单层过渡金属硫化物中拓扑激子态的研究

发布时间：2018-04-24 00:14

本文选题：拓扑激子 + 过渡金属硫化物　；参考：《深圳大学》2017年硕士论文

【摘要】：在固态系统中寻找拓扑非平庸的量子态一直是凝聚态物理中的前沿热门问题。对于电子这样的费米子体系,拓扑非平庸的边缘态已经在理论上广泛研究,并且在实验中也观测到了其存在的证据。实现拓扑非平庸的边缘态的关键在于实现自旋轨道耦合,尤其是相对论性狄拉克粒子类型的自旋轨道耦合。另一个关键则在于实现能带反转,这很大程度上决定于时间反演对称性被破坏。在费米子体系中发现拓扑态之后,能否在其他体系中实现同样拓扑非平庸的量子态就成了一个显而易见的研究课题。对于例如耦合谐振子腔,光子晶体等玻色子体系中,可以通过两种不同波色子的两分量等效从而得到必须的自旋轨道耦合,进而得到玻色子的拓扑态。在此基础上,我们提出了如下的问题,除了在基础粒子体系(玻色子,费米子)中实现拓扑量子态,在其他体系中能不能实现拓扑量子态?在本文中,我们部分回答了这个问题:在由电子和空穴相互吸引而构成的激子体系中可以找到非拓扑平庸的量子边缘态。我们提议在第六族过渡金属硫化物这种新型的二维材料中去实现这种拓扑态。由于单层的第六族过渡金属硫化物在天然的可见光波段内是直接带隙半导体,以及拥有特殊的能谷自由度,所以在这种体系中存在两种不同的能谷激子。这两种能谷激子通过其构成的带电粒子间的库伦相互作用有着旋度为2的自旋轨道耦合。当时间反演对称性进一步被磁场所破坏的时候,从而可以在磁场畴壁附近实现拓扑激子态。我们研究了拓扑激子随着外加控制参数变化下束缚能以及波函数形状的变化,以及对光场的响应的改变。更进一步,我们还研究了当外加上单一方向的应力时候的情形。由于应力会将旋度为2的狄拉克锥分裂为两个旋度为1的狄拉克锥,可以预见到拓扑激子的能谱形状也会随着狄拉克锥的移动而移动。我们在数值上证实了这点。总结一下,我们可以用光来激发拓扑激子,利用磁场畴壁来调节拓扑激子的能谱和波函数,然后用应力来控制拓扑激子的传播特性。我们发现了复合型粒子的拓扑非平庸的量子状态,找到了量子信息处理过程中新型的物理载体,预示了基于拓扑激子的新型光电学器件的潜在应用,为拓扑量子计算的实现增加了可能性。
[Abstract]:Searching for nontrivial quantum states in solid state systems has always been a hot issue in condensed matter physics. For fermionic systems such as electrons, topological non-mediocre edge states have been extensively studied in theory, and evidence of their existence has been observed in experiments. The key to realize the topological non-mediocre edge state is to realize the spin orbit coupling, especially the relativistic Dirac particle type spin orbit coupling. The other key is the realization of band inversion, which largely depends on the destruction of time inversion symmetry. After the discovery of topological states in fermionic systems, it becomes an obvious research topic whether we can realize the same topological non-mediocre quantum states in other systems. For the coupled resonator cavity, photonic crystal and other boson systems, the necessary spin orbit coupling can be obtained by equivalent two components of two different bosons, and then the topological states of the bosons can be obtained. On this basis, we propose the following questions: apart from the realization of topological quantum states in the basic particle system (boson, fermion), can the topological quantum states be realized in other systems? In this paper we partly answer the question that the nontopological mediocre quantum edge states can be found in the exciton system composed of electrons and holes. We propose to realize this topological state in a new two-dimensional material, the sixth group of transition metal sulphides. There are two different energy excitons in this system because the sixth transition metal sulfides in the monolayer are direct band gap semiconductors in the natural visible light band and have special energy valley degrees of freedom. The two energy excitons have spin-orbit coupling with a curl of 2 through the Coulomb interaction between the charged particles. When the time inversion symmetry is further destroyed by the magnetic field, the topological exciton states can be realized near the domain walls of the magnetic field. We study the change of binding energy, wave function shape and response to light field of topological excitons with the change of external control parameters. Furthermore, we study the case when the stress in a single direction is applied to the outside. Since the stress will split the Dirac cone with a curl of 2 into two Dirac cones with a curl of 1, it can be predicted that the shape of the energy spectrum of the topological excitons will also move with the movement of the Dirac cone. We have confirmed this numerically. To sum up, we can excite topological excitons by light, adjust the energy spectrum and wave function of topological excitons by using the domain walls of magnetic fields, and then control the propagation characteristics of topological excitons by stress. We have found the topological non-mediocre quantum state of composite particles, found a new physical carrier in the process of quantum information processing, and predicted the potential application of novel optoelectronic devices based on topological excitons. It increases the possibility for the realization of topological quantum computing.
【学位授予单位】：深圳大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O469

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