“…To date, the largest mobility of 140,000 cm 2 /Vs has been observed when STO is interfaced with γ-Al2O3 (GAO) [3], where oxygen vacancies account for the formation of the interface conductivity [3,17,18]. Contrary to the majority of other STO-based heterostructures [19,20], the highest mobilities in GAO/STO surprisingly occur at a high sheet carrier density exceeding 10 14 cm -2 , despite the abundance of oxygen vacancy donors in STO, which act as scattering sites [3,18,21]. A spatial separation of the electrons and donors within STO was recently proposed to be the origin of the high mobility in GAO/STO at low temperatures [21], but it remains to be settled unambiguously.…”