新型磁性外尔半金属的强磁场/高压物性研究

Magnetic Weyl semimetals usually host time-reversal symmetry breaking and long-range magnetic order, in which the electron correlations cooperate with band topology and spin-orbital interactions. Due to the coupling between topological Weyl semimetals and Mott physics/magnetism, it is possible to create some exotic topological quantum states and phenomena, which are absent in the non-interacting systems. Here we will focus on the physical properties of layered kagome frustrated materials Mn3(Sn,Ge) and Co3Sn2(S,Se)2, such as band topology and anomalous Hall effect. By combing the quantum magnetotransport, Hall resistance, and magnetic susceptibility measurements under high magnetic field, high pressure and low temperature, as well as Raman spectroscopy and x-ray diffraction experiments, we will systematical investigate the pressure-dependent band topology and anomalous Hall effect in these materials, constructing the magnetic field-pressure-temperature phase diagram. The results will probably elucidate the evolutions of the crystal structure, topological-correlated electronic states, and magnetism under pressure, accompanied by the emergent quantum states and quantum effects due to the pressure-tuned interactions between the band topology, electron correlations, and spin-orbital couplings.

磁性外尔半金属通常具有时间反演对称性破缺和长程磁有序，其中电子关联与能带拓扑、自旋轨道耦合之间的协同作用使外尔半金属和莫特物理或磁性耦合起来，可能产生非相互作用体系中难以观察到的新奇拓扑量子态和量子效应。本项目将针对磁性外尔半金属中的能带拓扑、反常霍尔效应等物理属性，选取层状kagome晶格阻挫的Mn3(Sn,Ge)和Co3Sn2(S,Se)2为研究对象，利用金刚石对顶砧装置开展强磁场、高压、低温综合极端条件下的量子输运、霍尔电阻和磁化率测量，结合高压下的拉曼光谱和同步辐射X射线衍射实验，详细研究磁性外尔半金属压力下的能带拓扑特性和反常霍尔效应，构筑磁场-压力-温度相图，阐明压力下晶体结构、电子态及磁性的演化规律，探索体系中能带拓扑与电子关联、自旋轨道耦合的协同作用在压力调控后可能出现的新奇量子态和量子效应。

磁性拓扑半金属由于磁性与非平庸拓扑电子结构作用而表现出丰富的物理性质，为拓扑自旋电子学提供了新平台。同时，其电子结构对晶体结构及磁结构的变化非常敏感，因而通过晶格的外部扰动可以有效调控其拓扑属性，进而可能诱导新奇量子态和量子效应。本项目以磁场和压力作为主要调控参量，通过结合综合极端条件下的量子输运、拉曼光谱、同步辐射X射线衍射实验和理论计算，系统研究了新型磁性半金属中晶体结构、拓扑电子态随压力的演化规律，构筑磁场-压力-温度相图，揭示了能带拓扑与电子关联作用在压力调控后可能出现的新奇量子态。主要研究成果包括：1、揭示了反铁磁狄拉克半金属NdSb中压力诱导的铁磁外尔半金属相，伴随立方-四方结构相变，并构筑完整的压力-磁场-温度相图；2、发现了铁磁外尔半金属Co3Sn2S2中反常霍尔效应可以被压力削弱甚至完全抑制，伴随低压区普通霍尔系数由正值变为负值，即载流子类型发生转变；3、发现了压力对反铁磁外尔半金属Mn3Sn中反常霍尔有明显的抑制现象，可能伴随反铁磁性逐渐被削弱甚至消失；4、揭示了拓扑节点线半金属Ta2PdSe6压力诱导的Lifshitz相变和超导电性。

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