拓扑半金属体系超导电性的理论研究

Due to its unique bulk band structure and surface state properties, topological semimetallic systems have attracted extensive theoretical and experimental research in recent years, however, the research on its superconductivity is still in the preliminary exploration stage, especially controversial issue on the pairing symmetry of superconducting phases which has been achieved experimentally. This project is to reveal the physical properties of topological semimetallic systems under different superconducting pairing symmetries, and the following contents are proposed: 1) By studying and analyzing the surface states of superconducting phases and their quasiparticle scattering interference effects, the characteristics of impurity scattering and impurity resonance/bound states under the possible pairing symmetries are obtained; 2) We will study the tunnel spectrum characteristics of the superconducting heterojunction, and use its phase sensitivity to give Andreev reflection spectrum properties under different superconducting pairing symmetries, and explore the feature of the existence of Majorana zero mode in topological superconducting phase; 3) Through the study on the physical properties of topological semimetallic surface superconductivity, we will explore new systems for realizing topological surface superconductivity. The above theoretical studies can reveal the bulk and surface states properties of topological semimetals under different superconducting pairing symmetries and provide theoretical references for relevant experimental tests. The applicant has the research background of topological semimetallic normal phase and the research foundation of certain ability, and has carried out the preliminary research of this project.

由于独特的体能带结构和表面态性质，拓扑半金属体系近年来引起了广泛的理论和实验研究，然而对其超导电性的研究目前尚处于初步的探索阶段，尤其是对实验上已经实现的超导相的配对对称性仍存在争议。本项目的研究目标为揭示拓扑半金属体系在不同超导配对对称性下的物理性质，拟做如下内容研究：1）通过研究和分析超导相下的表面态及其准粒子散射相干效应，得到可能配对对称性下的杂质散射和杂质共振/束缚态特征；2）研究超导异质结的隧道谱特性，利用其相位敏感性，给出不同超导配对对称性下的Andreev反射谱性质，并探索拓扑超导相中Majorana零能模存在的特征；3）研究拓扑半金属表面超导的物性，以探索实现拓扑表面超导性的新体系。上述理论研究能够揭示拓扑半金属在不同超导配对对称性下的体态和表面态性质，为相关的实验检测提供理论参考。申请人有对拓扑半金属正常相的研究背景，具有一定能力的研究基础，并已开展了项目的前期研究。

本项目围绕拓扑半金属体系超导相的物性主要进行了三个方面的研究，具体内容包括拓扑半金属超导相的表面态及其准粒子散射相干效应、拓扑半金属超导异质结的局域和非局域Andreev反射谱特性、拓扑半金属体系表面超导的物性。（1）我们系统性地研究了三维拓扑狄拉克半金属体系可能的超导配对对称性，揭示了其对杂质散射特征波矢的演化特性和杂质束缚态的性质；我们还扩展研究了二维非简单空间群拓扑狄拉克半金属体系的杂质态性质和三维高阶拓扑外尔半金属体系的准粒子散射相干效应。（2）我们研究了三维拓扑外尔半金属体系的正常/超导和正常/超导/正常异质结的微分电导谱特性，揭示了异质结的Andreev反射谱在不同方向上具有明显的各向异性，这为实验上测量和分析提供了重要的指导作用。（3）我们全面研究了三维拓扑节点半金属体系在不同超导配对对称性下的近邻效应。通过构造三维拓扑节点半金属/超导体复合体系，我们发现针对目前实验上已经证实的三维拓扑节点半金属体系模型，所有由超导近邻效应诱导的非本征超导相都是无能隙的。