自由费米子凝聚态体系中与拓扑相关的物理现象

发布时间：2018-05-07 18:46

本文选题：狄拉克半金属 + 量子反常霍尔效应　；参考：《清华大学》2016年博士论文

【摘要】：最近几年,拓扑态及对称性保护的拓扑态成为凝聚态物理研究的一个前沿和热点。在本论文中我们主要讨论了一些典型的拓扑态,结合理论模型和实际材料,我们预言了若干新的拓扑态存在。我们主要在论文中讨论以下三个方面的问题:二维狄拉克材料及量子反常霍尔效应,二维反铁磁材料中的量子反常霍尔效应及手征拓扑超导相,和三维拓扑晶体绝缘体。首先,我们根据第一原理计算和解析有效模型提出了一类二维的狄拉克半金属材料,其中一个典型的例子为(LaO)2(SbSe2)2。这类材料具有八个狄拉克锥,并且其特点在于狄拉克锥的性质可以通过外加门电压进行调控,包括狄拉克锥存在与否,位置,费米速度和各向异性。我们发现了这种可调控性的物理原因是体系中存在和原子层依赖的由自旋轨道耦合引起的自旋结构,并且狄拉克锥是被镜面反射对称性所保护的。更进一步,如果我们在体系中引入磁性,则可以实现高陈数的量子反常霍尔效应,并且体系的陈数也可以通过调节电场实现从4到0到-4的变化。其次,我们探究了另一种实现量子反常霍尔效应的方法,发现在具有双钙钛矿结构的反铁磁材料Sr2FeOsO6薄膜中,也可以通过外加电场产生能带翻转而实现量子反常霍尔效应。更有趣的是,在这个体系中通过近邻效应引入超导配对项之后,可能实现二维的手征拓扑超导态。最后,我们研究了三维拓扑晶体绝缘体,并进行了分类。具有一个表面的三维拓扑晶体绝缘体的对称性是由二维空间群来描述的。根据对称性和能带简并的关系,我们找到了所有二维空间群可能对应的非平庸的拓扑表面态,并给出了相应体材料的拓扑不变量和一些具体的模型来实现这样的表面态。
[Abstract]:In recent years, topological states and symmetrically protected topological states have become a frontier and hotspot in condensed matter physics. In this paper, we mainly discuss some typical topological states. Combining with theoretical model and practical materials, we predict the existence of some new topological states. In this paper, we mainly discuss the following three aspects: two-dimensional Dirac material and quantum anomalous Hall effect, quantum anomalous Hall effect and chiral topological superconducting phase in two-dimensional antiferromagnetic material, and three-dimensional topological crystal insulator. Firstly, we propose a class of two-dimensional Dirac semi-metallic materials based on the first principle calculation and analytical efficient model. This kind of material has eight Dirac cones, and its characteristic is that the properties of Dirac cones can be controlled by external gate voltage, including the existence of Dirac cones, position, Fermi velocity and anisotropy. We find that the physical reason for this controllability is the spin structure of the system which is dependent on the atomic layer by the spin-orbit coupling, and the Dirac cone is protected by the mirror reflection symmetry. Furthermore, if we introduce magnetism into the system, we can realize the quantum anomalous Hall effect with high aging number, and the aging number of the system can change from 4 to 0 to -4 by adjusting the electric field. Secondly, we explore another method to realize the quantum anomalous Hall effect. It is found that the quantum anomalous Hall effect can also be realized in the antiferromagnetic Sr2FeOsO6 thin films with double perovskite structure by the energy band inversion produced by the applied electric field. More interestingly, it is possible to realize two-dimensional chiral topological superconducting states by introducing superconducting pairing terms through the nearest neighbor effect in this system. Finally, we study and classify the three-dimensional topological crystal insulators. The symmetry of three-dimensional topological crystal insulators with a surface is described by two-dimensional space groups. According to the relation between symmetry and energy band degeneracy, we find the non-mediocre topological surface states corresponding to all two-dimensional space groups, and give the topological invariants of the corresponding bulk materials and some concrete models to realize such surface states.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O469

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