Near room-temperature ferromagnetism from double exchange in the van der Waals material <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>CrGeTe</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>: Evidence from optical conducti

The van der Waals material CrGeTe${}_{3}$ is a ferromagnetic charge-transfer insulator at ambient pressure. When compressed, the material transforms into a semimetal with near room temperature ferromagnetism. Here, the authors present temperature- and pressure-dependent measurements of its optical conductivity, combined with density functional theory and dynamical mean-field theory calculations. A novel approach to analyzing the experimental data reveals that the pressure-induced insulator-to-metal transition alters the mechanism of ferromagnetism in CrGeTe${}_{3}$ from superexchange to double exchange.