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Thursday 27 August

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

Sparse Delta Integration method for the calculation of spatiotemporal pressure fields of arbitrary ultrasound transducer geometries

Deyver E. Rivera, Charlie Demene and Mickael Tanter

Accurate and efficient simulation of ultrasound pressure fields and pulse-echo responses is essential for transducer design, beamforming optimization, and model-based imaging research. Conventional Spatial Impulse Response methods compute acoustic fields by explicitly sampling trapezoidal impulse responses for each rectangular aperture subdivision, which leads to high computational cost for large apertures, dense spatial grids, and high sampling frequencies. We introduce Sparse Delta Integration, a mathematical framework for the far-field SIR of rectangular apertures that expresses the trapezoidal spatial impulse response as the double integration of a sparse set of Dirac delta distributions. This formulation yields compact expressions for time-domain and frequency-domain SIRs and enables vectorized implementations whose computational cost is independent of the trapezoid duration. We further derive a spectral formulation for pulse-echo simulation that removes part of the conventional Fourier-domain convolution pipeline. Implemented in the open-source Python package eSDIva, these methods achieve speedups of up to 180x for temporal SIR computation and up to 20x for pulse-echo RF simulation relative to Field II, while maintaining high numerical accuracy with mean squared errors below 1e-5 and correlation coefficients close to unity.
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Applied Physics

Split Coaxial Cable Medium for Tunable Artificial Dielectrics and Plasmas

Alexander Zhuravlev, Jim A. Enriquez, Pavel A. Belov et al. (+1 more)

We introduce the Split Coaxial Cable Medium (SCCM), a mechanically tunable, capacitively loaded wire medium supporting artificial-dielectric and artificial-plasma Bloch regimes with high in-plane isotropy. Its unit cell comprises coaxial conductors interrupted by axial gaps. Relative axial displacement continuously varies their capacitive overlap and series capacitance while preserving the transverse lattice geometry and leaving the unit-cell inductance approximately unchanged. Equivalent RLC parameters are derived directly from the geometry and incorporated into complementary analytical models. A spatially dispersive local-field model predicts the Bloch dispersion and isofrequency contours, whereas a multilayer homogenization model provides the modal impedance, closed-form estimates of the low-frequency Bloch refractive index and plasma frequency, and loss-inclusive finite-slab scattering. Full-wave eigenmode and finite-slab simulations validate the predictions. Over the investigated displacement range, simulations yield tunabilities of $46\%$ in the low-frequency Bloch refractive index, from $n_{0,\min}=1.42$ to $n_{0,\max}=2.28$, and $21\%$ in the plasma frequency, from $f_{\mathrm{p},\min}=9.45~\mathrm{GHz}$ to $f_{\mathrm{p},\max}=11.61~\mathrm{GHz}$, while confirming high in-plane isotropy near the $\Gamma$ point in both regimes. These characteristics make the SCCM promising for gradient-index devices, directive antennas, and tunable plasma haloscopes.
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All authors Alexander Zhuravlev, Jim A. Enriquez, Pavel A. Belov, Juan D. Baena

Applied Physics · Cross-listed from physics.optics

Lower bound on the thickness of broadband dielectric mirrors

Mikhail A. Kats

We present a lower bound on the total physical thickness of a lossless, non-dispersive dielectric mirror for a given minimum reflectance across a wavelength band. The bound is based on a causality-based sum rule translated from a known result in acoustics, that expresses the wavelength integral of the logarithmic transmission of any lossless one-dimensional refractive-index profile as a function of the total thickness of each material comprising the profile, independent of how the layers are arranged. Calculating the thickness bound for a dielectric mirror, given some incident medium and substrate, requires only the lowest and highest refractive indices used in the thin-film stack and the minimum desired reflectance for a given wavelength span. We find that (1) the bound is set by the wavelength span so, for example, a 400-700 nm and an 800-1100 nm mirror have the same bound; (2) the figure of merit for materials minimizing the necessary thickness is $(n_H-n_L)^2/(n_H+n_L)$, where $n_H$ and $n_L$ are the indices of the high- and low-index materials; and (3) each additional "nine" of reflectance (e.g., from 99% to 99.9%) requirement adds a fixed amount of additional thickness to the bound. Non-exhaustive numerical calculations show that the readily achievable thickness is about twice our bound.
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Wednesday 26 August

Applied Physics · Cross-listed from cs.NE

Optimizing Train Driving to Minimize the Electricity Cost of an Entire Railway Traffic Mesh using Evolutionary Algorithms

Eduardo Pilo de la Fuente, Sudip K. Mazumder and Maria Antonia Simon

This paper presents a procedure to optimize the way trains are driven, which pursues, in addition to fulfilling operational constraints such as admissible speeds or journey durations, the minimization of the cost related to supplying electrical energy to the trains, including the cost of the energy consumption and the cost of the power capacity utilization. This procedure combines: (i) a traffic model that merges the energy and power footprint of each rail service part of the traffic mesh, and (ii) an evolutionary computation framework that enables searching for the optimal way to drive the trains to achieve an optimal traffic mesh. This procedure is applied to a 450 km long section of the high-speed line from Madrid to Barcelona (Spain).
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Applied Physics · Cross-listed from cond-mat.soft

Beyond Crease Geometry: Multistability in Origami-Inspired Structures through Local Fold Architectures

Sagi Senderovich, Ezra Ben-Abu, Shai Elbaz et al. (+3 more)

Origami-inspired tubular structures provide a versatile platform for shape morphing, with multistability achieved predominantly through crease-network geometry. Expanding the range of morphing behaviors can therefore require increasingly intricate crease patterns that become more difficult to model and fabricate, ultimately constraining the realizable morphing landscape. Here, we expand the design space of origami-inspired structures beyond geometry by introducing localized instabilities within the crease network, thereby creating compliant multistable structures whose local fold architectures govern global deformation and stability through both constitutive mechanics and geometric constraints. To relate local fold architectures to global multistability, we develop and experimentally validate a modeling framework in which compliant folds are represented as continuous fields that capture spatially varying bistable mechanics. Force- and displacement-controlled design maps demonstrate that global deformation and stability can be programmed through the fold architecture's local parameters. Redistributing bistability within a fixed crease-network topology shifts the global response between compliant, spatially distributed deformation in semi-bistable architectures and discrete transitions within a hierarchically organized space of stable configurations in fully bistable architectures. These results establish a local-to-global design principle for programming both the stable configurations of a structure and the transition pathways connecting them, expanding the design space for multistable metamaterials, adaptive morphing structures, and soft robotic systems.
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All authors Sagi Senderovich, Ezra Ben-Abu, Shai Elbaz, Nadav Zemah, Anna Zigelman, Amir Daniel Gat

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

Quantifying the effect of resonant amplitude and frequency of phononic material vibrations on the coupled fluid-structure interaction dynamics in separated aerodynamic flows

Vinod Ramakrishnan, Arturo M. Burgos, Sangwon Park et al. (+2 more)

Phononic materials (PMs) with engineered resonances have been leveraged for fluid-structure interaction (FSI) with fluid flow instabilities, yielding beneficial outcomes such as transition delay, stabilized hypersonic boundary layers, and increased aerodynamic lift. Prior PM-FSI studies primarily identify spatio-temporal flow scales of interest and choose PM structural parameters producing structural dynamics conducive for FSI. However, a fully-coupled FSI system generally produces complex coupled dynamics that is not accurately captured by studying either physical system in isolation. In this context, our prior work established behavioral parameters that govern the coupled PM-FSI dynamics in a separated aerodynamic flow over a limited parameter range. Adopting this framework, this paper explores strongly-coupled high-fidelity PM-FSI simulations over a broader range of two behavioral parameters—truncation resonance frequency and displacement amplitude—to establish their quantitative (linear/cubic) relations to the coupled frequency, lift force, and circulation in the coupled system response. In addition, the results indicate the presence of distinct FSI regimes, depending on the proximity of the truncation resonance frequency or its sub-/super-harmonics to the vortex-shedding frequency. FSI dynamics ranging from multi-/single-frequency dynamics, downshifted coupling frequency due to fluid-added mass effects, generation of non-linear harmonics to convergence of FSI dynamics to the rigid plate case are observed. These results reiterate the importance of the PM frequency and amplitude in determining the coupled FSI dynamics, and the proposed quantitative relations provide a new pathway for designing PMs for aerodynamic flow control to achieve beneficial outcomes, e.g., lift force enhancement.
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All authors Vinod Ramakrishnan, Arturo M. Burgos, Sangwon Park, Andres Goza, Kathryn H. Matlack

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

Watching a GaN Transistor Switch: Real-Time Nanoscale Strain and Heat Dynamics

C. Corley-Wiciak, N. T. Sammler, B. Butej et al. (+16 more)

Digital and energy technologies depend on microelectromechanical and power electronic components whose performance is critically impacted by rapid, cyclic deformations. Real-time information on their operation has remained inaccessible due to the need for nanosecond and nanometer resolution in fully integrated devices. We break this limitation by imaging the complete switching cycle of an industrial GaN high electron mobility transistor through stroboscopic dark field X ray microscopy at a fourth-generation synchrotron, resolving electromechanical and thermal micro strain fields across the entire device and correlating them with time dependent voltage characteristics. Coupled simulations benchmarked against the measurements reproduce electric field evolution and transient thermal hotspots. This combined approach provides direct insight into device physics and informs design strategies for next generation energy and information processing technologies.
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All authors C. Corley-Wiciak, N. T. Sammler, B. Butej, M. Petersmann, A.A. Corley-Wiciak, L. Neumann, Juan M. Carrillo-Larrea, P. Schmiedeke, M. Strätgen, P. A. Douissard, S. J. Leake, P. Boesecke, M. Sievers, P. Imrich, M. Nelhiebel, M. Glavanovics, D. Pogany, M. Reisinger, T.U. Schulli

Applied Physics · Cross-listed from cs.ET

Simultaneous Digital Communication and Deformation Sensing over a Single Stretchable Interconnect

Yuji Isano and Hiroki Ota

Stretchable hybrid electronics integrate rigid solid-state electronics with stretchable materials and structures to achieve both high deformability and stable electronic performance. However, most existing systems treat stretchability only as a mechanical attribute without exploiting device deformation to encode its own mechanical state. This problem arises from adapting conventional rigid circuit architectures to stretchable substrates, affording a loss in compatibility with the sensors required for strain measurement. This study addresses this issue by proposing a communication-integrated deformation sensing architecture for stretchable hybrid devices. In the proposed approach, standard universal asynchronous receiver-transmitter digital signals transmitted between rigid nodes are amplitude-modulated by strain-induced resistance changes in stretchable liquid metal interconnects. By reading both amplitude changes and digital patterns, the system enables simultaneous digital communication and self-deformation sensing without requiring additional stretchable sensing elements. The architecture is demonstrated in a multi-node system and applied to wearable sensing and self-deformation mapping devices. By extending the integration of rigid circuits and soft elements from the hardware level to the system level, this study provides a novel design paradigm for stretchable electronic systems that inherently utilize their own deformation as functional information.
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Applied Physics

Stringent Constraints on Spin-Spin-Velocity-Dependent Exotic Interactions with a Levitated Magnet Force Sensor

Kenan Tian, Siwen Chen, Lei Wang et al. (+12 more)

Exotic spin-spin-velocity-dependent interactions, predicted in extensions of the Standard Model involving new bosonic fields, could resolve fundamental puzzles from dark matter to cosmic asymmetry. However, exploring these weak potential interactions at centimeter scales presents formidable challenges, primarily due to the overwhelming dominance of electromagnetic backgrounds that can easily obscure the weak exotic signals. Here, we utilize a levitated magnet force sensor with ultrahigh electron spin density to probe these interactions. We constrain two interactions individually through a designed spin source and a multi-layer magnetic shielding system that suppresses electromagnetic backgrounds. In this study, we constrain two types of interactions: the V_6 potential at force ranges from $10^{-3}$ m to $6 \times 10^{-2}$ m and the V_{14} potential at ranges greater than $10^{-3}$ m. Our measurements establish 95% confidence-level bounds of $|f_6| \leq 2.12 \times 10^{-13}$ and $|f_{14}| \leq 2.34 \times 10^{-23}$ at $\lambda = 1.6 \times 10^{-2}$ m, improving prior limits by up to 12 and 13 orders of magnitude, respectively. Our result demonstrates the levitated magnet as a highly sensitive probe for detecting new bosonic fields in extensions of the Standard Model.
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All authors Kenan Tian, Siwen Chen, Lei Wang, Yuanji Sheng, Dingjiang Long, Rui Li, Han Xie, Yiming Chen, Xiang Bian, Hao Wang, Ruoyu Ding, Chang-Kui Duan, Peiran Yin, Xi Kong, Pu Huang

Tuesday 25 August

Applied Physics

Oscillator-Based Processing Unit for Formant Recognition

Tamás Rudner-Halász, Wolfgang Porod and Gyorgy Csaba

Oscillatory neural networks have been successfully applied to a number of computing problems, such as associative memories and computationally hard optimization tasks. In this paper, we show how to use oscillators to process time-dependent waveforms with minimal or no preprocessing. Since preprocessing and first-layer processing are often the most power-hungry steps in neural networks, our findings may open new doors to simple and power-efficient edge-AI devices.
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Applied Physics · Cross-listed from physics.chem-ph

Visualizing and Quantifying Atomic Contributions to Raman Intensities governed by Spatially-Resolved Atomic Interferences

Marc Bröckel, Johannes Gierschner, Alfred J Meixner et al. (+1 more)

Raman spectroscopy is commonly reduced to molecular fingerprint sensing, neglecting Raman intensities. Atomic Raman intensity contributions trace Raman intensities back to their microscopic origin and act as local electronic structure descriptors; however, a both physical but intuitive framework is missing by now. Therefore, in this work, we combine the two main lines of decomposing Raman intensities: atomic Raman tensors and atomic Raman Intensity Densities (RIDs). The former are used to define atomic Raman intensities which quantify both the magnitude and the phase of each atom's contribution to the global Raman signal, demonstrating that weak Raman bands may arise from destructive interference of individually strong atomic contributions. The latter build on redefined atomic Raman Polarizability Densities, RPDs, and are defined in analogy to our atomic Raman intensities. They show how the motion of an individual atom modulates the polarizability of the entire molecule. Atomic RIDs thus show local interferences of different atomic contributions. They integrate to the atomic Raman intensities bridging the two main lines. Additional (atomic) Charge Density Differences (CDDs) extend the RIDs to electronic structure effects. Finally, we apply the methodology to experimental surface-enhanced Raman spectra of substituted 2-mercaptobenzothiazole derivatives and discuss substituent-induced Raman intensity changes. We show that such changes do not necessarily stem from globally altered polarizabilities but from changes in the relative phase of atomic contributions. However, this method is not limited to SERS but widely applicable to all kinds of Raman, SERS or picocavity TERS experiments offering a basis for atomically resolved investigations of molecular processes such as adsorption, catalysis, and chemical reactions
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All authors Marc Bröckel, Johannes Gierschner, Alfred J Meixner, Kai Braun

Applied Physics

Imaging atomic scale stochasticity: noise in the nearly commensurate charge density wave of 1T-TaS$_2$ for leaky-integrator-and-fire neuromorphic emulator

Michael Verhage

Low-dimensional materials are promising materials for emulating neuron-like firing were understanding of the atomic-scale origin of this behavior can benefit integration into neurormophic hardware. Using scanning tunneling microscopy (STM) as a highly local probe of correlations in the charge density wave (CDW), we study atomic-scale CDW noise in $1T\text{-}\mathrm{TaS}_2$ at room temperature. We statistically analyze the tunnel-junction noise and, to explain the temporally correlated current bursts, introduce a mesoscopic model in which the fractal structure and reorganization of CDW discommensurations are related. This noise mimics leaky-integrate-and-fire neuron dynamics. Our results show that atomic-scale current bursts in the tunnel junction can act as effective nonlinear elements in spiking neural emulators, enabling bioinspired processing through rich CDW dynamics at room temperature and supporting the miniaturization of spiking devices.
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Monday 24 August

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

Can Strain or Anion Interchange Make an Unstable Structure Stable? Energetics, Lattice Dynamics and Strain-Tunable Band Gaps of Lithium Chalcohalide Antiperovskites (Li$_{3}$$BA$) and their Anion Interchange Variants (Li$_{3}$$AB$)

Ismail A. Buliyaminu, Ehsan Gowdini, Phillip Duxbury et al. (+1 more)

Lithium chalcohalide antiperovskites are a promising, non-toxic alternative to lead halide perovskites, with potential as solid electrolytes for Li-ion batteries. we computationally investigate a relatively unexplored anion-interchange mechanism by which cubic Li$_{3}$$AB$ derivatives are obtained from the parent cubic antiperovskite Li$_{3}$$BA$ ($A$ = O, S, Se, Te, Po; $B$ = F, Cl, Br, I). The calculated relative energy landscape provides a useful guide for anion-site selectivity and its role in structural stability. The energetic stability results reveal that the smaller anion inside the octahedron stabilizes the structures. The lattice-dynamic calculations confirm that Li$_{3}$F$A$ ($A$ = Te, Po) and Li$_{3}$O$B$ ($B$ = Cl, Br, I), which are the most energetically stable compounds, are dynamically stable cubic phases without imaginary phonon modes. However, Li$_{3}$FS and Li$_{3}$FSe, while energetically stable, are dynamically unstable at equilibrium and become dynamically stable under triaxial compressive strain. In addition, we report the electronic structure and density of states (DOS) of all compounds, which show a substantial change in band gap upon anion interchange. The strain engineering of the lithium chalcohalide family illustrates how a few percent of the strain can tune the electronic band gap within the electrochemical stability window for solid battery applications. This study unveils essential characteristics of the anion site-interchange mechanism and provides a foundation for the understanding and design of lithium chalcohalide antiperovskites.
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All authors Ismail A. Buliyaminu, Ehsan Gowdini, Phillip Duxbury, Jose L. Mendoza-Cortes

Applied Physics · Cross-listed from quant-ph

Sustained macroscopic quantum coherence in a superradiant solid under ambient conditions

Wei-Jiang Wu, Da-Wu Xiao, Wen-Tao Wang et al. (+5 more)

Macroscopic quantum coherence, such as in laser, Bose-Einstein condensates, superfluids, and superconductors, is important to fundamental physics and useful for quantum technologies. Superradiance provides a mechanism to produce coherence among a large number of particles and photons. Its implementation, however, has been limited to gaseous systems, solids at very low temperature, or short pulses. Here we demonstrate a solid-state superradiant maser under ambient conditions, which establishes long-lived coherence among about $10^{14}$ nitrogen-vacancy center spins in diamond and about $10^9$ photons in a microwave cavity. By varying the system parameters to access the above-threshold, well-above-threshold, and deep-above-threshold regimes, we observed continuous-wave masing, periodic amplitude modulation, and sequences of superradiant bursts, which are attributed, correspondingly, to macroscopic spin coherence synchronized at a fixed frequency, a coherent time crystal of large spins, and unsynchronized superradiant transients. This work demonstrates that macroscopic quantum coherence can be spontaneously generated and maintained in solids under ambient conditions and provides a solid-state platform for exploring bright quantum lights with many-body correlations.
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All authors Wei-Jiang Wu, Da-Wu Xiao, Wen-Tao Wang, Xin-Yu Chen, Xian-Feng Wang, Ming-Zhong Ai, Quan Li, Ren-Bao Liu

Applied Physics

Which transition can be used in sodium mirrorless lasing for mesospheric magnetometry?

Yucheng Yang, Chunyang Lei, Kai Guo et al. (+1 more)

Directed mirrorless lasing from the mesospheric sodium layer has been proposed as a way to overcome the isotropy of laser-guide-star fluorescence, with demonstrated cell-scale analogues and a demonstrated stand-off magnetometry application. Several transition paths on the Na ladder compete for the same pump photons, and which of them can sustain a population inversion—and under what pumping format—is usually settled by numerical scans of a multi-level rate model. Here the same question is answered in closed form, and three design-relevant results follow from the atomic data alone. (1) A cascade inversion on $u\to l$ requires $\tau_u/\tau_l>(g_u/g_l)b_{ul}$. The inequality reproduces the full continuous-wave classification—admitting $4P_{3/2}\to4S_{1/2}$ (2.21~\textmu m), $4P_{3/2}\to3D_{5/2}$ (9.1~\textmu m) and the fine-structure companion $4S_{1/2}\to3P_{1/2}$ (1138~nm), excluding $4D_{5/2}\to4P_{3/2}$ (2.34~\textmu m) and $3D_{5/2}\to3P_{3/2}$ (819~nm)—and shows the 2.34~\textmu m line to miss by only 9%, which is why it is transiently accessible. (2) Velocity selectivity reverses the naive scheme ranking because a Doppler-averaged treatment, exact for one-step pumping, underestimates two-step pumping by a participation factor of order the Doppler-to-natural width ratio, $\sim$$10^{2}$; equal division of power between two pump beams is exactly optimal. (3) The transient window on 2.34~\textmu m closes after $\sim$2$\tau(4P)\approx210$~ns, set by the reservoir lifetime rather than by the pump. Each conclusion is traceable to a lifetime, a branching ratio or a linewidth, and transfers to another species without rerunning a model.
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All authors Yucheng Yang, Chunyang Lei, Kai Guo, Chi Peng

Applied Physics

Movable Gate MOSFETs as Readout Devices for Cantilever-Based Nano-Electromechanical Sensors

Z. Geng, A. Hessel, S. C. Scholz et al. (+3 more)

This work proposes a novel readout mechanism for highly sensitive cantilever-based mass sensors using movable-gate (MG) MOSFETs. Traditional dynamic-mode cantilever sensors measure mass through shifts in resonance frequency, which offer high precision but require complex analog circuitry and large device areas, limiting integration and miniaturization. In contrast, the proposed approach exploits strong short-channel effects in MG MOSFETs, where the drain current depends exponentially on cantilever position, allowing for orders-of-magnitude changes without analog-to-digital conversion. Numerical simulations and initial experiments demonstrate the feasibility of this approach, which also avoids pull-in instability by using the electrostatic behavior of the gate-channel system to stabilize and even excite oscillations. The concept paves the way for scalable, low-complexity, high-resolution mass sensing with full circuit integration potential.
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All authors Z. Geng, A. Hessel, S. C. Scholz, F. Schwierz, M. Ziegler, J. Knoch

Applied Physics · Cross-listed from physics.optics

Extreme Ultrafast Dynamics of the Refractive Index in Transparent Conductive Oxides: Theory and Experiment

Noa Konforty, Graham G. Brown, Ohad Segal et al. (+5 more)

Recent experiments in transparent conductive oxides (TCOs) have revealed light-induced order-unity variations in the refractive index occurring at extreme time scales, as short as a few-femtoseconds. These experimental observations remain unexplained, especially the ultrafast 10-20 femtoseconds relaxation of the index change, that cannot be explained by known phonon-mediated relaxation processes. Here, we present a simplified model followed by comprehensive simulations describing the phenomena, relying on the microscopic dynamics of electrons in TCOs under powerful ultrafast laser pulses. With this physical model, we predict and experimentally observe the unexplored regime of intraband modulation of electrons in the conduction band, leading to ultrafast oscillations of the refractive index. The observation of the oscillations validates the theory as a predictive tool, utilizing it to design experiments targeting novel effects that hinge on extreme alterations of optical properties of materials, such as photonic time-crystals and a plethora of novel extreme ultrafast phenomena.
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All authors Noa Konforty, Graham G. Brown, Ohad Segal, Oded Schiller, Yonatan Plotnik, Vladimir M. Shalaev, Misha Ivanov, Mordechai Segev

Applied Physics

Transient Dynamics and Duty-Cycle Optimization in a Pulse-Wwidth Modulation Bell–Bloom Pumping

Ying-Hao Ye, Ling-Yan Hu, Dui-Gao Yi et al. (+2 more)

We investigate the duty-cycle-dependent atomic response under full-depth intensity pulse-width modulation in Bell–Bloom optical pumping. A time-domain Bloch model explicitly resolves the pump-on/off spin dynamics, yielding piecewise analytical transient solutions and a periodic steady-state description without cycle averaging or harmonic truncation. An extended free-induction-decay method independently determines the effective dark and pump-on transverse-relaxation rates, $W_0$ and $W$. The predicted lock-in responses agree well with experimental results. We find that for each Larmor frequency $\omega_0$, the slope is maximized at a finite pump rate that increases with $\omega_0$. These results provide a practical framework for sensitivity-oriented optimization of the duty cycle and pump rate in PWM-driven atomic magnetometers.
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All authors Ying-Hao Ye, Ling-Yan Hu, Dui-Gao Yi, Zhi-Fei Yu, Bing Chen

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

Collective self-sorting on a chip

Emanuel F. Teixeira, Thieu van den Bergh, Arjen Klok et al. (+2 more)

We harness two established ingredients for collective demixing: differential speed and curvature to create a self-sorting device. In binary mixtures, motility differences drive spontaneous spatial segregation, while confinement geometry determines how rapidly and strongly this demixing develops. Using particle based simulations, we systematically identify the geometrical conditions that promote efficient segregation and use these results to guide the design of a finite sorting architecture. We then translate these physical mechanisms into a sequence of curved microfluidic units that progressively amplify the separation of the two species and direct them toward distinct collection regions. Experiments with binary Quincke-roller mixtures confirm that an initially mixed suspension progressively demixes as it propagates through the device, leading to strong enrichment downstream. Our results demonstrate how collective active demixing can be converted into a functional continuous sorting strategy, providing a route toward autonomous microfluidic separation based on particle motility and confinement geometry.
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All authors Emanuel F. Teixeira, Thieu van den Bergh, Arjen Klok, Tijn Heesakkers, Alexandre Morin

Sunday 23 August

Applied Physics

UMEX Viewer - Software Suite for High-Speed AFM Data Analysis and Its Applications

Kenichi Umeda, Takahiro Watanabe-Nakayama, Yasuto Murayama et al. (+3 more)

Recent technical advances in atomic force microscopy (AFM) have led to the development of high-speed AFM (HS-AFM), which enables video-rate imaging and direct visualization of the nanoscale dynamics of biomolecules functioning in solution. Because HS-AFM rapidly generates large datasets, dedicated software is essential for efficient processing, organization, and analysis. Recent improvements in imaging speed have further increased data throughput, underscoring the need for faster analysis software with improved usability. To address this need, we developed Ultrafast Microscopy Exploration (UMEX) Viewer, a software suite for HS-AFM data analysis. UMEX Viewer provides an integrated environment for HS-AFM data handling, including image processing, drift correction, image and movie export, data management, and quantitative analysis. These capabilities have enabled the software to be applied to a wide range of recent studies. In this article, we describe the core functions of UMEX Viewer and demonstrate its practical applications for HS-AFM data analysis aimed at elucidating biological functions.
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All authors Kenichi Umeda, Takahiro Watanabe-Nakayama, Yasuto Murayama, Hiroki Konno, Mikihiro Shibata, Noriyuki Kodera

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

A Comprehensive Study of Charge-Carrier Mobility in Double Lateral-Gate Silicon Junctionless Transistors

Farhad Larki and Arash Dehzangi

We give in depth overview of charge-carrier mobility in p-type silicon double lateral-gate junctionless transistors (DLGJLT) through a mix of computer simulations and experimental results. The devices were built on low-doped silicon-on-insulator substrates using atomic force microscope nanolithography. Because the design uses air-gap side gates instead of a gate-oxide layer or junction, it allows electrical current to flow through a lightly doped silicon channel. This setup reduces impurity scattering and protects transport quality from interface damage. We used three-dimensional TCAD Sentaurus simulation tool to model the device's electrical behavior and confirm our experimental data for transconductance and drain conductance. We attempt to give a comprehensive view on the charge transition within the device.
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Saturday 22 August

Applied Physics

On the Fundamental Limits of Single-snapshot Compressive Ultrasound Imaging Using Random Aberrative Masks

Zehua Dou, Yaokuan Zhang, Jialong Zhang et al. (+3 more)

Compressive sensing emerges as a paradigm shift to realize real-time volumetric ultrasound imaging using a single element transducer equipped with an aberrative mask. Such a coded aperture encodes each scatterer in the FoV as a specific echo signal, compressing each volumetric into a time sequence that are reconstructed into image via computational methods. Compressive imaging (CI) can greatly reduce the data rate and simplify the electronics. Despite this potential, the practical performance of single-snapshot CI remains unclear, especially how it is influenced by mask design, imaging task complexity, and reconstruction strategy. For this, we separate the information budget provided by the mask from the algorithm-dependent extraction of the encoded information. First, the spatial impulse responses of random masks with different pixel sizes and time-delay ranges were calibrated, and the entropy-based effective rank of their similarity matrix was used to quantify the available encoding capacity. Masks with pixel size of approx. half wavelength and a time-delay range of two carrier periods provided higher encoding capacities, reaching up to 1.1% of the total sampled voxels. Algorithm-dependent information extraction was further evaluated for both ULM-motivated particle localization and B-mode imaging. For particle localization, L1-norm regularized least-squares method reconstructed particles corresponding to approx. 10% of the available encoding capacity, outperforming the matched filter. A transition from successful to failed reconstruction was observed when the number of particles exceeded this value, revealing the upper limit of the present CI systems using random masks. For B-mode imaging, LSQR achieved the highest SSIM among the evaluated methods, of up to 0.12, although the encoding capacity of the current random masks remained insufficient for high-fidelity reconstruction.
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All authors Zehua Dou, Yaokuan Zhang, Jialong Zhang, Cherif Othmani, Lars Büttner, Jürgen W. Czarske

Applied Physics · Cross-listed from physics.ins-det

An integrated micro-thermometer for mid-infrared photothermal spectroscopy of dense materials built in a CMOS 200 mm pilot line

Sandy Mathew, Sonia Messaoudène, Adrien Poizat et al. (+6 more)

Indirect photothermal infrared spectroscopy of dense materials typically relies on photoacoustic cells for detecting acoustic waves generated by light-induced heating. This detection approach can be challenging to implement as it is highly sensitive to the sealing quality of the interface between the cavity and the sample, as well as to the properties of the gas within the cavity. Here, we present a simplified and more robust method. This approach relies on direct photothermal temperature measurement using an optimized platinum microsensor fabricated on a thin silicon substrate that acts as a thermally transparent interface with the sample. The sensor design, fabrication in a 200 mm CMOS pilot line, assembly on a readout PCB, and experimental characterization are reported. The component achieves a signal-to-noise ratio close to 1000 making it well-suited for miniaturized and embedded infrared spectroscopic applications.
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All authors Sandy Mathew, Sonia Messaoudène, Adrien Poizat, Éléa Bourliaud, Marion Volpert, Jules Skubich, Stanislas Lhomme, Bertrand Bourlon, Kevin Jourde

Friday 21 August

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

Physics-integrated neural network modeling of heat and mass transfer in cryogenic liquid storage under static and dynamic conditions

Pedro Afonso Marques, Samuel Akatchi Ahizi and Miguel Alfonso Mendez

Accurate system-level prediction of cryogenic liquid storage remains challenging because reduced-order models rely on regime-dependent closures for unresolved heat and mass transfer, particularly under sloshing. We present a physics-integrated neural-network framework that combines a conservation-based zero-dimensional nodal model with data-driven closures for wall and interfacial heat transfer, phase change, pressurant quality, and liquid thermal-boundary-layer evolution. Thermal stratification and mixing within the liquid are represented through a first-order dynamical model for the boundary-layer thickness, while four operating-regime-specific neural networks infer the closure parameters for self-pressurization and relaxation, active pressurization, venting, and lateral sloshing. The framework was identified and evaluated using a dedicated database of 48 multi-stage cryogenic-tank experiments conducted in an optically accessible facility operated with liquid nitrogen. The experiments combine controlled wall heating, vapor injection and evacuation, and forced lateral sloshing, thereby covering both slowly evolving thermal states and strongly transient operating conditions. Generalization was assessed through experiment-level K-fold cross-validation, while an entropy-production penalty was included in the loss function to discourage violations of the second law of thermodynamics. Across the investigated cross-validation configurations, the global normalized root-mean-square error remained under 3%, with sloshing representing the most demanding regime. A final model trained on the complete database reconstructed the experiments with a global error of 1.6%. These results demonstrate that the proposed framework can extract physically interpretable and computationally efficient closure laws from a limited but information-rich experimental database.
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Applied Physics · Cross-listed from physics.comp-ph

Inverted model selection in physics-informed neural networks: when a lower residual selects a worse solution

Rabiu Musah

Physics-informed neural networks (PINNs) are commonly evaluated via a single aggregate residual, assuming a smaller residual indicates a better solution. Testing this directly across three constrained PDE systems, I find this assumption can systematically fail. In matched pairs of solvers differing only in whether a defining structural identity is hard-wired or penalized, the penalized variant frequently attains a lower equation residual while violating that identity by several orders of magnitude, causing the exact variant to be falsely ranked worse. Over 64 matched pairs spanning two systems, four network variants, and eight seeds, this inversion occurs in 83% of cases (95% Wilson CI: 72–90%), with rates from 72% to 94% across systems. Testing across six architectures–MLP, cPINN, XPINN, hp-VPINN, and physics-informed DeepONet and FNO–inverts the ranking in 46 of 48 pairs, indicating that this variability is problem-dependent rather than specific to the approximator. A third, larger vorticity–streamfunction problem shows the same ordering: the residual-optimal solver violates its structural identity by over six orders above tolerance, despite a residual margin of only 9.37%. Because a scalar loss cannot expose this, I introduce a lexicographic admissibility gate spanning the structural identity, boundary trace, and a solvability integral that must vanish independently of the equation residual. All three must pass before residuals can compete. This gate catches three artifact classes but misses a fourth: a prescribed-structure prior yields fields that pass every single-run check, yet deleting the source term reveals that 97% of the reported structure survives removal of the physics. Reference data and figures accompany the paper.
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Applied Physics · Cross-listed from physics.optics

Simultaneous Intensity and Frequency Control for Optical Waveform Generation using an Acousto Optic Modulator

Hariprasad Madathil, Shengzhi Wang and F. Elohim Becerra

We describe a method for calibrating the response of an acousto-optic modulator (AOM) to enable precise, arbitrary control of the intensity and frequency of optical fields. The method involves characterizing the nonlinear response of the AOM to its input RF drive voltage and applying an iterative calibration/correction algorithm to accurately map input RF amplitude and frequency drive to output optical intensity and frequency shifts. After a few calibration/correction iterations, the calibration of the AOM maintains the optical power within 1$\%$ of a constant target value over relatively wide frequency tuning range ($\approx$100 MHz), with $\sigma=0.2\%$ relative deviation. We apply this calibration method to generate programmable waveforms and optical pulses with tailored intensity and frequency profiles that closely match their target specifications. This technique offers a simple and robust method for applications that require high-accuracy optical modulation.
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Applied Physics · Cross-listed from cs.LG

Read, Write, Relax: Why Neural PDE Surrogates Need Both Global and Local Processing

Anuj Kumar, Heiko Zimmermann, Josiah Bjorgaard et al. (+4 more)

Recent mesh-based simulation advances have, in no small part, relied on neural surrogates of two distinct families: global models that route information through a small set of latent tokens, and local models that perform message passing across mesh edges. Consistent with both classes is the inability to perform beyond low-dimensional problems and small-scale or oversimplified meshes, the simulation regimes where industrial problems reside. Our work shows this explicitly and presents a unified formulation. In global approaches, latent-token attention acts as a spatial low-pass filter, while local message passing lacks the global reach necessary to propagate information across large mesh spaces. Viewed through the error, the two operators are the halves of a multigrid cycle: one corrects errors at the lower end of the spectrum, the other at the higher end, and neither can do the other's job. We introduce Read-Write-Relax (RWR), which interleaves latent attention with message-passing relaxation under a unified formulation. The interleaved processor lowers error across the entire spectrum, making RWR the most accurate model in nearly every comparison across our industrial and public benchmarks. It is also markedly data-efficient in the scarce-data regimes, accurate on the engineering quantities of interest, and scales full-field predictions to challenging, large-scale problems.
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All authors Anuj Kumar, Heiko Zimmermann, Josiah Bjorgaard, Jacan Chaplais, Nikolaos Bouklas, Matteo Salvador, Alexander Lavin

Applied Physics

Shaping liquids into space structures - microgravity-assisted design and manufacturing of minimal surfaces

Erez Hochman, Aaron Sprecher, Amos A. Hari et al. (+1 more)

This work advances a fundamentally new approach to space-based construction by using liquid self organization in microgravity as a generative design and fabrication principle. Building on the LiquiFab method, we demonstrate how minimal surface architectures - traditionally dependent on complex additive manufacturing - can instead emerge directly from the physics of fluid interfaces shaped by programmable boundary conditions. We present a simulation-to-fabrication workflow, that includes a boundary-driven minimal-surface solver integrated in Grasshopper/Rhino, and an experimental system that implements in a neutral buoyancy environment simulating microgravity. This enables the generation of customizable Schwarz-P-inspired with tunable geometry and thickness, illustrating a scalable pathway for material-efficient, on-orbit fabrication. To validate performance in true microgravity, a flight experiment on the International Space Station is scheduled for the first quarter of 2027 and we here detail the additional considerations required for this experiment.
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All authors Erez Hochman, Aaron Sprecher, Amos A. Hari, Moran Bercovici

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

Towards Ultra Scalability of Non-Volatile Magnetic Tunnel Junctions with a 3D Storage Layer

Nuno Caçoilo, Shunsuke Fukami, Olivier Fruchart et al. (+1 more)

The perpendicular Spin Transfer Torque Magnetic Random Access Memory is one of the most promising emerging non-volatile memory technologies, based on ultra-thin magnetic tunnel junctions. However, as these devices are limited by their thermal stability factor at technological nodes smaller than 20 nm, their scalability is compromised. A possible solution to this limitation relies on taking advantage of the shape anisotropy, by increasing substantially the thickness of the storage layer. Thanks to the combination of a vertical aspect-ratio and enhanced volume, high thermal stability can be maintained at sub-10 nm nodes. Here, we present the technological advancements and understanding of the magnetisation reversal that led to faster switching speeds at reduced switching voltage, providing a viable approach for dense arrays of ultra-small magnetic tunnel junctions.
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All authors Nuno Caçoilo, Shunsuke Fukami, Olivier Fruchart, Ioan-Lucian Prejbeanu

Thursday 20 August

Applied Physics

Electrostatic Influence of Diamond Heat-Spreaders on GaN FET Performance

Lincoln Hogan, MD Mazharul Islam and Ahmedullah Aziz

Diamond, with its exceptional thermal conductivity, is widely explored as a heat spreader to improve thermal management in GaN-based power and RF electronics. In this work, we use Sentaurus TCAD to model AlGaN/GaN HEMTs with integrated diamond heat spreaders, incorporating advanced physical models such as thermal boundary resistance (TBR) and temperature-dependent bandgap narrowing. While diamond significantly enhances heat dissipation, our simulations reveal an important but often overlooked tradeoff: electrostatic modulation at the diamond and semiconductor interface. We initially modeled a p-GaN HEMT with all-around diamond integration and show agreement to the experimentally reported electrothermal benefits of diamond heat spreader integration. However, we observe strong band bending at the diamond/GaN interface alongside electric field generation and increased valence band energy in diamond. As a result, an interfacial hole accumulation region forms at the GaN surface, altering vertical transport and hindering current injection which prevents high on-state current. These results indicate that although diamond improves thermal performance, it can also actively influence the electrostatics of the transistor. To address both the elevated TBR and the undesired interfacial band bending, we propose the incorporation of an engineered interlayer. Building on our Sentaurus TCAD results, we develop a Silvaco TCAD TLM test structure to characterize the extent of the hole accumulation region formation and give insight to future studies on mitigation through interlayer development.
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