Ref HAL: hal-03826961_v1
DOI: 10.3390/s22218131
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We introduce a Domain Decomposition Spectral Method (DDSM) as a solution for Maxwell’s equations in the frequency domain. It will be illustrated in the framework of the Aperiodic Fourier Modal Method (AFMM). This method may be applied to compute the electromagnetic field diffracted by a large-scale surface under any kind of incident excitation. In the proposed approach, a large-size surface is decomposed into square sub-cells, and a projector, linking the set of eigenvectors of the large-scale problem to those of the small-size sub-cells, is defined. This projector allows one to associate univocally the spectrum of any electromagnetic field of a problem stated on the large-size domain with its footprint on the small-scale problem eigenfunctions. This approach is suitable for parallel computing, since the spectrum of the electromagnetic field is computed on each sub-cell independently from the others. In order to demonstrate the method’s ability, to simulate both near and far fields of a full three-dimensional (3D) structure, we apply it to design large area diffractive metalenses with a conventional personal computer.

Ref HAL: hal-03806711_v1
Ref Arxiv: 2206.03022
DOI: 10.1103/PhysRevB.106.155404
Ref. & Cit.: NASA ADS
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Over the last few years, broken symmetry within crystals has attracted extensive attention since it can improve the control of light propagation. In particular, low-symmetry Bravais crystal can support shear polaritons, which has great potential in thermal photonics. In this work, we first use the fluctuation-dissipation theorem to investigate mechanisms of near-field thermal radiation (NFTR) in a low-symmetry Bravais crystal. The NFTR between such crystal slabs is nearly four orders of magnitude larger than the blackbody limit, demonstrating its remarkable potential for noncontact heat dissipation for nanoscale circuits or other devices. Moreover, we report a form of twist-induced near-field thermal control system employing the low-symmetry Bravais crystal medium (β-Ga2O3), showing that this crystal can serve as an excellent platform for twist-induced near-field thermal control. Due to the intrinsic shear effect, the twist-induced modulation supported by low-symmetry Bravais crystal exceeds that by high-symmetry crystal. We further clarify how the shear effect affects the twist-induced thermal-radiation modulation supported by hyperbolic and elliptical polaritons and show that the shear effect significantly enhances the twist-induced thermal control induced by the elliptical polariton mode. These results open directions for thermal-radiation control in low-symmetry materials, including geological minerals, common oxides, and organic crystals.

Ref HAL: hal-03783120_v1
Ref Arxiv: 2206.14561
DOI: 10.1103/PhysRevB.106.115203
Ref. & Cit.: NASA ADS
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Using the self-consistent Born approximation, we study a topological phase transition appearing in bulk HgCdTe crystals induced uncorrelated disorder due to both randomly distributed impurities and fluctuations in Cd composition. By following the density-of-states evolution, we clearly demonstrate the topological phase transition, which can be understood in terms of the disorder-renormalized mass of Kane fermions. We find that the presence of a heavy-hole band in HgCdTe crystals leads to the topological phase transition at much lower disorder strength than is expected for conventional three-dimensional topological insulators. Our theoretical results can also be applied to other narrow-gap zinc-blende semiconductors such as InAs, InSb, and their ternary alloys InAsSb.

Commentaires: 8 pages, 4 figures

Ref HAL: hal-03811148_v1
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In the first part we will show a study of the Casimir torque between two metallic one-dimensional gratings rotated by an angle θ with respect to each other. We find that, for infinitely extended gratings, the Casimir energy is anomalouslydiscontinuous at θ = 0, due to a critical zero-order geometric transition between a 2D- and a 1D-periodicsystem. We will comment on the relevant implication of this finding.In the second part I will discuss the Radiative heat transfer (RHT) and radiative thermal energy (RTE) for two-dimensional (2D) nanoparticle ensembles in the framework of many-body radiative heat transfer theory. We consider nanoparticles made of different materials: metals (Ag), polar dielectrics (SiC), or insulator-metallic phase-change materials(VO2). We start by investigating the RHT between two parallel 2D finite-size square-lattice nanoparticleensembles, with particular attention to many-body interactions (MBI) effects. We fix the particle radius (a)as the smallest length scale, and we describe the electromagnetic scattering from particles within the dipoleapproximation. Depending on the minimal distance between the in-plane particles (the lattice spacing p forperiodic systems), on the separation d between the two lattice and on the thermal wavelength,we systematically analyze the different physical regimes characterizing the RHT. Four regimes are identified,rarefied regime, dense regime, non-MBI regime, and MBI regime, respectively.

Ref HAL: hal-03811149_v1
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After a rapid introduction to the basic physical concepts of radiative heat transfer and the presentation of the general theory valid for arbitrary objects, I will focus on the study of the radiative heat transfer between two identical metallic one-dimensional lamellar gratings. To this aim I will present and exploit a modification to the widely used Fourier modal method, known as adaptive spatial resolution, based on a stretch of the coordinate associated with the periodicity of the grating. I show that this technique dramatically improves the rate of convergence when calculating the heat flux, and that there is a remarkable amplification of the exchanged energy, ascribed to the appearance of spoof-plasmon modes. By comparing our results to recent studies, we find a consistent quantitative disagreement with some previously obtained results going up to 50%.

Ref HAL: hal-03767404_v1
DOI: 10.1016/j.mtphys.2022.100828
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A radiative thermostat system senses its own temperature and automatically modulates heat transfer by turning on/off the cooling to maintain its temperature near a desired set point. Taking advantage of far- and near-field radiative thermal technologies, we propose an intelligent radiative thermostat induced by the combination of passive radiative cooling and near-field radiative thermal diode for thermal regulation at room temperature. The top passive radiative cooler in thermostat system with static thermal emissivity uses the cold outer space to passively cool itself all day, which can provide the bottom structure with the sub-ambient cold source. Meanwhile, using the phase-transition material vanadium dioxide, the bottom structure forms a near-field radiative thermal diode with the top cooler, which can significantly regulate the heat transfer between two terminals of the diode and then realize a stable temperature of the bottom structure. Besides, the backsided heat input of the thermostat has been taken into account according to real-world applications. Thermal performance of the proposed radiative thermostat design has been analyzed, showing that the coupling effect of static passive radiative cooling and dynamic internal heat transfer modulation can maintain an equilibrium temperature approximately locked within the phase transition region. Besides, after considering empirical indoor-to-outdoor heat flux, rendering its thermal performance closer to that of passive solar residential building walls, the calculation result proves that the radiative thermostat system can effectively modulate the temperature and stabilize it within a controllable range. Passive radiative thermostats driven by near-field radiative thermal diode can potentially enable intelligent temperature regulation technologies, for example, to moderate diurnal temperature in regions with extreme thermal swings.

Ref HAL: hal-03811151_v1
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We will discuss recent results: (i) on the theory of the Casimir torque between two gratings rotated by an angle theta with respect to each other, and (ii) on the theory and experiment on the Casimir force between interpenetrating gratings. These findings pave the way to the design of contactless quantum vacuum torsional spring and sensors with possible relevance to micro and nanomechanical devices.