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Monday 10 August

Applied Physics

A Concept of LNA with Low Input Impedance Using Common Base BJT for Low-Field MRI

Aleksei A. Nasonov, Mikhail V. Murzin, Nikolay V. Anisimov et al. (+4 more)

Purpose: In magnetic resonance imaging (MRI), preamplifier decoupling is used to improve the signal-to-noise ratio of a multichannel receive coil array. In low-field and ultra-low-field MRI, low-noise amplifier (LNA) solutions with low input impedance (LII) are poorly represented and consist mostly of field-effect transistors. We propose a low-cost LNA based on a common-base circuit with bipolar transistors to achieve LII (<5 Ohm), a low noise figure (<1.3 dB), and high gain (>30 dB). Methods: The proposed LNA circuits were simulated, fabricated, and tested at frequencies of 3 MHz and 21.2 MHz. The decoupling capabilities of the proposed LNA were experimentally evaluated, and MR imaging was performed in a 0.5T MRI scanner alongside a comparative study with a commercial LNA. At 3 MHz, the LNA was evaluated by analyzing free induction decay signals. Results: Proposed LNA solutions demonstrate a low noise figure below 1.3 dB with an input impedance of 3 Ohm. It was also shown that the presented LNA circuit enables high SNR values in MR imaging. The developed amplifiers demonstrate superior performance compared to available commercial options within the selected HF band. Conclusion: Due to the availability and cost-effectiveness of the selected transistors, the proposed LNA circuit is highly suitable for low-field MRI applications.
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All authors Aleksei A. Nasonov, Mikhail V. Murzin, Nikolay V. Anisimov, Vasily S. Severikov, Anna A. Dyatlovich, Anna A. Hurshkainen, Georgiy A. Solomakha

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

AES-Debye: an Accurate, Efficient, and Scalable Engine for Debye Scattering Calculations

Navid Panchi, Sebastian Kuckuk, Markus Wittmann et al. (+2 more)

Total scattering models are essential for characterizing the structure and disorder of nanoscale materials. The Debye scattering equation (DSE) provides a rigorous route to elastic total scattering, but its direct evaluation is computationally demanding because pairwise contributions must be accumulated at every scattering vector, whereas common acceleration strategies based on binned pair-distance distributions or gridded fast Fourier transforms can introduce discretization and aliasing artifacts that compromise diffuse-scattering accuracy. Here, we present AES-Debye, an accuracy-preserving DSE framework that aggregates pair distances into a pair distribution function (PDF) using corrected bin centers and numerically robust accumulation to suppress discretization and summation errors. A data-locality-aware parallel design enables efficient execution on CPUs and GPUs. We demonstrate strong scalability by computing a high-resolution total scattering profile for a system of 90 million atoms, $(0.1,\mu\mathrm{m})^{3}$, in minutes on a distributed-memory CPU platform. These capabilities extend accurate elastic total scattering calculations to large, complex systems while simultaneously providing high-resolution PDFs for downstream structural analysis.
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All authors Navid Panchi, Sebastian Kuckuk, Markus Wittmann, Michael Engel, Alberto Leonardi

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

Spatially resolved elastic strain and lattice rotation at threading dislocations in HgCdTe/CdZnTe epilayers by dark-field X-ray microscopy

C. Yildirim, A. Benhadjira, P. Ballet et al. (+5 more)

Threading dislocations (TDs) propagating from a Cd$_{1-y}$Zn$_{y}$Te (CZT) substrate into a liquid-phase-epitaxy Hg$_{1-x}$Cd$_{x}$Te (MCT) epilayer set the minority-carrier lifetime and dark-current floor of mid-wave infrared focal-plane arrays, yet at device-grade densities their local strain fields have been accessible only through topography, which conflates lattice tilt and elastic strain. We apply dark-field X-ray microscopy in reflection geometry to a \SI{7}{\micro\metre}-thick (111) MCT/CZT epilayer. Shallow Bragg angle and absorption makes the signal layer dominated while the numerical aperture of the objective keeps the layer and substrate rocking curves convolved, so weak-beam images on either side of the rocking curve and their difference image the correlated defects in a single frame: dot-like substrate TDs and the elongated, in-plane island features they nucleate in the layer. Kernel average misorientation resolves each TD as a \SI{7}{\micro\metre} signature, the layer thickness, alongside axial strain lobes of $\pm(4$ to $5)\times10^{-5}$.
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All authors C. Yildirim, A. Benhadjira, P. Ballet, T. N. Tran Caliste, J. Baruchel, C. Detlefs, D. Brellier, M. P. Kabukcuoglu

Applied Physics · Cross-listed from physics.optics

In-situ integrated nonlocal Huygens metasurfaces enable robust vortex beams from multimode fibers

Mingke Jin, Jieyu Zheng, Chaoyang Wang et al. (+4 more)

A fundamental hurdle for multimode fiber (MMF) integrated photonics is achieving robust and deterministic wavefront shaping against fiber perturbation, which induces random modal interference and scrambles the real-space output into speckle patterns. Existing wavefront shaping methods typically rely on pixelated phase or polarization pre-compensation, rendering them highly sensitive to fiber deformation. Here, we show that in-situ integration of a silicon nonlocal metasurface onto an MMF end facet enables direct conversion of arbitrary speckle patterns into optical vortex beams without pre-compensation. The metasurface supports overlapped Mie resonances and nonlocal bound states in the continuum (BICs), yielding high-transmission bands by satisfying the generalized nonlocal Huygens condition. Through momentum-space coupling between MMF modes and Huygens-BICs with topological polarization-vortex nature, the output maintains doughnut-shaped profiles under static and dynamic perturbations, demonstrating exceptional robustness against fiber deformation. This approach provides a compact, alignment-tolerant platform for robust structured light generation in MMFs for endoscopy, optical trapping and communications.
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All authors Mingke Jin, Jieyu Zheng, Chaoyang Wang, Yuhao Fang, Gongkai Zhang, Min Qiu, Jingyi Tian

Applied Physics

The Tilting Mode: A New Degree of Freedom for Magneto-Mechanical Resonator Sensors

Nora Timm, Florian Hartwig, Jonas Faltinath et al. (+3 more)

Magneto-mechanical resonators (MMRs) are an emerging class of passive, wireless sensors. Their torsional oscillation mode has recently been established for sensing and tracking applications. In this work, we report the identification and characterization of a second mechanical mode, the tilting mode, that provides sensitivity along an axis inaccessible to the torsional mode, opening up a new degree of freedom for tracking and sensing with a single MMR sensor. We derive an analytical model predicting the tilting frequency as a function of the geometric and magnetic parameters of the resonator, compare the tilting mode frequency to that of the torsional mode, and obtain a characteristic frequency ratio between the torsional and the tilting mode in the small angle approximation. Experimental characterization using three-axis excitation and detection confirms the mode's existence and its directional selectivity. Notably, the three-axis frequency response shows no observable cross-coupling between the torsional and the tilting mode. We further show that the tilting mode frequency follows the predicted dependence on magnet distance, confirming the analytical model and the mode's applicability for sensing, analogous to that of the torsional mode.
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All authors Nora Timm, Florian Hartwig, Jonas Faltinath, Sarah Reiss, Pascal Stagge, Tobias Knopp

Applied Physics

200 mm Wafer-Scale Monolithic 3D Integration of Atomic Layer-Deposited Oxide Semiconductors

Chang Niu, Linjia Long, Luqi Zheng et al. (+9 more)

Monolithic 3D (M3D) integration offers a pathway to overcome the scaling limits of conventional silicon complementary metal-oxide-semiconductor (CMOS) technology by extending dense vertical stacking of multifunctional logic and memory devices. Here, we demonstrate wafer-scale M3D integration of three tiers of atomic-layer-deposited (ALD) indium oxide (InOx)-based devices (>100,000 fabricated), including ferroelectric, enhancement-mode, and depletion-mode field-effect transistors, on 200 mm silicon wafers. We achieve threshold voltage standard deviation as low as 0.04 V, average electron mobility up to 91.6 cm2V-1s-1, and fully functional cross-tier circuits. A four-tier 3D computing-in-memory (CIM) accelerator targeting large language model workloads is developed using a custom InOx process design kit, delivering 1.4x to 2.9x speedup and comparable energy-delay product improvements over 2D baselines. These results establish ALD InOx M3D integration as a scalable and CMOS-compatible platform for next-generation artificial intelligence hardware and advanced electronics.
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All authors Chang Niu, Linjia Long, Luqi Zheng, Shuting Du, Jian-Yu Lin, Kisoo Nam, Zehao Lin, Chang Liu, Juanjuan Lu, Haiyan Wang, Haitong Li, Peide D. Ye

Applied Physics

A Superposition-Based Framework for Rapid Estimation of Arbitrary Antenna-Array Patterns

Amir Dayan, Nabeel Ali Khan, Inchara Lakshminarayan et al. (+4 more)

Antenna array theory is a well-established field. However, a systematic approach for fast pattern estimation in arrays with arbitrary antenna locations and orientations has not yet been developed. In this paper, based on simulated (or measured) radiation patterns of a single element, we present a Superposition-Based Framework (SBF) for numerically computing array radiation patterns in which the positions and orientations of the antenna elements can be readily modified. To validate the framework, a compact dual-layer circularly polarized patch antenna at 5.02 GHz (ESA's Celeste frequency) is designed and used as an array element in an 8-element ring antenna. Using the proposed framework and the single-element far-field pattern, the array radiation pattern is computed in 13s (excluding single-element simulation time), which is at least 50 times faster than the corresponding full-wave simulation while maintaining comparable accuracy. Comparisons with CST simulations show a peak E-field error of less than 0.5% for the intended polarization. Full-wave simulations are memory- and energy-intensive, and hence, impractical for larger arrays. The proposed SBF requires low computational power, making it energy-efficient and sustainable.
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All authors Amir Dayan, Nabeel Ali Khan, Inchara Lakshminarayan, Wahyudin Syam, Noori BniLam, William Whittow, Aakash Bansal

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

Coordinate-Residual Physics-Driven Neural Network for Inverse Scattering Imaging

Yutong Du, Zicheng Liu, Bo Qi et al. (+2 more)

Electromagnetic inverse scattering is a nonlinear and ill-posed computational imaging problem, where accurate reconstruction is challenging due to measurement limitations, noise, and high computational costs, especially for 3-D imaging. Although physics-driven neural networks (PDNNs) reduce the dependence on labeled training data, existing accelerated PDNN frameworks often rely on preliminary reconstruction-based region selection, which may introduce instability when the selected region is inaccurate. In this paper, a coordinate-residual physics-driven neural network (CRPDNN) is proposed for 3-D electromagnetic inverse scattering. CRPDNN represents the unknown complex contrast distribution using normalized spatial coordinates and a residual convolutional network, whose parameters are optimized by enforcing consistency between the measured and model-predicted scattered fields. Unlike existing subregion-accelerated PDNN approaches, CRPDNN does not require a preliminary reconstruction, thereby avoiding dependence on its accuracy. For the reported noise-free 3-D synthetic cases, CRPDNN achieves an average relative error of 2.10%, compared with 7.97% for CSI and 3.99% for $L_{2/3}$-FBE-WCIE, while providing approximately 5.5- and 12.1-fold speedups over the two baselines, respectively. Additional 2-D comparisons further demonstrate its stability and computational efficiency relative to existing PDNN frameworks. CRPDNN also maintains reliable reconstruction performance under noisy measurements, and the 3-D Fresnel experiments further indicate its potential for practical imaging applications.
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All authors Yutong Du, Zicheng Liu, Bo Qi, Yali Zong, Peixian Han

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

Magnetotransport evolution and nonlinear Hall effect in altermagnetic MnTe

Wei Zhou, Zhifeng Xue, Yunxing Li et al. (+6 more)

Hexagonal MnTe is a prototypical semiconducting altermagnet whose properties are heavily influenced by intrinsic disorder, yet how the resulting diverse transport regimes shape its magnetotransport behavior remains to be clarified alongside the role of relativistic spin-orbit coupling (SOC). Here, we present a systematic study of the anisotropic magnetoresistance (AMR), planar Hall effect (PHE), and nonlinear transport in MnTe bulk single crystals. Below the Néel temperature (TN ~ 304 K), the emergence of high-order harmonics in AMR and PHE within the high-temperature metallic regime reveals the interplay of magnetic order, crystalline symmetry, and SOC. At relatively lower temperatures, the disappearance of higher-order symmetries coincides with a transport crossover into the hopping conduction regime, suggesting that carrier localization diminishes the transport sensitivity to the Fermi-surface topology. In addition, we detect distinct second-order nonlinear Hall signals, providing evidence for a macroscopic inversion-asymmetric response in altermagnetic MnTe. Extending the investigations into the localized regime provides key insights into the subtle role of disorder and SOC in macroscopic charge transport. Our work thus underscores the necessity of exploring magnetotransport across diverse conducting regimes to comprehensively understand altermagnetic properties.
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All authors Wei Zhou, Zhifeng Xue, Yunxing Li, Nannan Tang, Ye Tao, Dingyong Zhong, Jiawei Luo, Donghui Guo, Huichao Wang

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

Openable Force-Balanced Halbach Magnets: From Fibonacci Sphere Simulations to Icosahedral Realizations

Ingo Rehberg, Helmut Soltner and Peter Blümler

A long-standing goal in magnet design is to completely surround a volume of highly homogeneous magnetic field with permanent magnets while maintaining practical access to that volume. In this work, we present a theoretical and experimental investigation of mechanically accessible spherical magnets in Halbach configuration that can be opened with minimal or vanishing force. Focusing on dipolar Halbach spheres composed of discrete magnetic subunits, we derive conditions for force-free opening along specific cutting planes. These conditions define a continuous set of geometries for which tensile magnetic forces cancel, leaving only shear components, enabling mechanically effortless opening. The theoretical predictions are validated experimentally using icosahedral approximations of the Halbach sphere, for which both opening forces and magnetic field properties are measured. The results demonstrate that excellent field homogeneity can be preserved while reducing opening forces by orders of magnitude. Although discussed in detail for the dipolar case, the theoretical framework is general and applicable to higher-order multipole Halbach systems. Finally, the concepts are extended to spherocylindrical Halbach configurations, highlighting their potential for large-volume, highly homogeneous, and mechanically accessible permanent-magnet systems for magnetic resonance
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Applied Physics · Cross-listed from cond-mat.mes-hall

Size-Dependent Band-Tail Localization in Oxide Semiconductors Revealed by Direct Density-of-States Mapping

Chang Niu, Kisoo Nam, Aravindh Shankar et al. (+5 more)

Disorder-induced localization is expected to become increasingly important as amorphous oxide semiconductor transistors are scaled toward low-dimensional channels, yet the electronic states responsible for this transport regime remain difficult to resolve experimentally. Here, we use a lock-in-based electric-field penetration technique to directly map the effective density of states (DOS) in In-based oxide semiconductor thin-film transistors (TFTs). The extracted quantum capacitance, carrier density, and chemical potential reveal a disorder-dominated transport regime in which band-tail states are not merely passive traps, but become screening-active and partially transport-active. Geometry-dependent DOS mapping shows an exponential suppression of the effective DOS with channel length, demonstrating size-dependent band-tail localization and providing a microscopic origin for a distinct localization-induced threshold-voltage roll-off mechanism. Temperature-dependent measurements show that the disorder-dominated DOS is strongly suppressed at low temperatures, while extended diffusive states remain nearly unchanged, confirming the localization origin. By tuning film thickness, O2 annealing, and In/Ga/Zn composition, we further demonstrate systematic suppression of disorder and effective-DOS localization. This work establishes direct DOS mapping as a device-level probe of localization physics and provides a pathway for engineering disorder in low-dimensional oxide semiconductor electronics.
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All authors Chang Niu, Kisoo Nam, Aravindh Shankar, Jian-Yu Lin, Sanjeev Khare, Sumi Lee, Pramey Upadhyaya, Peide D. Ye

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

Electronic conductivity in anharmonic crystals: Phonon dephasing in the electron-phonon interaction

Mingran Kong and Bartomeu Monserrat

The electron-phonon interaction underpins many material properties, for example, the conductivity of metals and the optoelectronic response of semiconductors. First-principles calculations of the electron-phonon interaction are a powerful tool to quantitatively describe many of these properties in increasingly complex materials. However, one key assumption of all calculations is that phonons have infinite lifetimes, an approximation that may break down when anharmonic phonon-phonon interactions are strong. In this work, we present a theory for the interaction of electrons with finite-lifetime phonons experiencing dephasing. Using a first-principles implementation of the theory, we find that anharmonic dephasing dramatically enhances electron-phonon scattering rates in metallic MgB2. Microscopically, phonon-phonon interactions create new scattering channels that increase the phase space available for electron-phonon scattering. As a result, anharmonic dephasing strongly suppresses conductivity in MgB2, bringing the calculated values substantially closer to experiment within the Boltzmann transport equation framework. This example establishes the importance of finite phonon lifetimes in the evaluation of electron-phonon scattering, and the microscopic mechanism suggests that anharmonic dephasing could play an important role in the conductivity of many metals. More broadly, our theory and first-principles implementation of anharmonic dephasing in the electron-phonon interaction provides a solid foundation to explore this regime in other materials.
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Applied Physics · Cross-listed from physics.optics

Population-inversion map of the mesospheric sodium ladder: continuous-wave and pulsed pumping schemes for directed emission

Yucheng Yang, Chunyang Lei, Kai Guo et al. (+2 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. We build a ten-level rate-equation model of the ladder from NIST transition probabilities and evaluate every electric-dipole line under four continuous-wave pumping schemes, both in a Doppler-averaged treatment and in a velocity-selective treatment appropriate for the collision-poor mesosphere. Three design-relevant results emerge. At practically accessible continuous-wave irradiances the column-gain exponents remain far below unity, consistent with published feasibility estimates; the value of the classification is to identify which lines, schemes, and pulse formats merit further study.
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All authors Yucheng Yang, Chunyang Lei, Kai Guo, Chi Peng, Zongpeng Pan

Applied Physics

Optimization of the Repumping Parameters for a Sodium Laser Guide Star Magnetometer

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

A sodium laser guide star operated as a mesospheric magnetometer modulates a 589 nm laser at the local Larmor frequency and usually diverts a fraction of its power to a repumping light that recovers atoms lost to the dark ground state.The polarization, read out for the most strongly driven velocity group, calls for 2.8 times the flux optimal fraction, and a shot noise figure of merit combining the two observables for 2 times, beyond the range commercial guide star lasers provide.
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All authors Yucheng Yang, Chunyang Lei, Kai Guo, Shuai Wang

Sunday 9 August

Applied Physics

Giant Rotational Meta-Doppler from Genetically Designed Superscatterers

Dmytro Vovchuk, Sergey Geyman, Konstantin Grotov et al. (+10 more)

The motion of a rigid body interacting with a wave leaves spectral signatures, with the Doppler shift as the dominant contribution. Since any motion can be decomposed into translational and rotational components, rotational Doppler provides additional information about the object's dynamics. In the electromagnetic domain, rotating objects generally produce rotational Doppler, or micro-Doppler, signals determined by the symmetry and spatial structure of the scattering process. For objects that are subwavelength or comparable in size to the wavelength, the response is typically dominated by the lowest dipolar scattering channel, so the leading spectral component commonly appears at twice the angular frequency. Here, we introduce the concept of artificially engineered rotational micro-Doppler by designing a compact, strongly scattering structure that operates through a high-order multipolar cascade of resonances, thereby producing a giant enhancement. Magneto-electric arrays composed of strongly coupled electric and magnetic resonators are optimized in the GHz range using a covariance matrix adaptation genetic algorithm to maximize the micro-Doppler frequency. Unlike conventional higher-order multipole designs used in superscatterers for a specific angle of incidence and polarization, our approach jointly optimizes excitation and scattering under radar-relevant conditions for a rotating blade. The resulting arrays exhibit a giant rotational meta-micro-Doppler response, exceeding the dipolar limit by two orders of magnitude and mapping rotations of tens of hertz into the kilohertz range. Beyond its fundamental significance, this mapping has practical value because it shifts rotor micro-Doppler signatures well above slow-moving radar clutter, thereby improving the detectability of slow motion.
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All authors Dmytro Vovchuk, Sergey Geyman, Konstantin Grotov, Dmitry Dobrykh, Andrey Machnev, Anna Mikhailovskaya, Susanna Rozental, Anton Kharchevskii, Mikhail Tsukerman, Vjaceslavs Bobrovs, Aviel Glam, Alexander Gumennik, Pavel Ginzburg

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

Time-Reversal-Invariant Altermagnetic Acoustic Crystals

Tianzhi Xia, Han-Rong Xia, Jinglin Liu et al. (+3 more)

Altermagnets have emerged as a new class of magnetic materials that combine spin-split electronic bands with zero net magnetization. Extending this paradigm to classical-wave systems has, however, been fundamentally challenging because conventional realizations require broken time-reversal symmetry (TRS). Here, we overcome this limitation by introducing two pseudospin degrees of freedom and constructing a pseudo-time-reversal operator that faithfully reproduces the action of its physical counterpart while preserving actual TRS. Building on this framework, we theoretically propose and experimentally realize the first time-reversal-invariant altermagnetic acoustic crystal. Acoustic measurements directly reveal pseudospin-dependent band splitting–a defining hallmark of altermagnetism–under strictly TRS-preserving conditions. Moreover, the altermagnetic acoustic crystal exhibits sublattice-pseudospin locking, enabling flexible control over acoustic pseudospin splitting and filtering. Our work establishes acoustic crystals as a versatile platform for exploring altermagnetic physics and opens new avenues for spin-inspired wave manipulation in nonmagnetic devices.
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All authors Tianzhi Xia, Han-Rong Xia, Jinglin Liu, Xiying Fan, Zebin Zhu, Zhen Gao

Applied Physics · Cross-listed from nucl-ex

High Precision Fundamental Physics Experiments at JLab with Spin-transparent Storage Rings of Low-energy Polarized Electron Beams

Vladimir Khachatryan, Riad Suleiman, Alberto Accardi et al. (+26 more)

A breakthrough in fundamental physics experiments measuring particle spin precession may happen if spin-transparent storage rings become adopted tools for such experiments. We present a new design of highly specialized table-sized storage rings, which use low-energy polarized electron beams and Mott polarimetry. Based on the spin transparency ansatz, the spin precession stemming from the magnetic dipole moment is canceled at any beam energy after an electron's turn along the periodic orbit in the ring. Meanwhile, a spin precession induced by the fundamental physics of interest, e.g., the electron's permanent electric dipole moment (EDM) and/or ultralight-dark-matter-mediated forces such as axions, will accumulate. However, capitalizing on such types of rings is not only desirable for measurements of EDMs and axion searches relevant to $CP$ violation and matter-antimatter asymmetry in the Universe, but may also find very promising applications in quantum computing.
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All authors Vladimir Khachatryan, Riad Suleiman, Alberto Accardi, Carlos Ayerbe Gayoso, Marco Battaglieri, Devesh Bhattarai, Silviu Covrig Dusa, Yaroslav Derbenev, Forrest Friesen, Joseph Grames, Paul Guèye, Tyler J. Hague, Ching Him Leung, Wenliang Li, Magno V.T. Machado, Preet Mann, Vasiliy Morozov, Son Nguyen, Michael Nycz, Howard Oh, Udit Raha, Mario Reig, Marco Schreck, Nathaniel Sherrill, Ye Tian, Zakia Tithi, Alexandre Vieira, Erik Wrightson, Zichen Yin

Applied Physics · Cross-listed from physics.optics

Fundamental limits of hot-carrier and photothermal plasmonic solar chemistry

Seungwoo Lee

Plasmonic catalysts convert sunlight through direct metal–adsorbate excitation, nonequilibrium hot carriers and photothermal heating, yet these channels lack a common efficiency limit analogous to the Shockley-Queisser (SQ) limit. Here, we formulate a channel-resolved detailed-balance theory for plasmonic solar chemistry. The theory enforces exclusive partition of absorbed power, microscopic reversibility, non-negative entropy production, electromagnetic passivity and causality, and one physical nanostructure shared by all wavelengths and operating states. A reduced tightly coupled cycle obeys a chemical diode law with closed-form stall and maximum-power free energies. It recovers a 33.68% single-threshold radiative limit and the 30.58% ideal single-junction water-splitting limit at a 1.23-eV chemical load, whereas a Fowler hot-carrier kernel lowers the limit to 8.53%. Finite one-structure benchmarks show that independent wavelength optimization overestimates shared-geometry performance by 6.6-33.8%, while cross-frequency correlations tighten semidefinite upper bounds by 21-56%. An exact multi-electron network yields a universal arrival-storage criterion and the low-flux scaling J_n\sim g^n\tau^{n-1}. A source-conditioned gold/p-type gallium nitride case study and a bias- and separation-complete ledger then distinguish enhanced product formation from net solar-energy conversion. The resulting framework provides a thermodynamically closed benchmark for hot-carrier and photothermal plasmonic chemistry.
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Applied Physics · Cross-listed from physics.optics

Simulating optical microcavities by inverting the thermal transfer function

Sudipta Nayak

I present a reduced-order approach for incorporating distributed thermal dynamics into nonlinear optical-microcavity simulations without repeatedly solving the time-dependent heat equation. A harmonic finite-element heat solve is used to obtain the thermal transfer function, which is introduced into the time domain through either a rational approximation or an impulse-response convolution. The method is validated against heat-equation-coupled finite-element simulations for prescribed TE1-mode heating and for nonlinear silicon microcavity dynamics. For the feed-forward TE1 tests up to 100 MHz and simplified cavity dynamics, the error remains below 4%. The reduced models reproduce the local self-pulsation dynamics, although long-time phase alignment is sensitive to the spatial definition of the thermal transfer function and to impulse-response truncation. These results establish a physics-based route for retaining multi-timescale thermal memory while substantially reducing the cost of coupled optical–thermal simulations.
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Saturday 8 August

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

Magnetoelastic coupling in stripe-domain states of yttrium iron garnet

Nimisha Arora, Daniel Prestwood, Takashi Kikkawa et al. (+4 more)

We study magnetoelastic coupling in stripe-domain magnetic states of $3\,\mathrm{\mu m}$-thick YIG thin films grown on a GGG substrate. Broadband ferromagnetic resonance reveals low-frequency stripe-domain magnon branches modulated by a field-independent phonon comb with a frequency spacing of $3.5\,\mathrm{MHz}$, matching the value predicted for confined thickness-shear modes of the GGG substrate. Analytical fitting yields coupling rates that vary between $0.33$–$0.54\,\mathrm{MHz}$ and cooperativities of order $10^{-1}$, indicating that the system is in the weak-coupling regime without resolvable avoided-crossing gaps. Magnon-phonon mode-overlap calculations using finite-element simulations show that the weak coupling arises from phase and domain-sign cancellation: the local magnetoelastic coupling is sizable, but more than $99\%$ of the coherent overlap cancels across the stripe texture. Fully coupled simulations further demonstrate phonon-mediated excitation of a remote YIG layer and show that efficient propagating-phonon generation requires spatially asymmetric magnon modes, establishing magnetic texture as a control parameter for magnon–phonon coupling.
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All authors Nimisha Arora, Daniel Prestwood, Takashi Kikkawa, Eiji Saitoh, Jack Gartside, Will Branford, Hidekazu Kurebayashi

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

Effects of high-pressure synthesis on phase formation and superconducting properties of PrFeAsO1-xFx

Priya Singh, Konrad Kwatek, Tatiana Zajarniuk et al. (+3 more)

Motivated by recent reports of enhanced superconducting performance in several families of iron-based superconductors (IBS) processed by high-pressure (HP) synthesis, we investigate the influence of high gas pressure and high-temperature synthesis (HP-HTS) process on the structural, microstructural, electrical transport, and magnetic properties of Pr-based oxypnictide PrFeAsO1-xFx (Pr1111) using the processing conditions of 0.5 GPa for 1 h previously optimized for other IBS families. Representative underdoped (x = 0.2), optimal doped (x = 0.3), and overdoped (x = 0.5) compositions from the ambient-pressure electronic phase diagram of Pr1111 are selected to evaluate its composition-dependent effects of HP-HTS. The results demonstrate that HP-HTS enhances fluorine incorporation, improves phase formation, and produces a denser microstructure with improved grain connectivity in the underdoped and optimal doped compositions. Magnetic measurements reveal increased in the superconducting transition temperature (Tc) of ~1 K for x = 0.2 and ~6 K for x = 0.3, whereas only a marginal improvement in the critical current density is observed. Electrical resistivity measurements of the underdoped composition show a slight increase in Tc accompanied by a broader resistive transition, indicating residual structural inhomogeneity. In contrast, the overdoped composition exhibits increased impurity phase segregation, accompanied by suppression of superconductivity. These results demonstrate that the effectiveness of HP-HTS in Pr1111 is strongly composition dependent and governed by the interplay among fluorine incorporation, phase stability, and microstructural evolution, highlighting the need for further optimization of the HP-HTS processing conditions.
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All authors Priya Singh, Konrad Kwatek, Tatiana Zajarniuk, Tomasz Cetner, Jan Mizeracki, Shiv J. Singh

Applied Physics

Measured LWC-Specific Fog Attenuation and Frequency Scaling in Low-THz Channels

Jiabiao Zhao, Xiaoxiang Li, Kefeng Huang et al. (+6 more)

Fog can reduce the link margin of terahertz (THz) wireless systems. Earlier channel measurements mainly relied on visibility, and almost no liquid water content (LWC) referenced attenuation coefficients have been reported. This letter reports controlled fog measurements at low-THz frequencies (120, 140, and 160 GHz) over a 22 m channel. LWC is retrieved from a time-aligned droplet size distribution (DSD) and paired with the fog-induced attenuation to obtain the relationship between attenuation and LWC at each frequency. The comparison with ITU-R P.840 is posed as an errors-in-variables problem. This separates the absolute coefficient from its frequency dependence - how the coefficient grows with frequency. Expressed as a power law of frequency, the measured exponent is 1.347, matching the value of 1.343 implied by P.840 at 20 oC. The results provide reference data and a compact scaling law for fog link budgeting at low-THz frequencies.
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All authors Jiabiao Zhao, Xiaoxiang Li, Kefeng Huang, Yapeng Ge, Hanchen Liu, Jie Yang, Weidong Hu, Houjun Sun, Jianjun Ma

Friday 7 August

Applied Physics

Slow dynamics in concrete: Effects of temperature, strength variation, and microcracking damage

Clayton Malone and Jinying Zhu

In this study, we investigated the slow dynamic behavior of concrete with varying compressive strengths ($f'_c = 32\sim56$ MPa) and alkali-silica reaction (ASR) damage. Concrete prisms were conditioned by compressive loading and recovery was monitored by coda wave interferometry (CWI). A self-referencing temperature correction technique was used to minimize the effect of ambient temperature changes, demonstrating the importance of careful temperature control and correction. For intact specimens, both the recovery rate, $m_v$, and velocity drop magnitude, $|c|$, generally increased with compressive strength. Recovery times were calculated from the fit parameters, and higher strength specimens were found to recover faster (9.9 h for $f'_c = 32$ MPa, 6.6 h for $f'_c = 56$ MPa). When the same stress was applied, ASR-damaged specimens had increased softening and faster recovery rates, but longer recovery times (up to 458 h). These findings demonstrate the potential of slow dynamics in concrete characterization, through its ability to evaluate the strength of intact samples and its sensitivity to microcracking in damaged samples.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci

Sn-Doping in LPCVD-Grown (010) $\beta$-Ga$_2$O$_3$ Films

Saleh Ahmed Khan, Ahmed Ibreljic, Sourav Sarker et al. (+1 more)

In this work, Sn-doped (010) $\beta$-Ga$_2$O$_3$ homoepitaxial films were grown by low-pressure chemical vapor deposition (LPCVD), and the influence of Sn incorporation on their structural, morphological, and electrical properties was systematically investigated. Controlled room-temperature carrier concentrations ranging from $1.17 \times 10^{17}$ to $3.06 \times 10^{18}$ cm$^{-3}$ were achieved, with corresponding Hall mobilities decreasing from 113 to 63 cm$^2$ V$^{-1}$ s$^{-1}$. The films exhibited the monoclinic $\beta$-Ga$_2$O$_3$ phase, near-stoichiometric composition, and well-defined step-flow morphology, with a minimum rocking-curve FWHM of 68.4 arcsec and an RMS roughness of 2.63 nm. Film thicknesses ranging from 1.66 to 11.3 $\mu$m were obtained at growth rates of 6.4 to 16.6 $\mu$m h$^{-1}$, demonstrating the ability of LPCVD to produce thick epitaxial layers. The sample with a room-temperature carrier concentration of $1.17 \times 10^{17}$ cm$^{-3}$ exhibited room-temperature and low-temperature Hall mobilities of 113 cm$^2$ V$^{-1}$ s$^{-1}$ and 380 cm$^2$ V$^{-1}$ s$^{-1}$ at 84 K, respectively. Both represent the highest reported values for LPCVD-grown Sn-doped $\beta$-Ga$_2$O$_3$. Transport modeling of the same sample yielded a shallow donor activation energy of 32.7 meV, a deeper donor level at 95 meV, and a low compensating acceptor concentration of $2.0 \times 10^{16}$ cm$^{-3}$, indicating efficient donor activation and a low degree of compensation. These results demonstrate that LPCVD enables controlled Sn doping while maintaining excellent structural and electrical quality, providing a viable route for realizing thick $\beta$-Ga$_2$O$_3$ epitaxial drift layers.
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All authors Saleh Ahmed Khan, Ahmed Ibreljic, Sourav Sarker, Anhar Bhuiyan

Applied Physics

Determination of acoustic nonlinearity parameters using thermal modulation of ultrasonic waves

Hongbin Sun and Jinying Zhu

This study presents a test method and its theoretical framework to determine the acoustic nonlinearity parameters ($\alpha,\beta,\delta$) of material using thermal modulation of ultrasonic waves. Temperature change induced thermal strain excites the nonlinear response of the material and modulates the ultrasonic wave propagating in it. Experimental results showed a strong correlation between the relative wave velocity change and the temperature change. With a quadratic polynomial model, the acoustic nonlinearity parameters were obtained from the polynomial coefficients by curve fitting the experimental curves. Their effects on thermal-induced velocity change were discussed. The parameters $\alpha,\beta,\delta$ govern the hysteretic gap, average slope, and curvature of the correlation curve, respectively. The proposed theory was validated on aluminum, steel, intact and damaged concrete samples. The obtained nonlinear parameters show reasonable agreements with values reported in the literature. Compared to other nonlinear acoustic methods using vibration or acoustic excitation, the thermal modulation method generates more uniform, slow changing, and larger strain field in the test sample. Employing thermal effect as the driving force for nonlinearity instead of an undesired influencing factor, this method can measure the absolute values of $\alpha,\beta,\delta$ with good accuracy using a simple ultrasonic test setup.
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Applied Physics · Cross-listed from cond-mat.mes-hall

Magneto-optical signal from $\mathrm{Co_2Mn}$-based Heusler thin films in MOKE and BLS

Anna Maria Friedel, Nicolas Fermon, Tobias Böttcher et al. (+3 more)

$\mathrm{Co_2Mn}$-based Heusler compounds offer a versatile, composition-tunable platform for magnonics and spintronics. Among them, the half-metallic $\mathrm{Co_2MnSi}$ is of particular interest for magnonics owing to its ultralow Gilbert damping, yet its weak magneto-optical response in the visible challenges optical probing such as Brillouin light scattering (BLS). We study the magneto-optical response of epitaxial $\mathrm{Co_2Mn}X$ films ($X = \{\mathrm{Al}_x\mathrm{Si}_{1-x}, \mathrm{Ga}_x\mathrm{Ge}_{1-x}, \mathrm{Sn}\}$) by magneto-optical Kerr effect (MOKE) spectroscopy and BLS. Angle-resolved MOKE resolves a significant, wavelength-dependent quadratic MOKE (QMOKE) only for $\mathrm{Co_2MnSi}$, whereas $\mathrm{Co_2MnAl}$, $\mathrm{Co_2MnGa}$ and $\mathrm{Co_2MnSn}$ respond dominantly linearly. Comparing BLS intensities of thermal magnons at two wavelengths, $\mathrm{Co_2MnSi}$ gives the weakest signal at 532 nm yet among the strongest at 457 nm, tracking the spectral dependence of its Kerr angle. These results emphasise the relation between the two magneto-optical techniques, guiding the choice of probing wavelength for $\mathrm{Co_2Mn}$-based Heusler compounds.
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All authors Anna Maria Friedel, Nicolas Fermon, Tobias Böttcher, Sébastien Petit-Watelot, Stéphane Andrieu, Philipp Pirro

Applied Physics

Roadmap on UV-C photodetectors: materials, applications and industry perspectives

Fabien Massabuau, Drew Riley, Paul Meredith et al. (+44 more)

UV-C photodetectors are poised to play an increasingly important role in future photonic technologies, driven by the rapid emergence of UV-C light sources and new wide bandgap semiconductors. These advances are enabling new levels of spectral selectivity, radiation hardness, sensitivity, and device integration, while opening opportunities across a broad range of applications. This roadmap provides a comprehensive overview of the current landscape of UV-C photodetection, spanning established and emerging material platforms (Ga2O3, AlGaN, BN, diamond, MgZnO, 2-dimensional materials, metal halide perovskites, micro-electromechanical systems), and their applications in metrology, astronomy, communications, environmental monitoring, fire detection, missile warning, gas sensing, and medical diagnostics. By identifying opportunities, bottlenecks, and future directions, this roadmap aims to support both newcomers and established researchers, with the aim of accelerating the translation of UV-C photodetectors into impactful technologies.
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All authors Fabien Massabuau, Drew Riley, Paul Meredith, Tilman Weiss, Damanpreet Kaur, Yuichi Oshima, Robert W. Martin, Eva Monroy, Le Chen, Hongwei Liang, Hong Yin, Keyun Gu, Meiyong Liao, Yaonan Hou, Fa Cao, Xiaosheng Fang, Ruiheng Li, Guoqiang Peng, Zhiwen Jin, Lijie Li, Nasim Zarrabi, Sebastian Wood, Jesper Skottfelt, Susan E. S. Spesyvtseva, Jonathan McKendry, Christopher G. Leburn, Daniel K. L. Oi, Ryan Pereira, Graeme Moore, Tom Lendrem, Christoph Wagner, David Maestre, Emilio Nogales, David J. Rogers, Eric Sandana, Michel Chamberlin, Ferechteh H. Teherani, Bianchi Méndez, Yana Suchikova, Marina Konuhova, Anatoli I. Popov, Luís F. da Silva, Eduard Llobet, Sangjin Yoon, Dohyung Kim, Sangwoo Hong, Seung Hwan Ko

Thursday 6 August

Applied Physics · Cross-listed from physics.optics

Grape expectations: direct thermographic imaging of electric fields in microwave Mie resonators

Kallan K. Ronholm, Yuchen Song and Aaron D. Slepkov

Internal electromagnetic fields determine the behaviour of dielectric nano-resonators, yet they remain exceptionally difficult to measure directly because subwavelength scales place them beyond conventional optical measurement, and any probe capable of local sensing perturbs the field it seeks to measure. We circumvent this limitation using water's high refractive index at microwave frequencies, which lets centimetre-scale aqueous spheres—grapes—serve as directly measurable, scale-invariant analogs of high-index nanophotonic resonators. Using polarization-controlled free-space excitation and infrared thermography, we show that internal heating patterns in grapes closely track simulated electric-, but not magnetic-, field distributions for both the fundamental magnetic- and electric-dipole Mie resonances. Extending this approach to grape dimers, we demonstrate that the massively sub-wavelength inter-object hotspot associated with microwave-induced sparking forms only under axial polarization, thus providing both a clue to its origin and a means for its control.
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Applied Physics

A 28-GHz Varactor-Based RIS With Continuous Phase Control: From Unit-Cell Modeling to Programmable Wavefront Control and Synthesis

Spandan Manna, Florian Reher, Karim El Isa et al. (+2 more)

This paper presents a 28 GHz varactor-based reconfigurable intelligent surface (RIS) platform with continuous phase control and establishes a unified device-to-system validation framework for programmable wavefront control and synthesis. The proposed RIS comprises 96 independently controlled elements, each employing a single varactor diode, with a board-integrated analog-bias control architecture. It builds on an experimentally validated unit-cell model providing approximately 300{\deg} of continuous reflection-phase tuning at normal incidence. An analytical framework incorporating measured horn illumination, finite phase availability, and unit-cell reflection losses consistently relates device-level characteristics to beamforming performance. It is evaluated via near-field-to-near-field characterization, near-field-to-far-field beam-steering, and far-field-to-far-field wireless-link experiments. The near-field-to-far-field results show close agreement among analytical predictions, full-wave simulations, and measurements, while the far-field-to-far-field response agrees with simulation and a first-order link-budget estimate. Accurate steering is demonstrated for all investigated angles within $\pm$45{\deg} across three azimuthal planes, with maximum deviation of approximately 2{\deg}. The complete prototype, including driver and bias network, draws only 0.85 W with an estimated full-aperture reconfiguration time of approximately 50 ms. Beyond beam steering, the same platform enables experimental investigation of 3-bit, 2-bit, and 1-bit phase quantization and programmable multi-beam wavefront synthesis using a common RF aperture and control architecture. Collectively, these results bridge realistic varactor behavior, analytical modeling, and programmable wavefront synthesis, providing a rigorous basis for developing and experimentally validating continuously tunable millimeter-wave RISs.
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All authors Spandan Manna, Florian Reher, Karim El Isa, Amar Al-Bassam, Dirk Heberling

Applied Physics · Cross-listed from astro-ph.EP

Asteroid Disruption and Deflection Simulations for Multi-Modal Planetary Defense

Alexander N. Cohen, Philip Lubin, Darrel Robertson et al. (+7 more)

Planetary defense from asteroids via deflective means alone does not offer viable solutions in terminal scenarios where there is little warning time before impact. The PI method of planetary defense enables operation in terminal interdiction modes where there is little warning time prior to impact, but can also operate in the same extended time scale interdiction modes as made possible by traditional deflection techniques, which results in a versatile, multi-modal planetary defense capability. The method is also practical and cost-effective since it relies solely on launch vehicles and penetrator materials already available today, and thus presents itself as a logical and competitive option for planetary defense. As per the PI method, we investigate the effectiveness of rubble pile asteroid disruption and deflection via hypervelocity impacts with 10:1 aspect ratio cylindrical tungsten penetrators. We present the results of an ongoing simulation campaign dedicated to investigating the PI method, using the Lawrence Livermore National Laboratory (LLNL) arbitrary Lagrangian-Eulerian (ALE) hydrodynamics code ALE3D run with the High-End Computing Capability (HECC) at NASA Ames Research Center. We model heterogeneous rubble pile asteroids with a distribution of spherical boulders of varying initial yield strengths set within a weak binder material. We find that rubble pile asteroids of this type in the 20 - 100 meter-class can be effectively mitigated via 20 km/s impacts with 100 - 1000 kg penetrators via the coupling of the penetrator kinetic energy into the bulk material of the asteroid.
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All authors Alexander N. Cohen, Philip Lubin, Darrel Robertson, Mark Boslough, Sasha Egan, Brin Bailey, Angela M. Stickle, Elizabeth A. Silber, Peter Meinhold, Dharv Patel