Giant thermal switching in ferromagnetic VSe 2 with programmable switching temperature.

Active and reversible modulation of thermal conductivity can realize efficient heat energy management in many applications such as thermoelectrics. Using first-principles calculations, this study reports a giant thermal switching ratio of 12, much higher than previously reported values, in monolayer 2H-VSe 2 above room temperature. Detailed analysis indicates that the high thermal switching ratio is dominated by the ferromagnetic ordering induced phonon bandgap, which significantly suppresses the phonon-phonon scattering phase space across the entire vibration spectrum. The thermal switching in bulk 2H-VSe 2 is also investigated and the thermal switching ratio reaches 9.2 at the magnetic transition temperature. Both the phonon-phonon scattering space phase and phonon anharmonicity are responsible for the 9.2-fold thermal switching. This study advances the understanding of heat energy transport in two-dimensional ferromagnets, and also provides new insight into heat energy control and conversion.