REVIEWS OF TOPICAL PROBLEMS
BCS-BEC crossover, collective excitations, and superfluid hydrodynamics in quantum fluids and gases
M. Yu. Kaganab, A. V. Turlapovcd
a P. L. Kapitza Institute for Physical Problems, Russian Academy of Sciences, Moscow
b Moscow Institute of Electronics and Mathematics — Higher School of Economics
c Federal Research Center The Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod
d Lobachevski State University of Nizhni Novgorod
A Fermi gas described within the Bardeen–Cooper–Schrieffer theory (BCS) may be converted into a Bose–Einstein condensate (BEC) of composite molecules (dimers) by adiabatically tuning the interaction. The sequence of the states that appears during this conversion is referred to as the BCS–BEC crossover. The review is devoted to theoretical and experimental results on the BCS–BEC crossover in three- and quasi-two-dimensional resonant quantum gases in the limiting geometry of traps and optical lattices. We shall discuss nontrivial phenomena in the superfluid hydrodynamics of the quantum gases and fluids including the spectrum of collective excitations in the BCS-BEC crossover, hydrodynamics of rotating Bose condensates with a large number of quantized vortices, and the complex unresolved problem of the chiral anomaly in the hydrodynamics of superfluid Fermi systems with anisotropic p-wave pairing. We shall also analyze spin-imbalanced quantum gases and the ability to realize the triplet p-wave pairing via the Kohn-Luttinger mechanism in these gases. The recent results on two-dimensional Fermi-gas preparation and observation of fluctuational phenomena related to the Berezinskii-Kosterlitz-Thouless transition in those gases will also be reviewed.
In addition we shall briefly discuss recently experimentally discovered BCS-BEC crossover and anomalous superconductivity in bilayer graphene and a possible role of graphene and 2D optical lattices as ideal systems for studying all the effects considered in this review.
Physics–Uspekhi, 2019, 62
Received: January 18, 2018
Revised: October 3, 2018
Accepted: October 31, 2018
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