正交钙钛矿SrIrO3的本征电子结构和反常半金属基态调控研究

Recently, much attention has been paid to the 5d transition-metal oxides in which the interplay of spin-orbit coupling and electron correlations can induce many novel quantum states and emergent phenomena. Among various 5d-iridum oxides, the orthorhombic perovskite SrIrO3 exhibits an exotic narrow-band semimetal ground state originating from the underlying lattice symmetry. It has been theoretically predicted to possess topological nontrivial band structure, and its semimetallic ground state was indeed found to be highly tunable. Based on our preliminary results, we propose to investigate and tune the intrinsic properties of perovskite SrIrO3 by taking advantage of the high-pressure and high-temperature (HPHT) synthesis. On the one hand, we will optimize the HPHT conditions to obtain larger size SrIrO3 single crystals, and then characterize its bulk electronic structure and intrinsic physical properties with an aim to verify the theoretically predicted topological nontrivial band structure. On the other hand, we will purposely substitute various isovalent cations for Ir4+ so as to tune and access different ground states. These systematic studies will enable us to clarify the responses of the semimetallic ground state of SrIrO3 to the following factors including the perovskite orthorhombic distortion, spin-orbit coupling, electron correlation, and different 3d/4d-orbital magnetic ions. Through this project, we hope to deepen our understanding and to establish some guidelines for tuning the exotic properties of perovskite SrIrO3.

强自旋轨道耦合与电子关联的协同作用使得高轨道过渡金属氧化物呈现出许多新奇的量子态和演生现象。在众多的5d铱氧化物中，具有钙钛矿结构的SrIrO3因特殊的正交结构对称性表现出奇特的窄能带半金属基态，理论预测其具有拓扑非平庸的电子能带结构，而且最新的研究显示其半金属基态具有高度可调性。基于我们前期工作基础，本项目拟借助于高压高温合成手段，对SrIrO3钙钛矿开展系统深入的物性表征和调控研究。一方面，优化合成条件获得较大尺寸的单晶样品，全面表征其电子结构和本征物性，检验其可能的拓扑电子结构；另一方面，选择不同的等价态离子取代部分Ir4+，有针对性地对钙钛矿SrIrO3的基态进行调控，系统研究正交钙钛矿结构畸变、自旋轨道耦合、电子关联和不同轨道磁性离子对其半金属基态的影响，最终建立钙钛矿SrIrO3反常基态的调控规律和认识。

强自旋-轨道耦合与电子关联的协同作用使得钙钛矿SrIrO3具有窄能带半金属特性，并且非常靠近金属-绝缘体转变的临界点。在前期研究中，我们通过Ir位掺杂非磁性Sn4+离子实现了从顺磁半金属到反铁磁绝缘体的转变。在此基础上，本项目进一步通过Ir位掺杂多种等价态的非磁性离子实现对其磁电基态的有效调控并建立规律性认识。在本项目取得了如下进展：(1)通过小步长精细掺杂调控，确定了SrIr1-xSnxO3体系中形成反铁磁绝缘基态的临界掺杂组分x <= 0.03，并获得了Slater金属-绝缘体相变的光谱证据；(2)建立了Ir位掺杂等价态非磁型M4+离子对SrIrO3磁电基态的调控规律，厘清了钙钛矿结构畸变造成的电子关联和能带宽度U/W变化对反铁磁有序温度的定性影响规律，并通过带宽调控验证了该规律；(3)建立了磁性Cr4+掺杂SrIrO3引起的晶体结构和磁电性质演化的相图。这些研究结果为深入理解5d铱氧化物-钙钛矿SrIrO3的反常物性及其调控规律提供了关键实验依据。