强磁场下的拓扑Dirac半金属输运特性研究

In recent years, topological semi-metal has attracted much attentions due to their exotic transport properties. ZrTe5 had been proved to be three-dimensional Dirac semi-metal (DSM) by recent experiments. However, the quantum transport properties of DSM under intense strong magnetic field is still lacking so far. Especially when the Fermi level of the system enters into the first Landau level n=1 (quantum limit) or n = 0 (ultra-quantum limit). Our previous experiments show that under a moderate magnetic field, the Fermi level of ZrTe5 can be driven to the quantum limit, revealing that ZrTe5 is an ideal platform to study the quantum transport properties of DSM under quantum limit or ultra-quantum limit. Moreover, due to its layered structure in ZrTe5, field effect device can be easily fabricated and controlled by both magnetic and electric fields. Thus, both time-reversal symmetry and spatial inversion symmetry can be broken, leading to a transformation from the Dirac semimetal to a Weyl semimetal. Thereby, we can explorer the theoretical predicted anomalous Hall effect as well as magnetic monopoles experimentally. This project, combining the back-gate techniques, will study the new quantum transport phenomenon of DSM under an intense magnetic field.

近年来拓扑半金属成为凝聚态物理领域研究的热点。最近出现的ZrTe5材料已经被实验证实是三维的Dirac半金属（DSM）。而在已经开展的实验研究中尚无极端强磁场下的输运特性的报道，特别是当系统的费米能级进入朗道能级n=1（量子极限）甚至n=0 (超量子极限)后的一些输运特性。我们的初步测量结果表明，层状材料ZrTe5在弱的磁场下就能驱动费米能级到达量子极限。这使得层状材料ZrTe5成为研究量子极限，甚至超量子极限条件下三维DSM输运特性的理想平台之一。而且，层状结构的ZrTe5易于制备成场效应器件，在同时受磁场和电场的调控下，时间反演对称性和空间反转对称性被破坏，使Dirac点在动量和能量空间中分离为两个Weyl点。从而可以开展理论预言的反常霍尔效应以及磁单极子等新奇量子现象的探索研究。该项目将以DSM材料为研究对象，系统研究其在强磁场下和受背栅调控的输运特性。

微纳米尺寸的机械振子已经广泛应用于极灵敏的力探测相关的研究领域。应用纯硅超低弹性系数的悬臂梁和激光干涉法测量悬臂梁位移的方法最为灵敏，然而目前已有的该类仪器结构复杂，操作繁琐，这也是到目前为止还没有相关商业仪器出现的原因。在该项目中，搭建了一套可用于常规商业磁体（比如QD公司的PPMS），基于悬臂梁和激光干涉测量法的磁扭矩转角测量杆。利用该装置我们测量了Sr3Ru2O7纳米片的磁性，结合输运测量的结果，证实了该材料中存在的Lifshitz相变。应用磁扭矩转角测量杆，转角测量了Cd3As2纳米片的量子震荡，发现了两套震荡一个是源于体态，一个源于表面态。目前已发表论文四篇，另有两篇已经完成准备投稿。