Small-polaron variable-range hopping in quasi-two-dimensional materials: application to PrBa2Cu3-xGaxO7-y

We have developed a theory for variable-range hopping (VRH) due to small po larons in quasi-two-dimensional systems at high temperatures. We included t he effects of temperature, electric fields, magnetic fields and scattering in the derivation of the conductivity. We found that the conductivity for q uasi-two-dimensional systems depends on these factors differently from thre e-dimensional systems. We applied the theory to explain the resistivity dat a of PrBa2Cu3-xGaxO7-y at high temperatures (T > 150 K). To explain the low -temperature data (T < 150 K), we used the pure electron VRH mechanisms. Go od agreement between theory and experiment was found.