EXCITON PHASE TRANSITION IN ATOMICALLY THIN 2D SEMICONDUCTORS

非技术摘要：半导体中的光激发产生电子和空穴对。这些准粒子负责许多设备应用中使用的材料的光电行为，包括光伏、发光二极管和光探测器。这些电子和空穴准粒子，类似于环境中的粒子，在足够高的密度和较低的温度下，可以经历从不相互作用的气体到凝聚液体的相变。与稀相相比，凝聚准粒子态表现出非常不同的电子性质。然而，到目前为止，有关电子-空穴凝聚的研究仅限于极低温度和高激光激发密度的有限组材料体系中。本项目致力于研究高温下原子薄半导体中的这些凝聚电子空穴状态。这项研究的教育部分涉及招募高中生到实验室，特别是从代表性不足的社区招募高中生。技术摘要原子薄的2D过渡金属二卤化物(TMDC)提供了一个显著的激子系统，它具有很大的激子结合能，比典型的半导体材料大一个数量级。这些材料可以为高温下量子多体物理的研究提供前所未有的机会。众所周知，在足够高的密度下，激子凝聚成电子-空穴等离子体，然后凝聚成液体。但总的来说，这种从气体到液体的转变是在低温下发生的。本文旨在研究二维TMDC材料中激子在室温及以上温度下向电子-空穴液体(EHL)态的相变。这种激子凝聚是经典气体凝聚成液滴的量子力学模拟。这项工作将对二维TMDC材料中的激子凝聚有一个深入的了解。

Nontechnical Abstract: Optical excitations in semiconductors create electron and hole pairs. These quasiparticles are responsible for optoelectronic behavior of materials used in many device applications including, photovoltaics, light emitting diodes and light detectors. These electron and hole quasiparticles, similar to particles in ambient, can go through phase transitions from noninteracting gas to condensed liquid phase at high enough densities and low temperatures. The condensed quasiparticle state exhibits very different electronic properties compared to dilute phase. However so far the studies involving the electron-hole condensation are limited to very low temperatures and high laser excitation densities in limited group of material systems. This project focuses on study of these condensed electron-hole states in atomically thin semiconductors at high temperatures. The educational component of the research involves recruiting high school students specifically from underrepresented communities to the labs. Technical AbstractAtomically thin 2D transition metal dichalcogenides (TMDC) provide a remarkable excitonic system with a large exciton binding energy, more than an order of magnitude larger than typical semiconductor materials. These materials can provide unprecedented opportunities for the studies of quantum many-body physics at elevated temperatures. It has been known that excitons at high enough densities condense into electron-hole plasma and then into a liquid. But in general this gas to liquid phase transition takes place at cryo-temperatures. Here the proposed work aims to study the phase transition of excitons in 2D TMDC materials into a state of electron-hole liquid (EHL) at room temperature and above. This exciton condensation is a quantum mechanical analogue of the classical gas condensation into a liquid droplet. This work will pursue a thorough understanding of the exciton condensation in 2D TMDC materials.