Room-Temperature Electron-Hole Condensation in Direct-Band-Gap Semiconductor Nanocrystals

Abstract

An electron-hole liquid (EHL) is a collective nonequilibrium macroscopic quantum state of matter arising from the condensation of charge carriers in the form of a droplet. However, achieving the EHL state in a direct-band-gap material at room temperature is extremely difficult due to the excess thermal energy, short carrier lifetime, and low binding energy. Herein, we report the experimental observation of an EHL in a direct-band-gap coupled metal-halide perovskite-nanocrystal film by exploiting the electron-phonon interaction at room temperature. The helicity-resolved transient-absorption measurements above a critical carrier density of approximately 10¹⁸⁺ cm^-3 reveal the EHL below the exciton and biexciton states. These results are consistent with our theoretical calculations of the ground-state energy and the thermodynamic phase diagram. The condensation and evaporation times of the EHL are approximately 0.80 ps and approximately 60 ps, respectively. Our study hopefully paves the way for many-body correlations in optical processes and may offer exceptional opportunities to develop futuristic quantum technologies.