Probing Quantum Confinement and Electronic Structure at Polar Oxide Interfaces.

Danfeng Li,Jean‐Marc Triscone,Sébastien Lemal,Alexandre Fête,Stefano Gariglio,Philippe Ghosez,Zhenping Wu,Margherita Boselli

doi:10.1002/advs.201800242

Abstract

Polar discontinuities occurring at interfaces between two materials constitute both a challenge and an opportunity in the study and application of a variety of devices. In order to cure the large electric field occurring in such structures, a reconfiguration of the charge landscape sets in at the interface via chemical modifications, adsorbates, or charge transfer. In the latter case, one may expect a local electronic doping of one material: one example is the two‐dimensional electron liquid (2DEL) appearing in SrTiO3 once covered by a polar LaAlO3 layer. Here, it is shown that tuning the formal polarization of a (La,Al)1− x(Sr,Ti)xO3 (LASTO:x) overlayer modifies the quantum confinement of the 2DEL in SrTiO3 and its electronic band structure. The analysis of the behavior in magnetic field of superconducting field‐effect devices reveals, in agreement with ab initio calculations and self‐consistent Poisson–Schrödinger modeling, that quantum confinement and energy splitting between electronic bands of different symmetries strongly depend on the interface total charge densities. These results strongly support the polar discontinuity mechanisms with a full charge transfer to explain the origin of the 2DEL at the celebrated LaAlO3/SrTiO3 interface and demonstrate an effective tool for tailoring the electronic structure at oxide interfaces.

Highlights

Polar discontinuities occurring at interfaces between two materials constitute both a challenge and an opportunity in the study and application of a variety of devices
In order to cure the large electric field occurring in such structures, a reconfiguration of the charge landscape sets in at the interface via chemical modifications, adsorbates, or charge transfer
One may expect a local electronic doping of one material: one example is the two‐dimensional electron liquid (2DEL) appearing in SrTiO3 once covered by a polar LaAlO3 layer

Summary

Polar discontinuities occurring at interfaces between two materials constitute

Functionalities offered by the interfaces between different materials have been the both a challenge and an opportunity in the study and application of a variety fundamental basis of modern electronic of devices. At the n3D,th (labeled in Figure 3c), the extension of the 2DEL is ≈10 nm for the LAO/STO interface and 31 nm for the LASTO:0.5/STO interface, values that agree with the estimation of the superconducting thickness extracted from the critical field measurements discussed above This suggests that the change in superconducting thickness and the confinement scale at the LASTO:0.5/STO interface is due to a reduced total charge density originating from a modified polar discontinuity (see discussion below). Despite the similar mobile carrier densities extracted from Hall measurements for the two interfaces,[32] calculations and superconducting critical fields measurements show that the increase in the characteristic thickness of the 2DEL for the LASTO:0.5/STO interface is a direct result of the reduced total transferred charges (from 0.5 to 0.25 e− per u.c.) upon modification of the polar discontinuity. This study shows that the control of the polar discontinuity at oxide interfaces by chemical composition is an effective tool for engineering novel electronic states in these compounds

Experimental Section

Findings

Conflict of Interest