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Saturday 10 October

Applied Physics

Directivity Estimates and Tolerance Tradeoffs in the Presence of Random Perturbations

Kurt Schab, Lukas Jelinek, Miloslav Capek et al. (+1 more)

The practicality of realizing high-directivity sources is studied using a generalized sensitivity metrics. These measures are based on the error model adopted in previous studies on array tolerance, but account for heterogeneous array characteristics in an arbitrary source-expansion basis, making it applicable to the study of continuous sources, ideal uncoupled arrays, and heterogeneous arrays with mutual coupling. The formulation provides the ensemble average of realized directivity under the selected error model, making it a fast predictor of anticipated directivity reduction due to source perturbation. The data required to compute these predictions are straightforward to obtain via simulation or measurement, with a significant simplification when the system can be approximated as lossless. The directivity and the proposed tolerance measures allow for the formulation of optimization problems illustrating the tradeoff between these measures. Several examples demonstrate these tradeoffs, special cases, comparison to previous estimates of maximum directivity, and the accuracy of sensitivity as a predictor of statistical performance over large ensembles of design realizations.
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All authors Kurt Schab, Lukas Jelinek, Miloslav Capek, Mats Gustafsson

Applied Physics

Sub-Micron Gate $\beta-Ga_{2}O_{3}$ FinFETs with Current Density $>$ 750 mA/mm and Ion/Ioff Ratio $>$ $10^{9}$

Nabasindhu Das, Cameron Gorsak, Pushpanshu Tripathi et al. (+7 more)

In this work, we demonstrate submicron-gate $\beta-Ga_{2}O_{3}$ FinFETs that integrate Si delta-doped channels with selectively regrown n++ source/drain contacts. The devices employ 100 nm-wide fins to improve electrostatic control of a high sheet charge density channel of $3.3\times 10^{13}$ cm-2. A 150 nm-gate-length FinFET exhibits a maximum drain current density of 764 mA/mm at VGS = 1 V and VDS = 10 V, an on-resistance of 9.1 $\Omega$.mm, and an Ion/Ioff ratio exceeding $10^9$. The device also shows a peak transconductance of 43 mS/mm and de-embedded $f_{T}/f_{MAX}$ values of 6.3/2.0 GHz. Pulsed I-V measurements indicate ~20 % current collapse, attributed primarily to trapping at etched fin sidewalls and the $Al_{2} O_{3}$/ $\beta-Ga_{2}O_{3}$ interface. These results show that delta-doped $\beta-Ga_{2}O_{3}$ FinFETs can simultaneously achieve high drive current, strong current modulation, and GHz-frequency operation, providing a scalable device platform for future power and RF electronics.
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All authors Nabasindhu Das, Cameron Gorsak, Pushpanshu Tripathi, Ankita Kashyap, Noor Jahan Nipu, Advait Gilankar, Hari Nair, Uttam Singisetti, Trevor Thornton, Nidhin Kurian Kalarickal

Applied Physics · Cross-listed from nlin.PS

Extreme Localization via a Singular Edge Mode in an Asymmetric Linkage System

Myeonggyun Joo, Dongwook Kwak, Rajesh Chaunsali et al. (+2 more)

Mechanical localized modes generally retain exponentially decaying tails, whereas confinement to a single structural unit is difficult to achieve without resonators, flat-band lattices or topological design. To address this need, an asymmetric linkage system is introduced in which geometry tunes a boundary mode from finite localization to its extreme limit. Each cell comprises two unequal rigid bars connected by a torsional spring and is described by one generalized coordinate. Linearization and coordinate transformation yield a tridiagonal model and closed-form expressions for the edge mode frequency and spatial decay ratio. The analysis identifies the configurations supporting a singular edge mode at which its decay ratio vanishes, leaving only the boundary cell active in the linear regime. Simulations show near-complete localization under finite-amplitude excitation, and experiments reproduce the configuration-dependent transition from bulk transmission to boundary confinement. These results establish a minimal and analytically tunable platform for mechanical localization
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All authors Myeonggyun Joo, Dongwook Kwak, Rajesh Chaunsali, Panayotis G. Kevrekidis, Jinkyu Yang

Applied Physics

UV-cured PVA-collagen co-network with staining-free photodynamic activity against chronic wound bacteria

Nikitia Mexia, Charles Brooker and Giuseppe Tronci

Chronic wounds affect 1-2% of the global population and represent an unsustainable healthcare, financial and economic burden. Delayed healing is largely associated with bacterial infection and inadequate moisture balance, both of which remain difficult to control due to increasing antimicrobial resistance and the limited exudate management capacity and mechanical performance of current dressings. To address these challenges, we introduce a staining-free photodynamic material with work-light-triggered antibacterial activity, significant water-induced swelling (more than nine-fold increase in dry weight) and tunable wet state compression modulus (Ec: 76+/-34 - 289+/-94 kPa). The material was prepared by UV co-curing of an aqueous solution containing polyvinyl alcohol functionalised with both phenothiazine and methacrylate residues, 4-vinylbenzyl-functionalised type 1 rat tail collagen, and a water-soluble photoinitiator. Fourier Transform Infrared spectroscopy and Differential Scanning Calorimetry of the co-networks indicated the presence of characteristic chemical and thermal features of both components. 96-hour co-network incubation in vitro (pH 7.4, 37 degC) confirmed the significant retention of toluidine blue (> 93 wt.%), suppressed medium colouration, and an average mass retention higher than 98 wt.%. Exposure of the UV-cured samples to 10-min work light resulted in at least 1 log10 reduction in Staphylococcus aureus and Pseudomonas aeruginosa viabilities, in contrast to dark-control conditions, while the metabolic activity of L929 fibroblasts remained above 90%. The antibacterial properties, staining-free photodynamic behaviour, water-induced swelling, and wet-state mechanical properties achieved via network integration with functionalised collagen, make this material appealing for chronic wound healing applications and for on-demand delivery of localised therapies.
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Applied Physics · Cross-listed from cond-mat.mes-hall

Magnon Klein paradox

D. Wang

By considering the energy transport of spin wave, we show that, like the electron Klein paradox, there is no magnon Klein paradox for reflectivity. Heuristically, this can be understood according to the fact that, even if the ground state is unstable, any energy-carrying wave cannot have greater-than-one reflectivity off a passive interface, which will violate the conservation of energy. The magnon Klein paradox discussed in the literature is derived from assigning a wrong sign to the transmitted spin wave.
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Applied Physics · Cross-listed from cs.LG

Active Neural Matter: A Finite-Window Response Framework for Physical Systems and Distributed AI Workflows

Tianchi Chen and Shihua Yu

Physical systems and distributed AI workflows can retain past information, receive delayed feedback and combine conflicting signals. These features pose a common modeling problem: determining what information about past interactions a state must retain to account for future responses. Active Neural Matter (ANM) addresses this problem through a finite-window response framework. Forward analysis uses each system's dynamics to predict state and output responses to perturbations, separating propagation from output sensitivity. Inverse analysis tests whether a candidate state retains enough information for these responses. With the system and future inputs or interaction rules fixed, distinguishable responses from histories assigned the same state identify distinctions the representation must preserve. Their distributional separation gives a lower bound on the worst-case error of approximating behavior from that state. Uncertainty bounds distinguish rejection, support within a fixed tolerance on tested comparisons, and unresolved cases. Delayed-consensus simulations check analytical predictions of response amplitude and phase over a narrow range of delays; flocking illustrates dependence on the chosen observable. An exact delayed-return construction establishes a sufficient state for a specified program. The AI studies identify distinctions in interaction history and evidence order that a representation must preserve to reproduce observed response distributions. Tests on new histories in a controlled feedback task provide bounded support for a state specified by the task instructions; the instructed rule predicts every observed action. ANM connects response prediction to measurable information requirements, separating behavioral fidelity from task correctness and initial-state adequacy from a closed evolution law for that state.
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Friday 9 October

Applied Physics

Optimization of Active Reconfigurable Surfaces for Spatiotemporal MU-MIMO Wave Routing in Disordered Media: Application to the Cocktail-Party Problem

Frederic J. N. Jorgensen, Florent Dorlot, Constant Bourdeloux et al. (+4 more)

We design an active reconfigurable intelligent surface (RIS) for acoustic multi-user multiple-input multiple-output (MU-MIMO) communication by solving a large-scale convex optimization problem, so that each emitter's broadband signal focuses in space and time at its intended receivers while crosstalk is suppressed. In acoustic experiments, we show that our approach outperforms existing time-reversal methods by 5.1-7.6 dB in crosstalk suppression, while achieving better temporal focusing.
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All authors Frederic J. N. Jorgensen, Florent Dorlot, Constant Bourdeloux, Mathias Fink, Fabrice Lemoult, Steven G. Johnson, Raphaël Pestourie

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

A Solution-Processed Ti/Pt/NiOx/Ag RRAM Device with Multiple Forming-Free Non-Volatile Intermediate States

Abhrajit Roy, Chopali Chanchal Sahu, Rudraksh Sangore et al. (+5 more)

Artificial neural networks (ANN) implemented on crossbar arrays of non-volatile synaptic devices are known to consume much less energy compared to that implemented on conventional computing units. Solution-processed resistive random-access memory (RRAM) devices based on transition-metal oxides are suitable as such synaptic devices because of their cheap and easy fabrication method, stability, and suitable memristive properties. Here, in NiO-based RRAM devices with Ti/Pt as the bottom electrode and Ag as the top electrode (NiO layer deposited through solution processing), we experimentally report forming-free binary switching between a high resistance state (HRS) and a low resistance state (LRS) as well as forming-free pulse-driven modulation (long-term potentiation (LTP), long-term depression (LTD)) through 30 intermediate synaptic states between HRS and LRS (around 5-bit synaptic weight resolution). Many of these states are measured to be stable at least up to 1000 seconds confirming their non-volatility and their utility in storage of synaptic weights for ANN crossbar arrays. On the contrary, most prior experimental reports (including reports both on solution-processing-based and sputtering-based RRAM devices) require forming to exhibit non-volatility. Avoiding forming reduces variability, eliminates the need for high voltage pulses, and makes the crossbar array design simpler. Further, we confirm the presence of oxygen vacancies in our materials stack using X-ray photo-electron spectroscopy (XPS). Finally, we show successful data classification on MNIST and CIFAR-10 data sets using a multi-layer perceptron (MLP) model and a convolution neural network (CNN) model respectively, where the synaptic weight updates of these ANN models are calibrated against the experimentally measured LTP-LTD characteristics of the NiO RRAM devices.
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All authors Abhrajit Roy, Chopali Chanchal Sahu, Rudraksh Sangore, Raman Hissariya, Poulomi Chakrabarty, Harsh Roniyar, Merlyne De Souza, Debanjan Bhowmik

Applied Physics · Cross-listed from physics.optics

UV Fluorescence Sensing of Medical-Chemical-and- Biological Analytes by an AlGaN/Si-on-Sapphire Optoelectronic Chip

Richard Soref

This paper proposes and analyzes a compact fluorescence-photometer lab-on-a-chip that is simpler than a fluorescence spectrometer, and that does not require spectrum reconstruction by a computer. An on-chip AlGaN VCSEL lasing at 280 nm, or at 310 nm, pumps an on-chip sample in the form of liquid or solid or tissue, thereby exciting signature fluorescence in the 300 to 540 nm wavelength range. This emission signal is detected and read out by an on-chip UV-enhanced Silicon photodiode. The 2 cm x 5 cm chip consists of C-plane (0001) Sapphire, and no lenses, prisms, or mirrors are utilized in the photometer. The chip is opto-electronic and features co-packaged electronics using tiny electronic chiplets that are bonded to the sapphire. These consist of an LD driver and transimpedance amplifier for the UV photonics, together with ASICs, ADC, microcontroller, micro-battery and RF-wireless or Ethernet chiplets. The mission of this self-contained cost-effective chip is sensing targeted medical-chemical-biological (MCB) agents in a local or network setting. Eight significant MCB applications are detailed here.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci

Latin squares as a model of perfect mixing of high-entropy alloys

P.S. Grinchuk

The structure of high-entropy alloys, which include 5 or more components in equimolar proportions, is proposed to be described in the mathematical language of Latin squares. This model is fundamentally discrete and allows for a quantitative description of ideal mixing, in which any given alloy element is guaranteed not to have an identical element as its nearest neighbor. For the two-dimensional case, the model possesses four axes of translational symmetry, which makes it possible to tile the plane with a single Latin square and, based on the properties of this square, describe the properties of macroscopic material samples. The model makes it possible to make quantitative estimates of the suitability of a particular atomic structure (configuration) for implementation in a perfectly mixed high-entropy alloy with maximum mixing entropy. A condition has been obtained for acceptable fluctuations in the concentration of components at which the thermodynamic stability of the alloy is maintained. The possibility of identifying superstructures in high-entropy alloys based on group theory, as applied to the description and construction of Latin squares, is discussed. Based on the proposed model, the probability of forming a multicomponent alloy with ideal mixing is estimated. For a five-component alloy, this probability is no more than 2.6*10^{-10}.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci

Evolution and breakdown of chiral anomaly in Weyl semiconductor tellurium

Zhifeng Xue, Jiaji Zhao, Yi Ji et al. (+16 more)

Chiral anomaly in topological materials manifests as negative longitudinal magnetoresistance, yet the tunability and evolution of this effect remain elusive. Here we show that doped tellurium serves as a versatile platform to realize a giant negative longitudinal magnetoresistance that is highly tunable via the Fermi level and magnetic field. By moving the Fermi level towards the Weyl point, we observe a pronounced enhancement of negative magnetoresistance, which arises from chiral anomaly and robustly persists up to ambient temperature. Beyond the quantum limit, the system exhibits positive linear magnetoconductance, serving as a compelling transport signature of the chiral anomaly in the lowest Landau level. Notably, in the extreme quantum limit at cryogenic temperatures, the magnetoresistance undergoes a dramatic reversal from negative to positive. This reversal points to a potential field-induced phase transition into a collective electronic state driven by enhanced electron-electron interactions. Our findings provide valuable insights into the unconventional chiral transport and emergent correlated quantum states under extreme magnetic fields.
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All authors Zhifeng Xue, Jiaji Zhao, Yi Ji, Fuyang Chen, Nannan Tang, Gangjian Jin, Bing Shen, Bin Wang, Yang Wang, Mingxi Chi, Jin-Zhu Zhao, Ruiqiang Wang, Qizhong Zhu, He Wang, Huakun Zuo, Donghui Guo, Dingyong Zhong, Mingxun Deng, Huichao Wang

Thursday 8 October

Applied Physics · Cross-listed from physics.optics

Harnessing Machine Learning for Ultrafast Science in Facility Settings: Opportunities and Challenges

Mousumi Upadhyay Kahaly, Ishraq Md Anjum, Davorin Peceli et al. (+2 more)

Ultrafast science is rapidly evolving from a collection of specialized laser experiments into a facility-scale, data-intensive research endeavour. High-repetition-rate femtosecond and attosecond sources, synchronized multidimensional diagnostics, and increasingly nonlinear laser-matter interactions now generate heterogeneous data streams whose volume, speed, and complexity often exceed the capacity of conventional manual workflows. This chapter examines how machine learning can become an enabling layer for next-generation ultrafast facilities, with emphasis on the Extreme Light Infrastructure (ELI) ecosystem. We discuss the scientific drivers for artificial-intelligence-assisted experimentation, propose a facility-scale digital architecture spanning acquisition, ingestion, storage, analytics, machine learning, adaptive feedback, and user interfaces, and review representative examples from ELI ALPS, ELI Beamlines, and ELI-NP. The central thesis is that machine learning should not be treated merely as an offline data-analysis tool; rather, when constrained by physical insight and embedded in robust data infrastructure, it can support real-time diagnostics, surrogate modeling, anomaly detection, experimental optimization, and progressively autonomous discovery workflows.
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All authors Mousumi Upadhyay Kahaly, Ishraq Md Anjum, Davorin Peceli, Zsolt Divek, Subhendu Kahaly

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

Homogeneous Charge Relaxation in Organic Mixed Ionic-Electronic Conductors

Silan Zhang, Scott T. Keene, Junfu Tian et al. (+11 more)

Organic mixed ionic-electronic conductors (OMIECs) couple ionic and electronic signals, enabling energy storage, neuromorphic computing, and bioelectronics. However, how charge relaxes in water once the bias is removed, which determines how long stored states persist, remains unclear. Using operando charge photometry, we tracked charge in OMIEC films during biasing and open-circuit relaxation. Under bias, charges moved as redox fronts. After bias removal, charge instead relaxed uniformly across the channel. Modeling and cryo-electron microscopy indicate that swelling creates connected water-rich pathways through the bulk. These pathways speed ion motion but also let stored charge leak away. Tuning the terminal side chain of a polythiophene controls water uptake and ion trapping. Bulky hydrophobic side chains enable stable programmable states, whereas hydrophilic side chains support fast electrophysiology sensing.
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All authors Silan Zhang, Scott T. Keene, Junfu Tian, Georgina E. Lindop, Simon M. Fairclough, Zhengkang Qu, Xian Wei Chua, Christopher Slaughter, Christina J. Kousseff, Caterina Ducati, Iain McCulloch, Henning Sirringhaus, Akshay Rao, George G. Malliaras

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

Robust skyrmion nucleation and transport via composition gradient in rare earth-transition metal ferrimagnets

Pietro Diona, Luca Maranzana and Sergey Artyukhin

Magnetic skyrmions are typically nucleated via localized excitation methods, such as laser heating, spin-orbit torques, or engineered defects, and their controlled transport is often limited by the skyrmion Hall effect. Here, we demonstrate that spatial gradients in rare-earth–transition-metal alloys, achievable through patterned laser writing, enable both deterministic nucleation and controlled transport. The strategy leverages engineered compositional gradient to cross the magnetization compensation point, defining regions with opposite magnetization. An out-of-plane magnetic field selectively reverses the magnetization, generating a skyrmion. Crucially, the same compositional design enables a channel tuned to the spin angular momentum compensation point, where skyrmions are driven by spin-orbit torques at high velocity with vanishing skyrmion Hall effect. Local composition variations act as pinning sites, enabling threshold-controlled trapping and release.
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Applied Physics · Cross-listed from cond-mat.soft

Autonomous thermodynamic cycles via robotic mobility and sensing

Sofia Kuperman, Ezra Ben-Abu, Yaron Veksler et al. (+3 more)

Thermodynamic cycles are the foundation of energy conversion across natural and engineered systems, transforming heat into useful work. However, these cycles traditionally operate between fixed thermal reservoirs, restricting them to specific locations and temperature differences. Here, we introduce autonomous thermodynamic cycles enabled by robotic mobility and sensing, allowing robots to perform thermodynamic cycles by accessing spatially varying temperature fields. We experimentally realize this concept using multistable gas-filled capsules that circulate within the system across a thermal gradient. Our model reveals that rapid transitions in the capsules' energy states allow the system to operate as a mobile heat engine that harvests and stores energy. By linking the capsule-scale internal energy dynamics to the robot's large-scale navigation strategy, we optimize locomotion paths that balance motion cost and energy harvesting. These findings demonstrate that thermodynamic cycles can emerge when autonomous systems navigate their environments, offering an artificial analog of organisms that forage for energy across spatial resources.
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All authors Sofia Kuperman, Ezra Ben-Abu, Yaron Veksler, Anna Zigelman, Sefi Givli, Amir D. Gat

Applied Physics · Cross-listed from physics.optics

Undetected Photon Spectroscopy in the Long-wave and Far Infrared

Jinghan Dong, Jingrui Zhang, Haichen Zhou et al. (+3 more)

Spectroscopy with undetected photons allows the spectral response of a sample at long wavelengths to be measured through interference of a shorter-wavelength signal field, without directly detecting the light that probes the sample. Previous demonstrations of undetected-photon spectroscopy in the molecular fingerprint region have reached approximately 10.5 microns, leaving longer wavelengths largely unexplored. Here, we extend this approach to 20 microns wavelength, demonstrating infrared undetected-photon spectroscopy using a BaGa2GeSe6 (BGGSe)-based nonlinear interferometer while only the near-infrared (NIR) signal is detected using a silicon detector. Rotation of the BGGSe crystal provides broad wavelength tuning, and Fourier-transform analysis of the signal interferograms yields the corresponding idler spectra and sample transmittance. Broadband absorption spectroscopy is demonstrated using Kapton across a 7.8-20 microns wavelength range, with the measured absorption agreeing with independent infrared measurements. The same system is further employed to detect sulfur hexafluoride (SF6) gas via spectroscopy near 10.55 microns. These results substantially extend the accessible spectral range of spectroscopy with undetected photons while retaining silicon-based NIR detection.
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All authors Jinghan Dong, Jingrui Zhang, Haichen Zhou, Weijie Nie, John G. Rarity, Alex S. Clark

Applied Physics · Cross-listed from physics.optics

Inverse Design of Integrated Photonic Components for Visible-Light Applications

Christoph Stockinger, Marko Šimić, John O. Adeniran et al. (+3 more)

Photonic integrated circuits (PICs) operating in the visible spectral range are crucial for quantum technologies, optical sensing, and nonlinear optics applications. However, their development is hampered by limited integration density and operational bandwidth, linked to low refractive index contrast and restricted parameter space in intuition-based PIC design. We address these bottlenecks with an adjoint-based, fabrication-aware inverse design workflow tailored for visible-spectrum photonics. By expanding the capabilities of FDTDX, an open-source, GPU-accelerated FDTD solver, we provide a versatile memory and runtime efficient inverse design platform. Demonstrating this approach on a silicon nitride (Si3N4) platform, we design, fabricate, and experimentally validate ultra-compact, broadband components for light routing, multiplexing, and polarization control. This work provides a scalable framework for high-density, high-performance visible-light PICs.
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All authors Christoph Stockinger, Marko Šimić, John O. Adeniran, Natale G. Pruiti, Marc Sorel, Peter Banzer

Applied Physics

Time-Domain Analysis of Surface Acoustic Wave Magnetoelectric Sensors

Mohsen Samadi, Henrik Wolframm, Felix Weisheit et al. (+4 more)

The transient response of surface acoustic wave sensors is important for understanding their dynamic behavior, propagation delay, and response to time-varying signals. In this work, the time-domain propagation characteristics of a magnetoelectric SAW sensor based on a multilayer Love-wave delay line are investigated using complementary numerical and experimental approaches. Time-domain analysis is employed to determine the delay time and to extract the phase and group velocities, while frequency-domain analysis provides an independent characterization of the wave dispersion. Both numerically and experimentally, the phase and group velocities are found to differ, reflecting the dispersion of the Love wave in the multilayer structure. At the operating frequency of 146 MHz, the simulated group velocity obtained from wave-field tracking agrees within 0.4% with the value determined from the frequency-domain dispersion relation. The simulated delay time and group velocity also show good agreement with experiment, with deviations of 2.7% in delay time and 0.9% in group velocity. These results demonstrate the consistency of the time- and frequency-domain analyses and provide a quantitative characterization of the transient propagation behavior of SAW sensors.
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All authors Mohsen Samadi, Henrik Wolframm, Felix Weisheit, Dirk Meyners, Eckhard Quandt, Michael Höft, Martina Gerken

Applied Physics · Cross-listed from cond-mat.supr-con

High-Efficiency and Large Supercurrent Rectification with Superconducting Coil

Takumi Ichikawa, Daisuke Takegami, Gen Nishijima et al. (+8 more)

Superconducting diodes (SDs) are devices that rectify supercurrent through the difference in the superconducting critical current (Ic) between forward and reverse current directions. For bringing such SDs closer to practical superconducting power electronics applications, a combination of both high rectification efficiency ({\eta}) and a large Ic difference ({\Delta}Ic) is required. Here, we propose and demonstrate a coil-shaped superconducting wire device concept to induce a large SD effect, arising from the compensation between an external magnetic field (Hext) and the field generated by the coil itself. From transport Ic measurements on coil-shaped SDs based on a Sn10-Pb90 solder wire, we achieved a {\eta} of 79% with a {\Delta}Ic of 140 A at Hext = 500 Oe (coil #2) and a {\eta} of 84% with a {\Delta}Ic of 125 A at Hext = 530 Oe (coil #3), confirming high rectification values at large supercurrents. The large-current high-efficiency SDE in the coil-shaped SDs will be highly useful for developing the potential field of supercurrent power electronics.
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All authors Takumi Ichikawa, Daisuke Takegami, Gen Nishijima, Shunsuke Kawakami, Tsutomu Nojima, Yuji Tsuchiya, Satoshi Awaji, Fuyuki Ando, Ken-ichi Uchida, Yuya Hattori, Yoshikazu Mizuguchi

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

Beam filamentation instability drives deuterium-tritium fusion with polarized neutron emission

Guanqi Qiu, Deji Liu, Dongchi Cai et al. (+3 more)

Filamentation instabilities are generally regarded as detrimental to fast-electron transport in fusion plasmas because they increase beam divergence and redistribute deposited energy. Here, we use two-dimensional particle-in-cell simulations coupled to a spin-dependent deuterium-tritium fusion module to investigate whether filamentation can instead transfer energy from counterstreaming electrons to prepolarized fusion ions. The simulations show that magnetic filaments, together with longitudinal inductive and transverse charge-separation electric fields, accelerate initially stationary deuterons and tritons to energies at which fusion reactions occur. Over the parameter range examined, the calculated neutron yield increases with the saturated magnetic-field energy. The model further predicts anisotropic, spin-resolved neutron emission. The direction of maximum neutron polarization is approximately perpendicular to the dominant deuterium-tritium collision direction and evolves with the angular distribution of the reacting ions. These results suggest that beam filamentation can couple relativistic-electron energy to fusion ions and that polarized neutron emission may provide a reaction-weighted signature of the underlying plasma dynamics.
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All authors Guanqi Qiu, Deji Liu, Dongchi Cai, Ronghao Hu, Zheng Gong, Xueqing Yan

Wednesday 7 October

Applied Physics · Cross-listed from physics.optics

Propagation-Invariant Transmission Eigenmodes in Weakly Scattering Media

J.C Osorio-Tascon and P. A. Quinto-Su

Propagation-invariant beams (PIBs) with annular angular spectra preserve their transverse intensity structure over extended propagation distances. Here, we investigate whether scattering invariant modes (SIMs) can simultaneously exhibit scattering and propagation invariance. We measure free-space and sample transmission matrices (TMs) in an orthonormal annular basis for weak, moderate, and strong scattering media and identify localized SIMs (LSIMs) whose angular spectra remain predominantly confined to one or a few neighboring rings. Under weak scattering, 75 of the 128 SIMs considered for annular localization satisfy this criterion, with LSIMs exhibiting Bessel-like propagation. Under moderate scattering, 25 LSIMs are recovered after filtering low-intensity spectral components, whereas none are found under strong scattering. Although increasing modal crosstalk progressively suppresses annular localization and nondiffracting behavior, SIMs retain higher transverse-intensity correlation over propagation than the Gaussian-like and Bessel beams in the moderate and strong regimes. These results show that annular localization enables SIMs to acquire propagation invariance when scattering is weak, whereas the enhanced propagation robustness of SIMs can persist even after this localization is lost.
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Applied Physics · Cross-listed from cond-mat.mes-hall

Millisecond phonon lifetimes in piezoelectric nanomechanical resonators

Oliver A. Hitchcock, Matthew P. Maksymowych, Kaveh Pezeshki et al. (+5 more)

Piezoelectric nanomechanical resonators operating at gigahertz frequencies are a promising platform for quantum information processing and precision sensing, but phonon lifetimes have been limited to the microsecond range, widely attributed to the higher intrinsic loss of piezoelectric materials. Here we show that this limitation is not fundamental. Using a fabrication process informed by recent studies of defect-mediated loss in lithium niobate, we combine chemical restoration of ion-milled surfaces with a shadow-mask metallization process to produce lithium niobate phononic crystal resonators with inferred internal phonon lifetimes of up to 21 milliseconds at 3.6 gigahertz, corresponding to quality factors exceeding $4\times10^8$ ($f\cdot Q_i > 10^{18}$) at millikelvin temperatures. By systematically varying the electrode-to-resonator spacing, we demonstrate that the measured lifetime is set by external coupling between the device and the measurement circuit rather than material loss. This establishes that lithium niobate, once fabrication-induced surface damage is removed, achieves an intrinsic quality comparable to the best mechanical materials while remaining an intrinsically piezoelectric platform with strong electromechanical coupling.
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All authors Oliver A. Hitchcock, Matthew P. Maksymowych, Kaveh Pezeshki, Takuma Makihara, Erik Szakiel, Chou-Wei Kiang, Daniel Rugar, Amir H. Safavi-Naeini

Applied Physics · Cross-listed from physics.optics

Lithography-free in situ photonic inverse design

Yiqi Zhao, Martin M. Stein, Fan O. Wu et al. (+6 more)

Inverse design has emerged as a powerful engineering approach in nanophotonics, leading to devices with unintuitive designs that extend beyond human intuition. However, inverse-designed devices have been limited by costly and time-consuming fabrication iterations, simulation-reality gaps, and the fixed nature of etched devices. Separately, programmable photonics has emerged as an approach to modify the function of photonic devices after fabrication; recent free-form programmable-photonic devices have been scaled to have many degrees of freedom, in principle providing platforms well-suited for programmably realizing inverse design of conventional linear-photonic functions. Here we demonstrate in situ training of a single free-form programmable-photonic device to achieve a variety of functions that each would have been implemented in separate devices in the conventional inverse-design paradigm. Our platform is a thin-film lithium niobate slab waveguide with full programmability over the refractive index of the two-dimensional slab, with a tuning range of up to 1.7e-3 for each of the 10^4 effective pixels. We demonstrate 4 x 4 Gaussian-mode permutations, 4 x 4 Hermite-Gaussian mode demultiplexing, and 8 x 8 Gaussian-mode permutations, with maximum crosstalk of -27dB, -13dB, and -13dB, as well as 4 x 4 matrix-vector multiplication. We further demonstrate engineering of spectral responses, showcasing both wavelength-independent operation throughout the 1500-1600 nm window and wavelength demultiplexing between 1310 nm and 1550 nm, with maximum crosstalk of -8.4dB. Since the device is reconfigured for each function after fabrication, the investment in device fabrication, characterization, and calibration can be amortized across the various photonic functions the device is ultimately used for.
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All authors Yiqi Zhao, Martin M. Stein, Fan O. Wu, Ryotatsu Yanagimoto, Benjamin A. Ash, Mandar M. Sohoni, Logan G. Wright, Tatsuhiro Onodera, Peter L. McMahon

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

Pseudospin Hall Transport Induced by Berry Curvature

Qinhui Jiang, Jidong Song, Qingyang Mo et al. (+4 more)

Pseudospin-1 Dirac systems exhibit unique physics distinct from conventional Dirac cones, such as flat-band crossings and non-Abelian characteristics, yet their topological transport properties have remained largely untapped in passive, time-reversal-invariant settings. Here we uncover an in-plane polarity of the Berry-curvature texture in a pseudospin-1 Dirac Hamiltonian, a previously unexplored geometric degree of freedom encoded in the sign-resolved distribution of Berry curvature despite zero net Berry flux, and reveal a new mechanics where Berry curvature induce pseudospin Hall behaviors in a system. We show that the oriented coupling between this momentum-space polarity and a real-space mass gradient governs a geometric selection rule that dictates the emergence of gapless pseudospin Hall modes. By engineering the intracell couplings of a four-site planar lattice, we independently program the Berry-curvature polarity and the spatial mass gradient without altering the host lattice symmetry. Acoustic experiments directly confirm this directional selection rule: reversing the mass gradient closes or reopens the dispersive gap, while pseudospin-selective source excitation launches counterpropagating pseudospin branches along arbitrary prescribed axes. Our work establishes quantum geometric polarity as a versatile tool for reconfigurable wave routing, sensing, and high-capacity quantum applications.
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All authors Qinhui Jiang, Jidong Song, Qingyang Mo, Bo Li, Dongyi Wang, Shuang Zhang, Mengyao Li

Applied Physics · Cross-listed from cs.LG

Matching of signal, noise and hardware timescales for filtering and forecasting of correlated noise signals

Joshua Donald, Alex Gabbitas, Arthur G. T. Coveney et al. (+2 more)

Physical reservoir computing exploits the nonlinear dynamics of physical systems to process time-dependent data with greater energy efficiency than conventional machine learning approaches. However, physical reservoirs have fixed intrinsic response timescales, whereas real-world signals combine deterministic and stochastic components across multiple timescales. Here we show, using a nanoporous niobium oxide reservoir, synthetic noisy signals and cryptocurrency-price volatility, that the relationship among noise correlation time, reservoir memory and forecast horizon determines whether correlated noise is filtered or predicted. Noise varying faster than the relevant reservoir memory and forecast horizon is averaged by the reservoir, whereas the temporal structure of slower-varying noise is sufficient for algorithmic forecasting. We introduce the reservoir memory horizon and forecasting regime index to distinguish these operating regimes. These contributions demonstrate that timescale matching can guide the encoding of input time series and development of physical reservoir architectures that filter, analyse and predict stochastic signal components across distinct temporal scales.
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All authors Joshua Donald, Alex Gabbitas, Arthur G. T. Coveney, Sergey Savel'ev, Pavel Borisov

Applied Physics · Cross-listed from cond-mat.supr-con

Delamination in Large REBCO Coils

Jun Lu, Yan Xin, Iain Dixon et al. (+6 more)

REBCO coated conductors have been used in ultrahigh field magnets for condensed matter physics research, nuclear fusion, particle accelerators, and NMR applications. It is well known, however, that they are not mechanically strong against delamination due to their intrinsic layered structures. As a result, the delamination issue has become one of the major design challenges of REBCO magnet coils. As a part of the development of the 40 T all-superconducting magnet at the National High Magnetic Field Laboratory, USA, large-scale coils wound by two-in-hand REBCO conductor with turn-to-turn insulation was designed and tested at 4.2 K in an 11.4 T background magnetic field. We found REBCO degradations within the windings and at the crossover joints during the tests. The postmortem inspection found that the degradation was caused by delamination. The delamination appears on the surface of the conductor as bubbles which were subsequently studied by microscopy. Additionally, a similar bubble was found on a short sample by torque magnetometry. This supports the inference that the delamination bubbles found in coils are due to electromagnetic stress. In this paper, we present these findings. The implication of these findings for future magnet designs and the method of mitigation will be discussed.
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All authors Jun Lu, Yan Xin, Iain Dixon, Brent Jarvis, Kwangmin Kim, Yu Suetomi, Jeremy Levitan, Jan Jaroszynski, Hongyu Bai

Tuesday 6 October

Applied Physics

Physics-Derived Natural Coordinates for Fast Uncertainty Propagation in Multilayer Thermoreflectance

Tao Chen, Dihui Wang and Puqing Jiang

Uncertainty quantification in thermoreflectance measurements of multilayer structures is challenging because thermophysical-property extraction involves nonlinear inverse problems with strongly coupled parameters. Covariance-based analytical propagation is efficient but assumes local linearity and approximately Gaussian fitted variables, whereas Monte Carlo (MC) propagation captures non-Gaussian behavior but is computationally expensive and can be unreliable when simultaneously fitting parameters spanning very different orders of magnitude. Here, we address these issues by combining normalized MC sampling, used to obtain reliable benchmark distributions, with physics-based variable transformations for analytical uncertainty propagation. From the multilayer heat-diffusion equation, we identify natural coordinates: the interfacial thermal resistance 1/G, the substrate combinations sqrt(k_z k_r) and sqrt(k_z C), and the thin-film combinations k_r/C, hC, and Ch^2/k_z. Across several representative multilayer systems and thermoreflectance modalities, these coordinates are approximately Gaussian even when the original physical parameters are skewed. Performing covariance-based propagation in the transformed space and mapping the results back to physical parameters yields asymmetric confidence intervals that closely match normalized MC benchmarks. The approach preserves the non-Gaussian uncertainty structure of the recovered parameters while avoiding repeated nonlinear refitting, providing a fast and physically interpretable methodology for thermoreflectance uncertainty quantification in multilayer systems governed by diffusive heat conduction.
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Applied Physics

Low-Cost Spectrophotometers: A Comparative Evaluation of Open-Source Architectures

Alex M. Rivera-Rivera, Daniela Martinez-Ortiz, François Quitin et al. (+4 more)

The rapid growth of low-cost and open-source spectrophotometers has created a need for systematic methodologies to evaluate and compare alternative instrument architectures. This study presents a comparative assessment of three representative open-source spectrophotometric platforms, encompassing discrete multispectral sensing and continuous-spectrum imaging approaches. Their performance was evaluated against a commercial Thermo Scientific Genesys 30 spectrophotometer in terms of spectral agreement, portability, implementation complexity, and cost. The results demonstrate that no single architecture is universally optimal; instead, each presents distinct trade-offs that determine its suitability for specific applications. Multispectral sensor-based systems offer compact, low-power solutions for field deployment, whereas imaging-based platforms provide spectral performance closer to laboratory-grade instrumentation. All hardware designs, firmware, and software developed in this work are released as open-source resources to support reproducibility and further development. The study highlights the importance of matching instrument architecture to application requirements and proposes a practical framework for the evaluation and selection of low-cost spectrophotometers, facilitating the adoption of open-source analytical tools for water quality monitoring and related applications.
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All authors Alex M. Rivera-Rivera, Daniela Martinez-Ortiz, François Quitin, Denis Terwagne, Stamatios C. Nicolis, Ernesto Altshuler, Alexandre Campo

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

Analytical Prediction of Buckling Limits in Isotropic Pentamode Lattices

M. Verbicaro, F.Braghin and R.V. Craster

Pentamode lattices are architected materials characterized by an elastic response dominated by a single deformation mode. The low stiffness of the other deformation modes, however, may result in limited stability under compressive prestress, thereby limiting their mechanical performance. In this work, we develop a general analytical framework to determine the buckling limits of prestressed 2D and 3D isotropic pentamode lattices with generic link geometries. Two distinct instability mechanisms are considered: a global instability associated with the loss of stability of the effective medium, and a local instability associated with finite-wavelength modes at the scale of the lattice cell. Closed-form expressions for the corresponding critical pressures are derived, and the buckling limit is obtained as the lower of the two. The analytical predictions are validated through numerical simulations of different PM lattices, showing good agreement over the configurations considered. The results reveal a trade-off between approaching the pentamode limit and maintaining sufficient buckling resistance, but also show that appropriate link designs can substantially increase the buckling limit while retaining the desired pentamode behavior.
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Applied Physics

Graded Orbital Interface Engineering for Enhanced Damping-like Torque Efficiency

Subhakanta Das, Bilal Jamshed, Kesavan Jawahar et al. (+1 more)

Orbitronics has emerged as a promising approach for generating orbital currents using low cost, abundant materials through the orbital Hall effect. Since orbital current cannot directly interact with the local magnetization of a conventional ferromagnet, a non-magnetic layer with strong spin orbit coupling is required for converting orbital current into spin current. However, the propagation of orbital current across the interface between an orbital source and an orbital to spin converter remains poorly understood. Here, we tuned the Ru/Pt orbital interface from an abrupt interface to a graded interface by introducing a controlled RuPt intermixed layer and quantified the resulting damping like torque efficiencies. A small, intermixed thickness of 0.26 nm enhances the damping like torque efficiency by 15% compared with the abrupt Ru/Pt interface and by 70% compared with the Pt reference. Further increasing the intermixing thickness progressively suppresses the torque efficiency. We attribute this nonmonotonic behavior to the competition between enhanced orbital transmission through a gradual crystal field transition and orbital current dephasing due to alloy disorder and scattering. Our results demonstrate that the orbital-source/converter interface is an active element for controlling orbital transport and provides an experimentally accessible approach for optimizing orbital current transmission and torque generation in orbitronic heterostructures.
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All authors Subhakanta Das, Bilal Jamshed, Kesavan Jawahar, S. N. Piramanayagam