Anomalous electronic transport in CuIr2S4 and CuIr2Se4

The resistivity (rho) and the thermopower (S) of spinel-type compounds CuIr2S4 and CuIr2Se4 have been measured at temperatures from 2 to 900 K under magnetic field from 0 to 15 T. The thermopower of both compounds is positive in the metallic phase except for the low-temperature region in CuIr2Se4. It is also positive in the insulating state of CuIr2S4, implying p-type charge carriers, in agreement with the recent photoemission results. The low-temperature resistivity of CuIr2S4 is well described by Efros-Shklovskii variable-range hopping conductivity mechanism: rho = rho(0) exp[(T*/T)(1/2)]. The most unusual feature of the transport is that the resistivity of both compounds in the metallic state reveals an activation type of the temperature dependence. (C) 2000 Elsevier Science B.V. All rights reserved.