Minisubbands in electron excitation spectra of layered short-coherence-length superconductors.

Abstract

Quasiparticle excitation spectra of short-coherence-length layered superconductors ($\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{S}$) are considered as-suming a periodic alternation of the superconducting order parameter $\ensuremath{\Delta}(x)$ versus the lateral coordinate $x$ in the $c$ direction. The found self-consistent solution suggests that the electron-hole Andreev scattering in such a periodic $\ensuremath{\Delta}(x)$ causes the appearance of minisubbands in the electron spectrum of $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{S}$, in a "clean" limit manifested as periodic spikes in the density of electron states at energies ${E}_{n}=(2n+1){\ensuremath{\Delta}}_{0}$ (${\ensuremath{\Delta}}_{0}$ is the energy gap amplitude; $n$ is a natural number).