Transport properties of V-4 and Mo-4-cluster compounds: An electron glass?

DC and AC conductivity, thermopower and non-ohmic conduction properties have been reported for GaV(4)S(8) and GaMo(4)Se(4)Te(4). The transport properties indicate the formation of electron glass state at low temperature. In a simplified model the band spread of localised states, DOS and localisation length are estimated. Coulomb gap effects in variable range hopping (VRH) and AC conductivity sigma(ac)(omega) are found in the more ordered Mo(4) compound. Both the compounds show negative resistance behaviour at high current densities that may indicate the melting of the electron glass.