Chikina Alla, Christensen Dennis V, Borisov Vladislav, Husanu Marius-Adrian, Chen Yunzhong, Wang Xiaoqiang, Schmitt Thorsten, Radovic Milan, Nagaosa Naoto, Mishchenko Andrey S, Valentí Roser, Pryds Nini, Strocov Vladimir N
Swiss Light Source, Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland.
Institute of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus, Denmark.
ACS Nano. 2021 Mar 23;15(3):4347-4356. doi: 10.1021/acsnano.0c07609. Epub 2021 Mar 4.
The rich functionalities of transition-metal oxides and their interfaces bear an enormous technological potential. Its realization in practical devices requires, however, a significant improvement of yet relatively low electron mobility in oxide materials. Recently, a mobility boost of about 2 orders of magnitude has been demonstrated at the spinel-perovskite γ-AlO/SrTiO interface compared to the paradigm perovskite-perovskite LaAlO/SrTiO interface. We explore the fundamental physics behind this phenomenon from direct measurements of the momentum-resolved electronic structure of this interface using resonant soft-X-ray angle-resolved photoemission. We find an anomaly in orbital ordering of the mobile electrons in γ-AlO/SrTiO which depopulates electron states in the top SrTiO layer. This rearrangement of the mobile electron system pushes the electron density away from the interface, which reduces its overlap with the interfacial defects and weakens the electron-phonon interaction, both effects contributing to the mobility boost. A crystal-field analysis shows that the band order alters owing to the symmetry breaking between the spinel γ-AlO and perovskite SrTiO. Band-order engineering, exploiting the fundamental symmetry properties, emerges as another route to boost the performance of oxide devices.
过渡金属氧化物及其界面丰富的功能特性具有巨大的技术潜力。然而，要在实际器件中实现这一点，需要大幅提高氧化物材料中目前仍相对较低的电子迁移率。最近，与典型的钙钛矿-钙钛矿LaAlO₃/SrTiO₃界面相比，在尖晶石-钙钛矿γ-Al₂O₃/SrTiO₃界面上已证明电子迁移率提高了约2个数量级。我们通过使用共振软X射线角分辨光电子能谱对该界面的动量分辨电子结构进行直接测量，探索了这一现象背后的基本物理原理。我们发现在γ-Al₂O₃/SrTiO₃中移动电子的轨道有序存在异常，这使得SrTiO₃顶层中的电子态减少。移动电子系统的这种重新排列将电子密度推离界面，这减少了其与界面缺陷的重叠，并削弱了电子-声子相互作用，这两种效应都有助于提高迁移率。晶体场分析表明，由于尖晶石γ-Al₂O₃和钙钛矿SrTiO₃之间的对称性破缺，能带顺序发生了改变。利用基本对称性质的能带顺序工程，成为提高氧化物器件性能的另一条途径。
