Nonlocal Mode Research Articles

Hydrodynamic density functional theory of simple dissipative fluids

In this paper, a statistical physical derivation of thermodynamically consistent fluid mechanical equations is presented for non-isothermal viscous molecular fluids. The coarse-graining process is based on (i) the adiabatic expansion of the one-particle probability density function around local thermodynamic equilibrium, (ii) the assumption of decoupled particle positions and momenta, and (iii) the variational principle. It is shown that there exists a class of free energy functionals for which the conventional thermodynamic formalism can be naturally adopted for non-equilibrium scenarios, and describes entropy monotonic fluid flow in isolated systems. Furthermore, the analysis of the general continuum equations revealed the possibility of a non-local transport mode of energy in highly compressible dense fluids.

Effect of AlN nanoparticle doping on thermophysical properties of nitrate via mechanical milling: Experimental studies and microscopic mechanisms

A compounding method based on ball milling was used to incorporate AlN into LiNO3 to effectively improve its thermal conductivity. The optimal doping ratio was determined to be 2 wt% with an increase in thermal conductivity of 112.09 % integrating the enthalpy decrease. From the perspective of molecular dynamics simulations, it is demonstrated that AlN achieves a better matching of vibrations with LiNO3 by changing its vibrational modes at the doping ratio of 2 wt% with the support of vibration density of states, overlapping energy and phonon participation ratio. When 2 wt% AlN was added, non-local vibrational modes of LiNO3 increased, which microscopically illustrated the intrinsic mechanism of 2 wt% as the optimal doping ratio. The radial distribution function was used to explain the microscopic mechanism behind the changes in the specific heat of LiNO3 concerning temperature. The reason why the enthalpy of LiNO3 would decrease after AlN added is that AlN can bind LiNO3 molecules on the surface, and LiNO3 is confined by stronger intermolecular forces, leading to a blockage of its phase change behavior. This study proposed a doping method that can uniformly disperse AlN and avoid crystallized water. It also provides a strategy for selecting the appropriate nanoaddictives for compositing in molten salts to enhance energy storage efficiency.

Exceptions to Fourier’s law at the macroscale

The usual basis to analyze heat transfer within materials is the equation formulated 200 years ago, Fourier's law, which is identical mathematically to the mass diffusion equation, Fick's law. Revisiting this assumption regarding heat transport within translucent materials, performing the experiments in vacuum to avoid air convection, we compare the model predictions to infrared-based measurements with nearly mK temperature resolution. After heat pulses, we find macroscale non-Gaussian tails in the surface temperature profile. At steady state, we find macroscale anomalous hot spots when the sample is topographically rough, and this is validated by using two additional independent methods to measure surface temperature. These discrepancies from Fourier's law for translucent materials suggest that internal radiation whose mean-free-path is millimeters interacts with defects to produce small heat sources that by secondary emission afford an additional, non-local mode of heat transport. For these polymer and inorganic glass materials, this suggests unique strategies of heat management design.

External chirality enhancing downconversion in a waveguide-coupled nonlinear plasmonic metasurface.

Metasurfaces, typically constructed from spatial arrangements of localized building blocks, can enhance light-matter interactions through local field enhancement or by coherent coupling to extended photonic modes. Recent works have explored how guided mode resonances influence the performance of nonlinear metasurfaces. Here we investigate the modal impact on difference-frequency generation in a waveguide-coupled metasurface platform. The system is constructed from gold split-ring resonators on a high-index TiO2 waveguide. We find that a symmetric configuration of the metasurface's localized modes and the extended waveguide modes lead to a modest enhancement of the downconversion process. However, when the mirror symmetry of the localized modes with respect to the guided mode propagation breaks, it introduces external chirality. This enables coupling to a higher quality mode, resulting in a 70-fold enhancement of the difference-frequency generation. The capacity to manipulate the nonlocal modes through the design offers broader control over the interaction and new avenues to tailor the nonlinear processes.

Quasi-Trapped Guided Mode in a Metasurface Waveguide for Independent Control of Multiple Nonlocal Modes

Quasi-Trapped Guided Mode in a Metasurface Waveguide for Independent Control of Multiple Nonlocal Modes

Hyperspectral Image Fusion via a Novel Generalized Tensor Nuclear Norm Regularization.

Recently, low-rank tensor regularization has received more and more attention in hyperspectral and multispectral fusion (HMF). However, these methods often suffer from inflexible low-rank tensor definition and are highly sensitive to the permutation of tensor modes, which hinder their performance. To tackle this problem, we propose a novel generalized tensor nuclear norm (GTNN)-based approach for the HMF. First, we define a novel GTNN by extending the existing third-mode-based tensor nuclear norm (TNN) to arbitrary mode, which conducts the Fourier transform on an arbitrary single mode and then computes the TNN for each mode. In this way, we can not only capture more extensive correlations for the three modes of a tensor, and also omit the adverse effect of permutation of tensor modes. To utilize the correlations among spectral bands, the high-resolution hyperspectral image (HSI) is approximated as low-rank spectral basis multiplication by coefficients, and we estimate the spectral basis by conducting singular-value decomposition (SVD) on HSI. Then, the coefficients are estimated by addressing the proposed GTNN regularized optimization. In specific, to exploit the non-local similarities of the HSI, we first cluster the patches of the coefficient into a 3-D, which contains spatial, spectral, and non-local modes. Since the collected tensor contains the strong non-local spatial-spectral similarities of the HSI, the proposed low-rank tensor regularization is imposed on these collected tensors, which fully model the non-local self-similarities. Fusion experiments on both simulated and real datasets prove the advantages of this approach. The code is available at https://github.com/renweidian/GTNN.

Vector rogue waves and their dynamics in the nonlocal three-component Manakov system

In this work, by combining the Darboux transformation and variable separation technique, we generate and discuss a semirational vector solution to the nonlocal three-component Manakov system. The semirational solution is expressed in separation-of-variables form. The semirational vector solution exhibits breathers and rogue waves on a bright-dark soliton background. Moreover, the dynamic behaviors of the semirational vector solutions are discussed with some graphics. Our results may contribute to explaining and enriching the corresponding rogue wave phenomena emerging in nonlocal wave modes.

Twisted moiré photonic crystal enabled optical vortex generation through bound states in the continuum

The twisted stacking of two layered crystals has led to the emerging moiré physics as well as intriguing chiral phenomena such as chiral phonon and photon generation. In this work, we identified and theoretically formulated a non-trivial twist-enabled coupling mechanism in twisted bilayer photonic crystal (TBPC), which connects the bound state in the continuum (BIC) mode to the free space through the twist-enabled channel. Moreover, the radiation from TBPC hosts an optical vortex in the far field with both odd and even topological orders. We quantitatively analyzed the twist-enabled coupling between the BIC mode and other non-local modes in the photonic crystals, giving rise to radiation carrying orbital angular momentum. The optical vortex generation is robust against geometric disturbance, making TBPC a promising platform for well-defined vortex generation. As a result, TBPCs not only provide a new approach to manipulating the angular momentum of photons, but may also enable novel applications in integrated optical information processing and optical tweezers. Our work broadens the field of moiré photonics and paves the way toward the novel application of moiré physics.

A switchable terahertz metamaterial absorber between ultra-broadband and dual bands

Based on the phase change properties of vanadium dioxide (VO2), we propose a terahertz metamaterial absorber that can be switched flexibly between ultra-broadband and dual bands. The absorber consists of a resonator array above a conductive ground layer separated with a dielectric spacer, which includes four square-loop VO2 resonators and a crossed gold resonator in each unit cell. By changing the conductivity of VO2 through thermal control, the absorber can achieve the switching between ultra-broadband absorption and dual-band absorption. Simulation results show that at high temperature, the absorber realizes more than 90% absorption bandwidth in the range of 3.98 to 9.06 THz, which can be elucidated by the wave-interference theory and impedance matching theory. At low temperature, up to 95% of the dual-band absorption occurs at 5.95 and 6.95 THz, which originates the dipole mode and nonlocal surface-Bloch mode of metal resonators. In addition, the absorber has the advantages of polarization-independence and wide-angle absorption. Compared with previous studies, our design can switch between two absorption modes and its absorption performance is greatly improved. The proposed absorber design scheme is expected to expand terahertz devices and enable a variety of applications in the terahertz range, such as modulation, sensing, stealth, and switching devices.

A black hole toy model with non-local and boundary modes from non-trivial boundary conditions

We study gauge theories between two parallel boundaries with non-trivial boundary conditions, which serve as a toy model for black hole background with two boundaries near the horizon and infinite, aiming for a better understanding of the Bekenstein–Hawking entropy. The new set of boundary conditions allows boundary modes and non-local modes that interplay between the two boundaries. Those boundary modes and Wilson lines stretched between the two boundaries are carefully analyzed and are confirmed as physical variables in the phase space. Along with bulk fluctuation modes and topological modes, the partition function and entropy of all physical modes are evaluated via Euclidean path integral. It is shown that there are transitions between the dominance of different modes as we vary the temperature. The boundary fluctuation modes whose entropy is proportional to the volume dominate at high temperatures, and the boundary-area scaled boundary modes and Wilson lines are the more important at low temperatures. At super-low temperatures, when all the fluctuation modes die off, we see the topological modes whose entropy is the logarithm of the length scales of the system. The boundary modes and non-local modes should have their counterparts in a black hole system with similar boundary conditions, which might provide important hints for black hole physics.

Hyperspectral Image Denoising via Weighted Multidirectional Low-Rank Tensor Recovery.

Recently, low-rank tensor recovery methods based on subspace representation have received increased attention in the field of hyperspectral image (HSI) denoising. Unfortunately, those methods usually analyze the prior structural information within different dimensions indiscriminately, ignoring the differences between modes, leaving substantial room for improvement. In this article, we first consider the low-rank properties in the subspace and prove that the structure correlation across the nonlocal self-similarity mode is much stronger than in the spatial sparsity and spectral correlation modes. On that basis, we introduce a new multidirectional low-rank regularization, in which each mode is assigned a different weight to characterize its contribution to estimating the tensor rank. After that, integrating the proposed regularization with the subspace-based tensor recovery framework, an optimization model for HSI mixed noise removal is developed. The proposed model can be addressed efficiently via the alternating minimization algorithm. Extensive experiments implemented with synthetic and real data demonstrate that the proposed method significantly outperforms other state-of-the-art HSI denoising methods, which clearly indicates the effectiveness of the proposed approach in HSI denoising.

Superconductor Vortex Spectrum Including Fermi Arc States in Time-Reversal Symmetric Weyl Semimetals.

Using semiclassics to surmount the hurdle of bulk-surface inseparability, we derive the superconductor vortex spectrum in nonmagnetic Weyl semimetals and show that it stems from the Berry phase of orbits made of Fermi arcs on opposite surfaces and bulk chiral modes. Tilting the vortex transmutes it between bosonic, fermionic, and supersymmetric, produces periodic peaks in the density of states that signify novel nonlocal Majorana modes, and yields a thickness-independent spectrum at magic "magic angles." We propose (Nb,Ta)P as candidate materials and tunneling spectroscopy as the ideal experiment.

Interlayer-Exchange-Dominant Spin Hall Nano-Oscillator

The spin Hall nano-oscillator (SHNO) is a promising spintronic device to produce high-frequency and low-linewidth microwave signals. We study a type of SHNO based on the $L{1}_{0}\text{\ensuremath{-}}\mathrm{Fe}\mathrm{Pt}/\mathrm{Ni}\mathrm{Fe}/\mathrm{Pt}$ exchange-spring system with an ultrahigh perpendicular magnetic anisotropy by micromagnetic simulation. The hard-soft magnetic exchange-spring system has a very high interlayer-exchange-interaction field, resulting in a more than 30-GHz emission frequency and 38.6-GHz/T field tunability. Apart from conventional localized and nonlocalized auto-oscillation modes, localized or nonlocalized modes with central antisymmetry also appear in this SHNO. Two oscillation centers possess nonequal amplitudes and opposite phases in these antisymmetrical modes. Different modes are determined by the competition between three factors: the exchange-interaction field, the perpendicular anisotropic field, and spin-orbit torque. The spin dynamics in the SHNO exhibit complex field and current dependence. Our results provide a possible direction for the design of SHNOs, which may be beneficial for the research and development of spintronic nano-oscillators.

Foreword to the special issue on new developments in structural stability.

Foreword to the special issue on new developments in structural stability.

Emerging Planar Nanostructures Involving Both Local and Nonlocal Modes

With the capabilities to localize light at the subwavelength scale and flexibly control the full dimensions of electromagnetic fields, planar optical artificial nanostructures have been widely explored to innovate next-generation multifunctional compact photonic devices in recent decades. To further improve the efficiency, quality (Q) factors, and design degrees of freedom of photonic devices, recent research advances have brought in comprehensive consideration of both local and nonlocal modes in nanostructures with blurred distinctions between metasurfaces and photonic crystals. In this Perspective, we review the recent progress in planar nanophotonics involving localized resonances, nonlocal modes, and their couplings. Many intriguing physical effects correlated to local and/or nonlocal modes and the corresponding applications are reviewed, as well as large-area optimization strategies to directly simulate local and nonlocal optical responses. We also summarize several current challenges and foresee various future directions of the attractive field.

Tailored Dispersion of Spectro-Temporal Dynamics in Hot-Carrier Plasmonics.

Ultrafast optical switching in plasmonic platforms relies on the third-order Kerr nonlinearity, which is tightly linked to the dynamics of hot carriers in nanostructured metals. Although extensively utilized, a fundamental understanding on the dependence of the switching dynamics upon optical resonances has often been overlooked. Here, all-optical control of resonance bands in a hybrid photonic-plasmonic crystal is employed as an empowering technique for probing the resonance-dependent switching dynamics upon hot carrier formation. Differential optical transmission measurements reveal an enhanced switching performance near the anti-crossing point arising from strong coupling between local and nonlocal resonance modes. Furthermore, entangled with hot-carrier dynamics, the nonlinear correspondence between optical resonances and refractive index change results in tailorable dispersion of recovery speeds which can notably deviate from the characteristic lifetime of hot carriers. The comprehensive understanding provides new protocols for optically characterizing hot-carrier dynamics and optimizing resonance-based all-optical switches for operations across the visible spectrum.

Tensor Cascaded-Rank Minimization in Subspace: A Unified Regime for Hyperspectral Image Low-Level Vision.

Low-rank tensor representation philosophy has enjoyed a reputation in many hyperspectral image (HSI) low-level vision applications, but previous studies often failed to comprehensively exploit the low-rank nature of HSI along different modes in low-dimensional subspace, and unsurprisingly handled only one specific task. To address these challenges, in this paper, we figured out that in addition to the spatial correlation, the spectral dependency of HSI also implicitly exists in the coefficient tensor of its subspace, this crucial dependency that was not fully utilized by previous studies yet can be effectively exploited in a cascaded manner. This led us to propose a unified subspace low-rank learning regime with a new tensor cascaded rank minimization, named STCR, to fully couple the low-rankness of HSI in different domains for various low-level vision tasks. Technically, the high-dimensional HSI was first projected into a low-dimensional tensor subspace, then a novel tensor low-cascaded-rank decomposition was designed to collapse the constructed tensor into three core tensors in succession to more thoroughly exploit the correlations in spatial, nonlocal, and spectral modes of the coefficient tensor. Next, difference continuity-regularization was introduced to learn a basis that more closely approximates the HSI's endmembers. The proposed regime realizes a comprehensive delineation of the self-portrait of HSI tensor. Extensive evaluations conducted with dozens of state-of-the-art (SOTA) baselines on eight datasets verified that the proposed regime is highly effective and robust to typical HSI low-level vision tasks, including denoising, compressive sensing reconstruction, inpainting, and destriping. The source code of our method is released at https://github.com/CX-He/STCR.git.

Tendon-inerter-damper helicopter blade augmentation for improved dynamic performance

A novel helicopter blade concept with an adjustable tendon internally supported by dynamically tuned squeeze film damper guides is proposed to suppress the resonant blade vibrations. A physics-based representation of the tendon guides equivalent to an inerter-damper connected in parallel is further adopted to develop a new integrated blade-tendon-device model. The concept is then studied in terms of its optimal dynamic tuning characteristics and damping augmentation potential. The study is focused on single and multi-modal tuning performance in the context of a variable speed rotor with realistic pre-twisted blades used in modern light weight class helicopters. Initially, the significance of modal veering, non-local modes and eigenvalue merging under control parameter variations which include tendon tension, device damping, inertance and span-wise location is elucidated. Across the two separate two-mode optimal tuning studies, it is shown that the typical nominal levels of 0.5–2.0% of the blade modal damping arising from the structural sources can be significantly increased, for instance to 4.3% in case of the second in-plane blade mode and 13.4% in case of the second out-of-plane blade mode. After performing the conceptual device sizing study under realistic constraints utilising the optimal tuning parameters and an adopted squeeze film damping model, it is shown that the concept can be realised within the existing limits of the blade envelope. The proposed concept is shown to be robust and adaptive in its nature with the ability to introduce highly focused blade damping.

Noise-resilient edge modes on a chain of superconducting qubits.

Inherent symmetry of a quantum system may protect its otherwise fragile states. Leveraging such protection requires testing its robustness against uncontrolled environmental interactions. Using 47 superconducting qubits, we implement the one-dimensional kicked Ising model, which exhibits nonlocal Majorana edge modes (MEMs) with [Formula: see text] parity symmetry. We find that any multiqubit Pauli operator overlapping with the MEMs exhibits a uniform late-time decay rate comparable to single-qubit relaxation rates, irrespective of its size or composition. This characteristic allows us to accurately reconstruct the exponentially localized spatial profiles of the MEMs. Furthermore, the MEMs are found to be resilient against certain symmetry-breaking noise owing to a prethermalization mechanism. Our work elucidates the complex interplay between noise and symmetry-protected edge modes in a solid-state environment.

A robust Moore–Penrose pseudoinverse-based static finite-element solver for simulating non-local fracture in solids

In this work, we develop a pseudoinverse-based static finite-element solver to model the elastic deformation and non-local brittle fracture of solids. The pseudoinverse of the finite-element stiffness matrix is calculated using a QR decomposition-based method which is faster than using the traditional approach based on the singular value decomposition method. This new finite-element framework has two advantages: (1) the finite-element equations can still be solved even when the finite-element stiffness matrix is singular, and (2) there is no need for introducing an artificial elastic rest energy or viscous regularization for the sole purpose of keeping the finite-element stiffness matrix non-singular in order to solve the finite-element equations. We also show that the proposed method is robust in solving chosen boundary value problems involving the elastic deformation and abrupt non-local mode I and mixed-mode brittle fracture of solids when compared to the traditional element kill method where a small but finite residual stiffness is maintained at a material in order to prevent the finite-element stiffness matrix from being singular. Hence, this proposed method allows the modeling of separation/fragmentation of solids when fracture occurs.Finally, we use the new computational framework to model the fracture of PMMA beam samples at room temperature. By calibrating the material parameters in the constitutive theory using analytical methods and fitting to a Mode I fracture experiment force–displacement response, we show that our newly-proposed computational method is able to predict the experimental fracture loci and crack propagation characteristics in PMMA beam samples undergoing mixed-mode fracture conditions to good accord.