Low Temperature Physics: 46, 516 (2020); https://doi.org/10.1063/10.0001056
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
Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX 78249, USA
Received November 8, 2019, published online March 24, 2020
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.