Low Temperature Physics: 46, 516 (2020); https://doi.org/10.1063/10.0001056
Fizika Nizkikh Temperatur: Volume 46, Number 5 (May 2020), p. 613-621    ( to contents , go back )

Collective-mode dispersion of atomic Fermi gases in a honeycomb optical lattice: speed of sound of the attractive Kane–Mele–Hubbard model at half filling

Zlatko Koinov

Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX 78249, USA
E-mail: Zlatko.Koinov@utsa.edu
pos Анотація:

Received November 8, 2019, published online March 24, 2020

Abstract

We examine the superfluid states that emerge in the Kane–Mele model as a result of the on-site shortrange attractive interaction U. The collective-mode dispersion is defined by the solutions of the Bethe–Salpeter (BS) equation in the generalized random phase approximation. The slope of the low-energy (Goldstone) mode and the corresponding sound velocity at half filling, calculated within the BS formalism, has been compared with the corresponding results obtained previously by the T-matrix approximation. The difference between the two approaches is that the T-matrix approximation takes into account only the ladder diagrams, and neglects the bubble ones. For this reason, the sound velocity in the direction toward point M, calculated within the T-matrix approximation, is about 4% less than the result obtained by employing the BS equation.

Key words: collective modes, sound velocity, superfluid state.

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