Small-polaron variable-range hopping in quasi-two-dimensional materials: application to PrBa2Cu3-xGax07-y

Abstract

We have developed a theory for variable-rangehopping (VRH) due to small polarons in quasi-two-dimensionalsystems at high temperatures.We included the effects of temperature, electric fields, magnetic fields and scattering in the derivation of the conductivity. We found that the conductivity for quasi-two- dimensional systems depends on these factors differently from three- dimensional systems. We applied the theory to explain the resistivity data of PrBa2Cu3p,Ga,07-l, at high temperatures ( T > 150K). To explain the low- temperature data ( T < 150K), we used the pure electron VRH mechanisms. Good agreement between theory and experiment was found.