Insulator-to-Metal Transition at Oxide Interfaces Induced by WO 3 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.