Concurrent weak localization and double Schottky barrier across a grain boundary in bicrystal SrTiO3

Stoichiometric SrTiO3 (STO) is a wide band-gap insulator in which oxygen deficiency generates a low-temperature metallic ferromagnetic state. Here, we report weak ferromagnetic-like and metallic transport in oxygen-deficient bicrystal of STO with a low-temperature electron mobility and surface carrier density of 2800cm2V-1s-1 and 3.500×1016cm-2, respectively. Moreover, we show that magnetotransport behavior in the bulk and across the grain boundary (GB) in STO single crystals are significantly different. In the bulk, our magnetotransport results agree with those reported in the literature. Importantly, low-temperature magnetotransport across the GB shows a disorder-induced metal-insulator transition, and it is modeled as a quasi-two-dimensional system below 10 K that accounts for weak localization (WL), supported by electron-electron, electron-phonon, and Hikami-Larkin-Nagaoka (HLN) quantum interference models. The HLN model accounts for realistic length scales: the dephasing length Lφ, and the spin-orbit (SO) scattering length LSO, which are comparable to the electron mean-free path, resembling the surface-conducting nature across the GB. Our experimental work shows the importance of structural defects in the interpretation of magnetotransport in SrTiO3 and shows that WL is concurrent with a double Schottky barrier at the GB interface.