CuCl: Some facts and thoughts on high-temperature superconductivity

CuCl under high pressure shows many phases, some of which are associated with moderately high conductivity. One of these at temperatures even somewhat above liquid nitrogen temperature will, under appropriate conditions, give a Meissner-effect-like response. In this paper, an excitonic-insulator-based mechanism for the various phenomena surrounding this event, founded upon indirect d/s overlap, is shown not to be a tenable option. Due study of the available literature shows that CuCl is incipiently unstable with regard both to cation sublattice disorder and to chemical disproportionation. Under pressure it is found that the situation becomes very complex and unusual, and does indeed present some hope that circumstances favourable to the appearance of excitonically mediated superconductivity could be realizable here.