Resonant tunneling through two symmetric centers

Abstract

A one-dimensional model of resonant tunneling through two symmetric localized centers is considered. The goal is to get an idea of the mechanism of c-axis transport in layered cuprates of the 214 family, where the doping is not by increasing of the oxygen content but by substitution of La by atoms of other valences. It is shown that two cases are possible. If the distance between the resonant sites is less than one half of the barrier thickness, the dependence on energy of the tunneling probability (transparency coefficient) contains two close maxima divided by a deep minimum. The transparency in the maxima is of the order of unity. In the opposite case the maxima merge into one, and the transparency is exponentially small, although much larger than the probability of direct tunneling. The structure of ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ corresponds to the first case.