The high critical field Chevrel phases

Abstract

Some of the Chevrel phase material of the type M x Mo 6X 8 (M = metal, X = S, Se, Te) present extraordinarily high critical fields ( H c2 of PbMo 6S 8 is about 600 kG). The reason for this is to be found in the particular pseudo molecular crystal structure of these compounds producing narrow bands at the Fermi surface. Single crystal investigations have revealed a surprisingly large anisotropy of about 15–20% in several of these materials. Of particular interest is the possibility in these materials to substitute M by magnetic rare earth ions without destroying the superconductivity. The anomalous behaviour of H c2 in these latter materials allows us to study the different pairbreaking mechanisms present in the Chevral phases.