Anisotropic two-dimensional electron gas at the LaAlO3/SrTiO3 (110) interface

Abstract

The observation of a high-mobility two-dimensional electron gas between two insulating complex oxides, especially LaAlO3/SrTiO3, has enhanced the potential of oxides for electronics. The occurrence of this conductivity is believed to be driven by polarization discontinuity, leading to an electronic reconstruction. In this scenario, the crystal orientation has an important role and no conductivity would be expected, for example, for the interface between LaAlO3 and (110)-oriented SrTiO3, which should not have a polarization discontinuity. Here we report the observation of unexpected conductivity at the LaAlO3/SrTiO3 interface prepared on (110)-oriented SrTiO3, with a LaAlO3-layer thickness-dependent metal-insulator transition. Density functional theory calculation reveals that electronic reconstruction, and thus conductivity, is still possible at this (110) interface by considering the energetically favourable (110) interface structure, that is, buckled TiO2/LaO, in which the polarization discontinuity is still present. The conductivity was further found to be strongly anisotropic along the different crystallographic directions with potential for anisotropic superconductivity and magnetism, leading to possible new physics and applications.

Anisotropic two-dimensional electron gas at SrTiO 3 (110)

“…Our results explain the dopant-dependent anisotropy at the (110)-oriented LaAlO 3 /SrTiO 3 interface that was observed recently (22). Although both d xy -and d yz =d zx -derived Fermi surfaces are strongly anisotropic, the difference along the [001] and ½110 directions themselves is not very pronounced at higher carrier density, when both ellipsoids are occupied (Fig.…”

Two-dimensional superconductivity at (110) LaAlO3/SrTiO3 interfaces

“…Recently, at (110) orientated LAO/STO interfaces, unexpected high mobility metallic conductivity was also found. 17,18 The quasi 2DEG of the (110) LAO/STO interfaces has similar values of the sheet carrier density, room temperature resistivity and electronic mobility to those found at the (001) LAO/STO interfaces. In addition, a unified mechanism of the origin of the 2DEG for both (001) and (110) LAO/STO interfaces has been proposed.…”

Electronic Reconstruction at the Interface Between Band Insulating Oxides: The LaAlO3/SrTiO3 System

“…Some attempts in these directions include the growth of LaAlO 3 /EuTiO 3 /SrTiO 3 [87], showing low T ferromagnetism and 2D-conductivity, LaTiO 3 /LaCrO 3 /SrTiO 3 systems [88], the deposition of ferromagnetic polar layer on STO and other oxides, or the use of other 3d 0 materials like KTaO 3 . Similarly, the atomic control achieved in the growth of these oxides has now provided ways to realize heterostructures where polar discontinuity can be engineered and modified using (110) and (111) interfaces [89,90]. In the latter case, theoretical papers have suggested interesting topological protected states with some analogies with topological insulators [91].…”