Unexpected Anisotropic Two Dimensional Electron Gas at the LaAlO3/SrTiO3 (110) Interface

TL;DR

This paper reports the surprising discovery of an anisotropic two-dimensional electron gas at the LaAlO3/SrTiO3 (110) interface, challenging previous assumptions about polarization discontinuity effects based on crystal orientation.

Contribution

It demonstrates the existence of conductivity and anisotropy at the (110) interface, supported by microscopy and theoretical calculations, revealing new physics in oxide interfaces.

Findings

Unexpected conductivity at LaAlO3/SrTiO3 (110) interface

Strong anisotropy in conductance depending on oxygen pressure

Atomic structure explains the observed electronic behavior

Abstract

The observation of a two dimensional electron gas (2DEG) (1, 2), superconductivity (3, 4), magnetic effects (5) and electronic phase separation (6-8) at the interfaces of insulating oxides, especially LaAlO3/SrTiO3, has further enhanced the potential of complex oxides for novel electronics. The occurrence of the 2DEG is strongly believed to be driven by the polarization discontinuity (9) at the interface between the two oxides. In this scenario, the crystal orientation plays an important role and no conductivity would be expected for e.g., the interface between LaAlO3 and (110)-oriented SrTiO3, which should not have a polarization discontinuity (10, 11). Here, we report the observation of unexpected conductivity at the LaAlO3/SrTiO3 interface prepared on (110)-oriented SrTiO3. The conductivity was further found to be strongly anisotropic, with the ratio of the conductance along the different directions parallel to the substrate surface showing a remarkable dependence on the oxygen pressure during deposition. The conductance and its anisotropy are discussed based on the atomic structure at the interface, as revealed by Scanning Transmission Electron Microscopy (STEM) and further supported by density functional theory (DFT) calculations.