Emergence and relaxation of an e-h quantum liquid phase in photoexcited MoS2 nanoparticles at room temperature

Abstract: Low-dimensional transition metal dichalcogenide, TMDC, materials are heralding a new era in optoelectronics and valleytronics owing to their unique properties. Photo-induced dynamics in these systems has mostly been studied from the perspective of individual quasi-particles, including excitons, bi-excitons or, even, trions. Their formation, evolution and decay. The role of multi-body and exciton dynamics, the associated collective behaviour, condensation and inter-excitonic interactions remain intriguing and seek attention, especially in room-temperature scenarios which are relevant for device applications. In this work we evidence the formation and decay of an unexpected electron-hole quantum liquid phase at room-temperature on ultrafast picosecond timescales in multi-layer MoS2 nanoparticles through femtosecond broadband transient absorption spectroscopy. Our studies reveal the complete dynamical picture: the initial electron-hole plasma, EHP, condenses into an quantum electron-hole liquid, EHL, phase which typically lasts as long as 10 ps, revealing its robustness, whereafter the system decays through phonons.