Peer Revenue Publish or profit

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Physics Applied Physics

physics.app-ph Watch Applied Physics

Thursday 1 October

Applied Physics

Upper Bounds on Efficiency of Pixel Antennas

Albert Salmi, Philipp del Hougne, Leo Lahti et al. (+1 more)

This letter presents a method to compute fundamental bounds on the total efficiency of pixel antennas. Using semidefinite relaxation, we obtain an upper bound on the optimization problem of maximizing the antenna's total efficiency subject to binary-valued pixel states. The bounds are demonstrated for antennas with varying numbers of pixels and compared with realizable solutions obtained using the genetic algorithm.
Read the full abstract

All authors Albert Salmi, Philipp del Hougne, Leo Lahti, Ville Viikari

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

Topo-Spectral Percolation Descriptors for Mechanistic Ion Transport Pathways from Static Crystal Structures

Diptendu Roy, Chiku Parida, Juan María García-Lastra et al. (+1 more)

Ion transport controls the macroscopic performance of solid electrolytes, battery electrodes, ion-selective membranes, electrolysis ceramics, mixed conductors, porous sorbents, and biological channels. In each case, ion transport is determined by structural characteristics, namely the available diffusion pathways and the specific bottleneck atoms that limit the ionic jumps. These are intrinsic properties of the crystalline framework, whereas temperature, carrier concentration, and correlated motion govern the transport rate. Ab initio molecular dynamics (AIMD) resolves the mechanism directly but is too costly for materials screening, and most surrogate models give only a single transport number. Here we present a calibration-free method for determining the mechanism, based on Topo-Spectral Percolation Descriptors (TSPD). TSPD obtains the transport mechanism from a single static structure in seconds. It constructs a periodic migration network whose edge barriers are computed from physics-based energetics. We then analyze the barrier-threshold topology of this network and the spectrum of its barrier-weighted graph Laplacian. To establish its validity for computational solid-state ionics, we test TSPD against AIMD ion densities and neutron diffraction data for eight materials, including cathodes and solid electrolytes, whose transport ranges from one- to three-dimensional. TSPD reproduces the established mechanism in every case and correctly identifies structures in which geometric openness does not imply viable ion percolation. The method is most informative for pathway-limited, direction-dependent transport, and it complements full dynamical simulations for strongly cooperative or nearly isotropic transport.
Read the full abstract

All authors Diptendu Roy, Chiku Parida, Juan María García-Lastra, Arghya Bhowmik

Applied Physics · Cross-listed from physics.optics

Cross-platform frequency-domain physical neural networks with identical models and parameters

Zichen Xi, Jun Ji, Liyang Jin et al. (+3 more)

Frequency-domain physical neural networks (PNNs) have emerged as a promising analog computing paradigm, achieving a reduced number of devices, enhanced robustness, and high inference accuracy. However, existing demonstrations across various physical domains, such as optics, acoustics, and electronics, are mostly specific to the target devices or platforms, usually requiring hardware-dependent models and post-fabrication parameter tuning. Here, we demonstrate cross-platform implementations of frequency-domain PNN across different wave-based computing platforms using identical, pre-trained parameters. By exploiting shared second-order nonlinear processes, the PNN model is implemented on optical, microwave, and acoustic-wave platforms without the need of fine tuning the parameters. Evaluated on a unified four-class classification task, the frequency-domain PNN achieves high inference accuracies of 97.6% in optics, 98.4% in electronics, and 98.2% in mechanics. Further, we systematically compare related performance metrics across these three distinct physical domains, paving the way to a universal neural network across different physical platforms.
Read the full abstract

All authors Zichen Xi, Jun Ji, Liyang Jin, Hsuan-Hao Lu, Wenjie Xiong, Linbo Shao

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

HVPE Homoepitaxy of $\beta$-Ga$_2$O$_3$: High-Temperature Growth and Orientation-Dependent Surface Evolution

Sourav Sarker, Saleh Ahmed Khan, Ahmed Ibreljic et al. (+2 more)

In this work, we systematically investigate homoepitaxial $\beta$-Ga$_2$O$_3$ growth by halide vapor phase epitaxy (HVPE) on (010), (001), and ($\bar{2}$01) native substrates over a broad growth parameter space, extending the growth temperature as high as 1150 $^\circ$C. The growth kinetics exhibit strong dependence on precursor supply, temperature, reactor pressure, and Ga-source-to-substrate distance. Increasing the HCl flow from 80 to 300 sccm enhances the growth rate by up to seven-fold, while increasing the temperature from 1050 to 1150 $^\circ$C nearly doubles the deposition rate. At 1150 $^\circ$C, atmospheric-pressure growth yields rates more than 2.5 times higher than those at 100 Torr, while reducing the O$_2$ flow to 5 sccm further increases the growth rate to 14.3 $\mu$m/h, producing films up to 42.9 $\mu$m thick in 3 h. Notably, phase-pure homoepitaxial layers with good crystalline quality are obtained across all three orientations, with low rocking-curve full width at half maximum (FWHM) values of 63.4, 66.6, and 42.8 arcsec for the (010), (001), and ($\bar{2}$01) epilayers, respectively. The surface morphology exhibits a pronounced crystallographic dependence and evolves strongly with the HVPE growth conditions. In particular, the ($\bar{2}$01) surface develops well-defined step-and-terrace morphology with local RMS roughness as low as 0.17 nm. These results extend $\beta$-Ga$_2$O$_3$ HVPE homoepitaxy into a higher-temperature regime and demonstrate a broad process window for high-rate growth of thick, high-quality epilayers with strongly orientation-dependent surface evolution.
Read the full abstract

All authors Sourav Sarker, Saleh Ahmed Khan, Ahmed Ibreljic, Pronoy Kanti Das, Anhar Bhuiyan

Wednesday 30 September

Applied Physics

Finite Element Simulation of Microwave Technologies for PowderBased Volumetric Additive Manufacturing Processes

Brendan Mackey, Levi Smith and Bosco Yu

Volumetric additive manufacturing (VAM) is a promising field of advanced manufacturing which reduces production times of conventional 3D printing while retaining application to complex geometries. Current VAM systems are limited to photo-polymerizing resins, which reduces the general applicability across industry. This work presents exploratory finite element simulations of microwave-based VAM systems compatible with ceramic, metal, or composite powder feedstock. The simulations explore three devices – a linear resonator, a cross interferometer, and a boundary heater – each with potential uses in manufacturing processes for one or multiple of the considered feedstock materials. We find that with precise control of input frequency, power, and waveguide transverse modes, thermal lattices can be engineered to selectively heat regions of the feedstock, allowing direct application to VAM. Resultant lattices have cellular dimensions on the order of 1 mm, and require input powers on the order of 100 kW. With advances in microwave technologies allowing for this precision, such devices could open pathways to VAM with materials currently outside the scope of optical methods.
Read the full abstract

Applied Physics · Cross-listed from cs.IT

AIR-LLM: Broadcasting AI Weights over Radio for Memory-Free Edge LLM Inference via RF Computing

Zhihui Gao, Tingjun Chen and Dirk Englund

Next-generation large language models (LLMs) are expanding from the cloud to ubiquitous edge devices. However, edge devices typically either lack the memory to store increasingly large LLM weights or, even with enough memory, spend unaffordable energy on loading the weights. This raises our question: can an edge device run an LLM without storing or loading its weights, but receive them over the air and consume them on the fly? Inspired by wireless broadcasting, we present AIR-LLM, an LLM inference architecture for edge devices, which is composed of: (i) a central radio (e.g., 5G base stations) that broadcasts the LLM weights into the air, and (ii) the edge user that receives the weights and completes the general matrix-vector multiplication (GEMV) of LLM inference directly in the radio frequency (RF) domain using RF mixers. To further shorten the airtime, AIR-LLM exploits MIMO spatial multiplexing and proposes an energy-efficient precoder-postcoder pair on the edge to calibrate its own wireless channel. Since the central radio stays user-unaware, AIR-LLM is user-scalable so that one broadcast serves unlimited users within its coverage. We implement AIR-LLM on the NVIDIA Sionna ray-traced channels of two real-world urban scenes and the profiling of a real RF mixer. With a WikiText-2 perplexity degradation of 4.0% on LLaMA-3.1-8B, AIR-LLM saves the energy by 157.7x/40.4x against the FP16 and weight-only quantization baselines; with 20 users, its airtime is 104.1x/26.0x shorter, respectively.
Read the full abstract

Applied Physics · Cross-listed from physics.optics

Design of Mechanically Compliant Membrane Reflectors for Giant Optical Phase Nonlinearity

Lior Michaeli and Harry A. Atwater

Optical nonlinearities arise when the response of a photonic system depends on light intensity. Radiation pressure can create such a nonlinearity by moving a mechanically compliant reflector, thereby shifting the phase of the reflected light. Based on measured properties, we predict a giant phase responsivity of 263 rad W$^{-1}$ and a device-equivalent $n_{2,\mathrm{eff}} = 5.4 \times 10^{-7}$ m$^2$ W$^{-1}$ for a silicon nitride membrane trampoline with serpentine springs. We introduce strength-range-aperture metrics for reflective phase elements. Among reported mechanical resonators compared under a common direct-reflection protocol, this trampoline is an outlier, combining high compliance, practical optical accessibility, and 99.85% retention of its small-signal phase responsivity through a full $2\pi$ reflected-phase shift. Practical implementation requires optical and thermal co-design. Our framework indicates design priorities for future mechano-optical phase elements.
Read the full abstract

Applied Physics

Bilayer Lithium Niobate Acoustic Resonators for Spurious-Free Wideband Operation at 6 GHz

Florian Hartmann, Silvan Stettler and Luis Guillermo Villanueva

The evolution of wireless communication standards toward higher frequencies and wider bandwidths places increasing demands on acoustic filter technologies. Conventional resonators face scaling limitations above 5 GHz, where lithographic constraints, reduced electromechanical coupling coefficient (k2eff), and spurious mode excitation hinder practical filter implementation. Here, we introduce a bilayer X-cut lithium niobate (LiNbO3) thickness-shear bulk acoustic resonator architecture that leverages symmetry engineering as a new design degree of freedom. By vertically stacking two piezoelectric thin films with a tailored bonding angle, the second-order thickness-shear mode (SH2, slow) is selectively excited. Furthermore, the fast thickness-shear modes inherent to X-cut LiNbO3 are suppressed, yielding a spurious-free in-band response. Devices operating around 6 GHz demonstrate a k2eff of approximately 35%, in close agreement with finite-element simulations and confirming the symmetry-driven mode selection mechanism. Proof-of-concept ladder filters demonstrate a fractional bandwidth of 18.6%, highlighting the wideband capabilities of the proposed architecture. The proposed configuration enables thickness-defined frequency scaling while maintaining high coupling and spectral purity, offering a promising platform for wideband radiofrequency filters in next-generation wireless systems.
Read the full abstract

Applied Physics · Cross-listed from physics.optics

Near-field Ultrafast Nondiffractive Laser Nanoscale Cutting of Glass with Quasi-null Interface Roughness

Rajeev Dwivedi, Anton Rudenko, Guodong Zhang et al. (+5 more)

Generally, ultrafast laser glass dicing is governed by explosive material removal, which restricts the achievable surface roughness. Here we report single-step dicing of aluminosilicate glass with residual interface roughness below 5 nm, producing optical-quality surfaces without post-processing, using near-field-enhanced 0th-order Bessel-Gauss beams. This exceptional interface quality cannot be explained by a conventional laser ablation mechanism, such as phase explosion, melt expulsion, or fracture-dominated material removal. Instead, quantitative analysis of local thermal dynamics indicates that material removal is consistent with a Hertz-Knudsen-type evaporation process, enabling layer-by-layer removal with precision approaching a few molecular layers. These results suggest that nanoscale optical confinement fundamentally alters the response of transparent materials to ultrafast laser irradiation and establish a route toward deterministic laser processing with near-atomic precision.
Read the full abstract

All authors Rajeev Dwivedi, Anton Rudenko, Guodong Zhang, Xxx Sedao, Yaya Lefkir, Ciro D'Amico, Guanghua Cheng, Razvan Stoian

Applied Physics

Evaluating Advanced Impact Mitigation Technologies for Concussion Risk Reduction in Youth Cycling Helmets

Jessica A Towns, Fady F Abayazid, Gerald A Grant et al. (+2 more)

The efficacy of advanced cycling helmet technologies under youth-specific impact conditions remains unclear. We evaluated how helmet technologies affect head kinematics and concussion risk and whether helmet deformation and helmet-headform relative rotation contribute to protection. Six youth bicycle helmet technologies were tested, including two conventional EPS controls (FOAM-A, FOAM-B) and four advanced technologies (CELL, SLIP, SLIDE, HYDRAULIC). Helmeted headforms were impacted at three locations using a 25 degree anvil at 2.9 m/s, and a 45 degree anvil at 5.2 m/s. Peak linear acceleration (PLA), peak rotational acceleration (PRA), and YGAMBIT-predicted concussion risk were quantified. Stereo high-speed videography measured anvil-normal headform displacement to approximate helmet deformation, and helmet-headform relative rotation. Helmet technology significantly affected predicted concussion risk under both conditions. At 2.9 m/s, all advanced technologies reduced risk relative to FOAM-A, while only SLIDE and HYDRAULIC reduced risk relative to FOAM-B. At 5.2 m/s, all advanced technologies reduced risk relative to both foam controls. HYDRAULIC produced the lowest risk in both conditions, reducing mean risk by 94-95% and 77-78% relative to the foam controls at 2.9 and 5.2 m/s, respectively. CELL, SLIP, and SLIDE significantly reduced PRA across both conditions, whereas HYDRAULIC significantly reduced both PLA and PRA. Greater anvil-normal headform displacement was associated with lower PLA, and greater relative rotation with lower PRA; both independently contributed to lower predicted concussion risk. Advanced technologies in youth cycling helmets can reduce youth concussion risk, but effectiveness depends on impact condition and mitigation mechanism. Designs maximizing controlled helmet deformation and rotational decoupling may provide robust protection in youth-relevant impacts.
Read the full abstract

All authors Jessica A Towns, Fady F Abayazid, Gerald A Grant, David B Camarillo, Nicholas J Cecchi

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

Multi-Branch Transport in a Back-gated WS$_2$ Transistor at Deep-Cryogenic Temperature

Megan Powell, Vilas Patil, Hazel Neill et al. (+5 more)

Two-dimensional materials are promising candidates for electronic applications beyond the operating limits of conventional semiconductor technologies. Within this class, transition-metal dichalcogenides offer attractive properties for field-effect transistor operation, with tungsten disulphide (WS$_2$) emerging as a particularly promising material for operation at cryogenic temperatures. Here, we investigate the electrical performance of a back-gated multilayer WS$_2$ transistor at deep cryogenic temperature, down to 20 mK. The device remains strongly gate-tunable throughout the cryogenic regime, with an effective on/off current ratio exceeding $10^{5}$. Most notably, the low-temperature turn-on characteristics exhibit reproducible shoulder-like features, which we describe using a phenomenological model comprising multiple effective conduction branches operating in parallel.
Read the full abstract

All authors Megan Powell, Vilas Patil, Hazel Neill, Stephen O'Sullivan, Paul K. Hurley, Lida Ansari, Farzan Gity, Alessandro Rossi

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

A transferable full-band Monte Carlo framework for complex alloy avalanche photodiodes

Shafat Shahnewaz, Hannaneh Karimi, Joe C. Campbell et al. (+1 more)

We present a physics-based multiscale full-band Monte Carlo framework for modeling avalanche multiplication and excess noise in complex alloy avalanche photodiodes (APDs), demonstrated on Al$_{0.7}$InAsSb as a representative quaternary system. The framework links atomistic material structure to device-level avalanche statistics: an environment-dependent $sp^3d^5s^\ast$ tight-binding calculation resolves the full conduction- and valence-band structure of the random- or digital-alloy configuration – including $\Gamma$, X, and L valley ordering, non-parabolicity, anisotropy, and spin-orbit-induced valence-band splitting – and supplies the band-structure inputs for stochastic high-field transport. A central element of the framework is a physics-derived treatment of alloy-disorder scattering, in which the quaternary disorder potential is constructed from atomic valence differences, covalent radii, and Thomas–Fermi screening through a composition-weighted decomposition into binary contributions, complemented by composition-interpolated polar-optical, acoustic, intervalley-phonon, impurity, and impact-ionization models. Because every material-dependent input is generated from the atomic composition and configuration by the same well-defined procedure, the framework transfers without structural modification to arbitrary zinc-blende ternary and quaternary alloys. Applied to a \SI{1}{\micro\meter} Al$_{0.7}$InAsSb p-i-n APD, the framework reproduces the measured gain and excess-noise characteristics with only the impact-ionization softness parameters calibrated. The approach provides a documented, reproducible route for analyzing and designing complex alloy APDs in which band structure, disorder, and scattering physics jointly determine gain and ionization statistics.
Read the full abstract

All authors Shafat Shahnewaz, Hannaneh Karimi, Joe C. Campbell, Avik W. Ghosh

Applied Physics · Cross-listed from cs.LG

TopTimeNet: Topologically-assisted time-series classification model

Sharareh Sayyad and Sophia Bazzi

Distinguishing periodic from chaotic dynamics in a time series is a fundamental challenge in both physics and engineering. Yet, end-to-end learned architectures must discover both a representation and a decision boundary from data, at substantial cost. We introduce TopTimeNet, which decouples these tasks: a fixed, non-learned stage extracts a $42$-dimensional geometric and topological descriptor from Takens delay embeddings and persistent homology, and a lightweight learnable stage performs classification. On a benchmark of $49$ nonlinear dynamical systems, a $1{,}638$-parameter configuration matches the mean accuracy of one with $33\times$ more trainable parameters. Additionally, this approach delivers mean accuracy comparable to convolutional neural networks and surpasses the average performance of converged Transformer models, while requiring three to four orders of magnitude fewer trainable parameters. Robustness also depends sharply on where noise is introduced: TopTimeNet degrades gracefully under perturbations to its precomputed features, but degrades sharply when noise is introduced into the raw signal and the full feature-extraction pipeline is recomputed, showing that robustness to perturbations of the precomputed features does not imply robustness of the complete raw-signal-to-prediction pipeline. These results show that decoupling fixed geometric and topological feature construction from a lightweight discriminative stage can achieve comparable classification accuracy with substantially fewer trainable parameters.
Read the full abstract

Applied Physics · Cross-listed from physics.comp-ph

MyTm: An Automated Melting Temperature Calculation Toolkit

Y. S. Huang, H. X. Song, Y. Sun et al. (+7 more)

Melting temperature calculation is one of the important topics in computational materials science. In high-throughput in silico screening and artificial intelligence assisted design of materials, it usually requires a rapid and autonomous assessment of the melting temperature of the target. Unfortunately, molecular dynamics (MD) simulations of the melting point require many cumbersome and manual operations, making large-scale calculation of the melting point challenging. In this work, we introduce MyTm, a toolkit that employs MD to automatically determine the melting point. The method is fully modularized, and by combining these modules, the program enables fully automated melting calculations by using commonly adopted approaches, including the direct-heating method, the void method, the modified void method, the solid-liquid coexistence method, and the Z method. Moreover, a machine learning (ML) method is proposed and employed to recognize and classify the solid like and liquid like atoms, which effectively resolve the low accuracy issue in conventional classification approaches, thus making the automated high throughput pipeline of melting-point calculation possible. The robustness and efficacy of MyTm have been demonstrated by several well studied systems.
Read the full abstract

All authors Y. S. Huang, H. X. Song, Y. Sun, J. L. Li, Y. L. Xu, F. C. Wu, Y. C. Gan, Y. F. Wang, H. Wang, Hua Y. Geng

Applied Physics

Light-driven Modulation of 1-bit Metamaterial Unit Cells and Arrays

Benjamin A Scott, Kieran J Cowan, Fraser Burton et al. (+2 more)

Shape-morphing materials have the potential to realise simple, tunable telecommunication arrays without the need for complex circuitry. However, existing devices either lack individual cell control, or require an integrated power supply, reducing their beamsteering ability and increasing size, weight and power consumption. This paper presents a simple, photothermally activated 1-bit reflectarray unit cell requiring no integrated power sources. The unit cell consists of dimer elements, which are connected or disconnected via a photothermally activated electrical bridge to achieve modulation. The paper discusses the shape memory materials used for switching, and presents a design for a photothermal switching mechanism. The unit cell is validated by waveguide experiments, showing strong agreement with simulations at the working frequency of 3.7GHz. Finally, a 4-cell array is created. Each cell is activated sequentially, with good agreement between simulation and experiment, demonstrating the ability to control each cell exclusively. This study therefore demonstrates that a 1-bit unit cell can be photothermally configured without complicated electronics or an integrated power supply, opening the door to a new class of shape-morphing reflectarray.
Read the full abstract

All authors Benjamin A Scott, Kieran J Cowan, Fraser Burton, Ken E Evans, Alexander W Powell

Applied Physics

Exchange-mediated directional coupling of short-wavelength spin waves

Zhen Zhu, Roman Verba, Philipp Pirro et al. (+2 more)

Miniaturizing magnonic circuits and increasing their processing speed require spin waves with progressively shorter wavelengths. However, conventional directional couplers rely on the dynamic dipolar interaction between spatially separated waveguides, which rapidly weakens in the exchange-dominated regime. As a result, their coupling length increases as the spin-wave wavelength decreases, limiting further device miniaturization. Here, we introduce an exchange-mediated directional coupler by replacing the nonmagnetic gap between two waveguides with a magnetically modified YIG spacer. The spacer provides a continuous exchange pathway and preserves the splitting between the symmetric and antisymmetric modes at large wavenumbers. We develop an analytical model to describe this mechanism and verify it using micromagnetic simulations. Based on this concept, we design a straight coupler without curved access waveguides, with a footprint of only 400 nm * 30 nm. For a spin-wave wavelength of approximately 100 nm, the device transfers approximately 98% of the normalized output power to the target waveguide. Its performance remains nearly unchanged even when the damping of the spacer is strongly increased. These results overcome the short-wavelength limitation of dipolar couplers and provide a route toward highly integrated magnonic circuits for information processing.
Read the full abstract

All authors Zhen Zhu, Roman Verba, Philipp Pirro, Andrii V. Chumak, Qi Wang

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

Operando Charge Carrier Dynamics by Intensity-Modulated Photoluminescence: From Perovskite Thin Films to Solar Cells

Constantin Bach, Dong Won Kim, Yitian Du et al. (+2 more)

The charge-carrier lifetime in halide perovskites often varies by orders of magnitude with the injection level, complicating the analysis of conventional time-resolved photoluminescence and comparisons of reported lifetimes. We use intensity-modulated photoluminescence spectroscopy (IMPLS) as a frequency-domain alternative. Carried out under operating conditions, it yields the lifetime at a specific injection level, e.g., one-sun-equivalent illumination. On thin films, IMPLS and steady-state photoluminescence yield comparable lifetimes. For perovskite/transport-layer stacks, the IMPLS response becomes more complex. A dedicated transfer function disentangles charge transfer from interface recombination and predicts an upper limit on the charge-carrier lifetime in the solar cell. In devices, electrical methods such as intensity-modulated photovoltage spectroscopy (IMVS) often fail to measure the lifetime due to capacitive effects. IMPLS shows not only the same two characteristic frequencies as IMVS, but also a third one, thereby resolving the lifetime itself.
Read the full abstract

All authors Constantin Bach, Dong Won Kim, Yitian Du, Yana Vaynzof, Carsten Deibel

Applied Physics · Cross-listed from math.AP

Magnetic Stabilization of the Greenhill Instability and Hysteretic Switching in Slender Rods

Vivekanand Dabade, Likhit Ganedi, Mohd Tahseen et al. (+1 more)

In a bulk ferromagnet, magnetic energy is six orders of magnitude weaker than elastic energy. Slenderness removes this disparity. In a thin ferromagnetic rod, the two energies scale differently with aspect ratio, and an ordinary nickel wire deforms nonlinearly even under modest remote fields. We develop a three-dimensional variational theory of a ferromagnetic Kirchhoff rod under gravity and magnetic loading and study it through bifurcation analysis, computation, and experiment. A uniform field can stabilize a vertical rod against buckling under its own weight, the classical Greenhill instability. We give sharp criteria for clamped and pinned supports in terms of an Airy-type principal eigenvalue, and give a fine description of the character of the bifurcation landscape, which has qualitatively different features than its non-magnetic counterpart. When subject to the field generated by a permanent magnet, we identify a rich bifurcation landscape as the magnet is rotated quasistatically along a circle of radius slightly larger than the rest length of the rod. We prove that instability occurs only through a planar mode and that each snap is a nondegenerate saddle-node. We also locate the two folds that produce hysteresis. Experiments on $50\,\mu$m nickel wires confirm the Greenhill threshold, restabilization at ~$30$ mT for both clamped and pinned supports, as well as the salient features of the hysteresis loop such as switching angles, width, and geometry of folds accurately. Our analysis and experiments offer principled design rules for field-stabilized filaments and remotely switched bistable actuators. Our analysis also offers a well-conditioned numerical method is valid near the switching events, where the direct numerical minimization is strongly ill-conditioned.
Read the full abstract

All authors Vivekanand Dabade, Likhit Ganedi, Mohd Tahseen, Raghavendra Venkatraman

2609.38676 · 30 Sep · This article is dedicated to the memory of Professor Robert V. Kohn, with respect and admiration. No generative AI tools were used in the development of the mathematical ideas, the derivation of the theoretical results, or the proofs. The authors are fully responsible for the content of the manuscript and for the accuracy, validity, and integrity of all results presented

Abstract PDF $MAG ×4$EIGN ×1$GRAV ×1

Tuesday 29 September

Applied Physics

Self-verifying time-resolved multicomponent gas analysis from raw sensor signals

YingCheng Zhou, Kosuke Minami and Genki Yoshikawa

Gas sensor arrays can estimate the composition of gas mixtures from their response patterns. However, when a sensor is used outside the laboratory, the true gas concentrations are unknown, so there is usually no direct way to determine whether the estimated result is reliable. Here, we develop a physics-constrained neural network that estimates time-varying gas concentrations and reconstructs the corresponding sensor signals at the same time. We tested the method with a twelve-channel membrane-type surface stress sensor array exposed to water-ethanol mixtures whose concentrations changed over time. The model reconstructed the concentration profiles of both components from the raw signals. Artificial offsets and sensitivity changes in one channel were detected from disagreement between the measured and reconstructed signals. Deletion or replacement of part of a measurement record was detected from violations of the sorption and mechanical equations. This approach enables time-resolved multicomponent gas analysis with self-verification from a single measurement.
Read the full abstract

Applied Physics · Cross-listed from quant-ph

Towards noble gas quantum optical magnetometry using direct ultraviolet detection

James Maldaner and Gil Porat

We analyze a novel approach for quantum magnetic sensing via optical detection of nuclear spin precession in a noble gas. The detection is carried out with an ultraviolet frequency comb laser, so no alkali vapor is required to be mixed with the noble gas during the sensing stage, allowing for hours-long spin relaxation time at room temperature. Our analysis reveals that combining high laser power and low laser intensity noise is crucial to achieving and exceeding state-of-the-art magnetometric performance, including that of cryogenic magnetometers. We find operational regimes where either fundamental or technical noise dominate, which directs experimental effort towards increasing laser power or lowering laser intensity noise, respectively. We also show that optimizing beam size is key to achieving optimal sensitivity. Our calculations predict that a record-breaking sensitivity of $24~\mathrm{aT}/\sqrt{\mathrm{Hz}}$ is achievable in 10 minutes with a 10 W ultraviolet laser with a relative intensity noise of -100 dBc/Hz.
Read the full abstract

Applied Physics · Cross-listed from physics.optics

Multimode radiation pressure actuation of a mechanical resonator using a spatial mode sorter

Morgan E. Choi, Daniel Allepuz-Requena, Diego Torres-Barajas et al. (+2 more)

Multimode optomechanical scattering is ubiquitous in free-space imaging protocols, but its radiation pressure counterpart is challenging to detect with extended objects. Here we demonstrate radiation pressure actuation of a nanomechanical membrane using dynamically structured light from a spatial mode demultiplexer (SPADE). Using single- and two-mode illumination, we directly image the position-dependent intermodal coupling between Hermite-Gauss (HG) modes as mediated by the membrane's motion. As an application, we use multimode radiation pressure feedback to simultaneously cool two nearly degenerate membrane modes. Our results are applicable to diverse mechanical systems and serve as a stepping stone to SPADE-based quantum optomechanics.
Read the full abstract

All authors Morgan E. Choi, Daniel Allepuz-Requena, Diego Torres-Barajas, Neshat Sadafi, Dalziel J. Wilson

Applied Physics · Cross-listed from cs.LG

An Efficient Machine Learning Approach for Degradation Forecasting in AEM Water Electrolysis

Marco Veneriano, Ani Gjergji, Sebastiano Bellani et al. (+3 more)

This study provides a data-driven analysis of a novel dataset of single-cell Anion Exchange Membrane water electrolyzers (AEMWE), operated under constant current load across multiple heterogeneous experimental campaigns. We train and evaluate a range of machine learning models with different complexity, including linear baselines, LSTMs and CNNs, to perform medium-term forecasting of the cell voltage degradation curve. The models are assessed within a rigorous training and evaluation framework specifically designed for heterogeneous industrial data.
Read the full abstract

All authors Marco Veneriano, Ani Gjergji, Sebastiano Bellani, Andrea Riva, Vito Paolo Pastore, Matteo Santacesaria

Applied Physics

Combined photoluminescence and electrical characterization of valley photovoltaic devices explained with an equivalent circuit

Daixi Xia, Abhinav S. Sharma, Andreas Pusch et al. (+9 more)

We present an equivalent-circuit analysis that simultaneously considers the photoluminescence and electrical responses of valley photovoltaic devices. Valley photovoltaics (VPV) are a novel concept for hot-carrier solar cells, where intervalley scattering of electrons in the absorbing material helps maintain the conduction-band electron populations at metastable satellite valleys, which are at energies higher than the conduction-band minimum. We measure intensity- and voltage-dependent photoluminescence and electrical signals of a VPV device, which has previously shown S-shaped current-voltage characteristics and thus low efficiency. We present an equivalent circuit that captures the S-shaped current-voltage curves and simultaneously describes our photoluminescence and electric measurements. The equivalent-circuit model indicates that a reverse diode causes inefficient extraction of electrons and thus the S shape. We use a Poisson/drift-diffusion model to demonstrate that the reverse diode can be either explained by the valley-scattering process itself or a heterojunction barrier. The reverse diode must be eliminated before VPV devices can achieve high efficiency.
Read the full abstract

All authors Daixi Xia, Abhinav S. Sharma, Andreas Pusch, Murad J. Y. Tayebjee, Michael P. Nielsen, Fiacre E. Rougieux, Kyle R. Dorman, Tetsuya D. Mishima, Michael B. Santos, Ian R. Sellers, Nicholas J. Ekins-Daukes, Jacob J. Krich

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

Disentangling octahedral distortion and symmetry breaking in the ordered double perovskite SrLaCoNbO$_6$

Ajay Kumar, Clemens Ulrich, Yaroslav Mudryk et al. (+1 more)

We report a comprehensive high temperature structural investigation of the B-site ordered double perovskite SrLaCoNbO$_6$ using combined Raman spectroscopy and x-ray diffraction (XRD) over the range 25–900~$^\circ$C. Two distinct temperature-driven anomalies are identified at $T_\mathrm{OD} = 300\pm 25~^\circ$C and $T_\mathrm{PT} = 750\pm 25~^\circ$C through pronounced renormalizations in the phonon frequency and linewidth, accompanied by the evolution and suppression of characteristic XRD reflections. The low-temperature anomaly at $T_\mathrm{OD}$ is associated with an isostructural octahedral distortion within the monoclinic $P2_1/n$ phase. At $T_\mathrm{OD}$, the radial and angular distortion parameters of the CoO$_6$ and NbO$_6$ octahedra decrease to near-zero values before reversing upon further heating due to an inversion of the in-plane Co–O and Nb–O bond-length hierarchy. The high-temperature anomaly at $T_\mathrm{PT}$ corresponds to a symmetry-breaking structural phase transition from $P2_1/n$ to the monoclinic $I2/m$ phase, confirmed by group-theoretical analysis and Rietveld refinement. These results demonstrate that integrating temperature-dependent Raman spectroscopy with laboratory-based XRD, complemented by quantitative octahedral distortion analysis, provides a robust approach to disentangle isostructural octahedral distortions from symmetry-breaking phase transitions in complex double perovskite oxides without recourse to synchrotron or neutron diffraction facilities.
Read the full abstract

All authors Ajay Kumar, Clemens Ulrich, Yaroslav Mudryk, Rajendra S. Dhaka

Applied Physics

PIN-Diode-Controlled X-/Ku-Band Frequency Reconfiguration of a CPW-Fed Quasi-Yagi Antenna

Huijuan Niu, Mengyu Dong, Yuanhao Li et al. (+9 more)

A PIN-diode-reconfigurable quasi-Yagi antenna fed by a coplanar waveguide (CPW) is presented for X-band and Ku-band frequency reconfiguration. PIN diodes are strategically introduced between the driven and parasitic elements to control the effective surface-current paths and thereby modify the operating frequency characteristics. By optimizing the diode locations, number, and switching states, two distinct operating modes are achieved. In Mode I, dual-band operation covering the X-band and Ku-band is obtained, with simulated impedance bandwidths of 9-11 GHz and 12.2-18.8 GHz. In Mode II, a simulated continuous impedance bandwidth from 10 to 14.2 GHz is achieved. The corresponding simulated peak gains are approximately 8 and 7 dBi for Mode I and Mode II, respectively. A prototype is fabricated and experimentally characterized in terms of its S-parameters, and the measured results confirm the frequency-reconfiguration behavior of the proposed antenna. The effects of the number and placement of the PIN diodes on the impedance characteristics are further investigated to clarify their roles in frequency reconfiguration and design complexity. The proposed antenna provides a compact CPW-fed quasi-Yagi configuration with PIN-controlled X-band and Ku-band frequency reconfiguration.
Read the full abstract

All authors Huijuan Niu, Mengyu Dong, Yuanhao Li, Bin Shao, Qingtao Chen, Junqiang Zhang, Jiawei Tao, Zhenzhong Chen, Gaoming Xu, Gongqing Li, Yongqing Huang, Chenglin Bai

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

A Bioinspired Magnetothermally Triggered Capsule for Rapid Microrobot Release

Mengfan Zhang, Zike Chen, Zhihao Lv et al. (+3 more)

Capsules are attractive platforms for microrobot delivery, combining structural simplicity with protected delivery and rapid release remains challenging. Inspired by the latched spring mechanism of Impatiens balsamina seed dispersal, a magnetothermally triggered capsule integrates a phase-change hydrogel latch, a monostable cover that serves as an elastic spring, and a payload-carrying base. Mechanical analysis guides the cover design to avoid bistability after assembly and premature hydrogel latch rupture before triggering. During transport, the hydrogel constrains the inverted cover. Under an alternating magnetic field, Fe3O4-mediated heating softens the hydrogel and induces cohesive failure, releasing stored energy to drive capsule opening and microrobot ejection. The capsule opens within 50 ms after hydrogel softening and ejects microrobots at an estimated initial velocity of 1.0 m/s. Demonstrations on a three-dimensional platform and ex vivo porcine stomach establish protected delivery, target-site opening, and post-release actuation.
Read the full abstract

All authors Mengfan Zhang, Zike Chen, Zhihao Lv, Zheng Jia, Rui Xiao, Guoyong Mao

Applied Physics · Cross-listed from eess.SP

Möbius Reparametrization of Multiport-Network Models of PIN-Diode-Programmable Metasurfaces for Accurate Low-Order Neumann Approximations

Philipp del Hougne

Accurate models of programmable metasurfaces based on multiport-network theory (MNT) account for mutual coupling (MC) through a configuration-dependent matrix inversion. The latter's high computational cost during gradient-based optimization (GBO) can be alleviated via a finite-order Neumann approximation. We show that the accuracy of this approximation depends strongly on the (tacitly) chosen MNT parametrization. For 1-bit-programmable meta-elements (e.g., meta-elements based on PIN diodes), we identify a closed-form Möbius reparametrization that depends only on the meta-element's two load states and requires neither training data nor numerical optimization. For an experimentally estimated proxy MNT model of a fabricated 96-element 19-GHz dynamic metasurface antenna with strong MC, a second-order Neumann approximation with our reparametrization achieves forward and control-gradient accuracies of 21.68 and 21.70 dB, respectively. Relative to the full proxy MNT, it reduces the runtime of a combined forward and control-gradient evaluation by a third and the saved-tensor memory by a factor of ten. In a prototypical GBO problem of end-to-end optimization for DMA-based scene classification, it achieves 94.97% test accuracy vs. 95.57% with the full model. We further note that MC-strength metrics and MC-unaware benchmarks should be parametrization-invariant, motivating, for instance, definitions based on the best directly fitted zeroth-order model.
Read the full abstract

Applied Physics · Cross-listed from physics.plasm-ph

Cold atmospheric plasma decontaminates Arabidopsis thaliana seeds and remodels seedling fungal microbiota

Lena Taras, Nicole Chaumont, Caroline Kunz et al. (+2 more)

Seed-associated microorganisms influence seed quality, seedling establishment, and plant health and also constitute a major source of seed-borne pathogens. Cold atmospheric plasma (CAP) has emerged as a promising alternative to chemical seed treatments because of its antimicrobial activity, although its effects on fungal communities associated with developing seedlings remain poorly understood. Here, Arabidopsis thaliana seeds from two ecotypes (Columbia and Landsberg erecta) were exposed to CAP for 5 or 15 min. Seed decontamination efficiency was assessed by culturing on malt extract agar and nephelometric analyses, while fungal communities associated with seedlings derived from treated and untreated seeds were characterized by ITS1 amplicon sequencing. CAP efficiently reduced fungal contamination without affecting seed germination. CAP altered the composition of fungal communities associated with developing seedlings, but the magnitude of these changes depended on seed batch and ecotype. Dominant taxa markedly declined after treatment, whereas several low-abundance taxa increased in relative abundance. These findings demonstrate that CAP is an effective pesticide-free technology for seed decontamination and can also reshape fungal communities associated with developing seedlings, highlighting broader ecological consequences of plasma-based seed treatments.
Read the full abstract

All authors Lena Taras, Nicole Chaumont, Caroline Kunz, Thierry Dufour, Christophe Bailly

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

Ohm's law for information revealed by a skyrmion Maxwell's demon

Soma Miki, Yoshishige Suzuki, Ryo Ishikawa et al. (+10 more)

Reducing the energy cost of computation-a pressing issue in the age of AI-requires a framework for circuit design based on information thermodynamics. By extending non-equilibrium statistical mechanics to information thermodynamics, it has been shown that a probability flow carrying information-hereinafter referred to as an 'information current'-is driven by its conjugate thermodynamic force, namely 'information affinity'. Since information affinity plays a role analogous to that of voltage in an electrical circuit, it is suggested that information transport also follows a linear response relationship analogous to Ohm's law. However, despite this theoretical prediction, experimentally establishing an Ohm-like constitutive relation for information transport remains an important unsolved problem. Here, we realise an information engine consisting of two magnetic skyrmions undergoing Brownian motion at room temperature. We demonstrate that the resulting information current is proportional to the information affinity generated by Maxwell's demon over a relatively wide range, establishing Ohm's law for information. Furthermore, we clarify that, in real information circuits, both Ohm's law for information and Kirchhoff's voltage law must be slightly modified to account for interactions between information carriers and the scattering of the information current.
Read the full abstract

All authors Soma Miki, Yoshishige Suzuki, Ryo Ishikawa, Yuki Hibino, Shunya Morishita, Hiroto Imanishi, Keigo Adachi, Yoichi Shiota, Takayuki Nozaki, Minori Goto, Hikaru Nomura, Shigemi Mizukami, Eiiti Tamura

Applied Physics

Study of LAGP coating on polyethylene separator for polysulfide suppression in thin Li-S batteries

Giovanni Ceccio and Jiri Vacik

The use of a thin solid electrolyte layer on polyethylene (PE) separators has been explored as a potential strategy to mitigate the polysulfide shuttle effect in lithium-sulfur (Li-S) batteries, a phenomenon responsible for significantly reducing their lifespan. While some solid electrolytes, such as LAGP , have demonstrated the ability to effectively suppress the shuttle effect, their brittle ceramic nature limits their application, particularly in flexible electronics. Coating PE separators with LAGP nanofilms offers a promising solution by combining the mechanical flexibility and thinness of polymer separators with the electrochemical advantages of LAGP, due to its NASICON-like structure and high ionic conductivity. In this study, PE separators were coated with LAGP nanofilms using the ion sputtering technique and further modified with ferroic elements such as Ni and Co. The surface morphology of the coated separators was analyzed using scanning electron microscopy (SEM), and staircase voltammetry was employed to evaluate the electrochemical performance and modifications induced by the coatings. The results demonstrate that the use of PE separators with a thin LAGP layer significantly influences polysulfide diffusion and suppresses the shuttle effect, thereby reducing unwanted processes in Li-S batteries.
Read the full abstract