Charge localization crossover from Mott to Efros-Shklovskii type variable range hopping mechanism in In1−xPbxTe compounds

Abstract

We have investigated the electrical transport properties of the In1−xPbxTe compounds. Small Pb-doping is not incorporated in the In-site but randomly distributed in the matrix, found from the X-ray diffraction and elemental mapping by energy-dispersive X-ray spectroscopy measurements. The random distribution of Pb elements induces robust charge localization at low temperatures causing the variable range hopping (VRH) transport. The electrical resistivity ρ(T) of pristine InTe exhibits semiconducting to metal transition near 175 K. From the analysis of temperature exponent, we found that the VRH transport is changed from Mott to Efros-Shklovskii (ES) type with decreasing temperature, where the crossover temperatures are found as 14.4 K (x=0.01) and 13.36 (x=0.02), respectively. The magnetoresistance (MR) of the InTe shows that the weak antilocalization at low temperature (T≤3 K) and low magnetic field (H≤1 T) competes with weak localization with increasing temperature (T≥5 K). It is noteworthy that small Pb-doping exhibits unconventional negative MR (NMR) behavior because it is not a magnetic or topological material. The unconventional NMR behavior of Pb-doped compounds is attributed to the quantum mechanical interference under the magnetic field in ES type VRH transport. The charge localization crossover from Mott to ES type VRH transport mechanism suggests the strong electron-electron Coulomb interaction in the compounds, leading to the significant change of density of states and inducing the Coulomb gap at low temperatures.