Abstract
Using the standard fluctuational electrodynamics framework, we analytically calculate the radiative heat current between two thin metallic layers, separated by a vacuum gap. We analyse different contributions to the heat current (travelling or evanescent waves, transverse electric or magnetic polarization) and reveal the crucial qualitative role played by the dc conductivity of the metals as compared to the speed of light. For poorly conducting metals, the heat current may be dominated by evanescent waves even when the separation between the layers greatly exceeds the thermal photon wavelength, and the coupling is of electrostatic nature. For well-conducting metals, the evanescent contribution dominates at separations smaller than the thermal wavelength and is mainly due to magnetostatic coupling, in agreement with earlier works on bulk metals.
Highlights
Separated objects may exchange heat via electromagnetic fluctuations [1,2,3,4,5]
The results presented in the previous section show two qualitatively different pictures of the near-field heat transfer between two metallic layers, depending on the value of their dimensionless 2D dc conductivity: for G 1, the heat transfer is mostly due to electrostatic coupling between the layers, up to distances significanly exceeding λT, while for G 1 the near-field magnetostatic coupling dominates up to distances d ∼ λT, in close analogy with earlier results on bulk metals
We have performed an analytical calculation of the radiative heat current between two thin metallic layers, using the standard framework of fluctuational electrodynamics and a local 2D Drude model for the electromagnetic response of each layer
Summary
Separated objects may exchange heat via electromagnetic fluctuations [1,2,3,4,5]. This radiative heat transfer arises due to electric charge density and current fluctuations inside the constituting materials, and is usually described within the phenomenological framework of fluctuational electrodynamics (FED) [1, 2, 6], for which the critical inputs are the material response functions and the system geometry. It is well known that in the near-field limit, energy may tunnel via evanescent electromagnetic waves causing a strong enhancement of the heat transfer, as has been observed experimentally (see the reviews [7,8,9,10] and references therein). In the extreme near-field limit, heat transfer due to the electrostatic Coulomb interaction has been studied [13,14,15,16,17,18,19]
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