arXiv subjects

Riccardo Messina

Publications and source records attributed to Riccardo Messina.

At least 19 recordsLinked to original sources

arXiv2026

Near-field Dressing of Thermal Emission

Radiative heat transfer at subwavelength distances is generally understood as enhanced energy exchange mediated by photon tunnelling between neighboring bodies. While near-field interactions can dramatically increase mutual heat transfer, whether they also modify the thermal radiation emitted by the bodies themselves remains an open question. Here we experimentally show that near-field electromagnetic coupling reshapes far-field thermal emission through a distance-dependent dressed emissivity. Using a dual-probe calorimetric platform, we independently monitor the radiative balance of two borosilicate microspheres over separations ranging from 120 micrometers to a few hundred nanometers, spanning the transition from the far field to the near field. Nanowatt-resolved differential radiometry reveals asymmetric heat fluxes and a non-monotonic response of the hotter sphere, demonstrating that thermal radiation is governed not only by emitter-bath interactions but also by coupling to the surrounding photonic environment. By analyzing the total power exchanged between the coupled system and the external thermal bath, we directly extract a dressed emissivity and show that near-field interactions renormalize the far-field thermal emission of the pair through a redistribution of the electromagnetic modes available to thermal fluctuations. These observations provide direct experimental evidence that thermal emitters are dressed by their electromagnetic environment, establishing a thermal analogue of the Purcell effect.

physics.optics↗

arXiv2025

Many-Body Floquet Theory for Radiative Heat Transfer in Time-Modulated Systems

We develop a general theory of radiative heat exchange between dipoles with time-modulated optical properties. This framework extends fluctuational electrodynamics beyond equilibrium by incorporating nonstationary correlations and memory effects induced by temporal modulation. Closed-form expressions for the heat currents in modulated many-body systems are obtained, together with a generalized Landauer-like formulation of the pairwise exchanges, where the transmission coefficient accounts for all inelastic frequency-conversion channels. Near-resonant modulation redistributes and amplifies thermal fluctuations across Floquet sidebands, acting as a parametric amplifier of thermal radiation and enabling active, frequency-selective control of nanoscale heat transfer.

physics.optics↗

arXiv2025

Near-field focusing and amplification of tip-substrate radiative heat transfer

The spatially resolved near-field radiative heat transfer between a nanoscale probe and a substrate is studied in the fluctuational electrodynamics framework within the dipolar approximation. It is shown that the introduction of a thin polar film atop a non-dispersive substrate can lead to both an enhancement and a lateral focusing of the heat exchange. The influence of the probe--substrate separation, film thickness and substrate permittivity is analyzed, revealing that the effect originates from near-field interactions governed by the interplay between film-induced modifications of electromagnetic mode dispersion and the distance-dependent coupling strength. The results highlight a viable route toward the active control of local radiative heat transfer at the nanoscale.

cond-mat.mes-hall↗

arXiv2025

Broadband directional thermal emission with anisothermal microsources

Thermal emission is naturally spatially incoherent and lacks directionality. Here, we demonstrate that by precisely controlling the spatial temperature distribution within a solid, directional thermal emission can be achieved across a broad spectral range. These anisothermal sources open new avenues for manipulating radiative heat flux at the microscale and hold promise for applications in thermal management and energy conversion, enabling more efficient and targeted thermal control.

physics.optics↗

arXiv2024

Effect of top metallic contacts on energy conversion performances for near-field thermophotovoltaics

The design of metallic contact grids on the front side of thermophotovoltaic cells is critical since it can cause significant optical and electrical resistive losses, particularly in the near field. However, from the theoretical point of view, this effect has been either discarded or studied by means of extremely simplified models like the shadowing methods, that consist in simply ignoring the fraction of the semiconductor surface covered by metal. Our study, based on a rigorous three-body theoretical framework and implemented using the scattering matrix approach with the Fourier modal method augmented with adaptive spatial resolution, provides deeper insight into the influence of the front metal contact grid. This approach allows direct access to the radiative power absorbed by the semiconductor, enabling the proposal of an alternative definition for the thermophotovoltaic cell efficiency. By modeling this grid as a metallic grating, we demonstrate its significant impact on the net radiative power absorbed by the cell and, consequently, on the generated electrical power. Our analysis reveals behaviors differing substantially from those predicted by previous simplistic approaches.

physics.optics↗

arXiv2024

Non-monotonic radiative heat transfer in the transition from far field to near field

We present high precision measurements of the radiative heat transfer of a glass microsphere immersed in a thermal bath in vacuum facing three different planar substrates (SiO2, SiC and Au), which exhibit very different optical behaviors in the infrared region. Using a thermoresistive probe on a cantilever, we show the nonmonotonic behavior of the radiative flux between the microsphere and its environment when the microsphere is brought closer to the substrate in the far-field to near-field transition regime. We demonstrate that this unexpected behavior is related to the singularities of dressed emission mechanisms in this three-body system sphere-substrate-bath with respect to the separation distance.

cond-mat.mes-hall↗

arXiv2024

Electron tunneling induced thermoelectric effects

We introduce a direct (Seebeck) and inverse (Peltier) thermoelectric effect induced by electron tunneling between closely separated conducting films. When a transverse temperature gradient is applied along one of two films, a bias voltage is induced in the second thanks to the heat transfer mediated by electrons tunneling through the separation gap. We highlight a non trivial behavior for this Seebeck effect with respect to geometric characteristics of interacting films. Conversely, when an electric current passes through one of two films a strong thermal power can be removed from or inserted in the second film through an induced Peltier effect. In particular we highlight conditions where the induced Seebeck and Peltier coefficients are larger than in the bulk. These induced thermoelectric effects could find broad applications in the fields of energy conversion and cooling at nanoscale.

cond-mat.mes-hall↗

arXiv2024

Deep sub-wavelength scale focusing of heat flux radiated by magneto-optical nanoemitters in the presence of an external magnetic-field

We introduce a theoretical framework to describe the heat flux radiated in the near-field regime by a set of magneto-optical thermal nanoemitters close to a substrate in the presence of an external magnetic field. Then, we investigate the particular case of a single emitter and we demonstrate that the external field can induce both an amplification of the heat exchanged between emittter and substrate and a focusing of the Poynting field at the substrate interface at deep sub-wavelength scale. These effects open up promising perspectives for the development of heat-assisted magnetic-recording technology.

cond-mat.mes-hall↗

arXiv2024

Tomography of near-field radiative heat exchange between mesoscopic bodies immersed in a thermal bath

A tomographic study of near-field radiative heat exchanges between a mesoscopic object and a substrate immersed in a thermal bath is carried out within the theoretical framework of fluctuational electrodynamics. By using the discrete-dipole-approximation method, we compute the power density distribution for radiative exchanges and highlight the major role played by many-body interactions in these transfers. Additionally, we emphasize the close relationship between power distribution and eigenmodes within the solid paving the way to applications for hot-spot targeting at deep sub-wavelength scale by shape optimization.

cond-mat.mes-hall↗

arXiv2024

Extreme near-field heat transfer between silica surfaces

Despite recent experiments exhibiting an impressive enhancement in radiative heat flux between parallel planar silica surfaces with gap sizes of about 10 nm, the exploration of sub-nanometric gap distances remains unexplored. In this work, by employing non-equilibrium molecular dynamics (NEMD) simulations, we study the heat transfer between two SiO2 plates in both their amorphous and crystalline forms. When the gap size is 2 nm, we find that the heat transfer coefficient experiences a substantial ~30-fold increase compared to the experimental value at the gap size of 10 nm confirming the dependence on the distance inversely quadratic as predicted by the fluctuational electrodynamics (FE) theory. Comparative analysis between NEMD and FE reveals a generally good agreement, particularly for amorphous silica. Spectral heat transfer analysis demonstrates the profound influence of gap size on heat transfer, with peaks corresponding to the resonances of dielectric function. Deviations from fluctuational electrodynamics theory at smaller gap sizes are interpreted in the context of acoustic phonon tunneling and the effects of a gradient of permittivity close to the surfaces.

cond-mat.mtrl-sci↗

arXiv2023

Radiative heat exchange driven by acoustic vibration modes between two solids at the atomic scale

When two solids are separated by a vacuum gap of thickness smaller than the wavelength of acoustic phonons, the latter can tunnel across the gap thanks to van der Waals forces or electrostatic interactions. Here we show that these mechanical vibration modes can also contribute significantly, at the atomic scale, to the nonlocal radiative response of polar materials. By combining molecular-dynamics simulations with fluctuational-electrodynamics theory, we investigate the near-field radiative heat transfer between two slabs due to this optomechanical coupling and highlight its dominant role at cryogenic temperatures. These results pave the way to exciting avenues for the control of heat flux and the development of cooling strategies at the atomic scale.

cond-mat.mes-hall↗

arXiv2023

Electronic heat tunneling between two metals beyond the WKB approximation

Two metals at different temperatures separated by large gaps exchange heat under the form of electromagnetic radiation. When the separation distance is reduced and they approach contact (nanometer and sub-nanometer gaps), electrons and phonons can tunnel between the bodies, competing and eventually going beyond the flux mediated by thermal photons. In this transition regime the accurate modeling of electronic current and heat flux is of major importance. Here we show that, in order to quantitatively model this transfer, a careful description of the tunneling barrier between two metals is needed and going beyond the traditional WKB approximation is also essential. We employ analytical and numerical approaches to model the electronic potential between two semi-infinite jellium planar substrates separated by a vacuum gap in order to calculate the electronic heat flow and compare it with its radiative counterpart described by near-field radiative heat transfer. We demonstrate that the results for heat flux and electronic current density are extremely sensitive to both the shape and height of the barrier, as well as the calculation scheme for the tunneling probability, with variations up to several orders of magnitude. Using the proximity force approximation, we also provide estimates for tip-plane geometries. The present work provides realistic models to describe the electronic heat flux, in the scanning-thermal-microscopy experiments.

cond-mat.mes-hall↗

arXiv2023

Long-range super-Planckian heat transfer between nanoemitters in a resonant cavity

We study radiative heat transfer between two nanoemitters placed inside different types of closed cavities by means of a fluctuational-electrodynamics approach. We highlight a very sharp dependence of this transfer on cavity width, and connect this to the matching between the material-induced resonance and the resonant modes of the cavity. In resonant configurations, this allows for an energy-flux amplification of several orders of magnitude with respect to the one exchanged between two emitters in vacuum as well as between two black-bodies, even at separation distances much larger than the thermal wavelength. On the other hand, variations of the cavity width by a few percent allow a reduction of the flux by several orders of magnitude and even a transition to inhibition compared to the vacuum scenario. Our results pave the way to the design of thermal waveguides for the long-distance transport of super-Planckian heat flux and selective heat transfer in many-body system.

cond-mat.mes-hall↗

arXiv2023

Atomistic modeling of extreme near-field heat transport across nanogaps between two polar dielectric materials

The understanding of extreme near-field heat transport across vacuum nanogaps between polar dielectric materials remains an open question. In this work, we present a molecular dynamic simulation of heat transport across MgO-MgO nanogaps, together with a consistent comparison with the continuum fluctuational-electrodynamics theory using local dielectric properties. The dielectric function is computed by Green-Kubo molecular dynamics with the anharmonic damping properly included. As a result, the direct atomistic modeling shows significant deviation from the continuum theory even up to a gap size of few nanometers due to non-local dielectric response from acoustic and optical branches as well as phonon tunneling. The lattice anharmonicity is demonstrated to have a large impact on the energy transmission and thermal conductance, in contrast to its moderate effect reported for metallic vacuum nanogaps. The present work thus provides further insight into the physics of heat transport in the extreme near-field regime between polar materials, and put forward a methodology to account for anharmonic effects.

cond-mat.mes-hall↗

arXiv2023

Conduction-radiation coupling between two distant solids interacting in near-field regime

In the classical approach to deal with near-field radiative heat exchanges between two closely spaced bodies no coupling between the different heat carriers inside the materials and thermal photons is usually considered. Here we make an overview of the current state of studies on this coupling between solids of different sizes by paying a specific attention to the impact of the conduction regime inside the solids on conduction-radiation coupling. We also describe how the shape of solids affects this coupling. We show that this coupling can be at the origin of a drastic change of temperature profiles inside each body and of heat flux exchanged between them. These results could have important implications in the fields of nanoscale thermal management, near-field solid-state cooling and nanoscale energy conversion.

cond-mat.mes-hall↗

arXiv2023

Role of Nottingham effect in the heat transfer in extreme near-field regime

We analyze the heat transfer between two metals separated by a vacuum gap in the extreme near-field regime. In this cross-over regime between conduction and radiation, heat exchanges are mediated by photon, phonon and electron tunneling. We quantify the relative contribution of these carriers with respect to both the separation distance between the two bodies and the applied bias voltage. In the presence of a weak bias ($V_{\rm b}<100$~mV), electrons and phonons can contribute equally to the heat transfer near contact, while the contribution of photons becomes negligible. On the other hand, for larger bias voltages, electrons play a dominant role. Moreover, we demonstrate that depending on the magnitude of this bias, electrons can either cool down or heat up the hot body by the Nottingham effect. Our results emphasize some inconsistencies in recent experimental results about heat exchanges in the extreme near-field regime and set a road map for future experiments.

cond-mat.mes-hall↗

arXiv2022

Smart windows passively driven by greenhouse effect

The rational thermal management of buildings is of major importance for the reduction of the overall primary energy consumption. Smart windows are promising systems which could save a significant part of this energy. Here we introduce a double glazing system made with a thermochromic metal-insulator transition material and a glass layer separated by an air gap which is able to switch from its insulating to its conducting phase thanks to the greenhouse effect occuring in the separation gap. We also show that this passive system can reduce the incoming heat flux by 30% in comparison with a traditional double glazing while maintaining the transmittance around 0.35 over 75% of visible spectrum.

physics.app-ph↗

arXiv2022

Coupling between conduction and near-field radiative heat transfer in tip-plane geometry

We analyze the coupling between conduction and radiative heat transfer in near-field regime between two coaxial cylinders separated by a vacuum gap. By solving the heat transport equation in the steady-state regime between metals or polar materials we highlight a flux saturation mechanism for the radiative transfer even without non-local effect. In the case of polar materials this saturation occurs in the separation distances range of 1 to 10 nm which can be experimentally explored.

cond-mat.mes-hall↗