[论文解读] Anomalous Interlayer Exciton Diffusion in Twist-Angle-Dependent Moiré Potentials of WS$_2$-WSe$_2$ Heterobilayers

Long Yuan, Biyuan Zheng+8 more|arXiv (Cornell University)|Oct 7, 2019

2D Materials and Applications参考文献 6被引用 48

一句话总结

本论文研究 twist-angle 相关的莫尔势如何影响 WS2-WSe2 异层激子的局域化与扩散，揭示了与密度和角度相关的异常传输行为。

ABSTRACT

The nanoscale periodic potentials introduced by moiré patterns in semiconducting van der Waals (vdW) heterostructures provide a new platform for designing exciton superlattices. To realize these applications, a thorough understanding of the localization and delocalization of interlayer excitons in the moiré potentials is necessary. Here, we investigated interlayer exciton dynamics and transport modulated by the moiré potentials in WS$_2$-WSe$_2$ heterobilayers in time, space, and momentum domains using transient absorption microscopy combined with first-principles calculations. Experimental results verified the theoretical prediction of energetically favorable K-Q interlayer excitons and unraveled exciton-population dynamics that was controlled by the twist-angle-dependent energy difference between the K-Q and K-K excitons. Spatially- and temporally-resolved exciton-population imaging directly visualizes exciton localization by twist-angle-dependent moiré potentials of ~100 meV. Exciton transport deviates significantly from normal diffusion due to the interplay between the moiré potentials and strong many-body interactions, leading to exciton-density- and twist-angle-dependent diffusion length. These results have important implications for designing vdW heterostructures for exciton and spin transport as well as for quantum communication applications.

研究动机与目标

• 理解来自扭转角度的莫尔势如何在 WS2-WSe2 异层双层中局域化异层激子。
• 使用瞬态吸收显微术在时间、空间与动量域表征激子动力学。
• 确定 K-Q 与 K-K 异层激子之间的能量差如何支配种群动力学。
• 量化在莫尔势场下激子扩散行为及其偏离正常扩散的程度。

提出的方法

• 结合瞬态吸收显微术与第一性原理计算研究异层激子动力学。
• 识别能量有利的 K-Q 异层激子并与 K-K 激子进行比较。
• 对激子种群在空间与时间上成像以观察因莫尔势 (~100 meV) 引起的局域化。
• 分析 twist angle 如何调控能量景观与激子传播。
• 评估多体相互作用在改变扩散长度和传输模式中的作用。

实验结果

研究问题

• RQ1 twist-angle-dependent moiré potentials 如何在 WS$_2$-WSe$_2$ 异层双层中局域化异层激子？
• RQ2 K-Q 与 K-K 异层激子在种群动力学与扩散中的作用是什么？
• RQ3 在莫尔势和多体相互作用下，激子扩散如何偏离正常扩散？
• RQ4 激子扩散长度如何依赖于激子密度与扭转角？

主要发现

• 激子局域化被直接可视化，并由约 ~100 meV 的 twist-angle-dependent 莫尔势所支配。
• K-Q 与 K-K 异层激子之间的能量差控制激子种群动力学。
• 由于莫尔势与强多体相互作用之间的耦合，激子输运偏离正常扩散。
• 扩散长度变得依赖于激子密度和扭转角。
• K-Q 异层激子在能量上更有利，影响整体传输行为。