Separation of the valley exciton-polariton in two-dimensional semiconductors with an anisotropic photonic crystal
Separation of the valley exciton-polariton in two-dimensional semiconductors with an anisotropic photonic crystal
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DOI：
10.1103/physrevb.101.245418
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发表时间：
2020-06
影响因子：
3.7
通讯作者：
Ruoming Peng;Changming Wu;Huan Li;Xiaodong Xu;Mo Li
中科院分区：
文献类型：
--
作者：
Ruoming Peng;Changming Wu;Huan Li;Xiaodong Xu;Mo Li
二维过渡金属二硫属化合物（TMDC）中激子具有较高的束缚能，在室温下是稳定的。它们可以基于独特的光学选择规则来选择性地解决，这些规则来自谷态的角动量守恒和圆偏振光的螺旋度。当激子与光腔中的光模耦合时，激子可以形成激子-极化激元，在2D TMDC中利用激子-极化激元可以导致室温操作的光电器件。然而，激子的谷自由度在形成激子-极化激元时大部分丢失，因为腔模通常不具有明确定义的自旋角动量。在这里，我们从理论上证明了激子-极化激元的谷信息可以在由双折射材料制成的光子腔中被保留和分辨。由于光学各向异性，引导共振模式具有净横向自旋角动量，并且选择性地耦合到具有相应谷态的激子-极化激元。在强耦合区，激子-极化激元的行为类似于固体中的Rashba效应。激子-极化激元的色散在动量空间中基于其谷态分裂，类似于Rashba系统中的电子自旋。实现谷依赖激子极化激元提供了一种可能性，探索谷激子动力学在强耦合系统，并将有助于激子，极化激元器件，玻色爱因斯坦凝聚，和超流性的研究在半导体。
Excitons in two-dimensional (2D) transition metal dichalcogenides (TMDC) are stable at room temperature because of high exciton binding energies. They can be selectively addressed based on the unique optical selection rules from angular momentum conservation for the $K/{K}^{\ensuremath{'}}$ valley state and the helicity of circularly polarized light. When coupled with the optical modes in optical cavities, excitons can form exciton-polaritons, exploiting which in 2D TMDC may lead to optoelectronic devices for room temperature operation. The valley degree of freedom of the excitons, however, is mostly lost when forming exciton-polaritons because the cavity mode usually does not have a well-defined spin angular momentum. Here, we theoretically demonstrate that the valley information of exciton-polaritons can be preserved and resolved in a photonic cavity made of birefringent materials. Because of the optical anisotropy, the guided resonance modes have a net transverse spin angular momentum and selectively couple to exciton-polaritons with the corresponding valley state. In the strong-coupling regime, the exciton-polariton behaves in a way like the Rashba effect in the solid. The dispersion of the $K/{K}^{\ensuremath{'}}$ exciton-polariton splits in momentum space based on its valley state, similar to electron spins in Rashba systems. Realizing valley-dependent exciton-polaritons affords a possibility to explore valley exciton dynamics in a strongly coupled system and will contribute to the study of excitonic, polaritonic devices, Bose-Einstein condensation, and superfluidity in semiconductors.