RESUMEN
The control of near-field radiative heat transfer (NFRHT) between two metasurfaces can be achieved by manipulating the geometric and dielectric parameters of their components. Based on a 2D effective medium approximation, we describe the dielectric response of each metasurface composed of graphene-coated nanoparticles (GCNPs) on a 2D square lattice as a homogeneous uniaxial film. Wrapping Drude-like nanoparticles (NPs) with graphene enhances the effective plasmonic response of metasurfaces by significantly broadening the frequency range in which surface and hyperbolic waves can be excited by thermal photons. Consequently, the NFRHT between GCNP metasurfaces improves that observed between uncoated Drude-like nanoparticle arrays. We found that the heat flux (Q) grows with increasing metasurface packing fraction (PF) and is also sensitive to GCNP size. By tuning the graphene chemical potential ( µ ) , Q reaches a maximum improvement of 88 % for µ ≈ 0.1 eV with cores made of Drude-like material, while using cores made of the polar dielectric SiC, Q increases up to 226 % for µ ≈ 0.45 eV. Our results show that, in addition to the geometric control achieved with uncoated NP arrays, the tunable optical properties of the graphene shell allow dynamic control of the heat flux, expanding the possibilities for NFRHT engineering offered by GCNP metasurfaces.
RESUMEN
We present a comprehensive analysis of the out-of-equilibrium Casimir pressure between two high-[Formula: see text] superconducting plates, each kept at a different temperature. Two interaction regimes can be distinguished. While the zero-point energy dominates in the near field, thermal effects become important at large interplate separations causing a drop in the force's magnitude compared with the usual thermal-equilibrium case. Our detailed calculations highlight the competing role played by propagating and evanescent modes. Moreover, as one of the plates undergoes the superconducting transition, we predict an abrupt change in the force for any plate distance, which has not been previously observed in other systems. The sensitivity of the dielectric function of the high-[Formula: see text] superconductors makes them ideal systems for a possible direct measurement of the out-of-equilibrium Casimir pressure.
RESUMEN
Near-field radiative heat transfer (NFRHT) management can be achieved using high-temperature superconductors. In this work, we present a theoretical study of the radiative heat transfer between two [Formula: see text] (YBCO) slabs in three different scenarios: Both slabs either in the normal or superconducting state, and only one of them below the superconductor critical temperature [Formula: see text]. The radiative heat transfer is calculated using Rytov's theory of fluctuating electrodynamics, while a two-fluid model describes the dielectric function of the superconducting materials. Our main result is the significant suppression of the NFRHT when one or both of the slabs are superconducting, which is explained in terms of the detailed balance of the charge carriers density together with the sudden reduction of the free electron scattering rate. A critical and unique feature affecting the radiative heat transfer between high-temperature superconductors is the large damping of the mid-infrared carriers which screens the surface plasmon excitation.