[论文解读] Spin Orbit Coupling Assistant Correlated Semimetal SrIrO3: at two-Dimensional Scale

Lunyong Zhang, Y. B. Chen+1 more|arXiv (Cornell University)|Nov 22, 2015

Advanced Condensed Matter Physics被引用 3

一句话总结

本文研究了二维正交晶系 SrIrO3 薄膜，表明自旋-轨道耦合与电子关联共同驱动一个具有小电子和空穴口袋的半金属态。通过基底应变工程和厚度调控，该体系展现出可调的拓扑与磁性相，包括在极薄极限下转变为倾斜反铁磁绝缘体，凸显其在氧化物基拓扑量子材料中的潜力。

ABSTRACT

Spin orbit coupling provides a mechanism to lock the momentum of electron to its spin degree, recent years was revealed to be essential in arousing many novel physical behaviors. SrIrO3 is a typical metallic member of the strong spin orbit coupling iridate family. Its orthorhombic phase was confirmed as a particular spin orbit coupling assistant electron correlated semimetal with small electron and hole pockets, and was supposed to host versatile topological phases, with prospect of opening a new topological matter field based on oxides. The existing experiments have demonstrated that orthorhombic SrIrO3 can be easily synthesized at two dimensional scale films under the substrate lattice constraint, and the films display Fermi-liquid behavior in high temperature and generally two dimensional weak localization resulted metal insulator transition. The properties of orthorhombic SrIrO3 film are sensitive to the rotation and tilting angle, as well as the interlayer coupling of the IrO6 octahedras, consequently can be tuned through substrate strain engineering and size scale. For example, the film was approached a state similar to Sr2IrO4 at the ultrathin limit to several unit cell, becoming a canted antiferromagnetic semiconductor/insulator. The existing knowledges suggest urgent demands of researches on the superlattices constructed with orthorhombic SrIrO3, for further understanding the evolution mechanism of the electron structure, and so the relevant magnetic state and topological phases in the orthorhombic SrIrO3 and its family.

研究动机与目标

• 理解在晶格约束下二维正交晶系 SrIrO3 薄膜的电子与拓扑性质。
• 研究在维度降低条件下，自旋-轨道耦合与电子关联在关联半金属中的相互作用。
• 通过应变工程与厚度控制，探索磁性与拓扑相的可调性。
• 确定 SrIrO3 薄膜转变为绝缘态或半导体态的条件，例如倾斜反铁磁相。
• 为设计 SrIrO3 超晶格以探测涌现量子相奠定基础。

提出的方法

• 利用外延薄膜生长技术，在基底晶格约束下稳定二维正交晶系 SrIrO3。
• 通过晶格匹配基底实施应变工程，调节层间耦合与 IrO6 八面体倾斜。
• 测量电输运性质，识别高温下的费米液体行为及二维弱局域化。
• 分析薄膜厚度对电子结构的影响，特别是极薄极限（少数单胞）下的行为。
• 将 SrIrO3 薄膜的电子行为与 Sr2IrO4 进行比较，识别相变行为。
• 采用理论建模，阐释自旋-轨道耦合在稳定拓扑半金属态中的作用。

实验结果

研究问题

• RQ1 自旋-轨道耦合与电子关联如何共同稳定二维 SrIrO3 中的半金属态？
• RQ2 基底诱导的应变对 SrIrO3 薄膜的电子结构与磁序有何影响？
• RQ3 SrIrO3 薄膜的厚度如何影响金属-绝缘体转变及倾斜反铁磁性的出现？
• RQ4 能否通过调控 IrO6 八面体的倾斜与旋转角度来控制 SrIrO3 中的拓扑相？
• RQ5 SrIrO3 超晶格在何种条件下可容纳新颖的拓扑态或量子自旋液体样态？

主要发现

• 二维正交晶系 SrIrO3 薄膜在高温下表现出费米液体行为，表明存在相干准粒子态。
• 该薄膜表现出二维弱局域化，表明存在量子干涉效应，具有潜在的拓扑保护特性。
• 在极薄极限（少数单胞）下，SrIrO3 趋近于倾斜反铁磁绝缘态，与 Sr2IrO4 类似。
• SrIrO3 薄膜的电子性质对基底应变、八面体倾斜与旋转角度高度敏感。
• 通过外延应变可调控 SrIrO3 中的层间耦合与八面体畸变，从而实现对电子关联与自旋-轨道耦合的调控。
• 该体系存在小电子与空穴口袋，表明其具有关联半金属基态，且具有实现拓扑序的潜力。