  Active control over the flow of heat in the near-field holds promise for
nanoscale thermal management, with applications in refrigeration,
thermophotovoltaics, and thermal circuitry. Analogously to its electronic
counterpart, the metal-oxide-semiconductor (MOS) capacitor, we propose a
thermal switching mechanism based on accumulation and depletion of charge
carriers in an ultra-thin plasmonic film, via application of external bias. In
our proposed configuration, the plasmonic film is placed on top of a
polaritonic dielectric material that provides a surface phonon polariton (SPhP)
thermal channel, while also ensuring electrical insulation for application of
large electric fields. The variation of carrier density in the plasmonic film
enables the control of the surface plasmon polariton (SPP) thermal channel. We
show that the interaction of the SPP with the SPhP significantly enhances the
net heat transfer. We study SiC as the oxide and explore three classes of
gate-tunable plasmonic materials: transparent conductive oxides, doped
semiconductors, and graphene, and theoretically predict contrast ratios as high
as 225%.
