Phase Diagram of High-Temperature Electron-Hole Quantum Droplet in Two-Dimensional Semiconductors

Quantumliquids, systems exhibiting effects of quantum mechanicsand quantum statistics at macroscopic levels, represent one of themost exciting research frontiers of modern physical science and engineering.Notable examples include Bose-Einstein condensation (BEC),superconductivity, quantum entanglement, and a quantum liquid. However,quantum liquids are usually only stable at cryogenic temperatures,significantly limiting fundamental studies and device development.Here we demonstrate the formation of stable electron-hole liquid(EHL) with the quantum statistic nature at temperatures as high as700 K in monolayer MoS2 and elucidate that the high-temperatureEHL exists as droplets in sizes of around 100-160 nm. We alsodevelop a thermodynamic model of high-temperature EHL and, based onthe model, compile an exciton phase diagram, revealing that the ionizedphotocarrier drives the gas-liquid transition, which is subsequentlyvalidated with experimental results. The high-temperature EHL providesa model system to enable opportunities for studies in the pursuitof other high-temperature quantum liquids. The results can also allowfor the development of quantum liquid devices with practical applicationsin quantum information processing, optoelectronics, and optical interconnections.