Ref HAL: hal-04172370_v1
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We present a numerical approach for the solution of EM scattering from a dielectric cylinder partially covered with graphene. It is based on a classical Fourier-Bessel expansion of the fields inside and outside the cylinder to which we apply the ad-hoc boundary conditions in the presence of graphene. Due to the singular nature of the electric field at the ends of the graphene sheet, we introduce auxiliary boundary conditions to better take this reality into account.

Ref HAL: hal-04171737_v1
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We present a simplification of the Fourier Modal Method (FMM) for crossed gratings with subwavelength heights. We show that in this case it is possible to compute the scattering matrix of the structure without solving the eigenvalue problem which is the most expensive computational part of the FMM algorithm. This approach is very efficient and thus suitable for periodic metasurfaces.

Ref HAL: hal-04171661_v1
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The Fourier Modal Method [1] (FMM) is very popular and efficient approach for modelling diffraction from gratings. It can be applied to graphene gratings either by using the Zero Thickness Model (ZTM) i.e. using directly the optical conductivity of graphene in the boundary conditions, or by using the Finite Thickness Model (FTM) where graphene is seen as a slab of atomic thickness and a relative dielectric permittivity deduced from its optical conduc- tivity. For 1D gratings, the FMM based on the ZTM proves to be very efficient for the transverse electric polarization case (electric filed parallel to the direction of invariance of the strips) but suffers from low convergence in the transverse magnetic polarization case (magnetic filed parallel to the direction of invariance of the strips). This is due to a an inappropriate use of the Fourier factorization rules [1]. The FMM based on the FTM, on the other hand, doesn’t experience such a limitation but at the expense of solving an eigenvalue problem inside the grating which has been given a finite thickness. This is very demanding from the computational point of view because solving an eigenvalue problem has a cost scaling with the third power of the dimension of the matrices in play. This increases the computational cost of the approach especially for crossed gratings. Furthermore, a in a recent work [2], the authors have shown the it is possible to avoid solving this eigenvalue problem if the grating has a deep subwavelength thickness. This condition is exactly fulfilled by graphene under the FTM where it is assumed to have an atomic thickness. I will show that using such a simplification lowers the computational cost of the FMM-FTM while giving reliable and accurate results.

Ref HAL: hal-04170736_v1
Ref Arxiv: 2306.17640
Ref INSPIRE: 2673548
DOI: 10.1103/PhysRevA.108.062811
Ref. & Cit.: NASA ADS
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We investigate the Casimir-Lifshitz force (CLF) between two identical graphene strip gratings, laid on finite dielectric substrate. By using the scattering matrix (S-matrix) approach derived from the Fourier Modal Method with local basis functions (FMM-LBF), we fully take into account the high-order electromagnetic diffractions, the multiple scattering and the exact 2D feature of the graphene strips. We show that the non-additivity, which is one of the most interesting features of the CLF in general, is significantly high and can be modulated in situ without any change in the actual material geometry, by varying the graphene chemical potential. This study can open the deeper experimental exploration of the non-additive features of CLF with micro- or nano-electromechanical graphene-based systems.

DOI: 10.1016/j.ijheatmasstransfer.2023.124462
Résumé:

Near-field radiative heat transfer (NFRHT) has received growing attention because of its high intensity far beyond the Planck's black-body limit. Insertion of a third object in proximity of the two particles can significantly influence and manipulate its NFRHT. However, for the system composed of many particles, the effect of many-body interaction (MBI) on NFRHT between arbitrary two particles is still not well understood. In this work, the MBI is studied for two particles with three typical proximate ensembles: particle chain, plane and grating. With the increasing of proximate particle size, the MBI on NFRHT will experience a radical change from inhibition to enhancement. The polarizability of the proximate particle increases with particle radius, which enhances the interaction between the proximate particles and the main particle, and then results in enhancement of NFRHT between the main particles. When twisting the proximate particle ensemble, the proximate MBI accounts for a smooth and non-oscillated twisting angle dependence of NFRHT, and it is different from the oscillation phenomenon of NFRHT for particle gratings. This work deepens the understanding of NFRHT in dense particulate systems.

Résumé:

We propose a scheme for a quantum thermal machine made by atoms interacting with a single nonequilibrium electromagnetic field. We show that these machines can deliver all thermodynamic tasks (cooling, heating, and population inversion) by establishing quantum coherence with the body on which they act. Remarkably, this system allows these machines to reach efficiencies at maximum power very close to the Carnot limit, which is much more than in existing models [1]. REFERENCES 1. Leggio, B., B. Bellomo, and M. Antezza, Phys. Rev. A, Vol. 91, 012117 (2015)

Résumé:

I will discuss recent results: (i) on the Casimir torque between two metallic onedimensional gratings rotated by an angle θ with respect to each other [1]; and (ii) on the quantitative effect of the presence of the metallic contact grid at the front side of thermophotovoltaic cells, based on a rigorous approach [2]. This effect can be tremendous both in terms of optical and electrical (resistive) losses. However, it has been theoretically either discarded or studied by means of extremely simplified models (like shadowing methods, consisting in just ignoring the fraction of the cell surface covered by metal). 1. Antezza, M., H. B. Chan, B. Guizal, V. N. Marachevsky, R. Messina, and M. Wang, Phys. Rev. Lett., Vol. 12, 013903, 2020. 2. Austry, K., Y. Jeyar, M. Luo, B. Guizal, R. Messina, R. Vaillon, and M. Antezza, 2023 (in preparation).