Superconductivity and charge-density waves

A theory of two competing order parameters—superconductivity and charge-density waves—as applied to layered compounds is presented. Both effects are caused by the phonon-mediated attractive interaction between itinerant electrons in narrow-band materials. The interplay between superconductivity and charge-density waves is analyzed. The main results of our model calculation are: (i) all metallic charge-density systems should be superconducting at low temperatures: (ii) the presence of superconductivity tends to reduce the charge-density wave and vice versa; (iii) under some conditions it is possible to have a charge-density-wave—induced semiconductor which, at low temperatures, makes a transition to a superconducting state. This last case is examined in detail.