Exciton Thermodynamics in Pure Diamond

Abstract

Low-temperature condensation thermodynamics is a fundamental research in the field of condensed matter physics. Prior studies have extensively explored the exciton condensation of indirect-bandgap semiconductors like silicon (Si) and germanium (Ge), which predominantly focus on temperature effects but neglect the relationship between the initial condensed state and the external excitation power density. Here, based on pure diamond, the impact of excitation power density on condensed-state thermodynamics is analyzed. With power density as a key variable, an inter-dependency among exciton, electron–hole plasma, and electron–hole droplets can be observed in diamond. For instance, as the average excitation power density increases (6.15 to 246 mW cm⁻²), the exciton emission quenching temperature rises from 60 to 120 K. This is because the variation in initial states of the excitonic condensed phase under different excitation power densities leads to the changes in quenching energy, which subsequently affects the temperature dependence of the exciton quenching. This study pioneers a novel approach to explore luminescent thermodynamics in indirect-bandgap semiconductors with both excitation power density and temperature considered as dimensions simultaneously.