Highly valley-polarized singlet and triplet interlayer excitons in van der Waals heterostructure
Highly valley-polarized singlet and triplet interlayer excitons in van der Waals heterostructure
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DOI：
10.1103/physrevb.100.041402
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发表时间：
2019-01
影响因子：
3.7
通讯作者：
Long Zhang;Rahul Gogna;G. William Burg;J. Horng;Eunice Y. Paik;Y. Chou;Kyounghwa Kim;E. Tutuc;H. Deng
中科院分区：
文献类型：
--
作者：
Long Zhang;Rahul Gogna;G. William Burg;J. Horng;Eunice Y. Paik;Y. Chou;Kyounghwa Kim;E. Tutuc;H. Deng
由于电子的自旋和动量谷被锁定，二维半导体具有电子电子现象。然而，在单层晶体中，谷间快速的电子-空穴交换本质上限制了谷极化。异质双层晶体具有较长的激子寿命和谷退极化时间。但已报道的河谷极化程度较低，河谷去极化的选择规则和机理仍存在争议。在这里，我们报道了单态和亮态三重态层间激子，它们的谷极化都超过80%，分别与泵浦激光交叉和共偏振。这是在具有精确动量谷排列和窄发射线宽的WSe2/MoSe2异质双层膜中实现的。高谷极化使我们能够识别异质结构中的带极小值，并明确地包括直接带隙激子跃迁、超快电荷分离、强抑制谷去极化。我们的结果为利用半导体异质双层膜来控制山谷选择规则的应用铺平了道路。
Two-dimensional semiconductors feature valleytronics phenomena due to locking of the spin and momentum valley of the electrons. However, the valley polarization is intrinsically limited in monolayer crystals by the fast intervalley electron-hole exchange. Hetero-bilayer crystals have been shown to have a longer exciton lifetime and valley depolarization time. But the reported valley polarization was low; the valley selection rules and mechanisms of valley depolarization remains controversial. Here, we report singlet and brightened triplet interlayer excitons both with over 80% valley polarizations, cross- and co-polarized with the pump laser, respectively. This is achieved in WSe2/MoSe2 hetero-bilayers with precise momentum valley alignment and narrow emission linewidth. The high valley polarizations allow us to identify the band minima in a hetero-structure and con_rm unambiguously the direct band-gap exciton transition, ultrafast charge separation, strongly suppressed valley depolarization. Our results pave the way for using semiconductor heterobilayers to control valley selection rules for valleytronic applications.