Anomalous electronic transport in CuIr 2S 4 and CuIr 2Se 4

Abstract

The resistivity ( ρ) and the thermopower ( S) of spinel-type compounds CuIr 2S 4 and CuIr 2Se 4 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 CuIr 2Se 4. It is also positive in the insulating state of CuIr 2S 4, implying p-type charge carriers, in agreement with the recent photoemission results. The low-temperature resistivity of CuIr 2S 4 is well described by Efros–Shklovskii variable-range hopping conductivity mechanism: ρ=ρ 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.