外尔半金属结构中由关联相引起的输运性质的理论研究

Massless relativistic fermions systems, as for the exceptional transport properties due to their unique linear band structures, have been the primary seeking goal in the whole physics society for many years. After the finding of graphene at the beginning of the 21st century, massless relativistic fermions systems have become the research hotspot of physicists. Recently, the fact of theoretical theory being built and experimental discovery of the so-called Weyl semimetals, which hold non-degeneracy linear band structure in 3D, during the past several years, brings the research hotspot from low dimensions to three dimensions. This makes Weyl semimetals have broader prospect for their potential application in the future. However, the key problem is how to apply the transport theory for low-dimensional degenerated linear band structure in graphene for the case of non-degeneracy three-dimensional linear band structure in Weyl semimetals, since this process is obstructed by the truth in Weyl semimetals that we can only keep either time-reversal symmetry or spatial-inversion symmetry, not both of them just like physicists did in graphene. In this project, under the division of zero-temperature limit and nonzero temperature case, we will apply the approach of charge neutrality to the numerical calculation of transport properties in Weyl semimetals in the clean limit. Based on the above concept for linear band structure, we will carry our research work in the following two directions: i) How the existence of correlated phase affects the electrical and heat transport properties in Weyl semimetals (such as electrical conductivity, Seebeck coefficient etc.); ii) in Weyl semimetals, what is the dependence of magnetic transport properties on the applied fields.

零质量相对论性费米子体系因其独有的线性能带结构带来的优异输运性能，而一直是物理学家探寻的重点目标。随着本世纪初石墨烯的发现，零质量相对论性费米子体系便成为研究热门，而同样具有线性能带的三维外尔半金属结构在过去几年间的出现，更是将这一研究从低维带向了高维，为其在未来的潜在应用带来更为宽广的前景。但目前亟待解决的问题是如何将石墨烯体系中的低维简并线性能带下的输运理论推广到外尔半金属结构中的高维非兼并线性能带情形，因这一过程中涉及到对空间反演对称性和时间反演对称性二者只能保一的问题。本项目拟在绝对零度和非零温度两种条件下，采用电荷中性的办法去进行干净极限下的输运模型数值运算。基于上述线性能带结构这一概念，申请人将重点在下述两个方面进行研究：一、外尔半金属结构体系中，关联相的存在对系统电和热输运性质的影响（例如电导性质、热电系数等）。二、外尔半金属体系背景下磁输运性质对外加场的依赖性。

本项目从理论角度将低维体系简并线性能级中的输运理论推广到三维结构，并在干净极限下进行输运模型的数值运算。我们重点研究了两部分内容。一是有机半导体薄膜结构中电信号对自旋流信号的性能影响；二是外尔体系中关联相对电热输运性能的提升研究。在第一部分中，我们从理论上发现通过改变注入自旋流比例可以实现对自旋输运信号的调控；此外我们还发现在一定范围内提高自旋注入界面层的阻抗强度（自旋翻转矩阵的非对角矩阵元）可实现自旋输出信号增强效果。在第二部分中，我们使用第一性原理计算发现外尔体系中自旋简并破缺使其关联相能在线性能级中打开一定强度能隙。我们从理论角度对能隙大小进行估计，并对费米面附近能态密度及载流子浓度进行模拟计算。使用电荷输运方程和热传导方程我们计算得出热电系数的各向异性分量及塞贝克系数散点曲线，其趋势揭示了线性能带结构中的弹道输运特性。