Coupling Lattice Instabilities Across the Interface in Ultrathin Oxide Heterostructures

Oxide
heterointerfaces constitute a rich platform for realizing
novel functionalities in condensed matter. A key aspect is the strong
link between structural and electronic properties, which can be modified
by interfacing materials with distinct lattice symmetries. Here, we
determine the effect of the cubic-tetragonal distortion of SrTiO3 on the electronic properties of thin films of SrIrO3, a topological crystalline metal hosting a delicate interplay between
spin-orbit coupling and electronic correlations. We demonstrate that
below the transition temperature at 105 K, SrIrO3 orthorhombic
domains couple directly to tetragonal domains in SrTiO3. This forces the in-phase rotational axis to lie in-plane and creates
a binary domain structure in the SrIrO3 film. The close
proximity to the metal–insulator transition in ultrathin SrIrO3 causes the individual domains to have strongly anisotropic
transport properties, driven by a reduction of bandwidth along the
in-phase axis. The strong structure–property relationships
in perovskites make these compounds particularly suitable for static
and dynamic coupling at interfaces, providing a promising route towards
realizing novel functionalities in oxide heterostructures.

氧化物异质结（oxide heterointerfaces）是凝聚态物理领域实现新奇功能的优质平台。其核心特征之一是结构与电子性质间存在强关联，而通过与具有不同晶格对称性的材料构筑异质界面，可对该关联进行有效调控。本文研究了钛酸锶（SrTiO3）的立方-四方畸变对铱酸锶（SrIrO3）薄膜电子性质的影响——铱酸锶是一类拓扑晶体金属（topological crystalline metal），其自旋轨道耦合（spin-orbit coupling）与电子关联（electronic correlations）之间存在微妙的相互作用。研究表明，在105 K的转变温度（transition temperature）以下，铱酸锶的正交畴（orthorhombic domains）会与钛酸锶的四方畴（tetragonal domains）直接耦合。该效应迫使同相旋转轴处于面内（in-plane），并在铱酸锶薄膜中形成二元畴结构（binary domain structure）。超薄铱酸锶紧邻金属-绝缘体转变（metal–insulator transition）临界点，使得单个畴呈现出强烈的各向异性输运（anisotropic transport）特性，该特性源于同相轴方向上的带宽（bandwidth）缩减。钙钛矿（perovskites）材料中普遍存在强结构-性能关联，使得这类化合物特别适合在界面处实现静态与动态耦合，为在氧化物异质结构中实现新奇功能提供了极具前景的研究途径。