高压强磁场下拓扑节线半金属的物性研究

Topological semimetals usually possess multi-degenerated band crossings protected by special crystalline symmetry, in which the low-energy excitations of the electron near the crossings behave as novel quasi-particles. These topological electronic materials show extensively application potentials in spintronics. Topological nodal-line semimetals host the line- or chain-like band crossings between conduction and valence band near the Fermi surface, which are characterized by the drumhead-like topological surface state. Topological nodal-line semimetal is in the vicinity of various topological states, which can be tuned to a new topological state under the spin-orbit coupling, i.e. topological insulator, Dirac semimetal, or Weyl semimetal. As one of the fundamental state parameters, high pressure is an effective and clean way to tune lattice and new matter states as well as quantum phase transition. Therefore, studying the topological properties and the evolution of the topological state under pressure is not only helpful to understand the physical nature of the topological semimetals, but also to provide a new idea for designing new topological electronic materials. In this project, we plan to investigate the evolution of crystal structure, electronic state, and to explore possible new quantum states and quantum effects under high pressure in recently experimentally discovered MSiX(M=Zr, Hf, X=S, Se, Te) series of the representative nodal-line semimetal, using a combination of electrical transport measurements under high magnetic field, Raman spectroscopy and synchrotron x-ray diffraction experiments.

拓扑半金属通常具有受特殊晶体对称性保护的多重简并能带交叉点，其附近电子的低能激发表现为新奇准粒子，在自旋电子学方面具有广阔的应用前景。拓扑节线半金属体内导带与价带在费米面附近相交呈线或链状，并具有鼓膜状平带拓扑表面态，它临近于各种拓扑量子态，在自旋轨道耦合作用下可以演变为拓扑绝缘体、狄拉克半金属、外尔半金属等。压力作为热力学参量，直接作用于晶格，是调节量子相变、诱导新物态的有效手段。因而，研究压力下材料拓扑特性及拓扑态如何演化不但有助于理解拓扑半金属的物理本质，同时也将为设计新的拓扑电子材料提供新思路。本项目计划选取最近实验发现的典型的节线半金属材料MSiX(M=Zr,Hf,X=S,Se,Te)为研究对象，以压力作为主要调控参量，结合强磁场下的电输运测量与拉曼光谱、同步辐射X射线衍射实验，调控研究这类新奇拓扑半金属中晶体结构、电子态的演化规律，并探索可能的新奇量子态和量子效应。

拓扑节线半金属在体内费米面附近具有线或链状的能带色散关系，表现出鼓膜状平带拓扑表面态，同时还临近拓扑绝缘体、狄拉克半金属、外尔半金属等各种拓扑量子态。压力直接作用于晶格，是调控量子相变、诱导新物态的一种有效手段。本项目以压力作为主要调控参量，通过结合强磁场下的电磁输运测量、拉曼光谱、同步辐射X射线衍射实验和理论计算，系统研究了拓扑半金属中晶体结构、拓扑电子态随压力的演化规律，主要研究成果如下：1、揭示了节线半金属ZrSiS拓扑半金属态受镜面和反演对称性破缺保护，发现了压力诱导了非平庸到平庸的拓扑量子相变；2、发现了节线半金属ZrSiSe0.97Te0.03中压力诱导的晶格局域畸变，伴随有多载流子型向单载流子型的过渡，可能暗示压力下发生了拓扑量子相变；3、给出了拓扑节线半金属SrAs3中超导电性共存的实验证据；4、实验发现了第二类狄拉克NiTe2中压力诱导的拓扑量子相变。