Near-Field Photon Nernst Effect.

We consider the consequence of having nonreciprocal photon transfer between two surfaces with temperature gradient. We demonstrate that in a system consisting of graphene and a magneto-optical substrate separated by a gap, a transverse electric field is generated in graphene perpendicular to magnetic field and temperature gradient, in analogy to the Nernst effect. Such photon Nernst effect is driven by nonreciprocal Casimir force carried by photons. We show that the thermal efficiency of near-field photon Nernst effect is bounded by the Carnot limit, and nonreciprocal high-k modes are needed for approaching the limit. The near-field photon Nernst effect enables electrical probing of nonreciprocal radiative transfer and provides a novel means of energy harvesting.