Dipolar excitons and interlayer coupling: Optics, dynamics and transport in Janus TMD heterostructures

将原子级薄的过渡金属二硫属化物（TMD）垂直堆叠成货车德瓦尔斯异质结构允许实现过多的物理现象和技术应用。这两种材料之间的界面决定了涌现的性质，这可以通过选择材料，扭曲和电场来调整。改变这些界面行为的根本方法是化学改性组成层。TMD单层由两个硫族元素层之间的过渡金属层组成。因此，通过用不同的硫族元素层替换这些硫族元素层中的一个，可以生长“Janus”TMD，例如MoSe 2变成SeMoS。Janus TMD中的固有偶极子预计将彻底改变其在Janus基TMD异质结构（Janus HS）中的界面行为，调制扭曲系统中的层间距离、波函数杂化和莫尔电位。内置偶极子的另一个结果是激子-声子相互作用被认为是增强的。因此，我们预计Janus HS可以促进非常有效的声子驱动的层间激子形成，最大限度地减少辐射损失。此外，我们预计一个非常有趣的激子输运Janus HS：一方面，增强的莫尔势和激子-声子散射的增加可能会阻碍激子的传播，但在另一方面，固有的偶极子肯定会导致一个有效的激子-激子排斥引起更快的激子输运。目前，对Janus HS的了解很少，只有少数的实验和理论研究。在这项提议中，我们将进行联合实验理论合作，将最先进的CVD生长与复杂的光学表征和微观多粒子理论相结合，以揭示Janus HS中激子光学，动力学和传输中的有趣现象。 特别是，我们将（i）探索堆叠顺序，材料选择，扭转角，温度和电场对Janus HS中层内和层间激子的光学指纹的作用，（ii）揭示Janus HS中激子的形成，弛豫和衰减，其中长辐射寿命，增强的声子散射和固有的电偶极子将是至关重要的，以及（iii）探索激子输运，并确定如何通过调节Janus HS中的堆叠顺序和扭转角来调制莫尔势以捕获或释放激子。我们设想提供一个全面的微观理解激子光学，动力学和输运在Janus的TMD异质结揭示途径对外部的可调谐性和控制这些多粒子现象，也是高度相关的光电应用的基础上Janus TMD材料。

The vertical stacking of the atomically thin transition metal dichalcogenides (TMDs) into van der Waals heterostructures allows the realization of a plethora of physical phenomena and technological applications. The interface between these two materials dictates the emergent properties, which can be tuned through choice of material, twisting and electric fields. A radical approach to alter the behaviour of these interfaces is to chemically modify the constituent layers. TMDs monolayers consist of a transition metal layer between two chalcogen layers. Therefore, by substituting one of these chalcogen layers with a different one, it is possible to grow a "Janus" TMD, as for example MoSe2 becomes SeMoS. The inherent dipole in Janus TMDs is expected to drastically alter their interfacial behaviour in Janus-based TMD heterostructures (Janus HSs), modulating the interlayer distance, the wave function hybridization, and the moiré potential in twisted systems. Another consequence of the built in-dipole is that the exciton-phonon interaction is believed to be enhanced. Therefore, we expect that Janus HSs could facilitate extremely efficient phonon-driven interlayer exciton formation, minimizing radiative losses. Furthermore, we expect a highly interesting exciton transport in Janus HSs: On one side the enhanced moiré potentials and the increased exciton-phonon scattering are likely to hinder the propagation of excitons, but on the other side the inherent dipole will certainly lead to an efficient exciton-exciton repulsion giving rise to a faster exciton transport. Currently, Janus HSs are poorly understood, with only a handful of experimental and theoretical studies. In this proposal we will undertake a joint experiment-theory collaboration combining state-of-the-art CVD growth with sophisticated optical characterization and microscopic many-particle theory to reveal intriguing phenomena in exciton optics, dynamics and transport in Janus HSs. In particular, we will (i) explore the role stacking order, choice of material, twist-angle, temperature and electric field have on the optical fingerprint of intra- and interlayer excitons in Janus HSs, (ii) reveal the exciton formation, relaxation and decay in Janus HSs, where the long radiative lifetime, enhanced phonon-scattering and inherent electric dipole will be of crucial importance, and (iii) explore the exciton transport and determine how the moiré potential can be modulated to either trap or release excitons through tuning the stacking order and twist angle in Janus HSs. We envision to offer a comprehensive microscopic understanding of exciton optics, dynamics and transport in Janus-based TMD heterostructures revealing pathways towards external tunability and control of these many-particle phenomena that are also highly relevant for optoelectronic applications based on Janus TMD materials.