Copper pyrites CuS2 and CuSe2 as anion conductors -: art. no. 155104

CuS2 and CuSe2 with pyrite structures were systematically studied by transport, magnetization, and specific-heat measurements. In remarkable contrast to other 3d transition-metal pyrites, a clear indication of strong electron correlations was absent in the electronic properties of Cu pyrites. We interpret this as a consequence of the dominant chalcogen p character rather than copper d character at the Fermi level. Photoemission results indeed support this picture, indicating that the Cu is predominantly monovalent. We therefore conclude that Cu pyrites, CuS2 and CuSe2, can be viewed as anion conductors.