过渡金属二硫族化合物激子谱的量子电动力学研究
Quantum-electrodynamical approach to the exciton spectrum in Transition-Metal Dichalcogenides
摘要：
操纵固有的电子自由度，如电荷和自旋，分别产生电子学和自旋电子学。具有蜂窝晶格结构的单层材料中的电子，例如过渡金属二硫属化物（TMD），可以根据它们所属的布里渊区的区域（谷）来区分。谷电子学，这种电子属性的操纵，有望在电子器件领域建立一个新的时代。在这项工作中，我们精确地确定了不同TMD材料，即WSe $_2$，WS $_2$和MoS $_2$的激子（电子-空穴）束缚态的能谱和寿命。对于所有这些，我们得到了170 meV的数量级的激子能量之间的分裂从不同的谷，对应于一个有效的塞曼磁场为1400 T。我们的方法，采用量子场论（QFT）技术的基础上的贝特-萨尔彼得方程和Schwinger-Dyson形式主义，考虑到充分的电磁相互作用之间的电子。谷选择机制通过时间反演（TR）对称性的动力学击穿来操作，该对称性最初将两个谷互连。这种对称性是自发破缺时，完整的电磁相互作用顶点是用来探测系统的响应，以一个外部的领域。
英文摘要：
Manipulation of intrinsic electron degrees of freedom, such as charge and spin, gives rise to electronics and spintronics, respectively. Electrons in monolayer materials with a honeycomb lattice structure, such as the Transition-Metal Dichalcogenides (TMD's), can be distinguished according to the region (valley) of the Brillouin zone to which they belong. Valleytronics, the manipulation of this electron's property, is expected to set up a new era in the realm of electronic devices. In this work, we accurately determine the energy spectrum and lifetimes of exciton (electron-hole) bound-states for different TMD materials, namely WSe$_2$, WS$_2$ and MoS$_2$. For all of them, we obtain a splitting of the order of 170 meV between the exciton energies from different valleys, corresponding to an effective Zeeman magnetic field of 1400 T. Our approach, which employs quantum-field theory (QFT) techniques based on the Bethe-Salpeter equation and the Schwinger-Dyson formalism, takes into account the full electromagnetic interaction among the electrons. The valley selection mechanism operates through the dynamical breakdown of the time-reversal (TR) symmetry, which originally interconnects the two valleys. This symmetry is spontaneously broken whenever the full electromagnetic interaction vertex is used to probe the response of the system to an external field.
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