Optics, dynamics and transport of exciton polaritons in atomically thin semiconductors

当原子级薄的过渡金属二硫属化物（TMD）被集成到合适的光学微腔中时，它们紧密结合的激子可以与腔光子杂交形成激子极化激元。这些准粒子继承了其组成部分的特性，潜在地将光子的空间相干性和长传播长度与基于材料的激发的可调谐性和非线性相结合。TMD激子的大振子强度导致大规模的拉比分裂，并且大的结合能允许室温激子极化激子。极化激元弛豫的微观理解对于解释光谱测量以及理解玻色爱因斯坦凝聚和谷极化保留等现象至关重要。迄今为止，TMD极化激元的理论大多依赖于简单的唯象速率方程的人口动力学和松弛。此外，动量间接激子的影响被忽略了。在这个项目中，我们建议发展一个复杂的多粒子理论的基础上的密度矩阵形式主义，结合Hopfield方法，治疗微观基础上的强和非常强的耦合制度的光-物质相互作用的TMD单层以及扭曲的TMD同质和异质双层。我们的研究计划包括两个主要目标：获得微观洞察激子，光子和声子的相互作用在TMD单层和扭曲双层的强耦合制度，并学习如何通过改变扭转角，腔长，温度和镜面反射率来控制激子-声子-极化激子物理。我们将使用一个结合的Wannier-Hopfield方法来开发一个模型的极化激元弛豫，认为完整的激子能量景观。这将使我们能够揭示时间和能量分辨的多粒子过程背后的形成，热化和衰减的内部和层间激子极化激元。了解非常强的耦合机制对激子光学、动力学和TMD中输运的影响。在这里，光-激子相互作用足够强以将激子耦合到电子-空穴连续谱。由于其大的振子强度，TMD提供了一个理想的平台来研究这种广泛未开发的制度。我们将发展一个新的微观模型，关键是包括束缚激子态和未束缚的电子-空穴跃迁，来描述光诱导的内部激子波函数的修改，并寻求这种新物理的实验签名。我们在多粒子物理学和光物质相互作用建模方面的长期专业知识使我们在应对这一提议的挑战方面处于有利地位。我们的研究将为在技术上有前途的原子级薄纳米材料中的强耦合和非常强的耦合机制的微观理解提供重大进展。

When atomically thin transition metal dichalcogenides (TMD) are integrated into suitable optical microcavities, their tightly-bound excitons can hybridize with cavity photons to form exciton polaritons. These quasi-particles inherit properties from their constituent parts, potentially combining the spatial coherence and long propagation lengths of photons with the tunability and nonlinearity of material-based excitations. The large oscillator strength of TMD excitons leads to a massive Rabi splitting, and the large binding energy allows for room-temperature exciton-polaritonics. A microscopic understanding of polariton relaxation is essential for interpreting optical spectroscopy measurements, as well as understanding phenomena, such as Bose Einstein condensation and valley polarization retention. To date, much of the theory of TMD polaritons has relied on simple phenomenological rate equations for population dynamics and relaxation. Furthermore, the impact of momentum-indirect excitons has been neglected. In this project, we propose to develop a sophisticated many-particle theory based on the density matrix formalism, combined with a Hopfield approach, to treat on microscopic footing the strong and very-strong coupling regimes of light-matter interaction in TMD monolayers as well as twisted TMD homo- and heterobilayers. Our research plan consists of two main goals: Gain microscopic insights into the interplay of excitons, photons, and phonons within the strong coupling regime for TMD monolayers and twisted bilayers, and learn how to control the exciton-phonon-polariton physics by changing the twist angle, cavity length, temperature, and mirror reflectivity. We will use a combined Wannier-Hopfield approach to develop a model of polariton relaxation that considers the full exciton energy landscape. This will allow us to reveal the time- and energy-resolved many-particle processes behind the formation, thermalization and decay of both intra- and interlayer exciton polaritons. Understand the impact of the very-strong coupling regime on exciton optics, dynamics, and transport in TMDs. Here, the light-exciton interaction is strong enough to couple excitons to the electron-hole continuum. Due to their large oscillator strength, TMDs offer an ideal platform to study this widely unexplored regime. We will develop a new microscopic model, crucially including both bound exciton states and the unbound electron-hole transitions, to describe the light-induced modification of the internal exciton wavefunction, and seek experimental signatures of this novel physics. Our long-standing expertise in modelling many-particle physics and light-matter interactions places us in a strong position to tackle the challenges of this proposal. Our study will provide a major advance for microscopic understanding of the strong and very-strong coupling regime in the technologically promising class of atomically thin nanomaterials.