The unexpected discovery of intrinsic ferromagnetism in layered van der Waals materials has sparked interest in both their fundamental properties and their potential for novel applications. Recent studies suggest near room-temperature ferromagnetism in the pressurized van der Waals crystal ${\mathrm{CrGeTe}}_3$. We perform a comprehensive experimental and theoretical investigation of magnetism and electronic correlations in ${\mathrm{CrGeTe}}_3$, combining broad-frequency reflectivity measurements with density functional theory and dynamical mean-field theory calculations. Our experimental optical conductivity spectra trace the signatures of developing ferromagnetic order and of the insulator-to-metal transition (IMT) as a function of temperature and hydrostatic pressure. With increasing pressure, we observe the emergence of a midinfrared feature in the optical conductivity, indicating the development of strong orbital-selective correlations in the high-pressure ferromagnetic phase. We find a distinct relationship between the plasma frequency and Curie temperature of ${\mathrm{CrGeTe}}_3$, which strongly suggests that a double-exchange mechanism is responsible for the observed near room-temperature ferromagnetism. Our results clearly demonstrate the existence of a charge-transfer gap in the metallic phase, ruling out its previously conjectured collapse under pressure.

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• Exchange interaction
• Metal-insulator transition
• Optical conductivity
• Chalcogenides
• Ferromagnets
• van der Waals systems
• Density functional theory
• Dynamical mean field theory