Level Shift of Rattling Atoms in Intermetallic Compounds

Abstract

A heavy atom enclosed in a large cage and interacting with metal electrons is considered. The interaction between the atom and the electrons causes a shift of the atomic energy levels. When the level spacing is smaller than k_BT, the shift turned out to vary with temperature according to logT. We consider a model, where the cage is represented by a potential of eight wells which are located at eight corners of a cube. We assume there is a localized “atomic” orbital at each well and a transfer integral between nearest neighbouring orbitals is considered. The electron–atom interaction renormalizes the transfer integral. The normalization factor involves logT and is the same as that in a two well problem.