Superconducting Transition Temperatures of Cu(Co1-xMx)2S4

Abstract

Superconducting transition temperatures T c have been measured for s -wave superconductors Cu(Co 1- x M x ) 2 S 4 with varying x . The system is often considered to be a three dimensional version of the triangular lattice, because it has a three dimensional network of corner-sharing (Co 1- x M x ) 4 tetrahedra. As the M atom, Cr, Ir and Rh, which can substitute for Co, are used. Although T c decreases linearly in x , the suppression rates |d T c /d x | are much smaller than the values expected from the pair breaking due to magnetic impurities in s -wave superconductors. They are, of course, much smaller than those expected for the pair breaking due to non-magnetic impurities in superconducting systems with anisotropic order parameter. The behavior is very similar to that observed in the newly found superconductor Na z CoO 2 · y H 2 O, which has two-dimensional layers of CoO 2 triangular lattice. It suggests that a same mechanism of the T c suppression is working in the two systems and presents useful information on the symmetry of the superconducting order parameter of Na z CoO 2 · y H 2 O. Brief arguments of a possible mechanism of the T c suppression of the present system are given.