非中心对称超导体高压隧道谱研究

The newly discovered non-centrosymmetric (NCS) superconductor, a class of unconventional superconducting materials, has attracted great interests, for its realization of a novel topological superconductivity, as the theoretists proposed. As a result of antisymmetric spin-orbital coupling (ASOC) arising from the absence of inversion symmetry, the superconducting pairing state of these compounds allows the admixture of spin-singlet and spin-triplet components. This is in contrast to other previously studied BCS superconductors, in which their pairing state is of either spin-singlet/even parity or the spin-triplet/odd parity due to the restrictions of the Pauli principles and parity conservation. Basically, the strength of ASOC completely determines the ratio of the admixture of spin-singlet and spin triplet components. It is crucial to unveil the relationship between ASOC and the pairing state of NCS superconductor. This project aims to explore and develop the technology of pressure dependent tunneling spectroscopy/micro-contact Andreev reflection spectroscopy, and by these techniques we investigate the nature of pressure-dependent tunneling/Andreev reflection spectrum of PbTaSe2 and BiPd high quality NCS superconducting single crystals as functions of temperature and pressure. Using the first-principle electronic structure calculations, we analyze superconducting gap size, gap structure and ASOC as a function of pressure. These gap-pressure relationships together with Tc-pressure phase diagram provide solid experimental data to reveal the weak-correlation NCS superconductivity.

非中心对称超导体是近年发现的一类新型非常规超导材料。由于晶体结构中缺失了空间反演对称中心，非中心对称的晶体势场产生一个有效的反对称自旋-轨道耦合（ASOC）并导致自旋简并的能级发生分裂,从而在超导配对态中允许自旋单态和自旋三重态的混合。理论上, ASOC强弱决定了自旋单态和三重态的混合比例。一个关键的问题是ASOC以何种方式影响非中心对称超导体超导能隙的结构和大小以及电子对的配对对称性。本项目致力于利用高压手段调控晶体结构，即ASOC强度，同时利用隧道谱/微接触Andreev反射谱仪技术，结合高压输运和第一性原理能带理论计算，测量弱关联非中心对称超导体PbTaSe2和BiPd单晶样品的隧道谱线以及随温度、压力的依赖关系，分析并研究非中心对称超导体的ASOC强度，能隙结构、能隙大小以及相关的压力演变规律，为揭示弱关联非中心对称超导电性提供有力的实验数据。

本项目我们致力于发展压力环境下的点接触隧道谱测量技术，并利用这项技术手段研究压力调控下的非常规超导电性。我们在成功发展的压力点接触隧道谱技术基础上，测量了非中心对称超导体PbTaSe2、Kagome超导体CsV3Sb5以及电荷密度波（CDW）超导体4H-NbSe2的压力点接触隧道谱，得到这些超导体超导序参量，即超导能隙和超导临界温度Tc随压力的演变规律，为揭示拓扑超导特征、CDW序超导电性提供重要的实验证据。