Pattern-free thermal modulator via thermal radiation between Van der Waals materials

- A noncontact thermal modulator is proposed based on the natural Van der Waals materials without requiring nanofabrication.
- The modulation contrast can be higher than 5 for hBN films of a nanoscale thickness separated by a gap distance of 10 nm.
- The modulation performance is mainly attributed to the mismatching Type I hyperbolic surface phonon polaritons between two hBN films with increasing rotation angle.

Modulating heat flux provides a platform for a plethora of emerging devices such as thermal diodes, thermal transistors, and thermal memories. Here, a pattern-free noncontact thermal modulator is proposed based on the mechanical rotation between two Van der Waals films with optical axes parallel to the surfaces. A modulation contrast can reach a value higher than 5 for hexagonal Boron Nitride (hBN) films separated by a nanoscale gap distance. The dominant radiative heat exchange comes from the excitation of both Type I and Type II hyperbolic surface phonon polaritons (HSPhPs) at the vacuum-hBN interface for different orientations, while the large modulation contrast is mainly attributed to the mismatching Type I HSPhPs induced by rotation. This work opens the possibility to design cheap thermal modulators without relying on nanofabrication techniques, and paves the way to apply natural Van der Waals materials in manipulating heat currents in an active way.