Impurity and fluctuation effects in charge-density-wave superconductors

We formulate a theory of a charge-density-wave (CDW) distorted superconductor, in the presence of impurities and CDW fluctuations. This theory is expected to be applicable to the layered compound 2H-NbSe2. Our primary aim is to compute the superconducting density of states Ns(). We also obtain the temperature dependence of the order parameter. We show, when all other parameters are fixed, that nonmagnetic impurities will raise the superconducting transition temperature and. Since the CDW gap WQ is expected to decrease with concentration, this effect should be even more pronounced. For nonmagnetic impurities, Ns() is found to be "BCS-like" with a gap at BCS, with subsidiary structure at =(2+WQ2)12. As the nonmagnetic impurity concentration is further increased this structure rounds out and Ns() approaches the strict BCS limit. CDW fluctuation effects are expected to lead to fine structure in Ns() at the characteristic phonon frequency. In principle, an analysis of (future) tunneling data will give detailed information about the CDW excitations, some of which has been obtained from Raman spectroscopy. © 1982 The American Physical Society.