Photon Tunneling Research Articles

HBN-based enhancement and regulation of radiative heat transfer between two monolayer graphene sheets

Near-field radiative heat transfer (NFRHT) in many-body systems has opened pathways for enabling novel thermal-radiation applications. In this Letter, we investigate hBN-based enhancement and regulation of NFRHT between two monolayer graphene sheets. On the one hand, we predict that adding an intermediate hBN plate can greatly compensate the exponential damping of evanescent waves due to its hyperbolic modes, thus leading to 1.5 times enhancement of the NFRHT without introducing additional thermal source compared to the graphene-graphene system. On the other hand, we find that adjusting the shift frequency of hBN can greatly change the coupling of its hyperbolic modes and graphene surface plasmon polaritons, thus enabling the remarkable thermal regulation with a ratio of 3.5. We hope that our work may facilitate nanoscale thermal management in many-body systems and benefit the comprehension of hBN-based photon tunneling.

Heat diffusion in nanoparticle systems via near-field thermal photons

Near-field radiative heat transfer (NFRHT) in system of nanoparticles is significantly different from that in the far field regime due to the photon tunneling effect and the complex many body interactions, which is not well understood yet till now. The existing particle-scale NFRHT theory cannot be applied to systems of large number of particles directly, due to the enormous computational efforts. To fill the gap, we derived a continuum-scale normal-diffusion type governing equation starting from the particle-scale fluctuational electrodynamics formulation. The radiative thermal conductivity tensor is rigorously derived as a coefficient of the diffusion term. An additional convection-like term appears naturally in the governing equation for system with asymmetric distribution of particles, indicating a violation of the Fourier's law. The derived new formula of radiative thermal conductivity tensor is demonstrated to be useful and powerful in calculating the radiative thermal conductivity in arbitrary multi-dimensional particulate systems with many-body interactions.

A multi-junction-based near-field solar thermophotovoltaic system with a graphite intermediate structure

A solar thermophotovoltaic (STPV) system can transform incident concentrated solar energy into electrical energy with an efficiency that could be higher than the Shockley–Queisser limit. Near-field thermophotovoltaic (NF-TPV) devices can generate larger electrical power output than traditional far-field TPV devices with the aid of photon tunneling. Moreover, multi-junction PV cells can boost the performance of TPV devices by effectively distributing the absorbed photon energy inside the PV cell. In this work, we design a multi-junction-based near-field STPV system with a practical and high-temperature stable graphite intermediate structure. To optimize the system configuration, we employ a genetic algorithm and a surrogate model based on an artificial neural network, which enables us to suggest a better design approach for the multi-junction-based NF-STPV system between the power output density and power conversion efficiency maximization scenarios. When the concentration factor of the incident solar energy is 5000 and the absorber-to-emitter area ratio is 3, we can achieve a system efficiency of 23%. By introducing a material whose emissivity is as high as a blackbody on the solar absorber, the system efficiency can be further enhanced up to 35%.

5 μm Level Long Photon Tunneling Distance in Near Field Thermal Radiation Through Metallic Patterns With/Without Dielectric Structures

Abstract By integrating wave-type analysis and fluctuation-dissipation theorem, the enhancement of photon tunneling distance in near field thermal radiation through metallic nanopatterns with/without dielectric structures is theoretically studied. When metallic patterns are in the immediate proximity of the conductive emitter, substantial thermal electric enhancement at surface plasmon frequency is observed between the metallic patterns and the emitter when the periodicity of the thermal electric field along the emitter surface is around integer times of the period of the metallic patterns. The mechanism of field amplification is similar to Fabry–Perot type resonance between two reflecting surfaces. The strong thermal electric field from resonance allows long-distance photon tunneling observed in near field radiation at a ∼5 μm separation distance when the same metallic patterns are placed on the collector surfaces. This value is nearly 50 times longer than that with bared emitter surfaces. This long-distance photon tunneling can also happen at a broader range of parallel wavenumbers (i.e., not determined by the period of the metallic patterns) at the surface plasmon frequency when the periodic metallic patterns' sizes are different each period. However, increasing the range of parallel wavenumbers in long-distance photon tunneling with this approach can reduce the strength of photon tunneling. The reduced tunneling strength can be brought up by attaching high refractive index dielectric resonators on top of the metallic patterns. The dielectric resonators on top of the metallic patterns show additional Mie-type resonance when displacement current is induced at the interface between the metallic patterns and the high refractive index dielectric. The higher intensity long-distance photon tunneling with a broad range of parallel wavenumbers can be valuable in harvesting the high intensity and high quality near field radiative energy with engineering feasible micron level vacuum gaps.

Tunable optically-induced transparency and fano resonance in a two mode coupled micro-cavity system with double optical Kerr effect

In this paper, we theoretically analyze optically-induced transparency and absorption properties of a weak probe field in a two-mode coupled micro-cavity system and explore the tunable asymmetric Fano line shape of the transmission rates of the probe field. Both the modes in our system consist of an optical Kerr medium, one of them being passive while the other mode can be either active or passive. The forward transmission and backward reflection profile of the probe field are investigated for both passive–passive and passive–active cavity systems by varying different system parameters such as probe field detuning, photon tunneling strength, gain-to-loss ratio, etc. The results of this study have the potential to be applied in construction of quantum telecommunication and photonic devices.

Photon tunneling reconstitution in black phosphorus/ hBN heterostructure

Excitation of hybrid modes constituted by different material-supported polaritons is a common way to enhance the near-field radiative energy transport, which has fascinating promise in applications of thermal photonics. Here, we investigate near--field thermal radiation mechanisms in heterostructure composed of $h\mathrm{BN}$ film and black phosphorus single layer. The results show that this heterostructured system can give rise to a remarkable enhancement for photon tunneling, outperforming the near-field thermal radiation properties of its building blocks, as well as some other representative heterostructures. Moreover, we find that the anisotropic hybrid effect can induce a remarkable topological reconstitution of polaritons for $h\mathrm{BN}$ film and black phosphorus, forming a novel anisotropic hybrid polaritons. Notably, such hybrid modes show significant topological differences compared to $h\mathrm{BN}$ film and black phosphorus in the type-I Reststrahlen band due to the anisotropic anticrossing hybridization effect. Lastly, we systematically analyze the evolution of such hybrid polariton modes as a function of $h\mathrm{BN}$ film thickness and the corresponding influence on radiative properties of the heterostructure. This work may benefit the applications of near-field energy harvesting and radiative cooling based on hybrid polaritons in anisotropic two-dimensional material and hyperbolic film.

Enhancement and Manipulation of Near-Field Thermal Radiation Using Hybrid Hyperbolic Polaritons

Owing to a high electromagnetic confinement and a strong photonic density of states, hyperbolic surface plasmon polaritons (HSPPs) provide a fascinating promise for applications in thermal photonics. In this work, we theoretically predict a possibility for the improvement of the near-field radiative heat transfer on the basis of tailoring the electromagnetic state of hyperbolic metasurfaces by the uniaxial hyperbolic substrate. By using the photonic tunneling coefficient and the polaritons dispersion, we present a comprehensive study of the hybrid effect of the hyperbolic substrate on HSPPs. We find that due to the hybrid effect of the hyperbolic substrate, the anisotropy surface state of hyperbolic metasurfaces would undergo significant deformations and even topological transition. Moreover, we systematically exhibit the evolution of such hybrid hyperbolic mode with different thicknesses of the hyperbolic substrate and analyze the thickness effect on radiative properties of the hybrid system. It is shown that the resulting heat transfer with the assistance of the hybrid hyperbolic mode by optimizing the substrate parameters is many times stronger than that of monolayer hyperbolic metasurface at the same vacuum gap. Taken together, our results provide a platform to tailor 2D hyperbolic plasmons as a potential strategy toward passive or active control of the near-field heat transfer, and the hybrid hyperbolic mode presented here may facilitate the system design for near-field energy harvesting, thermal imaging, and radiative cooling applications.

Control of photon transport in an optical structure of four microresonators using spectral engineering

A theoretical model of a photonic switch based on a T-shaped optical structure with combined switching control is considered. The transmission coefficient of photons through the structure varies between current and vacuum modes by several physical mechanisms. The main one is the resonant interaction between microresonators with adjustable photon tunneling energy. An alternative way is also pump compensation by switching on an additional laser field. The influence of the model parameters on the switching efficiency is studied. It is shown that this scheme can be implemented on the basis of already existing technologies.

Thermophotovoltaic Energy Conversion in Far-to-Near-Field Transition Regime

Recent experimental studies on near-field thermophotovoltaic (TPV) energy conversion have mainly focused on enhancing performance via photon tunneling of evanescent waves. In the sub-micron gap, however, there exist peculiar phenomena caused by the interference of propagating waves, which is seldom observed due to the dramatic increase of the radiation by evanescent waves in full spectrum range. Here, we experimentally demonstrate the oscillatory nature of near-field TPV energy conversion in the far-to-near-field transition regime (250-2600 nm), where evanescent and propagating modes are comparable due to the selective spectral response by the PV cell. Noticeably, it was possible to produce the same amount of photocurrent at different vacuum gaps of 870 and 322 nm, which is 10\% larger than the far-field value. Considering the great challenges in maintaining nanoscale vacuum gap in practical devices, this study suggests an alternative approach to the design of a TPV system that will outperform conventional far-field counterparts.

Enhanced Near-Field Radiative Heat Transfer between Graphene/hBN Systems.

Near-field radiative heat transfer (NFRHT) can exceed the blackbody radiation limit owing to the coupled evanescent waves, implying a significant potential for energy conversion and thermal management. Coupled surface plasmon polaritons (SPPs) and hyperbolic phonon polaritons (HPPs) with small ohmic losses enable a long propagation wavelength that is essential in NFRHT. However, so far, there still lacks knowledge about the experimental investigation of the coupling of SPPs and HPPs in terms of NFRHT. In this study, the NFRHT between graphene/hexagonal boron nitride (hBN) systems that can be readily transferred onto various substrates, with a gap space of ≈400nm is measured. NFRHT enhancements in the order of three and six times higher than the blackbody limit for graphene/hBN heterostructures and graphene/hBN/graphene multilayers, respectively are demonstrated. In addition, the largest ever radiative heat flux using graphene/hBN/graphene multilayers under similar gap space of 400nm is obtained. Consequently, analyzing the photon tunneling modes reveal that these phenomena are consequences of coupled SPPs of graphene and HPPs of hBN.

Comprehensive analysis of an optimized near-field tandem thermophotovoltaic converter

It is well known that performance of a thermophotovoltaic (TPV) device can be enhanced if the vacuum gap between the thermal emitter and the TPV cell becomes nanoscale due to the photon tunneling of evanescent waves. Having multiple bandgaps, multi-junction TPV cells have received attention as an alternative way to improve its performance by selectively absorbing the spectral radiation in each subcell. In this work, we comprehensively analyze the optimized near-field tandem TPV system consisting of the thin-ITO-covered tungsten emitter (at 1500 K) and GaInAsSb/InAs monolithic interconnected tandem TPV cell (at 300 K). We develop a simulation model by coupling the near-field radiation solved by fluctuational electrodynamics and the diffusion-recombination-based charge transport equations. The optimal configuration of the near-field tandem TPV system obtained by the genetic algorithm achieves the electrical power output of 8.41 W/cm$^2$ and the conversion efficiency of 35.6\% at the vacuum gap of 100 nm. We show that two resonance modes (i.e., surface plasmon polaritons supported by the ITO-vacuum interface and the confined waveguide mode in the tandem TPV cell) greatly contribute to the enhanced performance of the optimized system. We also show that the near-field tandem TPV system is superior to the single-cell-based near-field TPV system in both power output and conversion efficiency through loss analysis. Interestingly, the optimization performed with the objective function of the conversion efficiency leads to the current matching condition for the tandem TPV system regardless of the vacuum gap distances.

Tunable Near-Field Radiative Effect in a Td – WTe2 Single Layer

In contrast to artificial metamaterials, natural two-dimensional (2D) hyperbolic materials are able to support higher electromagnetic confinement and stronger photonic density of states. This means natural 2D hyperbolic materials have fascinating potential for applications in thermal photonics. In this work, we investigate mechanisms of near-field thermal radiation (NFTR) in a ${\mathrm{T}}_{d}$--${\mathrm{WTe}}_{2}$ single layer at the nanoscale using the fluctuation-dissipation theorem and density-functional theory. The results show that NFTR of ${\mathrm{T}}_{d}$--${\mathrm{WTe}}_{2}$ can be 3 orders of magnitude larger than the blackbody limit. By using the photonic tunneling coefficient and the plasmon dispersion, we present a comprehensive study of plasmonic properties of ${\mathrm{T}}_{d}$--${\mathrm{WTe}}_{2}$. Moreover, our first-principles calculations predict that application of a certain amount of mechanical stress can trigger topological transition between the elliptic and the hyperbolic surface states by regulating the Fermi surface and interband excitation threshold. Lastly, we systematically exhibit the evolution of surface plasmon polaritons in ${\mathrm{T}}_{d}$--${\mathrm{WTe}}_{2}$ under mechanical stress and analyze the performance of using mechanical stress to modulate the corresponding NFTR. Our work explores the great potential of tunable radiative heat flux in ${\mathrm{T}}_{d}$--${\mathrm{WTe}}_{2}$, which is explained here through the peculiar nature of hyperbolic surface plasmons.

Fast and accurate control of gates for quantum hypercomputation based on coherent domains of water

Quantum electrodynamics (QED) predicts that, under suitable conditions for temperature and density, liquid water can be described as a two-phases system composed by a coherent and a non-coherent phase. The first one is characterized by the formation of macroscopic regions, called “;coherent domains” (CDs), in which all the molecules are phase - correlated among them and with a self-trapped electromagnetic field that leaks out from the CDs in the form of an evanescent tail. This feature, along with the possibility for the CDs to have an excited energy spectrum, allow them to interact each other through quantum tunneling of virtual photons. We have already shown how to exploit this dynamics to realize quantum hypercomputation by using a set of universal quantum gates made of interacting water CDs. In this paper we discuss how to accurately and fast control the macroscopic quantum states of such water coherent domains, by using electromagnetic potentials to modify the phase of their wavefunctions. Finally, a possible experimental set-up designed to this aim, based on the electric version of the Aharonov-Bohm effect, is discussed.

Enhanced tunneling distance of near field radiative energy with high-index dielectric resonators

By placing high-index dielectric resonators on surfaces supporting surface plasmons in the near field, strong magnetic resonance can be observed in the high-index dielectric resonators with appropriate heights around the surface plasmon resonance frequencies. The strong magnetic resonance allows strong thermal photon tunneling across a 1 μm gap, which is one order longer than the previous demonstrations of near field radiation with surface plasmons. The thermal photon tunneling happens when the horizontal wavenumber is kx∼4πw with w is the width of the high-index resonators. The height of the high-index dielectric resonators should provide enough retardation of the electric field between the top and bottom of the resonator to form a displacement current loop. Therefore, similar magnetic field resonance occurs in the resonator when we triple rather than double the height of the high-index dielectric resonators. The usage of dielectric resonators to amplify the thermal electric field in the near field domain can be a potential method to increase the quasi-monochromatic radiation distance of an emission domain by one order or more at the frequencies of the surface waves.

Super-planckian thermal radiation in borophene sheets

Recently, borophene, a pioneering two-dimensional metal, has been attracting broad interest due to the in-plane anisotropic polaritons and large electrical tunability. Its attractive electronic and optical properties imply that borophene can find novel applications in electronics, thermionics, and photonics. Here, we study the near-field thermal radiation (NFTR) of monolayer borophene sheets; the results show that the NFTR of monolayer borophene is three-orders of magnitude larger than the black-body limit, even significantly exceeding the NFTR from traditional metals and metallic oxides with metallic behavior. An analysis of the photon tunneling coefficient and plasmon dispersion indicates that the coupling of quasi-elliptic surface plasmon polaritons (SPPs) of the borophene system extends robustly to the near- and mid-infrared frequencies, producing a broadband near-field emission from borophene. We also analyze the possibility of using the electrochemical method (that is, tuning the electron density) to modulate the NFTR between borophene sheets. The results reveal since the suppression on the wave-vector range and the anisotropy of SPPs by electron density, the switching coefficient of such electrochemical method can exceed up to 95%. Finally, the modulate effect of the mechanical decoupling on the NFTR is explored. We clarify the influence of decoupling effect at different frequencies on the mechanical thermal modulation of borophene. All in all, we explore the NFTR of the 2D borophene thoroughly for the first time, opening potential possibility for novel borophene-dependent thermal devices and thermal management.

Optimized Colossal Near-Field Thermal Radiation Enabled by Manipulating Coupled Plasmon Polariton Geometry.

Collective optoelectronic phenomena such as plasmons and phonon polaritons can drive processes in many branches of nanoscale science. Classical physics predicts that a perfect thermal emitter operates at the black body limit. Numerous experiments have shown that surface phonon polaritons allow emission two orders of magnitude above the limit at a gap distance of ≈50nm. This work shows that a supported multilayer graphene structure improves the state of the art by around one order of magnitude with a ≈1129-fold-enhancement at a gap distance of ≈55nm. Coupled surface plasmon polaritons at mid- and far-infrared frequencies allow for near-unity photon tunneling across a broad swath of k-space enabling the improved result. Electric tuning of the Fermi-level allows for the detailed characterization and optimization of the colossal nanoscale heat transfer.

Improving few-photon optomechanical effects with coherent feedback.

Few-photon effects such as photon blockade and tunneling have potential applications in modern quantum technology. To enhance the few-photon effects in an optomechanical system, we introduce a coherent feedback loop to cavity mode theoretically. By studying the second-order correlation function, we show that the photon blockade effect can be improved with feedback. Under appropriate parameters, the photon blockade effect exists even when cavity decay rate is larger than the single-photon optomechanical coupling coefficient, which may reduce the difficulty of realizing single-photon source in experiments. Through further study of the third-order correlation function, we show that the tunneling effect can also be enhanced by feedback. In addition, we discuss the application of feedback on Schrödinger-cat state generation in an optomechanical system. The result shows that the fidelity of cat state generation can be improved in the presence of feedback loop.

Thermodynamic bounds of work and efficiency in near-field thermoradiative systems

Thermoradiative (TR) device combined with near-field radiation has been recently proposed to enhance noncontact direct photoelectric energy conversion. Based on the fluctuation-dissipation theorem, we evaluate the maximum work flux and the fundamental efficiency limit of the near-field TR systems by analyzing the radiative heat flux and the entropy flux. For a near-field TR system, when the ZrC absorber is placed close to the TR cell with a vacuum gap down to 100 nm, photon tunneling through evanescent waves can significantly enhance the maximum work flux without a compromise in efficiency limit. Furthermore, the decrease in the temperature of the heat source would greatly weaken the performance of the TR system. We also would like to emphasize that the hyperbolic metamaterial (HMM) and Lorentz absorbers can remarkably improve the performance of the TR system as compared to the ZrC reference. In this paper, based on the proposed method for determining the thermodynamic bounds of work and efficiency, we establish a target for the performance of the near-field TR system. In addition, the fundamental understandings and insights obtained in this study will facilitate the design and application of the near-field TR system.

Parametric characteristics and optimization of a near-field thermophotovoltaic system considering cooling consumption

Near-field thermophotovoltaic (NF-TPV) system based on the photon tunneling effect can effectively increase the output power, which has shown great application potential in solar energy utilization. In order to evaluate the performance of NF-TPV system more reasonably, this study established an optimization model of NF-TPV combined with a water-cooling system to better reflect the physical process of system running. Taking into account the energy consumption of cell water cooling, the performance of NF-TPV system with tungsten emitter and InAs cell was analyzed and optimized through numerical simulation. The influence of operating parameters such as emitter and cell temperatures, applied voltage and vacuum gap on the system performance was investigated. It is found that the operating parameters of NF-TPV combined with water cooling system have their optimal ranges, which can ensure the high efficiency and output power of the system simultaneously. When NF-TPV is applied in waste heat recovery, the cooling energy consumption could be ignored. In solar energy conversion, the emitter temperature should be kept as high as possible, and the cooling energy consumption must be considered when the emitter temperature is above 1000 K. If fuel combustion is used as NF-TPV heat source, the emitter temperature should not exceed 1500 K. This study provides guidance for the practical application of NF-TPV systems.

Thermophonon flux in double-cavity optomechanics

We propose theoretically an optomechanical system with double cavities to explore the thermophonon transport from the thermal bath of the mechanical oscillator to the coupled system. We find that the direction and magnitude of thermophonon flux in the system can be controlled flexibly by coupling an active cavity with gain to the driven cavity. In particular, the injected squeezing vacuum can reverse the nonequilibrium characteristics of the system and change the thermophonon flux from positive to negative. We also investigate in detail the influence of the driving power and the photon tunneling strength on the flux, which can widen the energy transfer channel of the system. The results obtained here have a potential application in the thermal noise energy harvesting and rectification by the optomechanical setup.