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Measurement of Anomalous Heat Transfer in Sapphire

Abstract

On nearly every length scale radiated heat transfer between two objects can be described using the exact same theory. However, this theory, which is invariant with respect to the distances separating the objects, breaks down over distances of a few microns or less. Radiated heat flux between objects on these scales experiences an enhancement that grows as the distance between the objects shrinks. This enhancement, known as near field radiated heat transfer (NFRT) arises from phonon polartion resonances on the surfaces of the materials.

Not all materials experience these resonances and only those that have resonances in the near IR will experience this phenomenon. One material with such resonances is sapphire. Expanding and improving upon previous work we created a calorimeter capable of probing this effect in sapphire. Our new methods remove many of the previous issues associated with thermal drift and electrostatic forces. This novel system combined with new probing techniques has allowed us to measure fluxes as small as 30 nW at separation distances as small as a few tens of nanometers. Using this system we were able to observe anomalous radiated heat flow between sapphire near room temperature. Furthermore, the system was robust enough to function at low temperatures allowing us to confirm the temperature dependence of this effect down to temperatures as low as 100K.

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