Center for Multidimensional Carbon Materials (CMCM), Institute of Basic Science (IBS) , Ulsan 44919, Republic of Korea.
Department of Physics, Sogang University , Seoul 04107, Republic of Korea.
ACS Nano. 2017 Apr 25;11(4):4041-4050. doi: 10.1021/acsnano.7b00640. Epub 2017 Apr 6.
Interlayer excitons were observed at the heterojunctions in van der Waals heterostructures (vdW HSs). However, it is not known how the excitonic phenomena are affected by the stacking order. Here, we report twist-angle-dependent interlayer excitons in MoSe/WSe vdW HSs based on photoluminescence (PL) and vdW-corrected density functional theory calculations. The PL intensity of the interlayer excitons depends primarily on the twist angle: It is enhanced at coherently stacked angles of 0° and 60° (owing to strong interlayer coupling) but disappears at incoherent intermediate angles. The calculations confirm twist-angle-dependent interlayer coupling: The states at the edges of the valence band exhibit a long tail that stretches over the other layer for coherently stacked angles; however, the states are largely confined in the respective layers for intermediate angles. This interlayer hybridization of the band edge states also correlates with the interlayer separation between MoSe and WSe layers. Furthermore, the interlayer coupling becomes insignificant, irrespective of twist angles, by the incorporation of a hexagonal boron nitride monolayer between MoSe and WSe.
层间激子在范德华异质结构（vdW HSs）的异质结处被观察到。然而，目前尚不清楚激子现象如何受到堆叠顺序的影响。在这里，我们基于光致发光（PL）和 vdW 修正的密度泛函理论计算报告了 MoSe/WSe vdW HSs 中依赖扭转角的层间激子。层间激子的 PL 强度主要取决于扭转角：在完全堆叠的 0°和 60°角（由于强层间耦合）增强，但在非相干中间角度消失。计算证实了依赖扭转角的层间耦合：价带边缘的状态表现出长尾巴，在相干堆叠角度下延伸到另一个层；然而，对于中间角度，状态主要局限在各自的层中。这种能带边缘态的层间杂化也与 MoSe 和 WSe 层之间的层间分离相关。此外，通过在 MoSe 和 WSe 之间插入单层六方氮化硼，层间耦合变得不显著，而与扭转角无关。
