Self-consistent theory of phonon renormalization and electron-phonon coupling near a two-dimensional Kohn singularity

We show that the usual expression for evaluating electron-phonon coupling and the phonon linewidth in two-dimensional metals with a cylindrical Fermi surface cannot be applied near the wave vector corresponding to the Kohn singularity. Instead, the Dyson equation for phonons has to be solved self-consistently. If a self-consistent procedure is properly followed, there is no divergency in either the coupling constant or the phonon linewidth near the offending wave vectors, in contrast to the standard expression.