强自旋-轨道耦合的超导电性及其机理研究

In recent years, a host of new superconductors based on 4d or 5d electron systems have been discovered. In these systems, spin-orbit coupling may play a significant role and the pairing mechanism may go beyond the conventional Bardeen-Cooper-Schrieffer (BCS) scheme. Revealing the pairing symmetry proves to be a necessary ingredient in our understanding of their pairing mechanism. In this proposal, we aim to study the superconducting properties and the pairing symmetry of such new superconductors (including the very recently-discovered Nb2PdS5, PbTaSe2, SrPtAs and their related) by various experimental tools. Special emphasis will be placed on understanding the role of spin-orbit coupling on the superconductivity. Our proposal is dedicated to addressing the following important issues: (1) By using the chemical substitution, map out the evolution of superconducting transition temperature Tc with different masses of atomic substituent, and therefore clarify the interplay between spin-orbit coupling and superconductivity. (2) Via the low temperature specific heat measurements, explore the behavior of their low-lying quasi-particle excitations and hence determine the superconducting gap structure. (3) Study their low temperature (electrical and thermal) transport properties and look for the signature of proposed novel pairing mechanism, such as spin triplet pairing, due to strong spin-orbit coupling.

不断被发现的基于4d、5d电子超导材料，由于其强烈的自旋-轨道耦合，表现出许多新奇的特性，其超导机理很难用传统的BCS理论来解释。揭示超导电子配对对称性是正确理解其超导微观机理不可或缺的要素。因此，本项目计划以新型基于4d、5d电子超导体Nb2PdS5, PbTaSe2，SrPtAs等为研究对象，利用多种实验手段对如下几个重要的科学问题展开系统而深入的研究：(1) 通过化学掺杂方法，研究超导转变温度随不同元素掺杂变化关系，从而研究自旋-轨道耦合强度对其超导的影响。(2) 通过低温比热等测量，研究其低能准粒子激发，探索其超导能隙对称性。(3) 通过电输运、热输运等测量，探索其中可能的由于自旋-轨道耦合引起的奇异配对对称性，如spin triplet配对，从而为揭示其超导微观机制提供实验支持。

基于4d、5d电子的量子材料，由于其强烈的自旋-轨道耦合，表现出许多新奇的特性，如非常规超导电性、拓扑电子结构等。本项目以新型基于4d、5d电子材料Ta4Pd3Te16，PbTaSe2，PtBi2、β-PdBi2，RhSn4，PdSn4，(Ca, La)(Fe,Co)As2，La7Ir3，NiTe2等为研究对象，利用极端条件下（强磁场、极低温、超高压等）的输运、热力学性质测量等多种实验手段，结合第一性原理计算，重点研究了如下几个重要的科学问题：(1) 在实验中发现了几类具有拓扑电子结构的材料，如PbTaSe2，PtBi2，RhSn4，PdSn4，NiTe2等，研究了Dirac电子对其输运、热力学性质的影响。(2) 通过低温比热等测量，研究具有较强自旋-轨道耦合的超导体（如La7Ir3，Ta4Pd3Te16）的低能电子激发，探索其超导配对的微观机制。(3) 通过电输运、热输运等测量，探索了这些材料中由于自旋-轨道耦合引起的新物理，如拓扑相变、电子强关联效应等，从而为理解材料宏观物理现象的微观机制提供实验支持。