Superconductivity of TaS2-xSexlayer compounds at high pressure

The superconducting transition temperatures for layer compounds in the system TaS 2-x Se x have been measured as a function of hydrostatic pressure up to 25 kbar. When the coordination of the metal atoms is purely trigonal prismatic, T c is strongly enhanced by pressure, whereas for mixed octahedral-trigonal prismatic coordination the increase of T c is very much smaller. Increasing the interlayer spacing by intercalation reduces the influence of pressure upon T c such that for expansions >or=6 AA T c is essentially independent of pressure. It is suggested that an increase in the overlap of the d z2 wavefunctions in the interlayer region is responsible for the increase of T c .