LaTiO 3 /KTaO 3 interfaces: A New Two-Dimensional Electron Gas System

Emergent conducting channels at complex oxide interfaces display a wide range of solid state phenomena, ranging from superconductivity to magnetism. To date, the only transition metal oxide that has been found to host a conducting channel for a 2D electron gas (2DEG) is the perovskite SrTiO 3 . We present a new 2DEG system at the interface between a Mott insulator, LaTiO 3 , and a band insulator, KTaO 3 . For LaTiO 3 / KTaO 3 interfaces, we observe metallic conduction from 2 K to 300 K. One limitation of SrTiO 3 -based conducting oxide interfaces for electronics applications is the relatively low carrier mobility (0.5 - 10 cm 2 /Vs) of SrTiO 3 at room temperature. The mobility is a product of the carrier effective mass, an intrinsic property of the oxide band structure, and the carrier scattering rate, which is large in SrTiO 3 due to a strong interaction of carriers with optical phonons. By using KTaO 3 , we achieve mobilities in LaTiO 3 / KTaO 3 interfaces of 21 cm 2 /Vs at room temperature, a factor of 3 higher than observed in doped bulk SrTiO 3 . Ab initio calculations predict the formation of a 2DEG in the interfacial KTaO 3 layers that resides in bands having Ta 5d character. We attribute the higher mobility in the KTaO 3 2DEGs, compared to SrTiO 3 2DEGs, to the smaller effective mass for electrons in KTaO 3 in these bands.