Optical generation of excitonic valley coherence in monolayer WSe2
Optical generation of excitonic valley coherence in monolayer WSe2
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DOI：
10.1038/nnano.2013.151
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发表时间：
2013-09-01
影响因子：
38.3
通讯作者：
Xu, Xiaodong
中科院分区：
文献类型：
--
作者：
Jones, Aaron M.;Yu, Hongyi;Xu, Xiaodong
由于晶体对称性引起的简并，带边(山谷)的电子态有可能具有额外的自旋类量子数(1-6)。一个重要的问题是，在寻求量子技术的过程中，是否可以对这种山谷伪自旋进行相干操作，类似于使用真自旋实现的操作(7，8)。在这里，我们展示了山谷相干性可以被产生和检测。由于单个谷态中的激子发射圆偏振光子，线偏振只能通过两个谷态的相干叠加中的激子复合才能产生。利用单层半导体WSe2器件，我们首先建立了解决单个谷激子和三子的圆偏振光学选择规则。然后，我们通过观察线偏振发光证明了谷激子之间的相干性，在任何给定的偏振角下，线偏振发光的方向与线偏振激发的方向一致。相反，三子对应的光致发光没有被观察到是线偏振的，这与发射的光子偏振与谷伪自旋纠缠的预期一致。除了谷极化(11-15)之外，解决相干性(9，10)的能力是朝着实现相干山谷电子学所需的谷指数的量子操纵迈出的一步。
As a consequence of degeneracies arising from crystal symmetries, it is possible for electron states at band-edges ('valleys') to have additional spin-like quantum numbers(1-6). An important question is whether coherent manipulation can be performed on such valley pseudospins, analogous to that implemented using true spin, in the quest for quantum technologies(7,8). Here, we show that valley coherence can be generated and detected. Because excitons in a single valley emit circularly polarized photons, linear polarization can only be generated through recombination of an exciton in a coherent superposition of the two valley states. Using monolayer semiconductor WSe2 devices, we first establish the circularly polarized optical selection rules for addressing individual valley excitons and trions. We then demonstrate coherence between valley excitons through the observation of linearly polarized luminescence, whose orientation coincides with that of the linearly polarized excitation, for any given polarization angle. In contrast, the corresponding photoluminescence from trions is not observed to be linearly polarized, consistent with the expectation that the emitted photon polarization is entangled with valley pseudospin. The ability to address coherence(9,10), in addition to valley polarization(11-15), is a step forward towards achieving quantum manipulation of the valley index necessary for coherent valleytronics.