Search

The research on sensing the sensitivity of the light field in the whispering gallery mode (WGM) to the micro-cavity environment has already appeared, which uses the frequency shift of the light field in the WGM or the sensitivity of the resonance peak frequency shift. Multi-mode comb teeth of optical frequency comb(OFC) generated by nonlinear micro-cavity have excellent sensitivity to micro-cavity environment, and they have more sensitivity degrees of freedom compared with WGM light field (the strength of each comb tooth can be influenced by micro-cavity environment). The influence of different substances on the environmental parameters of micro-cavity is complex and nonlinear, so we use machine learning method to automatically extract the spectrum characteristics, the average accuracy of single-parameter identification attains to 99.5%, and the average accuracy of double parameter identification attains to 97.0%. Based on the integration of micro-cavity OFC and wave-guide coupling structure, we propose an set of fluid characteristics detection integrated device in theoretically., Comment: 7pages,7figures,26references

Artificial intelligence (AI) promotes the polymer design paradigm from a traditional trial-and-error approach to a data-driven style. Achieving high thermal conductivity (TC) for intrinsic polymers is urgent because of their importance in the thermal management of many industrial applications such as microelectronic devices and integrated circuits. In this work, we have proposed a robust AI-assisted workflow for the inverse design of high TC polymers. By using 1144 polymers with known computational TCs, we construct a surrogate deep neural network model for TC prediction and extract a polymer-unit library with 32 sequences. Two state-of-the-art multi-objective optimization algorithms of unified non-dominated sorting genetic algorithm III (U-NSGA-III) and q-noisy expected hypervolume improvement (qNEHVI) are employed for sequence-ordered polymer design with both high TC and synthetic possibility. For triblock polymer design, the result indicates that qNHEVI is capable of exploring a diversity of optimal polymers at the Pareto front, but the uncertainty in Quasi-Monte Carlo sampling makes the trials costly. The performance of U-NSGA-III is affected by the initial random structures and usually falls into a locally optimal solution, but it takes fewer attempts with lower costs. 20 parallel U-NSGA-III runs are conducted to design the pentablock polymers with high TC, and half of the candidates among 1921 generated polymers achieve the targets (TC > 0.4 W/(mK) and SA < 3.0). Ultimately, we check the TC of 50 promising polymers through molecular dynamics simulations and reveal the intrinsic connections between microstructures and TCs. Our developed AI-assisted inverse design approach for polymers is flexible and universal, and can be extended to the design of polymers with other target properties.

The thermal modulator based on the near-field radiative heat transfer has wide applications in thermoelectric diodes, thermoelectric transistors, and thermal storage. However, the design of optimal near-field thermal radiation structure is a complex and challenging problem due to the tremendous number of degrees of freedom. In this work, we have proposed a data-driven machine learning workflow to efficiently design multilayer hyperbolic metamaterials composed of ${\alpha}$-MoO$_{\rm 3}$ for near-field thermal radiative modulator with high modulation contrast. By combining the multilayer perceptron and Bayesian optimization, the rotation angle, layer thickness and gap distance of the multilayer metamaterials are optimized to achieve a maximum thermal modulation contrast ratio of 6.29. This represents a 97% improvement compared to previous single layer structure. The large thermal modulation contrast is mainly attributed to the alignment and misalignment of hyperbolic plasmon polaritons and hyperbolic surface phonon polaritons of each layer controlled by the rotation. The results provide a promising way for accelerating the designing and manipulating of near-field radiative heat transfer by anisotropic hyperbolic materials through the data-driven style.

Recent studies demonstrate that novel 2D triphosphides semiconductors possess high carrier mobility and promising thermoelectric performance, while the carrier transport behaviors in 2D semimetal triphosphides have never been elucidated before. Herein, using the first-principles calculations and Boltzmann transport theory, we reveal that the electron-phonon coupling can be significant and thus greatly inhibits the electron and phonon transport in electron-doped BP3 and CP3. The intrinsic heat transport capacity of flexural acoustic phonon modes in the wrinkle structure is largely suppressed arising from the strong out-of-plane phonon scatterings, leading to the low phonon thermal conductivity of 1.36 and 5.33 W/(mK) for BP3 and CP3 at room temperature, and at high doping level, the enhanced scattering from electron diminishes the phonon thermal conductivity by 71% and 54% for BP3 and CP3, respectively. Instead, electron thermal conductivity shows nonmonotonic variations with the increase of doping concentration, stemming from the competition between electron-phonon scattering rates and electron group velocity. It is worth noting that the heavy-doping effect induced strong scattering from phonon largely suppresses the electron transport and reduces electron thermal conductivity to the magnitude of phonon thermal conductivity. This work sheds light on the electron and phonon transport properties in semimetal triphosphides monolayer and provides an efficient avenue for the modulation of carrier transport by doping-induced electron-phonon coupling effect.

Geopolymer has been considered as a green and low-carbon material with great potential application due to its simple synthesis process, environmental protection, excellent mechanical properties, good chemical resistance and durability. In this work, the molecular dynamics simulation is employed to investigate the effect of the size, content and distribution of carbon nanotubes on the thermal conductivity of geopolymer nanocomposites, and the microscopic mechanism is analyzed by the phonon density of states, phonon participation ratio and spectral thermal conductivity, etc. The results show that there is a significant size effect in geopolymer nanocomposites system due to the carbon nanotubes. In addition, when the content of carbon nanotubes is 16.5%, the thermal conductivity in carbon nanotubes vertical axial direction (4.85 W/(mk)) increases 125.6% compared with the system without carbon nanotubes (2.15 W/(mk)). However, the thermal conductivity in carbon nanotubes vertical axial direction (1.25 W/(mk)) decreases 41.9%, which is mainly due to the interfacial thermal resistance and phonon scattering at the interfaces. The above results provide theoretical guidance for the tunable thermal conductivity in carbon nanotube-geopolymer nanocomposites.

The efficient and economical exploitation of polymers with high thermal conductivity is essential to solve the issue of heat dissipation in organic devices. Currently, the experimental preparation of functional thermal conductivity polymers remains a trial and error process due to the multi-degrees of freedom during the synthesis and characterization process. In this work, we have proposed a high-throughput screening framework for polymer chains with high thermal conductivity via interpretable machine learning and physical-feature engineering. The polymer thermal conductivity datasets for training were first collected by molecular dynamics simulation. Inspired by the drug-like small molecule representation and molecular force field, 320 polymer monomer descriptors were calculated and the 20 optimized descriptors with physical meaning were extracted by hierarchical down-selection. All the machine learning models achieve a prediction accuracy R2 greater than 0.80, which is superior to that of represented by traditional graph descriptors. Further, the cross-sectional area and dihedral stiffness descriptors were identified for positive/negative contribution to thermal conductivity, and 107 promising polymer structures with thermal conductivity greater than 20.00 W/mK were obtained. Mathematical formulas for predicting the polymer thermal conductivity were also constructed by using symbolic regression. The high thermal conductivity polymer structures are mostly {\pi}-conjugated, whose overlapping p-orbitals enable easily to maintain strong chain stiffness and large group velocities. The proposed data-driven framework should facilitate the theoretical and experimental design of polymers with desirable properties.

Structural manipulation at the nanoscale breaks the intrinsic correlations among different energy carrier transport properties, achieving high thermoelectric performance. However, the coupled multifunctional (phonon and electron) transport in the design of nanomaterials makes the optimization of thermoelectric properties challenging. Machine learning brings convenience to the design of nanostructures with large degree of freedom. Herein, we conducted comprehensive thermoelectric optimization of isotopic armchair graphene nanoribbons (AGNRs) with antidots and interfaces by combining Green's function approach with machine learning algorithms. The optimal AGNR with ZT of 0.894 by manipulating antidots was obtained at the interfaces of the aperiodic isotope superlattices, which is 5.69 times larger than that of the pristine structure. The proposed optimal structure via machine learning provides physical insights that the carbon-13 atoms tend to form a continuous interface barrier perpendicular to the carrier transport direction to suppress the propagation of phonons through isotope AGNRs. The antidot effect is more effective than isotope substitution in improving the thermoelectric properties of AGNRs. The proposed approach coupling energy carrier transport property analysis with machine learning algorithms offers highly efficient guidance on enhancing the thermoelectric properties of low-dimensional nanomaterials, as well as to explore and gain non-intuitive physical insights.

Topological phonon polaritons (TPhPs) are promising optical modes relevant in long-range radiative heat transfer, information processing and infrared sensing, whose topological protection is expected to enable their robust existence and transport. In this work we show that TPhPs can be supported in one-dimensional (1D) bichromatic silicon carbide nanoparticle (NP) chains, and demonstrate that they can considerably enhance radiative heat transfer for an array much longer than the wavelength of radiation. By introducing incommensurate or commensurate modulations on the interparticle distances, the NP chain can be regarded as an extension of the off-diagonal Aubry-Andr\'e-Harper (AAH) model. By calculating the eigenstate spectra with respect to the modulation phase that creates a synthetic dimension, we demonstrate that under this type of modulation the chain supports nontrivial topological modes localized over the boundaries, since the present system inherits the topological property of two-dimensional integer quantum Hall systems. In this circumstance the gap-labeling theorem and corresponding Chern number can be used to characterize the features of band gaps and topological edge modes. Based on many-body radiative heat transfer theory for a set of dipoles, we theoretically show the presence of topological gaps and midgap TPhPs can substantially enhance radiative heat transfer for an array much longer than the wavelength of radiation. We show how the modulation phase that acts as the synthetic dimension can tailor the radiative heat transfer rate by inducing or annihilating topological modes. We also discuss the role of dissipation in the enhancement of radiative heat transfer. These findings therefore provide a fascinating route for tailoring near-field radiative heat transfer based on the concept of topological physics., Comment: 13 pages, 7 figures, comments are welcome

Designing thermal radiation metamaterials is challenging especially for problems with high degrees of freedom and complex objective. In this letter, we have developed a hybrid materials informatics approach which combines the adversarial autoencoder and Bayesian optimization to design narrowband thermal emitters at different target wavelengths. With only several hundreds of training data sets, new structures with optimal properties can be quickly figured out in a compressed 2-dimensional latent space. This enables the optimal design by calculating far less than 0.001\% of the total candidate structures, which greatly decreases the design period and cost. The proposed design framework can be easily extended to other thermal radiation metamaterials design with higher dimensional features.

In this work, both thermal and electrical transport properties of diamond$-$cubic Si (Si$-$I) and metastable R8 phase of Si (Si$-$XII) are comparatively studied by using first$-$principles calculations combined with Boltzmann transport theory. The metastable Si$-$XII shows one magnitude lower lattice thermal conductivity than stable Si$-$I from 300 to 500~K, attributed from the stronger phonon scattering in three$-$phonon scattering processes of Si$-$XII. For the electronic transport properties, although Si$-$XII with smaller band gap (0.22 eV) shows lower Seebeck coefficient, the electrical conductivities of anisotropic $n$$-$type Si$-$XII show considerable values along $x$ axis due to the small effective masses of electron along this direction. The peaks of thermoelectric figure of merit ($ZT$) in $n$$-$type Si$-$XII are higher than that of $p$$-$type ones along the same direction. Owing to the lower lattice thermal conductivity and optimistic electrical conductivity, Si$-$XII exhibits larger optimal $ZT$ compared with Si$-$I in both $p$$-$ and $n$$-$type doping. For $n$$-$type Si$-$XII, the optimal $ZT$ values at 300, 400, and 500 K can reach 0.24, 0.43, and 0.63 along $x$ axis at carrier concentration of $2.6\times10^{19}$, $4.1\times10^{19}$, and $4.8\times10^{19}$~cm$^{-3}$, respectively. The reported results elucidate that the metastable Si could be integrated to the thermoelectric power generator.

We propose a novel ultrasonic sensor structure composed of Cantilever arm structure slot dual-micro-ring resonators(DMRR).We present a theoretical analysis of transmission by using the coupled mode theory.The mode field distributions and sound pressure distributions of transmission spectrum are obtained from 3D simulations based on Comsol Multi-physics(COMSOL)method.Our ultrasonic sensor exhibit theoretical sensitivity as high as 1462.5mV/kPa,which is 22 times higher than that of single slot-based micro-ring ultrasonic sensor.Our ultrasonic sensor offers higher sensitivity and a larger detection frequency range than conventional piezoelectric based ultrasound transducer.The results show that the sensing characteristics of our system can be optimized through changing the position and the angle of sound field.Our ultrasonic sensor with an area of 25um*60um, the-factor can be approximately 1540 with radius of 5um We detect an angular range of -90o to 90o and a minimum distance of 0.01um. Finally,we calculate the Cantilever arm structure slot DMRR array ultrasonic sensor's optical performance. Our proposed design provides a promising candidate for a hydrophone., Comment: 11 pages,8 figures,33 references

We propose a novel bio-sensor structure composed of slot dual-micro-ring resonators and mono-layer graphene.Based on the electromagnetically induced transparency (EIT)-like phenomenon and the light-absorption characteristics of graphene,we present a theoretical analysis of transmission by using the coupled mode theory and Kubo formula.The results demonstrate the EIT-like spectrum with asymmetric line profile.The mode-field distributions of transmission spectrum obtained from 3D simulations based on finite-difference time-domain (FDTD) method.Our bio-sensor exhibit theoretical sensitivity of 330nm/RIU, a minimum detection limit of 3600RIU,the maximum extinction ratio of 4.4dB,the quality factor of 1288 and a compact structure of 15um*10um.Finally, the bio-sensor's performance is simulated for glucose solution.Our proposed design provide a promising candidate for on-chip integration with other silicon photonic element., Comment: 11 pages,7 figures, 27 references

Ultracold atom arrays in optical lattices emerge as an excellent playground for the integration of topological photonics and quantum optics. Here, we study high-order topological quantum optics in an ultracold atom metasurface intended to mimic the two-dimensional Su-Schrieffer-Heeger model. We find the existence of long-range interactions beyond nearest-neighbor ones leads to isolated corner states in the band gap, and show a corner atom can be addressed by a laser drive far away from it via these nontrivial states. We demonstrate the Purcell factor can be used as a powerful tool to examine the existence of topological edge and corner states. We predict topological edge states can mediate strong coherent interactions between two remote impurity quantum emitters while suppressing dissipative losses thanks to the higher-order topology, generating robust and long-lived quantum entanglement, without the need for additional photonic structures., Comment: 6 pages, 4 figures with an 11-page Supplementary Material

Realization of electromagnetic energy confinement beyond the diffraction limit is of paramount importance for novel applications like nano-imaging, information processing, and energy harvest. Current approaches based on surface plasmon polaritons and photonic crystals are either intrinsically lossy or with low coupling efficiency. Herein, we successfully address these challenges by constructing an array of nonradiative anapoles that originate from the destructive far-field interference of electric and toroidal dipole modes. The proposed metachain can achieve ultracompact (1/13 of incident wavelength) and high-efficiency electromagnetic energy transfer without the coupler. We experimentally investigate the proposed metachain at mid-infrared and give the first near-field experimental evidence of anapole-based energy transfer, in which the spatial profile of anapole mode is also unambiguously identified at nanoscale. We further demonstrate the metachain is intrinsically lossless and scalable at infrared wavelengths, realizing a 90$^\circ$ bending loss down to 0.32 dB at the optical communication wavelength. The present scheme bridges the gap between the energy confinement and transfer of anapoles, and opens a new gate for more compactly integrated photonic and energy devices, which can operate in a broad spectral range., Comment: 10 pages, 6 figures, comments are welcome. Supplementary materials are available upon request

The miniaturization of infrared gas sensors is largely hindered by expensive and bulky laser sources as well as the use of optical filters. In this work, we propose a dual-band, directional thermal emitter based on compact W-Si-Cu metasurfaces to address this issue. This metasurface emitter is designed to support two nondispersive magnetic polariton modes that exhibit distinct directional thermal emission profiles, thus enabling dual-band detection without the need of optical filters. Specifically, we evaluate the feasibility of such dual-band filterless detection by adapting the metasurface emitter to CO2 sensing. The model of sensing system shows a selective relative sensitivity of CO2 which is 3.2 times higher than that using a blackbody emitter, and a relative sensitivity of temperature of emitter about 1.32%/K., Comment: 12 pages, 8 figures

On-chip realization of complex photonic functionalities is essential for further progress in planar integrated nanophotonics, especially when involving nonclassical light sources such as quantum emitters (QEs). Hybrid plasmonic nanocircuits integrated with QEs have been attracting considerable attention due to the prospects of significantly enhancing QE emission rates and miniaturizing quantum nanophotonic components. Spin-orbit interactions on subwavelength scales have been increasingly explored in both conventional and quantum nanophotonics for realization and utilization of the spin-dependent flow of light. Here, we propose and realize a dielectric-loaded plasmonic nanocircuit consisting of an achiral spin-orbit coupler for unidirectional routing of pump radiation into branched QE-integrated waveguides. We demonstrate experimentally the circular-polarization controlled coupling of 532-nm pump laser light into polymer-loaded branched waveguides followed by the excitation of spatially separated (by a distance of ~ 10 {\mu}m) QEs, nanodiamonds, with multiple nitrogen vacancy centres, that are embedded in and efficiently coupled to the corresponding waveguides. The realization of on-chip spin-orbit controlled excitation of different QEs coupled to branched waveguides opens new avenues for designing complex quantum plasmonic nanocircuits exploiting the spin degree of freedom within chiral quantum nanophotonics.

The dependent scattering effect (DSE), which arises from the wave nature of electromagnetic radiation, is a critical mechanism affecting the radiative properties of micro/nanoscale discrete disordered media (DDM). In the last a few decades, the approximate nature of radiative transfer equation (RTE) leads to a plethora of investigations of the DSE in various DDM, ranging from fluidized beds, photonic glass, colloidal suspensions and snow packs, etc. In this article, we give a general overview on the theoretical, numerical and experimental methods and progresses in the study of the DSE. We first present a summary of the multiple scattering theory of electromagnetic waves, including the analytic wave theory and Foldy-Lax equations, as well as its relationship with the RTE. Then we describe in detail the physical mechanisms that are critical to DSE and relevant theoretical considerations as well as numerical modeling methods. Experimental approaches to probe the radiative properties and relevant progresses in the experimental investigations of the DSE are also discussed. In addition, we give a brief review on the studies on the DSE and other relevant interference phenomena in mesoscopic physics and atomic physics, especially the coherent backscattering cone, Anderson localization, as well as the statistics and correlations in disordered media. We expect this review can provide profound and interdisciplinary insights to the understanding and manipulation of the DSE in disordered media for thermal engineering applications., Comment: Submitted to Annual Review of Heat Transfer. Comments are welcome

Topological quantum optical states in one-dimensional (1D) quasiperiodic cold atomic chains are studied in this work. We propose that by introducing incommensurate modulations on the interatomic distances of 1D periodic atomic chains, the off-diagonal Aubry-Andr\'e-Harper (AAH) model can be mimicked, although the crucial difference is the existence of long-range dipole-dipole interactions. The discrete band structures with respect to the modulation phase, which plays the role of a dimension extension parameter, are calculated for finite chains beyond the nearest-neighbor approximation. It is found that the present system indeed supports nontrivial topological states localized over the boundaries. Despite the presence of long-range dipole-dipole interactions that leads to an asymmetric band structure, it is demonstrated that this system inherits the topological properties of two-dimensional integer quantum Hall systems. The spectral position, for both real and imaginary frequencies, and number of these topologically protected edge states are still governed by the gap-labeling theorem and characterized by the topological invariant, namely, the (first) Chern number, indicating the validity of bulk-boundary correspondence. Due to the fractal spectrum arising from the quasiperiodicity in a substantially wide range of system parameters, our system provides a large number of topological gaps and optical states readily for practical use. It is also revealed that a substantial proportion of the topological edge states are highly subradiant with extremely low decay rates, which therefore offer an appealing route for controlling the emission of external quantum emitters and achieving high-fidelity quantum state storage., Comment: Final version, 15 pages, 10 figures, comments are welcome

Droplet impact on hot surfaces results in either droplet-surface contact or droplet-surface non-contact, i.e., the Leidenfrost state. The Leidenfrost droplet is levitated upon its vapor, deteriorating the heat transfer. The Leidenfrost temperature depends on the thermal properties of the surface, which are usually characterized by two parameters: the thermal diffusivity and the thermal effusivity. In this paper, the effects of these two parameters on the Leidenfrost temperature are clarified experimentally by varying the one of interest while keeping the other one constant. The experimental results indicate that the Leidenfrost temperature is affected by the thermal effusivity rather than by the thermal diffusivity; the higher the thermal effusivity is, the lower the Leidenfrost temperature; and the increase of the Leidenfrost temperature with the droplet impact velocity is greater for the surface with the lower thermal effusivity. To further understand the experimental findings, a theoretical model is proposed, which considers the transient heat transfer in the surface. The theoretical analysis shows that the Leidenfrost temperature scales as the inverse of the thermal effusivity and the root square of the impact velocity, in good agreement with the experimental results.

Light propagation in disordered media is a fundamental and important problem in optics and photonics. In particular, engineering light-matter interaction in disordered cold atomic ensembles is one of the central topics in modern quantum and atomic optics. The collective response of dense atomic gases under light excitation, which crucially depends on the spatial distribution of atoms and the geometry of the ensemble, has important impacts on quantum technologies like quantum sensors, atomic clocks and quantum information storage. Here we analyze near-resonant light transmission in two-dimensional dense ultracold atomic ensembles with short-range positional correlations. Based on the coupled-dipole simulations under different atom number densities and correlation lengths, we show that the collective effects are strongly influenced by those positional correlations, manifested as significant shifts and broadening or narrowing of transmission resonance lines. The results show that mean-field theories like Lorentz-Lorenz relation are not capable of describing such collective effects. We further investigate the statistical distribution of eigenstates, which are significantly affected by the interplay between dipole-dipole interactions and position correlations. This work can provide profound implications on collective and cooperative effects in cold atomic ensembles as well as the study of mesoscopic physics concerning light transport in strongly scattering disordered media., Comment: 15 pages, 8 figures, comments are welcome

We investigate the topological plasmon polaritons (TPPs) in one-dimensional dimerized doped silicon nanoparticle chains, as an analogy of the topological edge states in the Su-Schrieffer-Heeger (SSH) model. The photonic band structures are analytically calculated by taking all near-field and far-field dipole-dipole interactions into account. For longitudinal modes, it is demonstrated that the band topology can be well characterized by the complex Zak phase irrespective of the lattice constant and doping concentration. By numerically solving the eigenmodes of a finite system, it is found that a dimerized chain with a nonzero complex Zak phase supports nontrivial topological eigenmodes localized over both edges. Moreover, by changing the doping concentration of Si, it is possible to tune the resonance frequency of the TPPs from far-infrared to near-infrared, and the localization length of the edge modes are also modulated accordingly. Since these TPPs are highly protected modes that can achieve a strong confinement of electromagnetic waves and are also immune to impurities and disorder, they can provide a potentially tunable tool for robust and enhanced light-matter interactions light-matter interaction in the infrared spectrum., Comment: 9 pages, 7 figures, comments are welcome. arXiv admin note: text overlap with arXiv:1807.08276

We theoretically investigate the application of topological plasmon polaritons (TPPs) to temperature sensing for the first time. Based on an analogy of the topological edge states in the Su-Schrieffer-Heeger model, TPPs are realized in a one-dimensional intrinsic indium antimonide (InSb) microsphere chain. The existence of TPPs is demonstrated by analyzing the topology of the photonic band structures and the eigenmode distribution. By exploiting the temperature dependence of the permittivity of InSb in the terahertz range, the resonance frequency of the TPPs can be largely tuned by the temperature. Moreover, it is shown that the temperature sensitivity of the TPP resonance frequency can be as high as $0.0264~\mathrm{THz/K}$ at room temperature, leading to a figure of merit over 150. By calculating the LDOS near the chain, we further demonstrate that the temperature sensitivity of TPPs is experimentally detectable via near-field probing techniques. This sensitivity is robust since TPPs are highly protected modes immune to disorder and can achieve a strong confinement of radiation. We envisage these TPPs can be utilized as promising candidates for robust and enhanced temperature sensing., Comment: 6 pages, 4 figures. comments are welcome

We show that during evaporation of a pore network, liquid can refill the gas occupied pores, snapping off a gas bubble, which then moves to a stable configuration. This phenomenon is induced by the capillary instability due to the wettability heterogeneity of the pore network and has a much smaller time scale as compared to the evaporation process. The capillary instability induced liquid refilling and bubble movement are explained in detail based on the analysis of the images obtained from the visualization experiment. The capillary valve effect, which hinders the movement of the gas-liquid interface and is induced by the sudden geometrical expansion between small and large pores, can be suppressed by the residual liquid in the large pore. For better understanding of the capillary instability induced gas-liquid two-phase transport during evaporation, a novel pore network model is developed, which considers not only the capillary and viscous forces but also the inertial forces that are seldom taken into account in the previous models. The pore network modeling results are in good agreement with the experimental data, demonstrating the effectiveness of the developed pore network model, which opens up a new route for better understanding of the role of inertial forces in two-phase transport in porous media.

During evaporation in porous media, two types of corner films are distinguished. A continuous corner film is connected to the bulk liquid, while a discontinuous one is not. To disclose their effects on evaporation in porous media, a pore network model with both continuous and discontinuous corner films is developed, which considers the capillary and viscous forces as well as the effects of corner films on the threshold pressures of pores. The capillary valve effect induced by the sudden geometrical expansion between the small and large pores is also taken into account in the model. The developed pore network model agrees well with the evaporation experiment with a quasi 2D micro model porous medium, in terms of not only the variation of the liquid saturation in each pore but also the variation of the total evaporation rate. The pore network models that neglect the corner films or the liquid viscosity are also compared with the experiment so as to shed light on the roles of the corner films. The continuous corner films, which contribute to sustain the high evaporation rate, can be interrupted to be the discontinuous ones not only by the gas invasion into pores but also by the capillary scissors effect due to the local convex topology of the solid matrix.

In this work, we study the near-field heat transfer between composite nanostructures. It is demonstrated that thermally excited surface plasmon polaritons, surface phonon polaritons, and hyperbolic phonon polaritons in such composite nanostructures significantly enhance the near-field heat transfer. To further analyze the underlying mechanisms, we calculate energy transmission coefficients and obtain the near-field dispersion relations. The dispersion relations of composite nanostructures are substantially different from those of isolated graphene, silicon carbide (SiC) films, and SiC nanowire arrays due to the strong coupling effects among surface polaritonic modes. We identify four pairs of strongly coupled polaritonic modes with considerable Rabi frequencies in graphene/SiC film composite structures that greatly broaden the spectral peak. We confirm that near-field strong coupling effects between surface plasmon polaritons and hyperbolic phonon polaritons in the in-plane Reststrahlen band are different from those in the out-of-plane Reststrahlen band due to the different types of hyperbolicity. In addition, we analyze the effective tunability of the near-field heat transfer of graphene/SiC nanowire arrays composite structures by adjusting the chemical potential of graphene, the height and volume filling factor of the SiC nanowire arrays. This work provides a method to manipulate the near-field heat transfer with the use of strongly coupled surface polaritonic modes., Comment: 10 pages, 8 figures, comments are welcome

Understanding the mechanisms of thermal conduction in graphene is a long-lasting research topic, due to its high thermal conductivity. Peierls-Boltzmann transport equation (PBTE) based studies have revealed many unique phonon transport properties in graphene, but most previous works only considered three-phonon scatterings and relied on interatomic force constants (IFCs) extracted at 0 K. In this paper, we explore the roles of four-phonon scatterings and the temperature dependent IFCs on phonon transport in graphene through our PBTE calculations. We demonstrate that the strength of four-phonon scatterings would be severely overestimated by using the IFCs extracted at 0 K compared with those corresponding to a finite temperature, and four-phonon scatterings are found to significantly reduce the thermal conductivity of graphene even at room temperature. In order to reproduce the prediction from molecular dynamics simulations, phonon frequency broadening has to be taken into account when determining the phonon scattering rates. Our study elucidates the phonon transport properties of graphene at finite temperatures, and could be extended to other crystalline materials., Comment: 31 pages, 8 figures

In the quest to enhance light-matter interactions and miniaturize photonics devices, it is crucial to create a strong field enhancement with lower material losses. Here we combine a plasmonic Fano resonance supported by the silver cluster and anapole states realized by the silicon disk to create a larger field enhancement with less loss through a strong coupling effect. Besides, by varying the gap size we find that the resonances wavelength and the Rabi-splitting can be tuned over a wide range of wavelength, which can achieve a giant splitting energy over 300 meV. We further demonstrate that it is the interference of magnetic currents loops which induces the strong coupling. Due to the strong coupling, the hybrid antenna can provide both larger decay rate and radiative decay rate, which makes it promising for high-performance miniaturized optical devices., Comment: 4 pages, 6 figures, comments are welcome

With the rise of artificial magnetism and metamaterials, the toroidal family recently attracts more attention for its unique properties. Here we propose an all-dielectric pentamer metamolecule consisting of nano-cylinders with two toroidal dipolar resonances, whose frequencies, EM distributions and Q factor can be efficiently tuned due to the additional electric dipole mode offered by a central cylinder. To further reveal the underlying coupling effects and formation mechanism of toroidal responses, the multiple scattering theory is adopted. It is found that the first toroidal dipole mode, which can be tuned from 2.21 to 3.55 $\mu$m, is mainly induced by a collective electric dipolar resonance, while the second one, which can be tuned from 1.53 to 1.84 $\mu$m, relies on the cross coupling of both electric and magnetic dipolar responses. The proposed low-loss metamolecule and modes coupling analyses may pave the way for active design of toroidal responses in advanced optical devices., Comment: 14 pages, 9 figures

Understanding light-matter interaction in disordered photonic media allows people to manipulate light scattering and achieve exciting applications using seemingly scrambled media. As the concentration of scattering particles rises, they are inclined to step into near fields of each other in deep subwavelength scale. The fundamental physics involving the interplay between disorder and near-field interaction (NFI) is still not fully understood. We theoretically examine the role of NFI by analyzing the underlying multiple scattering mechanism. We find NFI leads to a stronger collective behavior involving more particles and widens the photonic pseudo-bandgap of disordered media. It also excites more weakly decayed longitudinal modes and results in higher local density of states. By introducing a sticky short-range order, we demonstrate the possibility of enhancing off-momentum-shell NFI of multiple scattering process. Our results have profound implications in understanding and harnessing nanoscale light-matter interaction for novel disordered photonic devices., Comment: 7 pages, 5 figures, plus a 9-page supplementary material, comments are welcome

Topological phonon polaritons (TPhPs) are highly protected and localized edge modes that are capable of achieving a strong confinement of electromagnetic waves and immune to impurities and disorder. Here we realize TPhPs by constructing one-dimensional dimerized silicon carbide nanoparticle chains, which mimic the topological property of the well-known Su-Schrieffer-Heeger (SSH) model. We analytically calculate the complex band structure of such chains by taking all near-field and far-field dipole-dipole interactions into account. For longitudinal modes, we demonstrate that, despite the non-Hermiticity and breaking of the chiral symmetry, the band topology can be still characterized by the complex Zak phase, which is quantized and indicates a topological phase transition when the dimerization parameter $\beta$ changes from less than 0.5 to larger than 0.5, like the conventional Hermitian SSH model. By calculating the eigenmodes of a finite chain, we find such a dimerized chain with $\beta>0.5$ supports nontrivial topological eigenmodes localized over both of its edges, indicating the validity of the bulk-boundary correspondence. On the other hand, for transverse modes, we discover a topological phase transition by increasing the lattice constant, which is due to the presence of strong long-range far-field transverse dipole-dipole interactions decaying with the distance $r$ as $1/r$ for an infinitely long chain. However, we surprisingly find the emergence of non-Hermitian skin effect in a finite chain, which leads to the breakdown of the bulk-boundary correspondence. Furthermore, by incorporating the effect of localized bulk eigenmodes and proposing a modified complex Zak phase for a finite lattice, we still recover the topological behavior of the conventional SSH model. We also demonstrate the excitation of topological phonon polaritons and show their enhancement to the photonic LDOS., Comment: 17 pages, 15 figures, abstract is too long to be fully displayed

We study the topological optical states in one-dimensional (1D) dimerized ultracold atomic chains, as an extension of the Su-Schrieffer-Heeger (SSH) model. By taking the fully retarded near-field and far-field dipole-dipole interactions into account, we describe the system by an effective non-Hermitian Hamiltonian, vastly different from the Hermitian Hamiltonian of the conventional SSH model. We analytically calculate the complex bandstructures for infinitely long chains, and show that the topological invariant, i.e., the complex Zak phase, is still quantized and becomes nontrivial when the dimerization parameter $\beta>0.5$, despite the broken chiral symmetry and non-Hermiticity. We have verified the validity of the bulk-boundary correspondence for this non-Hermitian system by further analyzing the eigenstate distributions along with their inverse participation ratios (IPRs) for finite chains, where topologically protected edge states are unambiguously identified. We also reveal that such topological edge states are robust under symmetry-breaking disorders. For transverse eigenstates, we further discover the increase of localization length of topological edge states with the increase of lattice period due to the presence of strong far-field dipole-dipole interactions. Moreover, the ultra-strong scattering cross section and ultra-narrow linewidth of a single cold atom allow us to observe in more detail about topological states than in conventional systems, such as the frequency shift with respect to the single-atom resonance and the largely tunable bandgap. We envisage these topological photonic states can provide an efficient interface between light and matter., Comment: 13 pages 10 figures Comments are welcome

The structural correlations in the microscopic structures of random media can induce the dependent scattering mechanism and thus influence the optical scattering properties. Based on our recent theory on the dependent scattering mechanism in random media composed of discrete dual-dipolar scatterers (\textit{Physical Review A 97, 023836}), in this paper, we study the hard-sphere Yukawa (HSY) random media, in order to further elucidate the role of structural correlations in the dependent scattering mechanism and hence optical scattering properties. Here, we consider charged colloidal suspensions, whose effective pair interaction between colloids is described by a screened Coulomb (Yukawa) potential. By means of adding salt ions, the pair interaction between the charged particles can be flexibly tailored and therefore the structural correlations are modified. It is shown that this strategy can affect the optical properties significantly. For colloidal $\mathrm{TiO_2}$ suspensions, the modification of electric and magnetic dipole excitations induced by the structural correlations can substantially influence the optical scattering properties, in addition to the far-field interference effect described by the structure factor. However, this modification is only slightly altered by different salt concentrations and is mainly because of the packing-density-dependent screening effect. On the other hand, for low refractive index colloidal polystyrene suspensions, the dependent scattering mechanism mainly involves the far-field interference effect, and the effective exciting field amplitude for electric dipole almost remains unchanged under different structural correlations. The present study has profound implications for understanding the role of structural correlations in dependent scattering mechanism., Comment: 8 pages, 6 figures

The dependent scattering mechanism is known to have a significant impact on the radiative properties of random media containing discrete scatterers. Here we theoretically demonstrate the role of dependent scattering on the radiative properties of disordered media composed of nonabsorbing, dual-dipolar particles. Based on our theoretical formulas for the radiative properties for such media, we investigate the dependent scattering effects, including the effect of modification of the electric and magnetic dipole excitations and the far-field interference effect, both induced and influenced by the structural correlations. We study in detail how the structural correlations play a role in the dependent scattering mechanism by using two types of particle system, i.e., the hard-sphere system and the sticky-hard-sphere system. We show that the inverse stickiness parameter, which controls the interparticle adhesive force and thus the particle correlations, can tune the radiative properties significantly. Particularly, increasing the surface stickiness can result in a higher scattering coefficient and a larger asymmetry factor. The results also imply that in the present system, the far-field interference effect plays a dominant role in the radiative properties while the effect of modification of the electric and magnetic dipole excitations is more subtle. Our study is promising in understanding and manipulating the radiative properties of dual-dipolar random media., Comment: 33 pages, 10 figures. arXiv admin note: text overlap with arXiv:1801.01667

Structural correlations have a significant effect on light propagation in disordered media. We numerically investigate the role of short-range order in light absorption in thin films with disordered nanoholes. Two types of disordered distributions, including stealthy hyperuniform (SHU) and hard disk (HD) patterns with different degrees of short-range order, are studied. We find that Bragg scattering induced by short-range order results in the appearance of a gradually sharper absorption peak with the increasing of degrees of short-range order ($\chi$, $\phi$). A physical model is proposed to calculate the in-plane angularly differential scattering cross section $d \sigma^*/d \theta$ of thin-film nanostructures with consideration of {the} structure factor $S(q)$. Results reveal that higher level of short-range order can enhance in-plane Bragg scattering in certain wavelengths and directions corresponding to rich and sharp peaks in {the} structure factor $S(q)$, which can further modify morphology-dependent-like resonances of an individual scatterer {and leads } to {large} improvement of absorptivity in thin films. Besides, the comparison results show that SHU structures exhibit better integrated absorption ($IA$) enhancement than both HD and periodic structures. And there is a transition of local-order phase between hexagonal lattice{s} and square lattice{s for SHU structures}, leading to an optimal absorption performance when $\chi$ is around 0.5 of interest. The present study paves a way in controlling light absorption and scattering using novel disordered nanostructures., Comment: 10 pages, 12 figures

Understanding radiative transfer in random media like micro/nanoporous and particulate materials, allows people to manipulate the scattering and absorption of radiation, as well as opens new possibilities in applications such as imaging through turbid media, photovoltaics and radiative cooling. A strong-backscattering phase function, i.e., a negative scattering asymmetry parameter $g$, is of great interest which can possibly achieve unusual radiative transport phenomena, for instance, Anderson localization of light. Based on the multipole expansion of Foldy-Lax equations and quasicrystalline approximation (QCA), we have rigorously derived analytical expressions for effective propagation constant and scattering phase function for a random system containing dual-dipolar particles, by taking the effect of structural correlations into account. Here we demonstrate that by utilizing structural correlations and the second Kerker condition for a disordered medium composed of randomly distributed silicon nanoparticles, a strongly negative scattering asymmetry factor ($g\sim-0.5$) for multiple light scattering can be realized in the near-infrared. As concentration of scattering particles rises, the backscattering is also enhanced. Moreover, we show that in this circumstance, transport mean free path is largely reduced and even smaller than that predicted by independent scattering approximation. We further explored the dependent scattering effects, including the modification of electric and magnetic dipole excitations and far-field interference effect, both induced by the structural correlations, for volume fraction of particles up to $f_v\sim0.25$. Our results have profound implications in harnessing micro/nanoscale radiative transfer through random media., Comment: 16 pages, 7 figures

The approximate nature of radiative transfer equation (RTE) leads to a bunch of considerations on the effect of "dependent scattering" in random media, especially particulate media composed of discrete scatterers, in the last a few decades, which usually indicates those deviations RTE (combined with ISA) lead to from experimental and exact numerical results due to electromagnetic wave interference. Here we theoretically and numerically demonstrate the effect of dependent scattering on absorption in disordered media consisting of highly scattering scatterers. By making comparison between the independent scattering approximation-radiative transfer equation (ISA-RTE) and the full-wave coupled dipole method (CDM), we find that deviations between the two methods increase as scatterer density in the media increases. The discrepancy also grows with optical thickness. To quantitatively take dependent scattering effect into account, we develop a theoretical model using quasi-crystalline approximation (QCA) to derive dependent-scattering corrected radiative properties, based on the path-integral diagrammatic technique in multiple scattering theory. The model results in a more reasonable agreement with numerical simulations. The present work has profound implications for the coherent scattering physics in random media with absorption, correctly modeling light absorptance in random media and interpreting the experimental observations in various applications for random media such as solar energy concentration, micro/nanofluids, structural color generation, etc., Comment: 30 pages, 8 figures, submitted