The Eliashberg equations are solved for the transition temperature of a superconductor for the case that the phonons are harmonic but the electron-phonon interaction is anharmonic. The anharmonic interaction increases the transition temperature for the same coupling strength. Reentrant behavior is predicted for large anharmonicity.

• Received 6 March 1997

DOI:https://doi.org/10.1103/PhysRevB.56.8322