强磁场下烧绿石铱氧化物新奇量子态的调控和反常物性研究

Pyrochlore Iridates (A2Ir2O7,A=Y, Rare earth elements) have been attracting an exceptional attention for their combined effects of magnetic order, electronic correlation and spin-orbital coupling with comparable energy scales, harboring a wonderful platform to explore the exotic quantum phases and emergent phenomena among the strongly correlated electron systems. However, the scarcity of high quality single crystals become the bottleneck problem for further systematical research, thus the breakthrough of high quality single crystal will pave the way for discovering new emergent phases and related physical property. Motivated by the previous research works including our contributions in this area, this proposal will focus on the investigation of novel quantum states and unusual magnetotransport behaviors driven by high magnetic field. Based series of high quality A2Ir2O7（A=Pr,Nd,Dy,Er）single crystals, the following research work will be addressed:(1) Characterize the typical physical features of the metal-insulator quantum phase transition induced by high magnetic field, and establish the correlation between spin configuration and electronic structures. (2) Map out the high-field phase diagram from antiferromagnetic insulator to non-trival semimetal phases, reveal the possible novel quantum criticality phenomena and unusual magnetotransport behavior near the quantum critical points, clarify the physical origins of quantum phase transition. (3) To exploit the exotic quantum phases by simultaneously tuning the spin-orbit coupling and electron correlations under high magnetic fields and high pressure, and then understand the physical mechanism of multi-field tunable exotic quantum phases and anomalous behaviors.

烧绿石铱氧化物A2Ir2O7（A=Y,稀土元素）具备磁有序、电子关联和强自旋轨道耦合等多重竞争相互作用，呈现出许多新奇的量子态和反常物性，是当前强关联电子体系的前沿课题。高质量单晶缺乏成为制约当前物性研究的瓶颈，材料的突破将为探寻该体系中新奇量子态和物性提供锲机。本项目将在申请人前期研究基础上，以高质量烧绿石铱氧化物单晶样品为研究对象，着重开展强磁场下新奇量子态和物性的调控研究，包含如下工作：（1）探讨强磁场驱动的绝缘体-金属量子相变的典型性物理特征，揭示高场下自旋构型和电子结构之间的物理关联。（2）绘制强磁场下反铁磁绝缘相到半金属相量子相变的相图，探寻量子相变中可能的量子临界性或相变点附近的反常输运特性，澄清其物理机制。（3）探索强磁场和高压协同作用对奇异量子态和物性调控的新途径，对自旋-轨道耦合作用和电子关联作用进行共同调控，探讨多场调控下新奇异量子态和相关的反常物性行为。

稀土铱氧化物RE2Ir2O7(RE=稀土元素)，由于具备磁有序、拓扑电子态和电子关联作用的耦合和竞争，成为探寻新奇量子态和反常物性的重要平台。本项目围绕Pr2Ir2O7和Pr基体系中的量子自旋液体态以及强磁场下铱氧化物反常磁电输运特性开展研究，取得了一系列研究成果，丰富了关联电子体系中自旋量子态和拓扑电子态的新奇物性。具体研究成果包含：1）观测到铱氧化物Eu2Ir2O7单晶中非对称磁电阻和霍尔效应，提出界面磁耦合诱导非对称磁化反转的物理机制；2）发现强磁场(B>30T)下铱氧化物RE2BIrO6(B=Zn,Mg)的场致磁相变行为，绘制高场磁相图，论证了非磁性离子Zn2+/Mg2+(3d10/3d0)对Ir4+磁基态具备不同的调控作用；3）通过化学掺杂实现Pr2Ir2O7自旋液体半金属到反铁磁绝缘体的量子相变，揭示相关的反常电输运特性。4）拓展Pr基量子自旋液体材料新体系，揭示量子自旋液体态的低温热力学和磁激发特性。此外，在本项目资助下，我们拓展研究内容到强磁场(B>30T)下磁性半金属的场致磁相变和量子输运特性。以上研究结果，大部分以SCI学术论文形式发表，包含在Phys. Rev.系列期刊发表论文9篇。