Super-Planckian far-field radiative heat transfer

We present here a theoretical analysis that demonstrates that the far-field radiative heat transfer between objects with dimensions smaller than the thermal wavelength can overcome the Planckian limit by orders of magnitude. To guide the search for super-Planckian far-field radiative heat transfer, we make use of the theory of fluctuational electrodynamics and derive a relation between the far-field radiative heat transfer and the directional absorption efficiency of the objects involved. Guided by this relation, and making use of state-of-the-art numerical simulations, we show that the far-field radiative heat transfer between highly anisotropic objects can largely overcome the black-body limit when some of their dimensions are smaller than the thermal wavelength. In particular, we illustrate this phenomenon in the case of suspended pads made of polar dielectrics like SiN or SiO2. These structures are widely used to measure the thermal transport through nanowires and low-dimensional systems and can be employed to test our predictions. Our work illustrates the dramatic failure of the classical theory to predict the far-field radiative heat transfer between micro- and nanodevicesWe acknowledge funding from the Spanish MINECO (FIS2015-64951-R, MAT2014-53432- C5-5-R, FIS2014-53488-P, FIS2017-84057-P), the Comunidad de Madrid (S2013/MIT-2740), the European Union Seventh Framework Programme (FP7-PEOPLE-2013-CIG- 630996, FP7-PEOPLE-2013-CIG-618229), and the European Research Council (ERC-2011-AdG-290981 and ERC-2016- STG-714870). V.F.-H. acknowledges support from “la Caixa” Foundation and J.C.C. thanks the DFG and SFB767 for sponsoring his stay at the University of Konstanz as Mercator Fello