极端条件下新型拓扑材料CoSi的量子调控研究

Chiral topological nodes are robust energy band crossing points with non-zero Chern numbers, whose chirality as a kind of pseudo-spin can be applied to spin and energy valley electronics. It is expected to solve the energy consumption problem due to miniaturization and multifunction of electronic devices. People have been exploring chiral topological points, but only the Weyl points have been confirmed by various experiments. Recently, angle-resolved photoemission spectroscopy (ARPES) experiments show that there may be two new chiral topological points in CoSi. Different from the Weyl points, the new topological points are degenerate and thus can be easily quantum-controlled, which has great fundamental research and application value. At present, there is no systematic research on the CoSi system. Therefore any significant progress made in this system will enrich the understanding of the system. The applicant will conduct in-depth research on the CoSi system by quantum control study (electrical transport, infrared spectroscopy, nuclear magnetic resonance) under extreme conditions (strong magnetic field, very low temperature, strong hydrostatic pressure). On the one hand, it is expected to establish the universal law of topological chirality and further promote the application of chirality in electronic devices. On the other hand, it is expected to try to control the transitions between different topological properties through multi-parameter quantum control, which might lay a foundation for topological theory research and material application.

手性拓扑点是具有非零陈数的能带交叉点，其手征性作为一种赝自旋，可以应用到自旋和能谷电子学中，有望解决当前电子器件小型化和多功能化所面临的能耗问题。人们一直在探索手性拓扑点,但是至今得到多种实验确认的只有外尔（Weyl）点。最近，角分辨光电子能谱实验表明在CoSi中可能存在除外尔点以外的两种新型手性拓扑点。不同于外尔点，新型拓扑点均是简并的，可以进行量子调控，存在很大的基础研究和应用价值。目前，对CoSi这一体系还没有系统的研究，因此在这一体系中所取得的任何重要进展都将丰富对该体系的认识。申请人将通过极端条件(强磁场、极低温、强静水压)下的量子调控（电输运、红外光谱、核磁共振）对CoSi展开系统深入的研究，一方面期望建立拓扑手征性的普适规律，推动手征性在器件中的应用；另一方面期望通过多参量量子调控，尝试进行不同拓扑物性之间的有目的调控，为拓扑理论研究和材料应用奠定基础。

最近，角分辨光电子能谱实验证明拓扑材料 CoSi 的能带结构中存在两种新型手性拓扑点，为人们提供了进一步研究手征性及其应用的平台。目前，对 CoSi 这一体系能带结构的研究还不够清楚。本项目通过核磁共振测量研究了CoSi的局域磁化率和自旋晶格弛豫率随温度的变化，从而可以分析得到其体拓扑能带结构，从体测量的角度证明了其存在三维的线性色散能带。另外，使用极低温核磁共振技术获得了LiFeP中其London穿透深度随温度变化，与LiFeAs进行对比，给出了其超导能隙函数存在线节点的微观证据。参与了笼目超导体CsV3Sb5中电荷有序态的核磁共振研究，给出了笼目超导体CsV3Sb5中电荷序结构的最直接证据。

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