Insulator-to-Metal Transition at Oxide Interfaces Induced by WO₃ Overlayers

Interfaces between complex oxides constitute a unique playground for two-dimensional electron systems (2DESs), where superconductivity and magnetism can arise from combinations of bulk insulators. The 2DES at the LaAlO 3 /SrTiO 3 interface is one of the most studied in this regard, and its origin is determined by the polar field in LaAlO 3 as well as by the presence of point defects, like oxygen vacancies and intermixed cations. These defects usually reside in the conduction channel and are responsible for a decrease of the electronic mobility. In this work, we use an amorphous WO 3 overlayer to obtain a high-mobility 2DES in WO 3 /LaAlO 3 /SrTiO 3 heterostructures. The studied system shows a sharp insulator-to-metal transition as a function of both LaAlO 3 and WO 3 layer thickness. Low-temperature magnetotransport reveals a strong magnetoresistance reaching 900% at 10 T and 1.5 K, the presence of multiple conduction channels with carrier mobility up to 80 000 cm 2 V –1 s –1, and quantum oscillations of conductance.