EXCITON PHASE TRANSITION IN ATOMICALLY THIN 2D SEMICONDUCTORS

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 Abstract

Atomically 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.