The role of collective motion in the ultrafast charge transfer in van der Waals heterostructures.

Han Wang,Yiyang Sun,Vincent Meunier,Junhyeok Bang,Liangbo Liang,Damien West,Shengbai Zhang

doi:10.1038/ncomms11504

Abstract

The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that van der Waals heterostructues can exhibit ultrafast charge transfer despite the weak binding of these heterostructures. Here we find, using time-dependent density functional theory molecular dynamics, that the collective motion of excitons at the interface leads to plasma oscillations associated with optical excitation. By constructing a simple model of the van der Waals heterostructure, we show that there exists an unexpected criticality of the oscillations, yielding rapid charge transfer across the interface. Application to the MoS2/WS2 heterostructure yields good agreement with experiments, indicating near complete charge transfer within a timescale of 100 fs.

Highlights

The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications
We find that the gap is indirect with the valence band maximum (VBM), in which the wave function is delocalized to both WS2 and MoS2, at G and the conduction band minimum (CBM), in which the wave function is localized to MoS2, at the K-point of the Brillouin zone, consistent with previous findings[17,30]
Investigating how the model describes the physics of charge transfer as a function of Mz, we find that criticality exists and that the hole dynamics undergoes a qualitative change depending on the magnitude of the dipole-induced coupling

Summary

Introduction

The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. A model for the hole transfer shows that this mechanism is critically dependent on the magnitude of the dipole transition matrix element, which determines the coupling across the heterostructure.

Results

Conclusion