二维量子材料的低温输运性质及调控研究

Recently, exploring the exotic transport properties of two-dimensional quantum materials and tuning them through various methods have been hot topics in condensed matter physics. beta-PtBi2 has recently been identified as a triple degenerate topological semimetal, however, the Fermi level does not cross the triple degeneracy point and the nearby bulk states are complex, so the transport properties dominated by the triple degenerate fermions were not detected, but its quasi-two-dimensional structure provides further opportunities tuning the electronic properties. Recently, theoretical calculations predict the topological band structure of the transition metal compound Cu2-xTe, then the linear magnetoresistance and abnormal resistance behavior near 150K were preliminarily observed. However, its transport properties at low temperature have not been systematically explored so far. In this project, the size effect and ionic liquid technology will be combined to tune the transport properties of beta-PtBi2. We will establish the thickness dependence of its properties, at the same time, through regulate its Fermi levels on a large scale, the novel quantum phenomena induced by triple degenerate fermions will be studied. Besides, we will systematic study the transport properties of bulk Cu2-xTe under low temperature to explore its topological properties and understand its abnormal resistive behavior. Then we will further explore its possible exotic phenomena and physics through the size effect and ionic liquid technology.

探索二维量子材料中的奇异输运性质并通过多种手段对其进行调控是最近凝聚态物理研究的热点。beta-PtBi2最近被证实是三重简并拓扑半金属，由于费米能级没有穿越三重简并点且附近体带较为复杂，实验没有观测到三重简并费米子主导的输运性质，但其准二维结构为进一步调控其电子性质提供了可能。最近理论预言了过渡金属层状化合物Cu2-xTe的拓扑能带结构，实验上初步观测到线性磁阻和150K附近电阻异常行为，但其低温下的输运性质还没有被系统的探索。本课题中，我们将结合尺寸效应和离子液体技术调控beta-PtBi2的输运性质，建立其物性与材料厚度的依赖关系；并通过对它们费米能级的大范围调控，研究三重简并费米子诱导的新奇量子现象。此外，我们将在低温下系统的研究Cu2-xTe块材的输运性质，探索其拓扑特性并理解其电阻异常行为；在此基础上，通过尺寸效应和离子液体技术探索其可能蕴含的新现象、新物理。

探索二维量子材料中的奇异输运性质并通过多种手段对其进行调控是最近凝聚态物理研究的热点。本项目中，我们探索通过固相熔融法、自助溶剂法等多种方法合成更高质量的低维量子材料单晶样品。对一些材料如Cu2-xTe、EuSn2As2、SrIn2P2的单晶块材样品，我们系统的研究了它们在低温强磁场下的电学、磁学性质，发现了一系列新奇物理现象。通过研究，我们揭示了磁性拓扑绝缘体EuSn2As2复杂的磁结构与反常霍尔效应；准二维量子材料Cu2-xTe低温下的连续电荷密度波转变；Zintl相层状化合物SrIn2P2中的弱局域化现象与电子-声子耦合相互作用等。通过进一步优化实验方案并结合理论分析，我们阐明了部分量子效应的物理起源，深化了人们对这些材料低温物性的认知。同时，我们选取了几种二维拓扑半金属材料，如beta-PtBi2、beta-PdBi2和SnTaS2，对其进行了多场调控研究。我们通过研究温度、磁场、尺寸效应对其载流子性质、费米面变化进而电学性质的影响，建立了体系电学性质随厚度的演化相图，发现了一些新现象、新规律、新物理。我们发现了SnTaS2和beta-PdBi2随厚度减薄后无序度增强导致的超导转变温度逐渐被抑制的现象，以及SnTaS2中电子-声子相互作用主导的弱反局域化效应；我们还探测到beta-PdBi2和SnTaS2在临界厚度以下出现的二维量子振荡、高迁移率等可能的拓扑表面态的电输运信号等。这些结果为全面理解磁场、温度、尺寸等多场对低维量子材料性质的调控提供了重要实验依据。