Effective particle-particle interaction in incommensurable CDW systems

We study the pairing potential induced by fluctuations around a static charge-density wave (CDW) with scattering Vector Q by means of the Frohlich transformation. For general commensurability M, defined as \k + MQ] = \k], we find that the intraband pair scattering within the M subbands scales with M, whereas the interband pair scattering becomes suppressed with increasing CDW order parameter. As a consequence, superconductivity is suppressed when the Fermi energy is located between the subbands, as it is usually the case for nesting induced CDWs, but due to the vertex renormalization it can be substantially enhanced when the chemical potential is shifted sufficiently inside one of the subbands. Additional magnetic stripe order restricts this enhancement to the case in which the stripes are half-filled.