Theory of surface polarons

We investigate the possibility that an electron may be trapped at the surface of an ionic crystal by the electron-surface optical phonon interaction. For a model Hamiltonian used earlier in a discussion of the inelastic scattering of low energy electrons by surface optical phonons, we find that for all values of the polaron coupling constant α, this trapping does occur. We refer to these surface states as surface polaron states. By the use of a variational procedure, we calculate the surface polaron binding energy and effective mass as a function of α. The present treatment does not include the coupling of the electron to bulk LO phonons.