Quantum Thermal Rectification to design thermal diodes and transistors

We study in this article how heat can be exchanged between two level systems (TLS) each of them being coupled to a thermal reservoir. Calculation are performed solving a master equation for the density matrix using the Born markov-approximation. We analyse the conditions for which a thermal diode and a thermal transistor can be obtained as well as their optimization.

Thermal emission by a subwavelength aperture

We calculate, by means of fluctuational electrodynamics, the thermal emission of an aperture filled by vacuum or a material at temperature T. We show that thermal emission is very different whether the aperture size is large or small compared to the thermal wavelength. Subwavelength apertures filled with vacuum (subwavelength blackbody) have their thermal emission strongly decreased compared to classical blackbodies. A simple expression of their emissivity can be calculated and their total emittance scales as T 8 instead of T 4 for large apertures. Thermal emission of disk of materials with a size comparable to the wavelength is also discussed. It is shown in particular that emissivity of such a disk is increased when the material can support surface waves such as phonon polaritons.

Energy density above a resonant metamaterial in the GHz: an alternative to near-field thermal emission detection

This paper proposes an experiment to easily detect radiative heat transfer in the microwave range. Following an idea given by Pendry more than a decade ago [1], we show that a 3D array of tungsten 2micron radius wires with a 1 cm period makes a low cost material exhibiting a surface plasmon in the microwave range around 2.9 GHz. Such a heated material should exhibit an emission peak near the plasmon frequency well above ambient emission. Analysis of the signal detected in the near-field should also be a tool to analyze how homogenization theory applies when the distance to the material is of the order of the metamaterial period. It could also be give a model to non-local dielectric properties in the same conditions.

Near field radiative heat transfer between two nonlocal dielectrics

We explore in the present work the near-field radiative heat transfer between two semi-infinite parallel nonlocal dielectric planes by means of fluctuational electrodynamics. We use atheory for the nonlocal dielectric permittivityfunction proposed byHalevi and Fuchs. This theory has the advantage to includedifferent models performed in the literature. According to this theory, the nonlocal dielectric function is described by a Lorenz-Drude like single oscillator model, in which the spatial dispersion effects are represented by an additional term depending on the square of the total wavevector k. The theory takes into account the scattering of the electromagneticexcitation at the surface of the dielectric material, which leads to the need of additional boundary conditions in order to solve Maxwells equations and treat the electromagnetic transmission problem. The additional boundary conditions appear as additional surface scattering parameters in the expressions of the surface impedances. It is shown that the nonlocal modeling deviates from the classical $1/d^2$ law in the nanometerrangeat distances still larger than the ones where quantum effects are expected to come into play.

Nonlocal study of the near field radiative heat transfer between two n-doped semiconductors

We study in this work the near-field radiative heat transfer between two semi-infinite parallel planes of highly n-doped semiconductors. Using a nonlocal model of the dielectric permittivity, usually used for the case of metallic planes, we show that the radiative heat transfer coefficientsaturates as the separation distance is reduced for high doping concentration. These results replace the 1/d${}^2$ infinite divergence obtained in the local model case. Different features of the obtained results are shown to relate physically to the parameters of the materials, mainly the doping concentration and the plasmon frequency.

Radiative Thermal Rectification between SiC and SiO2

By means of fluctuationnal electrodynamics, we calculate radiative heat flux between two pla-nar materials respectively made of SiC and SiO2. More specifically, we focus on a first (direct) situation where one of the two materials (for example SiC) is at ambient temperature whereas the second material is at a higher one, then we study a second (reverse) situation where the material temperatures are inverted. When the two fluxes corresponding to the two situations are different, the materials are said to exhibit a thermal rectification, a property with potential applications in thermal regulation. Rectification variations with temperature and separation distance are here reported. Calculations are performed using material optical data experimentally determined by Fourier transform emission spectrometry of heated materials between ambient temperature (around 300 K) and 1480 K. It is shown that rectification is much more important in the near-field domain, i.e. at separation distances smaller than the thermal wavelength. In addition, we see that the larger is the temperature difference, the larger is rectification. Large rectification is finally interpreted due to a weakening of the SiC surface polariton when temperature increases, a weakening which affects much less SiO2 resonances.

Fundamental limits for non-contact transfers between two bodies

We investigate energy and momentum non-contact exchanges between two arbitrary flat media separated by a gap. This problem is revisited as a transmission problem of individual system eigenmodes weighted by a transmission probability obtained either from fluctuational electrodynamics or quantum field theory. An upper limit for energy and momentum flux is derived using a general variational approach. The corresponding optimal reflectivity coefficients are given both for identical and different media in interaction.

Heat Transport Through Plasmonic Interactions in Closely Spaced Metallic Nanoparticles Chains

We report a numerical investigation on the heat transfer through one dimensional arrays of metallic nanoparticles closely spaced in a host material. Our simulations show that the multipolar interactions play a crucial role in the heat transport via collective plasmons. Calculations of the plasmonic thermal conductance and of the thermal conductivity in ballistic and diffusive regime, respectively have been carried out. (a) Using the Landauer-Buttiker formalism we have found that, when the host material dielectric constant takes positive values, the multipolar interactions drastically enhance by several order of magnitude the ballistic thermal conductance of collective plasmons compared with that of a classical dipolar chain. On the contrary, when the host material dielectric constant takes negative values, we have demonstrated the existence of non-ballistic multipolar modes which annihilate the heat transfer through the chains. (b) Using the kinetic theory we have also examined the thermal behavior of chains in the diffusion approximation. We have shown that the plasmonic thermal conductivity of metallic nanoparticle chains can reach 1% of the bulk metal thermal conductivity . This result could explain the anomalously high thermal conductivity observed in many colloidal suspensions, the so called nanofluids.