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Wednesday 14 October · still arriving

Applied Physics

Effect of deep-trap density of states for a-Si:H layers on HIT cell performances: Modeling Framework

Tewfik Souier and Adel Gougam

In this work, an aSi and cSi heterojunction solar cell with an intrinsic layer is simulated using AFORS-HET software. The study focuses on the role of the electronic density of states DOS of the amorphous emitter, p type aSiH, in governing the performance of the HIT cell and the electronic transfer across the heterointerface. It is found that the DOS of the p type aSiH emitter can cause an unfavorable recombination and trapping effect, which becomes more severe and difficult to avoid when the bulk dangling-bond density in the a-Si emitter approaches or exceeds the doping concentration. An increase in deep trap density beyond a critical value causes a drop in the built in voltage and shifts the depletion layer into p type aSi. This situation leads to a sharp decline in HIT cell performance, namely the open circuit voltage and the fill factor, and to the appearance of an S shaped IV characteristic. The simulation results suggest that the emitter activation energy needs to be optimized to achieve high efficiency. Under optimal conditions, holes accumulate near the heterojunction interface, leading to the formation of an inversion layer. This paper presents a physical mechanism for recombination processes within the emitter and concludes with the optimized parameters required to achieve a HIT cell efficiency comparable to Sanyo record of 23 percent on a thin silicon wafer.
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Applied Physics · Cross-listed from physics.optics

Polaritonic self-hybridized critical coupling by Brillouin zone folding induced quasi-bound states in the continuum in bulk WS2 metasurfaces

Kuidong Wang, Xiongwei Guo, Fu Liu et al. (+2 more)

Maximizing the absorption of exciton-polaritons in transition-metal dichalcogenides (TMDCs) under critical coupling conditions is crucial for developing high-efficiency polariton-based photodetectors, solar cells, and perfect absorbers. Here, we propose a polaritonic critical self-hybridized coupling between Brillouin zone folding driven quasi-bound states in the continuum (BZF-QBIC) mode and A excitons in a bulk WS2 metasurface. This polaritonic critical coupling shows robust behavior with respect to the asymmetric parameters of the involved BZF-QBIC mode, in contrast to the asymmetry-sensitive conventional QBIC-based critical coupling. By changing the height of WS2 metasurfaces, we observe a typical anti-crossing behavior with a Rabi splitting of 246.5 meV. Moreover, the maximum absorption value of 0.5 for exciton-polaritons is achieved at the polaritonic critical coupling condition. The large population of excitons provided by bulk WS2 is essential for achieving polaritonic critical coupling and can further enhance polaritonic absorption. This work enables the realization of robust, high-absorption self-hybridized polaritonic critical coupling in TMDCs, and further expedite their applications in high-absorption low-dimensional polaritonic devices.
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All authors Kuidong Wang, Xiongwei Guo, Fu Liu, Jinhai Si, Xun Hou

Applied Physics · Cross-listed from cond-mat.mes-hall

Magnetic field induced modulation of heat transport in CrPS$_4$ probed by TaIrTe$_4$ transverse Seebeck thermometry

Krishnaraajan Sundararajan, Sergio Alvarruiz, Cédric A. Cordero-Silis et al. (+5 more)

Understanding and controlling heat flow in low-dimensional magnetic materials is central to thermoelectrics and spin caloritronics. One of the challenges is the absence of sensitive probes of small, field-dependent modulations in thermal transport. Here we demonstrate transverse Seebeck thermometry using exfoliated TaIrTe$_4$ as a probe of thermal conductivity modulated by an external magnetic field on a van der Waals magnet, CrPS$_4$. With a temperature gradient oriented at $45^\circ$ to its principal crystallographic axes, TaIrTe$_4$ exhibits a transverse thermopower exceeding $200~\mathrm{\mu V\,K^{-1}}$ for 900 nm wide and 30 $\mu$m long electrodes, enabling precise detection of variations in the local temperature gradients. Exploiting this with CrPS$_4$ in a nonlocal geometry, we resolve distinct field dependent thermal conductivity changes associated with both the spin-flip and spin-flop magnetic transitions which we attribute to variations in the magnon$-$phonon coupling in CrPS$_4$. At 5 K, the transverse Seebeck response is modulated by more than 8$\%$ by an external magnetic field, demonstrating strong magnetic control of heat transport in CrPS$_4$. This all van der Waals platform offers high sensitivity to modulations of thermal conductivity and a broad adaptability to a wide range of exfoliated magnetic systems.
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All authors Krishnaraajan Sundararajan, Sergio Alvarruiz, Cédric A. Cordero-Silis, Majid Ahmadi, Marcos H.D. Guimarães, Jagoda S\lawińska, Joseph Barker, Bart J. van Wees

Applied Physics · Cross-listed from physics.optics

Computational compressive imaging reconstruction with a simulated-annealing-based Ising solver

Ze Zheng, Xiaoyan Wu, Hang Xu et al. (+3 more)

Computational compressive imaging, such as single-pixel imaging and lensless imaging, is a promising imaging technique, enabling the reconstruction of objects from under-sampled measurements through compressed sensing algorithms or deep learning methods. However, the demand for electronic computational resources grows rapidly when recovering high-resolution and multi-dimensional images and training neural networks with numerous parameters, which has become a bottleneck for the widespread adoption of this technique. Here, we propose a physics-driven reconstruction framework that formulates imaging inverse problems as Ising models and directly recovers target objects through the self-evolution of non-von Neumann Ising machines toward the ground state of the Hamiltonian. We employ a simulated-annealing-based Ising solver to demonstrate this proof-of-concept by reconstructing objects in both single-pixel imaging and a lensless diffuser camera at sampling rates ranging from 1% to 25%. By further incorporating a foreground-sparsity constraint and a smoothness constraint, the reconstruction quality of our method is comparable to or even better than that of mainstream algorithms. This approach has the potential to substantially reduce the electronic computational burden of inverse reconstruction, paving the way for real-time, low-power computational imaging.
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All authors Ze Zheng, Xiaoyan Wu, Hang Xu, Jingzheng Huang, Tailong Xiao, Guihua Zeng

Applied Physics · Cross-listed from physics.flu-dyn

Response of Confined Mesoscale Flames to Acoustic Forcing

Akhil Aravind, Balasundaram Mohan and Saptarshi Basu

Mesoscale combustion plays a vital role in applications ranging from portable power generation to micro-propulsion systems. This study investigates the response of mesoscale flames to upstream acoustic forcing across three characteristic flame regimes: Flames with Repetitive Extinction and Ignition (FREI), Stable Flames (SF), and Propagating Flames (PF). Acoustic forcing is applied over a broad range of pressure intensities at the first harmonic of the combustor tube. At low forcing intensities, all the flame regimes exhibit oscillations at the forcing frequency without qualitative changes in their respective flame behaviours. However, as the acoustic pressure increases, all flame regimes transition to a common unsteady regime characterised by periodic ignition-extinction cycles (resembling FREI) alongside strong oscillations at the forcing frequency. This response is identified as the oscillating FREI (O-FREI) regime, in which increasing forcing intensity leads to a reduction in the mean heat release rate, an amplification of oscillations at the forcing frequency, and a drop in the Strouhal number associated with the ignition-extinction cycle. The response characteristics across all flame regimes are examined in detail and are further complemented using reduced-order mathematical models.
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Applied Physics · Cross-listed from physics.optics

Two-Photon Spatial Multiplexing: Image Encoding in Gaussian Noncircularity of Light

Wanting Hou, Zhiyuan Ye, Hong-Chao Liu et al. (+2 more)

The search for new degrees of freedom (DoF) of light is central to advancing optical information encoding and multiplexing. Gaussian statistics are ubiquitous in nature, and here we unlock an unexpected statistical DoF in the joint noncircularity of Gaussian light. For a pair of Gaussian light fields, the covariance- and pseudocovariance-dominated two types of correlations dictate the propagation rules and the image-encoding responses, mapping optical information into coordinate-difference and coordinate-sum momentum spaces, respectively. A hybrid random-phase grating array enables the experimental preparation of noncircular Gaussian light with programmable coexistence, yielding X-shaped intensity correlations while subtly reducing the degree of second-order coherence. Two independently programmed images coexist in the same beams at identical wavelength and polarization, yet are selectively decoded through two-photon correlation geometry without physical filters. Remarkably, both images remain recoverable even when structured stray light is as intense as the signal. These results unlock a hidden statistical dimension of optical information encoding, transforming Gaussian fluctuations into a dual-channel information carrier and joint noncircularity into a programmable optical DoF.
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All authors Wanting Hou, Zhiyuan Ye, Hong-Chao Liu, Jun Xiong, Kaige Wang

Applied Physics · Cross-listed from physics.optics

Femtosecond all-optical polarization manipulation of harmonic generation in an anisotropic strongly coupled plasmon-epsilon-near-zero metasurface

Yingying Zhang, Jinhai Si, Xun Hou et al. (+1 more)

Ultrafast manipulation of light polarization plays a key role in modern high-speed photonics and optoelectronic operations. However, most current polarization-active modulation schemes are restricted by a limited operating wavelength range (visible to infrared), narrow-band resonant fundamental wavelength working condition, and relatively long modulation time (> 1 picosecond). Here, by taking advantage of the transient anisotropic nonlinearity of optical strong coupling between the epsilon-near-zero mode of indium tin oxide (ITO) film and polarization-selective plasmonic resonance, we achieve femtosecond polarization manipulation of broadband light that spans ultraviolet (UV) to visible region by controlling harmonic generation of the signal light under resonant pumping. We demonstrate polarization elliptic rotation of 23.3{\deg} at 407 nm for third-harmonic generation (THG) and 55.0{\deg} at 610 nm for second-harmonic generation (SHG) simultaneously within ~600 fs. In addition, the strongly coupled system can also serve as a universal femtosecond polarization modulation source, imprinting a 32.9{\deg} polarization rotation in the UV region by converting the modulation information of the fundamental signal light to that of THG light via a uniform ITO film in a cascaded configuration. Our study establishes a new paradigm for UV-based, ultrahigh-speed broadband polarization photonics with direct implications for high-speed optical information processing and programmable nonlinear photonic devices.
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All authors Yingying Zhang, Jinhai Si, Xun Hou, Kuidong Wang

Applied Physics · Cross-listed from physics.optics

Strong field confinement in air and enhanced optical Kerr nonlinearity of high-index star-shaped pore membrane metasurfaces

Andrey V. Panov

The optical Kerr effect in high-refractive-index membrane metasurfaces patterned with a square lattice of five-pointed star-shaped pores is investigated numerically using gallium phosphide as a model material. The star geometry supports resonances with pronounced electromagnetic energy confinement, including an anapole state. The sharp tips of the star-shaped pores concentrate the electric energy density in air, exceeding that of Mie voids by a factor of seven. The effective second-order refractive index is enhanced by up to three orders of magnitude relative to bulk GaP, with the largest values obtained near the anapole resonances. The nonlinear response remains stable under polarization rotation and random misalignment of the nanoholes, indicating tolerance to fabrication imperfections. These results establish star-shaped pore lattices in freestanding membranes as a promising platform for nonlinear optics exploiting strong field confinement.
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Tuesday 13 October · still arriving

Applied Physics

Topologically Protected Surface Acoustic Wave Edge States in Phononic Integrated Circuits

Jack Guida, Niccolo Scalise Pantuso, Cristian Cassella et al. (+2 more)

Phononic integrated circuits enable the development of compact systems to manipulate radio frequency signals through interconnected networks of acoustic waveguides. Introducing topologically protected robustness in these circuits to counter fabrication imperfections and local perturbations, remains a challenge. This work presents a validated modeling framework for topologically protected edge states using surface acoustic waves in etch-defined waveguides consisting of scandium aluminum nitride on silicon carbide, directly comparing analytical, full-wave numerical simulation, and laser Doppler vibrometer measured experimental approaches and their agreement. This work represents the first experimental demonstration of topological edge states on a ScAlN on SiC platform, validated through direct quantitative comparison with analytical and numerical analyses, with future implications for topological protection in phononic and optomechanical integrated circuit platforms.
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All authors Jack Guida, Niccolo Scalise Pantuso, Cristian Cassella, Sunil Mittal, Siddhartha Ghosh

Applied Physics · Cross-listed from physics.optics

High-resolution retinal matrix imaging via computational motion and aberration correction

Aymeric Melt, Léo Puyo, Victor Barolle et al. (+3 more)

High-resolution optical imaging of the human retina is essential for diagnosing ophthalmic and neurodegenerative diseases. While adaptive optics combined with coherence gating can resolve retinal structures at the cellular scale, it requires complex, costly, and cumbersome hardware to physically correct for ocular aberrations and motion. Matrix imaging offers a powerful digital alternative by leveraging wave linearity to undo aberrations and multiple scattering; however, its in vivo deployment has been hindered by continuous, involuntary eye movements that destroy phase coherence during acquisition. Here, we overcome this fundamental barrier and demonstrate the first in vivo reflection matrix imaging of the human retina using an ultra-simplified optical setup without physical correctors. We introduce a fully computational framework that tracks and compensates for multi-axial ocular motion directly from raw interferometric data, thereby restoring the phase coherence of a multi-spectral distortion matrix. This enables local, high-order aberration correction to achieve diffraction-limited, volumetric imaging of retinal tissues. By shifting the hardware burden to physics-guided numerical computation, this paradigm opens the way for accessible, non-invasive, and high-resolution digital ophthalmology.
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All authors Aymeric Melt, Léo Puyo, Victor Barolle, Claude Boccara, Gereon Hüttmann, Alexandre Aubry

Applied Physics · Cross-listed from physics.optics

Engineering Color and Angular Stability in Building-Integrated Photovoltaics Using Metal-Oxide Photonic Glasses

Sinan Genc, Talat Ozden and Alpan Bek

Coloring building-integrated photovoltaics poses a dilemma: absorptive pigments cost photocurrent, while ordered photonic structures are iridescent. Amorphous photonic glasses, disordered packings of high-index nanospheres, are proposed to avoid both, yet their angle-independent color has rarely been quantified on a realistic module stack. A non-absorbing scatterer needs a high index with visible transparency, which the Moss rule caps near 2.35. Coupling Mie scattering, the Percus-Yevick structure factor, the exact phase function, and two-flux transfer with absorption and refraction at the front glass, we fix four target colors that a crowd-sourced naming survey calls unambiguously blue, green, gold, and terracotta, and map the recipes reaching them across four metal oxides, four encapsulants, two cell technologies, and wide ranges of particle size, packing fraction, and layer number. All four are reached in a laminated three-layer coating, to within DeltaE00 of 0.8 to 2.5, but not from one oxide: transparent TiO2 renders the blue and only pale warm tones; the green, gold, and terracotta require the blue-band absorption of V2O5, and the low-contrast oxides turn grey at the warm end. The encapsulant governs the color, and the cell technology does not. Disorder does not confer angle independence: the colors hold for an observer moving under a fixed sun but drift by DeltaE00 of 5 to 18 over the day, terracotta least, and a facade lit from above and viewed from below shifts every color towards the blue. Oxide, layer number, and facade geometry must therefore be designed together.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci

Direct growth of crystalline spinel GaON films: A wide-bandgap mixed-anion semiconductor

Baikui Li, Zecheng Yang, Wenhao Yin et al. (+5 more)

Mixed-anion semiconductors offer opportunities for bandgap engineering beyond conventional multication alloys, but competing phases and disorder complicate their synthesis and the identification of their electronic properties. Gallium oxynitride (GaON) could connect the technologically important GaN and Ga2O3 systems, yet establishing a clear relation between its crystal structure, composition and bandgap remains challenging. Here we report the direct growth of crystalline spinel gamma-GaON films by nitrogen-plasma-assisted pulsed-laser deposition. Varying the nitrogen and oxygen supply yields monoclinic beta-Ga2O3, predominantly disordered films and crystalline spinel GaON. Complementary diffraction, atomic-resolution microscopy and elemental analysis establish the spinel structure and nitrogen incorporation. Temperature-dependent photocurrent spectroscopy reveals a clear redshift of the crystalline gamma-GaON response, supporting assignment of a band-edge transition near 4.3 eV at room temperature. These results open opportunities to investigate mixed-anion wide-bandgap semiconductor physics and develop heterostructures.
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All authors Baikui Li, Zecheng Yang, Wenhao Yin, Zijing Wu, Haitao Zhao, Yunwei Sheng, Honglei Wu, Jiannong Wang

Applied Physics · Cross-listed from cond-mat.mtrl-sci

A Transferable Machine-Learned Potential Enabling Large-Scale Copper-Carbon Simulations from Equilibrium to Extreme Conditions

Feiyu Zhou, Wei Qiu, Yan Chen et al. (+4 more)

Cu-C materials and interfaces are central to diamond thermal management, metallization, graphene growth and carbon-coating technologies, but atomistic simulations across these applications require a potential that describes metallic Cu, diverse carbon bonding, heterogeneous Cu-C interactions and close atomic encounters. Here we develop NEP-CuC, a transferable neuroevolution potential trained on a dataset of 2,727 uniformly relabelled configurations selected from a heterogeneous Cu-C candidate pool. Disagreement within an ensemble of five independently trained models provides an internal indicator of model sensitivity. A Ziegler-Biersack-Littmark (ZBL) correction describes short-range nuclear repulsion, while a runtime D3(BJ) correction supplements dispersion-sensitive calculations. Tests on source-derived held-out and independent external datasets, together with structural, elastic, defect, interfacial, vibrational and finite-temperature transport benchmarks, establish broad but property-dependent physical fidelity across elemental Cu, diverse carbon environments and heterogeneous Cu-C configurations. Large-scale simulations of amorphous-carbon formation and orientation-dependent shock compression of Cu further test transferability under strongly non-equilibrium conditions. For Cu/diamond interfaces, the same potential describes deposition, annealing and tensile response: preparation history leaves persistent differences in interphase structure, while the mean peak nominal tensile stress at 500 K decreases from $12.35\pm0.71$ to $6.65\pm0.98$ GPa as the incident Cu energy during the initial deposition stage increases from 1 to 50 eV. NEP-CuC provides an atomistic framework for linking processing, interfacial structure and physical response across Cu-C systems, with direct relevance to Cu/diamond thermal-management interfaces, diamond metallization and non-equilibrium Cu-C processing.
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All authors Feiyu Zhou, Wei Qiu, Yan Chen, Jiahui Liu, Yilun Liu, Shengying Yue, Penghua Ying

Applied Physics

Stability and Optimal Design of Adaptive Linear Bus Holding on Open Chains and Loops

Li Zhen, Weihua Gu, Miny Shen et al. (+2 more)

Bus holding can suppress bunching, but its stability and performance depend on the feedback structure and on how the bus sequence is bounded. This paper develops a common analytical framework for adaptive linear holding on finite open chains and loops and relates both to the bi-infinite system studied in the literature. Matrix and Fourier methods yield necessary and sufficient stability conditions for current- and leading-bus kernels on open chains and general cyclic kernels on loops, together with computable covariance bounds on open chains and exact variance formulas on loops. The analysis shows when periodic closure changes stability, when coefficient-sum stability tests in the literature are conservative, and why a stable open chain can still accumulate substantial variance before boundary effects arrive. For loops with same-lap feedback, modal analysis links control coefficients to fleet-wide schedule drift and to relative headway patterns, explaining the behavior of existing rules and yielding closed-form Pareto-optimal designs for schedule-holding and headway-holding tradeoffs. Cross-lap output corrections relate these designs to physical headway and holding performance. Numerical experiments show that the analytical design and a three-tap approximation, both obtained from closed-form coefficients and a one-dimensional search, outperform four established controls at the tested moderate and loose headway-variance budgets, with holding variances within 0.35% and 3.5% of the full cyclic numerical frontier across these budgets and other parameter variations. The framework thus provides a tractable design procedure and an explanation of how feedback structure and boundary conditions shape service reliability and holding effort.
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All authors Li Zhen, Weihua Gu, Miny Shen, Wenbo Fan, Feng Xiao

Applied Physics · Cross-listed from cs.ET

Two-State Dynamical Synapses as a Physical Substrate for Equilibrium Propagation

Dongshu Liu and Julie Grollier

Equilibrium Propagation (EqProp) updates each synapse by comparing a local term at the free and nudged equilibria. Because these two values occur at different times, a physical implementation requires temporary local memory. We show that this memory can emerge from a two-timescale synaptic model in which neural and volatile synaptic dynamics are jointly derived from a single energy function. A volatile state $w$ relaxes toward the product of the pre- and postsynaptic activities, while a non-volatile state $M$ stores the learned parameter. At equilibrium, $w$ equals the local term entering the EqProp update. Using its net change between phases implements phase-based EqProp, while transferring its successive changes during nudging yields continual EqProp, in which the temporal comparison is carried by the synaptic dynamics themselves. On MNIST with a single-hidden-layer network, the phase-based model reaches $2.01 \pm 0.09\%$ test error versus $2.00 \pm 0.13\%$ for standard EqProp, and the continual model reaches $2.24 \pm 0.11\%$ versus $2.28 \pm 0.16\%$ for continual EqProp. The framework further specifies the dynamical requirements that a volatile–non-volatile synaptic device must satisfy to implement this learning mechanism.
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Applied Physics

Device Model Linking Singlet and Triplet Spin-State Properties to Organic Photovoltaic Device Characteristics

Jun Du, Liming Liu and Jun Yan

This work proposes an exciton-kinetics coupled drift-diffusion (EKDD) model that bridges device-level charge transport with singlet and triplet excited-state kinetics. State populations and reversible photophysical transitions are solved self-consistently, enabling transient and steady-state device response calculations. We investigate how LE-CT, CT-CS, and LE-T energy offsets, together with triplet-transfer kinetics, govern charge generation, recombination, voltage loss, and extraction in organic photovoltaics. We identify CT-CS offset as a primary, largely overlooked factor controlling charge generation and voltage loss. A positive offset makes CT3-CS separation exothermic and improves generation, but lowers CS energy and increases voltage loss; a negative offset makes separation endothermic and highly temperature-sensitive. The model reproduces triplet-mediated recombination in PM6:Y6 and material-dependent triplet recycling in D18:NFA blends. We propose design rules for balanced generation and voltage loss via two charge-transfer channels: the LE-CT-CS pathway favors a moderate LE-CT offset of about 0.15-0.20 eV and a weakly exothermic CT-CS offset of about 0.05-0.075 eV; the T-CT3-CS pathway requires the same CT-CS alignment plus a small CT-T offset, no more than about 0.1 eV, corresponding to a recycling factor K greater than about 10^-2, to maintain fast T-to-CT3 recycling. CT-CS alignment is the main determinant of the charge-generation-voltage-loss trade-off, while triplet-recycling kinetics determines whether this balance survives at the device level. This work provides a unified theoretical description from exciton generation to free charge collection, offering a convenient tool for transient and steady-state analysis in organic photovoltaics.
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Applied Physics · Cross-listed from physics.optics

Non-contact lens metrology from optical flow and differentiable ray tracing

Hector A. Jimenez-Romero and Wolfgang Heidrich

Accurate lens surface metrology is essential to determine the manufactured geometry of refractive optical elements and their deviation from the specified design. We demonstrate a transmission metrology method that reconstructs refractive lens surfaces from the displacement of a wavelet-noise-patterned mask. Lens-induced distortion is represented by a dense displacement field. A differentiable ray tracer fits the lens geometry using a calibrated near-telecentric camera model with an effective finite ray origin. We validate the method on commercial lenses. The recovered geometries agree with nominal specifications, and the plano-aspheric reconstruction is compared with chromatic confocal profilometry.
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Monday 12 October

Applied Physics

Supercell-enabled inverse design of boundary-state dispersion for group-velocity control in pseudomagnetic phononic crystals

Hua-Yang Chen, Nan-Xin Yu, Zhen-Hui Qin et al. (+2 more)

Topological boundary states offer a platform for guided-wave propagation within bulk bandgaps. Their propagation characteristics depend not only on the spectral extent of the states but also on their dispersion within the operating bandwidth. A nearly linear dispersion provides more uniform group velocity across frequency, whereas a reduced slope enables slow-wave propagation. Despite advances in inverse design of prescribed dispersion relations and topological dispersion tuning, application-oriented characteristics of boundary-state dispersion have rarely been direct inverse-design objectives. Here, we develop a supercell-enabled, surrogate-assisted framework for the inverse design of boundary-state dispersion in a phononic crystal with pseudomagnetic fields. Area-preserving anisotropic deformation shifts the local Dirac points, and independent variation of 21 rows within the supercell provides distributed control over the boundary-state branch. A constraint-preserving surrogate reconstructs the dispersion from an initial frequency and positive frequency increments, with first- and second-difference losses introduced to capture local slope and curvature. Coupled with a genetic algorithm, the framework targets two prescribed-bandwidth design tasks: highly linear dispersion and slow-wave dispersion. For the former, finite-element verification yields relative group-velocity variations of 0.142% to 1.183% over prescribed bandwidths of 4% to 6%. For slow-wave designs, mean group velocities of 190 to 385 m/s are obtained over bandwidths of 0.2% to 0.8% while satisfying a 5% group-velocity variation limit. These results establish boundary-state dispersion as a direct inverse-design target beyond conventional bandwidth optimization, opening a flexible route to group-velocity control through application-oriented dispersion engineering over prescribed relative bandwidths.
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All authors Hua-Yang Chen, Nan-Xin Yu, Zhen-Hui Qin, Yan-Feng Chen, Si-Yuan Yu

Applied Physics · Cross-listed from quant-ph

Imaging the topological sign of a Dirac mass with spin-polarized tunneling

Payman Kazemikhah, Ruolun Zhang, Byunghoon Kim et al. (+5 more)

A Dirac mass is characterized not only by its magnitude but also by its sign, which influences the Berry curvature, Hall response, and the propagation direction of chiral boundary modes. However, local spectroscopy of magnetic topological surfaces has so far accessed only the gap magnitude $|M|$. Here we show how the topological sign of $M$ can be determined locally. We first establish the sign information that spin-resolved tunneling can access and the reference required to obtain an absolute Hall sign. Although spin–orbital entanglement generally obscures the relation between measured spin and Dirac pseudospin, crystalline rotation symmetry alleviates this ambiguity at the band edge. On a $C_3$ axis, an axial tip couples to a fully spin-polarized state whose tunneling asymmetry directly reveals the sign of the occupied-band Berry curvature, independent of orbital composition. We further show that the zeroth Landau level provides an independent mass-sign measurement with an unpolarized tip, while opposite domains and their chiral domain-wall modes provide self-consistency checks. These results pave the way for imaging the locations where the topological character changes within a material, rather than merely identifying where a spectral gap appears.
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All authors Payman Kazemikhah, Ruolun Zhang, Byunghoon Kim, Xiangyu Luo, Zachary Ducorsky, Yu-Peng Zhu, Md. Shafayat Hossain, M. Zahid Hasan

Applied Physics

Progress in Cavitated Front Gridline Ag Paste for PERC Solar Cell Architecture

Donald Intal, Sandra Huneycutt, Abasifreke Ebong et al. (+2 more)

This paper reports on the progress made with the cavitated silver paste on passivated emitter rear contact cells (PERC) to reduce the series resistance. Thus, electrical and microscopy characterizations are used to examine these resistive losses. Fifteen 252 cm2 PERC cells were fabricated for this assessment. Under standard test conditions, these cells achieved a mean conversion efficiency of 21.87% and a maximum of 22.07%. The mean measured fill factor was 79.98%, compared with a pseudo-fill factor of 83.60%, giving a mean deficit of 3.62 percentage points. Fill factor decreased with increasing area-normalized series resistance, which ranged from 0.53 to 0.83 ohm-cm2, while open-circuit voltage and short-circuit current remained unvaried. These electrical trends support resistive current extraction as the principal contributor to fill-factor variation. Electroluminescence imaging revealed localized emission nonuniformity. Cross-sectional scanning transmission electron microscopy showed variation in the glass interfacial layer, while scanning electron microscopy identified micrometer and sub micrometer silver particles. Conductive atomic force microscopy after sequential removal of the bulk metal and glass revealed spatially heterogeneous current response. These observations are consistent with nonuniform electrical access at the contact, where restricted conducting pathways may concentrate on current and increase local voltage drops. The combined characterization identifies interfacial heterogeneity and the connectivity of conducting pathways as priorities for understanding and reducing extraction losses in cavitated silver metallization.
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All authors Donald Intal, Sandra Huneycutt, Abasifreke Ebong, Dana Hankey, Marshall Tibbetts

Applied Physics · Cross-listed from physics.optics

Chiral Vector Beams for Topological Enantio-Sensitive Imaging

A. Rodriguez, J. Edginton, A. Löhr et al. (+7 more)

Molecular chiral discrimination is vital across chemistry and life sciences, yet optical approaches remain highly inefficient for small organic molecules. Here we turn vector beams, whose polarization carries a topological charge, into an efficient probe of molecular handedness. We show that the combination of a tightly focused radially polarized beam at the fundamental frequency {\omega} and an azimuthally polarized beam at 2{\omega} creates chiral vector beams, a locally chiral field with structured handedness. Using state-of-the-art computational modeling in the chiral molecule carvone, we show that the nonlinear response (notably sum-frequency generation) of randomly oriented chiral molecules to this chiral vector beam captures the fields' local handedness and is highly enantio-sensitive. The two enantiomers emit light at frequency 3{\omega} with topological ring structures of different divergence, and thus the molecular handedness can be read out directly from the ring radius. The signal inherits the Poincaré index of the driving field, opening up new ways to robust, ultrafast, and and all-optical chiral discrimination.
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All authors A. Rodriguez, J. Edginton, A. Löhr, J. Terentjevas, P. Vindel-Zandbergen, A. Ordóñez, J. Vogwell, O. Smirnova, D. Ayuso, L. Rego

Applied Physics

Wireless Energy Transfer for Space Applications: A Review of Technologies, Mission Architectures, Energy Routing, and System Integration

Lyuye Lin, Zhifu Feng, Ermanno Miele et al. (+6 more)

Wireless energy transfer (WET) decouples energy generation from energy use, offering strategic advantages for distributed spacecraft, lunar surface networks, mobile assets, and high-power remote loads. This review organizes the field along four axes: physical mechanism, energy reference plane, mission architecture, and evidence maturity. It examines near field inductive and resonant transfer, microwave and millimeter wave power beaming, optical and laser-based transfer, space-based solar power, lunar and cislunar energy delivery, inter-spacecraft power sharing, intraspacecraft contactless interfaces, and reconfigurable or relay assisted routing within a common R0,R7 energy-accounting framework. Three conclusions emerge. First, WET is most valuable when spatial or temporal mismatches separate energy generation from load demand; it does not universally replace local generation or onboard storage. Second, dominant losses vary across system architectures. Beam collection, rectification, receiver output, and useful load efficiencies are therefore not directly comparable without explicitly defined energy reference planes. Third, technological maturity is uneven. High power ground demonstrations and short range flight applications are relatively well established, whereas long-range radiative inter spacecraft transfer, spaceborne routing hardware, lunar energy networks, and deep space applications remain supported primarily by models, simulations, and mission studies rather than hardware demonstrations. Progress requires validated end to end energy budgets under mission realistic constraints, including pointing and tracking, thermal management, environmental exposure, reliability, energy storage, and regulatory compliance.
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All authors Lyuye Lin, Zhifu Feng, Ermanno Miele, Quanbo Ge, Manuel Iori, Chunbo Liu, Kwok-Tong Chau, Denis Garoli, Remo Proietti Zaccaria

Applied Physics · Cross-listed from cond-mat.mes-hall

1/f frequency-noise reduction in nanomechanical resonators by dissipation dilution

Kostas Kanellopulos and Silvan Schmid

The frequency noise of a resonant nanomechanical sensor is well understood down to its thermomechanical limit, but the longest useful averaging time is set by a flicker, or $1/f$, frequency-noise floor whose origin has remained unknown. We show that this floor is the thermal noise of the tension. By the fluctuation-dissipation theorem, the tension of a resonator with fixed ends fluctuates by an amount set by the loss angle of its material; for structural damping, these fluctuations produce $1/f$ frequency noise with a flicker coefficient $h_{-1}=E k_{\mathrm{B}} T/(2\pi V\sigma_0^2 Q_{\mathrm{el}})$, with $Q_{\mathrm{el}}$ the intrinsic loss under elongation, that contains no free parameter and is diluted by the tensile stress $\sigma_0$ in the same way as damping is in dissipation dilution. Silicon nitride strings and membranes from 30 to 340~nm thickness follow the predicted volume scaling, the predicted $\sigma_0^{-2}$ dilution across resonators and within stress-engineered strings, and the predicted thickness dependence, which places noise-active two-level systems in the volume and at the surfaces of the resonators, all at the absolute level set by the independently measured intrinsic loss. The same relation accounts for published data between 78 and 296~K; below 78~K, the loss measured at the resonance no longer represents the loss probed by the noise, marking the limit of the structural-damping assumption. Dissipation dilution therefore lowers the $1/f$ floor, and the longest useful integration time of a resonant sensor is set by its prestress, volume, temperature, and intrinsic loss angle.
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Applied Physics · Cross-listed from quant-ph

Reverse quantum aging: Restoring rhythmicity from quantum aging state

Bulti Paul, Biswabibek Bandyopadhyay and Tanmoy Banerjee

Quantum aging transition has recently been reported, whereby the oscillatory dynamics of a network of globally coupled quantum self-sustained oscillators is degraded sharply when the fraction of inactive nodes exceeds a critical value. Here we explore the reverse process: the revival of rhythmic dynamics from an aged state in a quantum oscillator network by introducing a controlled incoherent single-boson pumping channel. Using a self-consistent quantum master equation in the Lindblad form for globally coupled active–inactive quantum Stuart–Landau oscillators, we show that increasing the pumping strength progressively suppresses the aging transition and eventually eliminates it, restoring rhythmicity even when all oscillators are inactive. Remarkably, complete compensation of the coupling-induced dissipative loss is not required; a substantially weaker pumping strength is sufficient to eliminate the aging transition. We show that the revival is governed by a redistribution of the Fock-state population of the inactive oscillators toward higher-occupation states. Our results establish controlled incoherent pumping as an effective mechanism for restoring dynamical robustness in quantum oscillator networks.
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Applied Physics · Cross-listed from cond-mat.soft

Dynamical-state switching controls active microrod navigation in porous media

Ana Cazorla, Maria L. Jimenez, Raul A. Rica-Alarcon et al. (+2 more)

Adaptive search and travel strategies enable biological swimmers to explore complex environments, but remain difficult to encode in minimal synthetic microswimmers. Here, we unveil multiple dynamical and orientational states of rod-like Janus microswimmers actuated via electric fields: planar active, oriented chiral and persistent rods. We discover a hidden dynamical state after pre-orienting them, which allows us to switch on demand from strong chiral to persistent motion. We harness this phenomenological orientation and chirality switch for exploration in microstructured porous arrays. Here, strong chirality promotes local scanning but drives circular trapping and poor net displacement, whereas the pre-aligned dynamical state enables efficient obstacle sorting, and trap escape. Comparing experiments with simulations of active Brownian particles in the very same experimentally-extracted obstacle geometries, we quantify navigation efficiency via first-passage time statistics, revealing how chirality tuning optimizes the trade-off between local exploration and long-range transport.
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All authors Ana Cazorla, Maria L. Jimenez, Raul A. Rica-Alarcon, Carla Fernandez-Rico, Laura Alvarez

Sunday 11 October

Applied Physics · Cross-listed from physics.optics

Transfer learning-aided, artificial intelligence approach to evaluate optical properties of materials for classical and quantum photonic applications

Mohammad Reza Habibi, Luca Sapienza and Juan C. Vasquez

In this study, an artificial intelligence-assisted evaluation of the refractive indices of different materials is performed. The evaluation of the refractive index is necessary to design photonic devices for various classical and quantum photonic applications, and to theoretically analyse experimental results. The refractive index is one of the crucial parameters that affect the interaction of light with matter. Although the refractive index can be measured experimentally, its estimation via computational means provide the advantage of not requiring costly instrumentation, trained researchers and could avoid potential laboratory-based uncertainties. Therefore, in this study, artificial intelligence is implemented to estimate the optical constants of two types of materials, i.e., noble metals, and semiconductors. To this end, an artificial neural network is used to estimate the real and the imaginary parts of the refractive index of a specific material for various wavelengths of light. Then, the knowledge of the trained neural network is employed to initiate and train new neural networks to estimate the refractive indices of other materials. For the training of a neural network, various methods can be deployed. However, the application of the training can be a time-consuming process. A transfer learning approach is here implemented to provide a faster training solution for the problem under study. The implementation of transfer learning allows training the neural networks for a new material with higher speed or accuracy when compared to non-knowledge transfer-based training. Our results show the efficiency of the proposed technique in accurately evaluating the real and imaginary parts of the refractive index of different materials.
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Applied Physics

Acoustic Scattered Field Calculation for a Moving Source Using Time-Dependent Physical Optics

Asaf Kor, Gal Ben Yelid, Amir Boag et al. (+1 more)

We present a time-dependent physical optics (TDPO) formulation for computing the acoustic scattered field of a stationary object in response to a moving source in three-dimensional space. Due to the motion of the source, which may be fast, the conventional frequency-domain PO method is not employed. Instead, a time-domain variant that explicitly accounts for the motion is formulated. The study focuses on the near-field regime, where source motion induces a complex wave field beyond a simple Doppler effect. The proposed algorithm accommodates arbitrary source trajectories and arbitrary signal bandwidth, as well as high source velocities relative to the speed of sound. Near and beyond the shadow boundary, where PO is least accurate, the formulation is supplemented by a Fock correction of the surface field, extended here to a moving source with a harmonic signal. The method matches or exceeds the accuracy of finite element simulations at a computational cost lower by orders of magnitude.
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All authors Asaf Kor, Gal Ben Yelid, Amir Boag, Lea Beilkin-Sirota

Applied Physics · Cross-listed from cond-mat.soft

Unlocking the potential of polymer networks for high strength through topology

Zheqi Chen, Yu Zhou, Chenghai Li et al. (+2 more)

A covalent polymer network is orders of magnitude weaker than individual covalent bonds. This large gap reveals an unrealized potential. The weakness of a network comes not from individual covalent bonds, but from how they are connected. Here we unlock this potential by identifying a topological criterion, involving optimally sparse crosslinks, long chains, and dense entanglements. Optimizing each topological variable alone is insufficient for high strength, yet exceptional strength emerges when they are combined within a narrow regime. We describe the physics of this synergy, and use the criterion to strengthen networks widely used but known to be weak. For example, we prepare a polyacrylamide hydrogel of 90 wt% water, amplifying strength from a commonly reported value of ~0.1 MPa to ~6.5 MPa. The exceptional strength is achieved without sacrificing other properties, such as softness, toughness, and elasticity. The criterion establishes topology as a general design principle for strong polymer networks.
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All authors Zheqi Chen, Yu Zhou, Chenghai Li, Ho Cheung Shum, Zhigang Suo

Applied Physics · Cross-listed from physics.optics

Dual deconvolution multifocal fluorescence response matrix microscopy for aberration-free high-throughput super-resolution imaging

Sumin Lim, Sanghyeon Park, Tran Thinh Le et al. (+3 more)

Fluorescence response matrix imaging enables separate computational correction of excitation and emission aberrations through dual deconvolution, but single-focus acquisition requires a large number of camera frames, limiting its practical use. Multifocal excitation can accelerate acquisition by recording many illumination positions in parallel, but denser foci also increase inter-focus crosstalk, which can bias the estimated excitation and emission optical transfer functions and degrade aberration correction. Here, we introduce high-throughput aberration-free fluorescence response matrix imaging with adaptive multifocal illumination, in which the inter-focus spacing of the multifocal lattice is adjusted according to specimen-dependent crosstalk. A programmable digital micromirror device generates multifocal excitation lattices, and the resulting detector-resolved fluorescence responses are assembled into a two-coordinate fluorescence response matrix. Dual deconvolution separately estimates and corrects the excitation and emission optical transfer functions, and the aberration-corrected matrix is then combined in the spatial-frequency domain to reconstruct the aberration-free image. This strategy reduces the number of required camera frames by approximately three orders of magnitude, allowing response matrices with $\sim 10^6$ illumination positions to be acquired within seconds to a few minutes. The accelerated acquisition preserves the aberration-correction capability of dual deconvolution and achieves an estimated lateral resolution of $\sim$100 nm. Applied to heterogeneous mouse brain and kidney tissue, the method enables high-resolution, depth-resolved volumetric imaging while correcting specimen-dependent aberrations. Together, these results establish adaptive multifocal illumination as a practical route to high-throughput aberration-free fluorescence response matrix imaging.
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All authors Sumin Lim, Sanghyeon Park, Tran Thinh Le, Jin Hee Hong, Seokchan Yoon, Wonshik Choi

Applied Physics · Cross-listed from cs.ET

Localized Joule heating and carbonization process optimization of 3D printed polymer structures for lab-on-CMOS applications

Mohammad Aminul Haque, Andalib Nizam, Nickolay Lavrik et al. (+1 more)

Use of carbon electrodes integrated with CMOS technology has great promise for lab-on-chip, biomedical, environmental, and industrial applications. One method of developing carbon electrodes is to 3D print polymer nanostructures on a CMOS chip, and use a thermal annealing process to pyrolyze them into carbon at high temperature, approximately 950 {\deg}C. Such high temperature is detrimental to the CMOS sensor circuits, causing severe degradation. We present a novel solution of localized Joule heating of these polymer nanostructures to achieve complete carbonization of the electrodes. Both analytical and COMSOL simulations guided the experiments to characterize the carbonization process conditions. Partial carbonization was achieved at 500-600 {\deg}C of global temperature, and complete carbonization was achieved by localized Joule heating. Pyrolized nanostructures monolithic samples on a silica wafer were fabricated using standard material processing, such as 2-Photon Polymerization. Pyrolysis was achieved by Rapid Thermal Processing (RTP). Observations using optical microscopy, scanning electron microscopy, and Raman spectroscopy demonstrated the feasibility of polymer carbonization within a CMOS compatible temperature window.
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All authors Mohammad Aminul Haque, Andalib Nizam, Nickolay Lavrik, Nicole Mcfarlane