Effect of anisotropy on the energy gap and the critical temperature in a strongly coupled layered superconductor

Abstract

The Eliashberg theory is applied to study the critical temperature and a gap anisotropy of strongly coupled layered superconductors. The electron-ion pseudopotential, the electron, and the phonon energy spectra are proposed to be anisotropic in layered crystals with an open Fermi surface. The anisotropic electron-phonon spectral density [α2F(z)]pz is found to be expanded in cos(npzd) functions. Such an expression for [α2F(z)]pz demands the energy gap Δ(pz, ω) to present also as an expansion in the harmonic functions. Therefore, the value of the energy gap along the c axis should display pz dependence. The value of Δ differs from that obtained by in-plane measurements. By using McMillan's method we present each amplitude Δn(ω) in the harmonic expansion of the energy gap Δ(pz, ω) by trial function. The infinite set of coupled homogeneous equations for Δ0, Δ1, Δ2, … is obtained, the solution of which should yield the critical temperature. We estimate only those equations which include the three amplitudes, Δ0, Δ1, and Δ2, in the harmonic expansion of the energy gap. An approximate calculation of Tc shows that the critical temperature must be enhanced due to the influence of anisotropy.

Source-reported materials — not catalogue approval

Similar papers