Coulomb correlations and two-channel conduction in CuIr2S4 and CuIr2Se4 compounds

The resistivity rho of CuIr2S4 and CuIr2Se4 have been measured at temperatu res from 2 to 300 K under hydrostatic pressures up to 2 GPa. The conductivi ty a at low temperature in the insulating phase of CuIr2S4 is expressed as follows: sigma = exp[ - (T-i*/T)(0.5)]. The pressure dependence of the acti vation energy and metal-insulator transition temperature give evidence that Coulomb correlations are important. Appearance of the insulating phase in CuIr2Se4 is at a lower pressure than it had been assumed. The total resisti vity under pressure can be represented as the resistivity in two parallel c hannels: the metallic resistivity which is exponentially dependent on tempe rature and the semiconducting one. The effective cross-section of the semic onducting channel rapidly increases with pressure above 1 GPa. (C) 2001 Els evier Science B.V. All rights reserved.