拓扑节线半金属中关联效应、光和无序引起新奇量子现象的理论研究

Line-node semimetal is a newly discovered topological semimetal after Weyl semimetal. Unlike Weyl semimetals, in which the conduction band touches the valence band at discrete points in the momentum space, the conduction and valence bands in topological line-node semimetals touch each other on closed lines. Line-node semimetals show some exotic physical features like the high surface density of states caused by drumhead surface state, the spin-orbit line-node semimetal PbTaSe2 becoming superconducting at 3.79 Kelvin. In this project, we will study novel quantum phenomena in topological line-node semimetals induced by electron correlation, light and disorder. We will study three problems in this project: (1) Unconventional superconductivity and possible topological superconductivity in the non-centrosymmetric line-node semimetal PbTaSe2 with strong spin-orbit coupling; (2) Magnetism and superconductivity of line-node semimetal induced by electron correlation; (3) Topological phase transition of line-node semimetal induced by polarized light and metal-insulator transition caused by disorder.

节线半金属是继外尔半金属后被发现的一类新型三维拓扑半金属。与外尔半金属不同的是，节线半金属体电子导带和价带在布里渊区相交形成受对称性保护的节线而不是离散的点。节线半金属表现出许多新颖、有趣的物理。例如，体态拓扑造成具有平坦能带的鼓面状表面态；自旋轨道耦合节线半金属材料PbTaSe2在3.79 K会发生超导转变等。本项目拟采用平均场理论和量子输运理论分别研究节线半金属中电子关联、光和无序引起的新奇物理现象，主要包含以下三个问题：（1）非中心对称结构节线半金属材料PbTaSe2的非传统超导电性以及拓扑超导电性。（2）拓扑半金属中电子相互作用引起的关联量子态。（3）光诱导的拓扑相变与无序导致的金属-绝缘体相变。

拓扑半金属是拓扑绝缘体之外另一种具有代表性的拓扑物态，它包含节点半金属（如狄拉克、外尔半金属）和节线半金属。本项目旨在探索新的节线半金属态以及相互作用、光与无序等引起的新奇现象。本项目得到的重要结果有： (1)发现了一类新的拓扑节线半金属并研究了其中圆偏振光诱导的拓扑相变；(2)提出拓扑节线超导/超流的实现方案；(3)理论上研究了拓扑节线半金属材料PbTaSe2的表面超导电性；(4)系统研究了拓扑半金属中无序、磁性杂质问题；(5)在准晶系统发现了一类超越现有拓扑物态分类的高阶拓扑绝缘体；(6)揭示了非厄密拓扑系统中尺寸效应引起的独特复能隙；(7)严格可解的相互作用拓扑超导模型。我们的发现拓展和丰富了拓扑物态的分类，加深了人们对节线半金属等拓扑材料的理解。在本项目支持下负责人累计发表SCI论文16篇(7篇通讯作者论文)，其中Physical Review Letters 1篇，Physical Review A/B 14篇(含两篇Rapid Communications)，远超预期成果目标。