Excitonic Effect Drives Ultrafast Dynamics in van der Waals Heterostructures
Excitonic Effect Drives Ultrafast Dynamics in van der Waals Heterostructures
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DOI：
10.1021/acs.nanolett.0c01519
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发表时间：
2020-06-10
期刊：
影响因子：
10.8
通讯作者：
Lu, Gang
中科院分区：
文献类型：
--
作者：
Liu, Junyi;Zhang, Xu;Lu, Gang
最近的实验揭示了在过渡金属二硫属化合物货车德瓦尔斯（vdW）异质结中的堆叠构型无关的和超快的电荷转移，这是令人惊讶的，因为强激子结合能和跨异质结的大动量失配。以前的理论未能提供一个全面的物理图片的电荷转移机制。为了解决这一挑战，我们开发了一个第一性原理框架，它可以捕捉激子-声子相互作用的扩展系统。我们发现，激子效应并不阻碍，但实际上驱动超快的电荷转移在vdW异质结构。多体电子-空穴相互作用提供了电子之间的合作，这放松了动量守恒的约束并减小了电荷转移的能隙。我们揭示了激子动力学的两个步骤的过程：超快空穴转移，其次是更长的中间“热”激子弛豫。这一工作证实了多体激子效应对超快动力学的重要性，并为理解vdW异质结中的相关现象提供了基础。
Recent experiments revealed stacking-configuration-independent and ultrafast charge transfer in transition metal dichalcogenides van der Waals (vdW) heterostructures, which is surprising given strong exciton binding energies and large momentum mismatch across the heterojunctions. Previous theories failed to provide a comprehensive physical picture for the charge transfer mechanisms. To address this challenge, we developed a first-principles framework which can capture exciton-phonon interaction in extended systems. We find that excitonic effect does not impede, but actually drives ultrafast charge transfer in vdW heterostructures. The many-body electron-hole interaction affords cooperation among the electrons, which relaxes the constraint on momentum conservation and reduces energy gaps for charge transfer. We uncover a two-step process in exciton dynamics: ultrafast hole transfer followed by much longer relaxation of intermediate "hot" excitons. This work establishes that many-body excitonic effect is crucial to the ultrafast dynamics and provides a basis to understand relevant phenomena in vdW heterostructures.