Hopping transport in SrTiO3 / Nd1−xTiO3 / SrTiO3 heterostructures

Electronic transport near the insulator-metal transition is investigated in the molecular beam epitaxy-grown $\mathrm{SrTi}{\mathrm{O}}₃$/$\mathrm{N}{\mathrm{d}}_{1\text{\ensuremath{-}}x}\mathrm{Ti}{\mathrm{O}}₃$/$\mathrm{SrTi}{\mathrm{O}}₃$ heterostructures using temperature dependent magnetotransport measurements. It was found that Nd vacancies introduce localized electronic states resulting in variable range hopping transport at low temperatures. At a fixed Nd-vacancy concentration, a crossover from Mott to Efros-Shklovskii variable range hopping transport was observed with decreasing temperature. With increasing disorder, a sign reversal of magnetoresistance from positive to negative was observed revealing interplay between intra-state interaction and the energy dependence of the localization length. These findings highlight the important role of stoichiometry when exploring intrinsic effects using heterostructure and interfaces in addition to offering broad opportunities to tailor low temperature transport using nonstoichiometry defects.