Unveiling pseudospin and angular momentum in photonic graphene
Unveiling pseudospin and angular momentum in photonic graphene
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揭示光子石墨烯中的赝自旋和角动量
DOI：
10.1038/ncomms7272
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发表时间：
2015-02-01
影响因子：
16.6
通讯作者：
Chen, Zhigang
中科院分区：
文献类型：
--
作者：
Song, Daohong;Paltoglou, Vassilis;Chen, Zhigang
赝自旋是石墨烯固有的一个额外的自由度，在理解许多基本现象中起着关键作用，如反常量子霍尔效应，电子手性和克莱因悖论。与电子自旋不同，赝自旋在传统上被认为是一个不可测量的量，不受斯特恩-格拉赫实验的影响。然而，最近有人提出，石墨烯赝自旋是一个真实的角动量，可能会表现为一个可观测的量，但到目前为止，这种动量的直接测试仍然没有成果。在这里，通过选择性激发两个子晶格的人工光子石墨烯，我们证明了赝自旋介导的涡旋产生和拓扑电荷翻转，否则均匀的光束与布洛赫动量穿越狄拉克点。通过线性无质量Dirac-Weyl方程的数值解的验证，我们证明了赝自旋可以完全转化为轨道角动量，从而坚持了赝自旋不仅仅是理论上的优雅，而是物理上可测量的信念。
Pseudospin, an additional degree of freedom inherent in graphene, plays a key role in understanding many fundamental phenomena such as the anomalous quantum Hall effect, electron chirality and Klein paradox. Unlike the electron spin, the pseudospin was traditionally considered as an unmeasurable quantity, immune to Stern-Gerlach-type experiments. Recently, however, it has been suggested that graphene pseudospin is a real angular momentum that might manifest itself as an observable quantity, but so far direct tests of such a momentum remained unfruitful. Here, by selective excitation of two sublattices of an artificial photonic graphene, we demonstrate pseudospin-mediated vortex generation and topological charge flipping in otherwise uniform optical beams with Bloch momentum traversing through the Dirac points. Corroborated by numerical solutions of the linear massless Dirac-Weyl equation, we show that pseudospin can turn into orbital angular momentum completely, thus upholding the belief that pseudospin is not merely for theoretical elegance but rather physically measurable.