Influence of On-Site Coulomb Interaction on Parameters of Superconducting State in Two-Dimensional Lattices

M.M. Adamczyka, K.A. Kroka, K.P. Kosk-Jonieca, R. Szczęśniaka, b aDepartment of Theoretical Physics, Jan Długosz University in Częstochowa, al. Armii Krajowej 13/15, 42-200 Częstochowa, Poland bInstitute of Physics, Częstochowa University of Technology, al. Armii Krajowej 19, 42-200 Częstochowa, Poland

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The study examined the effect of electron correlations characterized by the on-site Coulomb integral (U) on the parameters of the superconducting state in two-dimensional model lattices: square and triangular. In the electronic dispersion relation, we included the U parameter using the Zubarev-type thermodynamic Green functions formalism. We determined the Eliashberg function (α2F(ω)) using standard analytical formulas. In particular, we examined the course of the electron density of state function (ρ(ε)) and α2F(ω) depending on U. Having the explicit Eliashberg functions, derived for specific values of the U parameter, we analyzed the influence of on-site electron correlations on the parameters of the superconducting state: the electron-phonon coupling constant (λ) and critical temperature (Tc). We obtained completely different results between the two systems under consideration: in a square lattice, for the increasing Coulomb repulsion force, the superconducting state disappears. In a triangular lattice, there is a range of U values for which the superconducting state is amplified. This is due to the decreasing (increasing) density of states at the Fermi level with the increase of the U parameter for a square (triangular) lattice.

DOI:10.12693/APhysPolA.139.578 topics: on-site Coulomb interaction, superconducting parameters, two-dimensional lattice