拓扑半金属强磁场诱导奇异输运性质的研究

Topological electronic state has become one of the hot topics in the multi-disciplinary of condensed matter physics and materials science. Over the years, many topological semimetal systems with exotic states induced by magnetic field have been discovered and host a fertile landscape of intriguing phenomena. However, the high-field behavior of those topological materials remains poorly explored owing to the limited experimental approaches in such extreme conditions. On the basis of our previous expertise in this topic, we propose here to study the magneto-transport properties of several topological semimetals with relatively low quantum limit. Primary emphasis will be placed on the following important aspects: (1) We will study how high field exotic states of ZrTe5 (such as logarithmic quantum oscillation and quantum hall effect) evolve in the presence of pressure/ electrical field and illustrate the relation between those exotic states and their topologic state; (2) In order to explore the exotic states after Weyl point Annihilation transition, we propose to study thermoelectric properties of Weyl semimetal TaAs and TaP in high magnetic field; (3) we will study the magentotransport properties of mesoscopic devices made from topological semimetal to explore the exotic phenomena induced by surface Fermi arc. Our experiments are therefore of general interest and will help guiding future research into understanding the exotic electronic state and the unusual physical phenomena in intense magnetic field for topological materials.

拓扑材料是近期凝聚态物理学和材料科学等多学科领域研究关注的热点之一。现有的研究表明在强磁场的诱导下拓扑半金属会表现出许多奇异的物理性质。由于所需磁场较高（>20T），这类研究一般需要在强磁场装置中进行。极端条件下（强磁场、低温）研究手段的匮乏制约了我们深入地理解这些现象背后的物理机制。在本项目中，我们将依托于稳态强磁场装置，利用自主研发的一些特色测量手段和调控手段对以下几个问题展开研究: 1、通过压力、电场等调控手段对ZrTe5的高磁场奇异量子态进行调制，澄清它们与拓扑态之间的关联；2、通过强磁场下热电效应、面间电阻等物性的测量，对TaAs、TaP等外尔半金属磁场诱导的奇异相变展开研究，并揭示其背后的物理内涵；3、研究几类拓扑半金属介观器件在强磁场下的输运性质，探索由费米弧表面态导致的奇特现象。项目的完成将有助于我们对拓扑材料强磁场诱导的奇异电子态以及相关反常物理现象的深入理解。

在本项目的支持下，申请人依托于强磁场装置发展了热电效应、隧道电流谱等一系列物性表征技术。利用这些独具特色的测试技术，项目团队聚焦于拓扑材料强磁场诱导的奇异电子态以及相关反常物理现象的研究。项目执行期间申请人以主要作者（一作/通讯）发表论文4篇，包括一篇Nature Physics，一篇Physical Review Letters，另外还有多篇论文正在审稿中。主要工作包括：1）通过研究ZrTe5强磁场下的塞贝克/能斯特效应，揭示了能带反转这一拓扑特性导致的反常热电效应; 2）通过研究NbAs纳米片巨大的二倍频电阻，澄清了一种由热电效应导致的非互易电输运机制；3）通过研究β-钨超导薄膜上临界磁场，观测到了一种由厚度调控的普适类。4）通过研究少层2M-WS2超导的上临界磁场以及超导能隙随磁场的演化，首次在实验上发现了自旋-轨道-宇称耦合超导电性 。