding good agreement. Our work highlights the interplay between vortex-bound quasiparticles and delocalized thermal excitations in shaping vortex dynamics in unitary Fermi superfluids. Further, it provides a novel testbed for studying out-of-equilibrium vortex matter at finite temperatures
References
[1] Edouard B. Sonin. Dynamics of Quantised Vortices in Superfluids. Cambridge University Press, December 2015. doi: 10.1017/ cbo9781139047616
[2] C Caroli, PG De Gennes, and J Matricon. Bound fermion states on a vortex line in a type ii superconductor. Physics Letters, 9(4):307–309, 1964.
[3] Rajdeep Sensarma, Mohit Randeria, and Tin-Lun Ho. Vortices in superfluid fermi gases through the bec to bcs crossover. Phys. Rev. Lett., 96(9):090403, 2006.
[4] Nicola Grani, Diego Hernandez-Rajkov, Cyprien Daix, Pierbiagio Pieri, Michele Pini, Piotr Magierski, Gabriel Wlazłowski, Marcia Frómeta Fernández, Francesco Scazza, Giulia Del Pace, et al. Mutual friction and vortex hall angle in a strongly interacting fermi ´ superfluid. arXiv preprint arXiv:2503.21628, 2025.
[5] Max Heyl, Kyosuke Adachi, Yuki M Itahashi, Yuji Nakagawa, Yuichi Kasahara, Emil JW List-Kratochvil, Yusuke Kato, and Yoshihiro Iwasa. Vortex dynamics in the two-dimensional bcs-bec crossover. Nature communications, 13(1):6986, 2022.
[6] NB Kopnin and MM Salomaa. Mutual friction in superfluid he 3: Effects of bound states in the vortex core. Phys. Rev. B, 44(17):9667, 1991.
[7] AP Finne, T Araki, Rob Blaauwgeers, VB Eltsov, NB Kopnin, Matti Krusius, Ladislav Skrbek, M Tsubota, and GE Volovik. An intrinsic velocity-independent criterion for superfluid turbulence. Nature, 424(6952):1022–1025, 2003.
[8] Nikolai B Kopnin. Vortex dynamics and mutual friction in superconductors and fermi superfluids. Reports on Progress in Physics, 65(11): 1633, 2002.
[9] NB Kopnin, GE Volovik, and U Parts. Spectral flow in vortex dynamics of 3he-b and superconductors. Europhysics Letters, 32(8):651, 1995.