Piezochromism in the magnetic chalcogenide MnPS3

van der Waals materials are exceptionally responsive to external stimuli. Pressure-induced layer sliding, metallicity, and superconductivity are fascinating examples. Inspired by opportunities in this area, we combined high-pressure optical spectroscopies and first-principles calculations to reveal piezochromism in MnPS3. Dramatic color changes (green -> yellow -> red -> black) take place as the charge gap shifts across the visible regime and into the near infrared, moving systematically toward closure at a rate of approximately -50 meV/GPa. This effect is quenched by the appearance of the insulator-metal transition. In addition to uncovering an intriguing and tunable functionality that is likely to appear in other complex chalcogenides, the discovery that piezochromism can be deterministically controlled at room temperature accelerates the development of technologies that take advantage of stress-activated modification of electronic structure.