Electron-optical phonon coupling in superconductors

Abstract

We investigate the role of the optical phonons in superconductivity in the case of compounds with different atomic massesM _k . We show that the electron mass enhancement factorλ is independent ofM _k if the force constant matrix is mass independent. However, when usingλ to calculateT _c , it must be decomposed into its acoustical and optical contributions, which depend separately onM _k . We study interference scattering from a light and a heavy mass and its contributions toλ within the free electron approximation. Numerical results are presented for a rocksalt structure crystal with nearest and next nearest neighbour coupling. These results indicate that the optical phonon contributions toλ may substantially increaseT _c .