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Thursday 24 September

Applied Physics

Topological-Insulator Heterophase Gate Stacks for Transistor Electrostatics

Minuk Song, Jiwan Kim, MD Gius Uddin et al. (+25 more)

Conventional gate-stack scaling reduces dielectric thickness and increases permittivity while largely treating the position and electronic character of the gate-side screening boundary as fixed. Here we show that this boundary can be engineered by converting the surface of the topological insulator Bi\textsubscript{2}Se\textsubscript{3} into insulating high-$\kappa$ BiF\textsubscript{3}. Position-resolved calculations reveal a gap-opened immediate amorphous-BiF\textsubscript{3}/crystalline-Bi\textsubscript{2}Se\textsubscript{3} interface and a reconstructed gap-closed Bi\textsubscript{2}Se\textsubscript{3}-derived state in the adjacent subinterface layer, accompanied by a localized interfacial dipole. Capacitor measurements independently resolve a finite series response consistent with electronic compressibility at this boundary; this response lowers the nominal stack capacitance. Despite this capacitance penalty, MoS\textsubscript{2} transistors with closely matched BiF\textsubscript{3} thicknesses and a common BiF\textsubscript{3}/MoS\textsubscript{2} channel-side material interface exhibit near-thermionic-limit switching, negligible hysteresis and substantially weaker subthreshold drain-bias dependence than BiF\textsubscript{3}-only controls. These results identify the position and electronic character of the gate-side screening boundary as additional design variables for transistor electrostatics beyond nominal dielectric capacitance.
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All authors Minuk Song, Jiwan Kim, MD Gius Uddin, Wonseok Kim, Jihun Park, Han Uk Lee, Dong Won Jeon, Dohyung Lee, Lide Yao, Jouko Lahtinen, Gyunghyun Jang, Soohyun Min, Yonas Tsegaye Megra, Xiaoqi Cui, Seungwoo Choi, Yunyun Dai, Sang Hoon Chae, Keun Su Kim, Dong-Ho Kang, Hyeon-Jin Shin, Wooseok Song, Seth Ariel Tongay, Chul-Ho Lee, Manish Chhowalla, Sung Beom Cho, Zhipei Sun, Kibog Park, Hoon Hahn Yoon

Applied Physics

Integration of p-type Cr2O3 on Ultra-Wide Bandgap AlGaN PolFETs with 2.5 kV Breakdown Voltage

Jonathan Pratt, Yizheng Liu, Ijaas Mohamed et al. (+8 more)

We demonstrate UWBG AlGaN polarization-graded field-effect transistors (PolFETs) incorporating room-temperature sputtered p-type oxide Cr2O3 as a P-N heterojunction gate, enabling superior field management for lateral device breakdown compared to conventional Schottky gates. Devices using reverse-graded n-AlGaN contact layers achieved a record-low Rc of 0.56 {\Omega}-mm. The Cr2O3 gate exhibits a turn-on voltage VON > 3.5 V and a positive threshold voltage shift of +1.63 V relative to Schottky gates, displaying enhanced channel depletion from the P-N junction. Fabricated devices show high Imax (590 mA/mm) and ION/IOFF of 3x10^7. Devices exhibited state-of-the-art VBR > 2.5 kV with 11.2 m{\Omega}-cm^2 specific on-resistance (LGD = 9.55 um, average breakdown field > 2.5 MV/cm), while shorter gate-drain devices showed high breakdown fields up to 5.3 MV/cm with 0.28 m{\Omega}-cm^2 specific on-resistance. These results showcase sputtered p-Cr2O3 as a viable, low thermal budget P-N junction gate technology for high-Al-composition AlGaN transistors in RF and power electronics.
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All authors Jonathan Pratt, Yizheng Liu, Ijaas Mohamed, Seungheon Shin, Akilesh Srikanth, Md Saklain Morshed, Brianna A. Klein, Andrew Armstrong, Andrew A. Allerman, Sriram Krishnamoorthy, Siddharth Rajan

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

Spin-Polarized Magnetic Metal Electrodes for Magnetic Tunnel Junctions

Zhiyuan Duan, Peixin Qin, Li Liu et al. (+7 more)

Magnetic tunnel junctions are foundational components of spintronic memory, sensing, and computing, and their performance depends critically on the magnetic metallic electrodes. This Perspective examines electrode materials through the lens of magnetic order and the distinct microscopic mechanisms that generate spin-selective tunneling. Conventional ferromagnets, including CoFeB and half-metallic Heusler alloys, support exchange-split electronic states and symmetry-filtered tunneling, whereas compensated collinear and noncollinear antiferromagnets exploit sublattice selectivity, spin-orbit anisotropy, vector spin textures, and magnetic multipoles. Altermagnets provide a collinear, zero-net-moment route based on symmetry-allowed momentum-dependent spin splitting. Across these material classes, we compare the origins of tunneling polarization, the roles of barrier evanescent states and interface termination, and strategies for electrically writing and reading the relevant magnetic order. This comparison reveals a broader design principle: effective electrode polarization is not a scalar bulk quantity, but a momentum-, orbital-, symmetry-, and interface-resolved transport property. Beyond the pursuit of ever larger tunneling magnetoresistance, future progress will depend on converting the unconventional spin polarization of emerging magnetic metals into electrically addressable, thermally robust, and reproducible tunneling functionality at realistic interfaces.
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All authors Zhiyuan Duan, Peixin Qin, Li Liu, Guojian Zhao, Sixu Jiang, Xiaoyang Tan, Jingyu Li, Xiaoning Wang, Ziang Meng, Zhiqi Liu

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

Cavity-waveguide coupling in phononic crystals

Jakub Rosiński, Benjamin Mayer, Hubert J. Krenner et al. (+1 more)

Phononic crystal platforms provide a promising route toward scalable on-chip quantum networks, where mechanical excitations mediate interactions between solid-state qubits. A key building block of such architectures is the cavity-waveguide system, in which localized mechanical modes couple to propagating phononic modes. However, a quantitative understanding of the mechanisms governing this coupling remains incomplete. In this work, we investigate the interaction between localized modes of snowflake-type phononic crystal cavities and a phononic crystal waveguide using finite-element simulations and experimental measurements. We show that the coupling strength is primarily governed by the spatial overlap between the displacement fields of the corresponding isolated cavity and waveguide modes. After accounting for the effective-mass dependence of the normalized cavity displacement amplitude, we establish a strong correlation between the spatial overlap and the interaction strength across a wide range of mode combinations. Deviations from this leading-order behavior are associated with Bloch-phase effects, variations in waveguide group velocity, and intrinsic hybridization of waveguide modes. Furthermore, we provide experimental evidence for cavity-waveguide coupling in a GaAs phononic crystal membrane by observing a clear resonance in the spectral broadening of the photoluminescence emission from an embedded quantum dot, which serves as a local probe of the mechanical field. The observed resonance at approximately 398 MHz is in good agreement with the corresponding cavity resonance near 395 MHz predicted by finite-element simulations. Our results identify spatial mode overlap as a leading-order design parameter for cavity-waveguide coupling and provide practical guidelines for controlling interactions between localized and propagating modes in phononic crystal structures.
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All authors Jakub Rosiński, Benjamin Mayer, Hubert J. Krenner, Paweł Machnikowski

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

Microscopic origin of the Baumgärtel-Schausberger-Winter Relaxation Spectrum in Polymer Melts and Particle Rafts

Dario Nichetti, H. Henning Winter and Alessio Zaccone

Entangled polymer melts exhibit the robust two-branch Baumgärtel-Schausberger-Winter (BSW) relaxation spectrum, while related spectra occur in nonpolymeric monodisperse disordered systems. In spite of the successful application of BSW to many different materials, a molecular derivation of these spectra is lacking. We construct a molecular theory in which a chain segment moves relative to a screened, dynamically responding multichain environment. Gaussian-chain preaveraging gives $M_{\rm seg}(\Delta m)\sim(\Delta m)^{-1/2}$, hence $\lambda_p\sim p^{3/2}$ and, after stress projection, $H(\tau)\sim\tau^{-2/3}$. Independently, longitudinal primitive-path diffusion gives contour-length fluctuations with $H(\tau)\sim\tau^{1/4}$. A molecular-weight-constrained implementation is tested simultaneously against experimental $G'(\omega)$ and $G''(\omega)$ data for four monodisperse polybutadiene (PBD) melts, without fitting spectral exponents or individual modal weights. The resulting BSW spectrum exhibits a continuous transfer from the fast cooperative to the slow constraint-renewal cascade before a finite-chain terminal edge. A common two-sector caged dynamics then connects polymers to particle rafts without assuming identical microscopic mechanisms.
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Applied Physics

Dynamical Diversity for Reservoir Computing in Reconfigurable Nanomechanics

Humayun Ahmed, Inês S. Garcia, Filipa C. Mota et al. (+7 more)

Physical reservoir computing uses nonlinear dynamics and a trained linear readout to process information. Nanoelectromechanical (NEMS) resonators combine geometric Duffing nonlinearity with fading memory, but most electromechanical implementations use a single resonance mode. Here, we demonstrate reservoir computing with two interacting modes of a single NEMS resonator measured through one readout port. We introduce dynamical diversity through complementary modal drive settings: the same input sequence is replayed under different allocations of drive amplitude between the modes, and the responses are concatenated into a single feature matrix. This multiplexing expands the representation available to the readout without additional devices or training of internal parameters. On NARMA-2, it reduces variance-normalized test error more than 28-fold relative to single-mode operation and more than threefold relative to the best individual two-mode setting. Linear memory-capacity measurements show that accessible recall spans only a few symbols at the tested symbol duration. Its rapid decline with delay, consistent with mechanical dissipation, accompanies rising NARMA error and the eventual loss of multiplexing gains at higher orders. We also use electrical feedthrough as an internal reference for assessing the computational contribution of the NEMS response. Separate linear readouts are trained on feedthrough features and features derived from the measured NEMS response, using the same recordings and matched drive settings and processing. On challenging nonlinear mapping tasks, the multiplexed NEMS features yield substantially lower errors than the feedthrough features. These results demonstrate how dynamical diversity through variations in modal drive amplitudes expands the computational capability of a single multimode NEMS resonator.
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All authors Humayun Ahmed, Inês S. Garcia, Filipa C. Mota, Muhammad Asim, Ghaith Mahook, Suleyman Celik, Yunus Selcuk, Filipe S. Alves, Alper Demir, M. Selim Hanay

Applied Physics · Cross-listed from quant-ph

A low-temperature entropy source for on-chip true random number generation: universal robustness beyond device quality

Y. Q. Chai, M. Y. Wang, X. N. Feng et al. (+1 more)

True random number generation is a critical capability for fault-tolerant quantum computing at millikelvin temperatures. Yet existing Josephson-junction-based TRNGs all rest on a widely accepted but untested assumption: that reliable entropy extraction requires precisely controlled device parameters. Here we show that this assumption does not always hold. We demonstrate a counterintuitive finding: a single current-biased Josephson junction, regardless of its parameter quality, can serve as a cryptographic-grade true random number generator. To establish the universality of this conclusion, we deliberately selected the most extremely deviated devices from fabrication, with critical currents three orders of magnitude away from theoretical predictions and $I_cR$ products an order of magnitude above conventional values, as the ultimate stress test. Even under these extreme conditions, the raw Shannon entropy reaches 0.9981~bit (99.8% of the theoretical maximum), with a min-entropy of 0.9271~bit. Using a square-wave pulsed-bias scheme, we tune the switching probability to $P\approx0.5$. After SHA-256 post-processing, the bitstreams pass all 15 NIST SP 800-22 tests under a conservative $m=3$ criterion that is more demanding than the standard recommendation, and this certification holds across the entire 100-700~mK operating window of a dilution refrigerator.
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All authors Y. Q. Chai, M. Y. Wang, X. N. Feng, L. F. Wei

Applied Physics · Cross-listed from physics.optics

Zero-forward Kerker scattering via synthesized complex-frequency excitation

Jianfei Liu{\dag}, Zheng Gong{\dag}, Ao Li et al. (+3 more)

All objects illuminated with light inevitably cast a shadow – a universal phenomenon encapsulated in the fundamental property that all passive systems with plane-wave illumination feature a non-zero forward scattering amplitude. Since Kerker's landmark 1983 paper, considerable effort has been devoted to overcoming this limitation and achieving the elimination of forward scattering – an objective now widely known as the zero-forward Kerker scattering. However, this objective is fundamentally restricted to active systems, requiring either physical gain in materials or virtual gain in the excitation source. Despite advances in active materials science and non-Hermitian photonics, the experimental realization of zero-forward Kerker scattering still remains an open challenge. Here, we show, both theoretically and experimentally, how zero-forward Kerker scattering can be effectively synthesized by a weighted superposition of readily accessible real-frequency responses. Our synthetic recipe builds on creating an artificial pole at a complex frequency that prevails over inherent scattering poles. These findings not only unlock a realistic experimental framework for non-Hermitian light-matter interactions, but also hold technological relevance for non-invasive sensing and imaging.
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All authors Jianfei Liu{\dag}, Zheng Gong{\dag}, Ao Li, Hongsheng Chen, Stefan Rotter, Xiao Lin

Applied Physics · Cross-listed from cs.LG

Growth-Inspired Graph Generation and Inverse Design of Mechanical Lattices via Dot Matrices Database Augmentation and GCNN

Weiyun Xu and Jiamu Liu

Natural load-bearing and transport networks are not assembled in a single step; they emerge through a temporally ordered process of growth, branching, reinforcement, and loop formation. Inspired by this developmental logic, this work introduces a morphogenetic graph-generation framework for mechanical lattices in which a discrete dot matrix provides potential nodes and the final architecture is created by sequential cross-layer and intra-layer growth. The same rule is visualized in two dimensions as a leaf-vein-like developmental sequence and implemented in three dimensions on a 3x3x3 nodal matrix containing 27 candidate nodes. A dataset of distinct three-dimensional lattices was evaluated by beam-based finite element analysis and represented directly as graphs. A graph convolutional neural network (GCNN) with three graph-convolution layers and dual global pooling learns the topology-property mapping and predicts effective compressive stiffness. Coupling the GCNN surrogate with rapid structural sampling enables inverse design: for a target stiffness of 1000 MPa, the selected design was predicted at 1042.43 MPa and validated by finite element analysis at 1027.49 MPa. Beyond straight members, the framework has also been extended to parameterized horseshoe-shaped curved beams made of nonlinear materials, enabling topology-geometry design toward prescribed deformation shapes. Our work provides a paradigm for augmenting the database of mechanical metamaterials, and the resulting perspective links biological morphogenesis, graph learning, and nonlinear shape programming in a unified generative design framework for architected materials.
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Applied Physics

Teaching an LLM agent to fit XRR curves with X-Ray Calc 3

Oleksiy V. Penkov, Jingjing Peng and Haoyu Fu

The structure of a periodic multilayer X-ray mirror is obtained by fitting its X-ray reflectivity (XRR) curve, and the result depends on how the operator normalizes and trims the curve, frees parameters, and accepts a fit. The manual of the fitting program and the papers describing its engine leave these decisions to the operator, whose practice is tacit, so the fitting stays with the expert. To solve this problem, we proposed to develop a skill for a large language model (LLM) agent via elicitation: the expert's decisions were recorded during fitting and written as thirteen steps and a 22-item report template. The agent runs X-Ray Calc 3 through a Model Context Protocol (MCP) tool server. Fresh sessions, each given the skill, one curve, and a nominal design, were scored against fits the expert had withheld, under six tolerances fixed beforehand. The skill was developed on XRR curves of Co/C mirrors and of Ru/C mirrors from a public data deposit. The final version of the skill was tested on W/B4C multilayers. It was demonstrated that the skill recovered the mean period within 0.3 Å of the expert's fits and the period drift through the stack on both W/B4C specimens, and the W and B4C thicknesses within 1 Å on one of them.
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Applied Physics · Cross-listed from physics.ins-det

Characterization and Active Control of Position-Dependent Timing Dynamics in Superconducting Strip Single-Photon Detectors

Sahil R. Patel, Kristen M. Parzuchowski, Eli Mueller et al. (+6 more)

Superconducting strip single-photon detectors (SSPDs) have emerged as scalable, wide-strip variants of traditional nanowire counterparts. Despite practical advantages including improved optical fill factors and enhanced signal-to-noise ratios the fundamental detection physics governing these micro-scale geometries remains largely unexplored. Here, we investigate the underlying photoresponse of a 20 um-wide tungsten silicide SSPD, demonstrating a slew-rate-corrected timing jitter of 13.2 ps at 532 nm and 20.5 ps at 1550 nm, alongside saturated internal detection efficiency up to 1550 nm. Using focused free-space optical scanning, we reveal that detector timing jitter is strongly influenced by a spatially dependent slew rate between edge and center absorption events. To mitigate this impact, we utilize a parallel superconducting rail architecture to actively redistribute supercurrent. This in-situ tuning minimizes the latency mismatch and mitigates thermally activated intrinsic dark counts, extending the device's ability to operate at higher temperatures. Finally, comparing these dynamics with time-dependent Ginzburg-Landau (TDGL) modeling elucidates the physical origins of the position-dependent photoresponse, highlighting how superconducting rails or specialized readout electronics can mitigate negative impacts on timing jitter.
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All authors Sahil R. Patel, Kristen M. Parzuchowski, Eli Mueller, Boris Korzh, Emanuel Knehr, Adam N. McCaughan, Martin J. Stevens, Matthew D. Shaw, Jason P. Allmaras

Wednesday 23 September

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

Shape matters: DEM investigation of geometry-controlled mechanical response in irregular rock fragments under static and dynamic loading

Athena Bahramiyarahmadi and Rick Chalaturnyk

Mechanical characterization of subsurface rock formations typically requires standardized cylindrical core specimens, which are often unavailable from fractured or unconventional reservoir sequences. This study uses a Discrete Element Method (DEM) framework calibrated to Sulphur Mountain Formation siltstone to investigate how fragment geometry governs mechanical response in irregular rock particles, which are direct analogues of drill cuttings. Nineteen specimens (18 procedurally generated irregular geometries and one reference Brazilian disk), normalized to a 10 mm bounding sphere radius, were tested under quasi-static (Brazilian-type) and dynamic (Short Impact Load Cell) loading modes. Four mechanical outputs of failure force (Ff), apparent strength ({\sigma}f), apparent stiffness (Ka), and stiffness (E) were regressed against seven retained shape descriptors. Results show that force-based quantities are strongly controlled by the surface-area-to-volume (SA/V) ratio under static loading (Adj. R2 = 0.69), while area-normalized quantities ({\sigma}f and E) are geometrically insensitive. Dynamic loading amplifies geometric sensitivity for failure force and introduces an independent role for surface concavity depth. These findings establish a preliminary quantitative framework for interpreting mechanical measurements from irregular rock fragments when a standardized core is unavailable.
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Applied Physics · Cross-listed from physics.optics

All-Dielectric Ceramic 3-D Printed Unidirectional Leaky-Wave Antenna at mm-Wave Frequencies

Guillaume François, Masoud Sakaki, Henrik Jansen et al. (+3 more)

An all-dielectric leaky-wave antenna, radiating unidirectionally at broadside without the use of a metallic ground plane, is designed and manufactured. It operates in the 70-90 GHz frequency range with a design broadside frequency of 77 GHz. The design process makes use of the theory of photonic bandgaps to position a -1 harmonic at the broadside frequency on the second Bragg-condition point. The structure is then modified to close the bandgap and to simultaneously guarantee maximum total field coupling to the relevant radiating harmonic, ensuring radiation unidirectionality. The antenna is manufactured with an Al2O3 ceramic printing process, demonstrating its manufacturing potential for complex low-loss high-frequency structures. Simulations agree well with measurements, with the main deviation being a 1 GHz frequency shift that could be reproduced in simulation. The antenna prototype shows a scanning range of -18{\deg}-22{\deg} and gain values above 23 dBi. More than 85 % of the radiation power is radiated unidirectionally at broadside, with simulations showing potential to attain 98 %.
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All authors Guillaume François, Masoud Sakaki, Henrik Jansen, Amar Al-Bassam, Niels Benson, Dirk Heberling

Applied Physics

Thermoreflectance-Based Techniques for Micro- and Nanoscale Thermophysical Property Measurements: Principles, Methods, and Recent Advances

Puqing Jiang, Shanshan Chen, Xiaobo Li et al. (+1 more)

As semiconductor devices shrink toward the nanoscale, heat transport and thermal-energy-storage behavior in materials and interfaces become increasingly dependent on length scale, structure, and interfaces. Accurate characterization of thermophysical properties, including thermal conductivity, interfacial thermal conductance, and volumetric heat capacity, is therefore essential for functional-material design and thermal management of advanced electronic devices. Photothermal thermoreflectance techniques provide noncontact measurements with high spatial and temporal resolution and a broad measurement range, making them important tools for micro- and nanoscale thermophysical characterization. This review examines the physical principles and technical characteristics of transient thermoreflectance (TTR), time-domain thermoreflectance (TDTR), frequency-domain thermoreflectance (FDTR), steady-state thermoreflectance (SSTR), spatial-domain thermoreflectance (SDTR), and the square-pulsed source (SPS) method. A unified heat-diffusion framework is established to compare these methods in terms of parameter sensitivity, measurement uncertainty, and applicability. Representative applications illustrate their suitability for low-thermal-conductivity materials, anisotropic films, crystalline materials, and multilayer heterostructures, as well as their complementary capabilities for characterizing thin-film thermal conductivity, interfacial thermal conductance, and in-plane/cross-plane heat transport. Finally, emerging directions are discussed, including ultrahigh spatiotemporal resolution, multiphysics coupling, in-line industrial inspection, intelligent data processing, and natural-language-driven analysis.
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All authors Puqing Jiang, Shanshan Chen, Xiaobo Li, Ronggui Yang

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

Integration of Retrieval-Augmented Generation for Knowledge Access in the ELBE Accelerator Control System

Najmeh Mirian

The efficient operation of accelerator facilities increas- ingly relies on rapid access to heterogeneous operational knowledge, including logbooks, interlock reports, machine parameters, and historical archive data. At ELBE, we pro- posed a Retrieval-Augmented Generation (RAG) frame- work that integrates facility documentation and operational records into a unified AI-assisted support tool for operators. The system is expected to index electronic logbooks, ma- chine archive time-series data, and subsystem manuals using domain-adapted embeddings stored in a vector database. User queries will be expected to be processed through a large language model that retrieves the most relevant oper- ational context and generates structured, operator-oriented responses with traceable source references. This contribu- tion presents the system architecture, data integration strat- egy, and challenges toward real-time AI-assisted accelerator operation
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Applied Physics · Cross-listed from physics.optics

Spectral Lock-in Detection for High-Sensitivity Spectroscopy

Szu-An Tsao, Joseph J. Hwang and Mona Jarrahi

The ability to recover weak signals without sacrificing their spectral information is central to precision spectroscopy, yet conventional lock-in detection achieves noise rejection at the expense of spectral dimensionality and ultimately imposes a trade-off between detection bandwidth and sensitivity. Here, we introduce spectral lock-in detection, a versatile framework that extends lock-in noise rejection independently to every resolved component of a broadband spectrum. By separating the fast-time coordinate encoding spectral information from the slow-time coordinate carrying temporal modulation, the measured waveform is spectrally resolved before demodulation, enabling each frequency channel to be independently detected and integrated. We show analytically that, for spectrally stable signals, the signal power in each spectral channel remains invariant, while the noise power ideally decreases by 10 dB per decade of integration time, enabling spectral features buried beneath the instantaneous noise floor to emerge without loss of frequency information. We experimentally validate this framework in both phase-incoherent heterodyne terahertz spectroscopy and phase-coherent terahertz time-domain spectroscopy, demonstrating more than six orders of magnitude of sensitivity enhancement across the spectrally resolved channels. Because spectral discrimination is performed computationally on the acquired waveform, the approach requires neither sequential spectral scanning nor additional spectral-selection, multichannel-detection, or interferometric hardware. Spectral lock-in detection therefore provides a broadly applicable route to enhancing sensitivity across diverse spectroscopic platforms and frequency regimes, opening new opportunities for high-sensitivity, information-rich measurements across the electromagnetic spectrum.
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Tuesday 22 September

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

Detecting a large magneto-optical shift in Py/NiO bilayers

Adrielson Dias, Maria Clara, Ozéas Rodrigues et al. (+3 more)

Here, magneto-optical magnetometry measurements on Py/NiO bilayers reveal a pronounced magnetic-field-induced wavelength shift, demonstrating strong magneto-optical coupling in this antiferromagnetic system. A systematic and monotonic spectral shift of up to ~ 400 nm is observed as the applied magnetic field increases, saturating at higher fields. Quantitative analysis shows that the associated magneto-optical energy variation is on the order of 107 eV, comparable to the magnon energy scale in NiO. Owing to the large NiO thickness, the observed effect originates from magnons intrinsic to the antiferromagnetic NiO layer rather than from spin currents injected by the Py underlayer. These results provide direct experimental evidence for magnetic-field control of antiferromagnetic magnon energies via magneto-optical interactions, establishing Py/NiO bilayers as a promising platform for optically probing and manipulating antiferromagnetic spin dynamics.
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All authors Adrielson Dias, Maria Clara, Ozéas Rodrigues, Gabriel Henrique, José Lucas, José Holanda

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

Resonantly Enhanced Phonon Transport by Magnon Pumping in a Ferromagnetic/Piezoelectric Bilayer

André José, Carlos Eduardo, Adrielson Dias et al. (+2 more)

We report the first experimental observation of resonantly enhanced propagating phonon transport induced by magnon pumping in a ferromagnetic/piezoelectric bilayer. Surface acoustic waves (SAWs) generated in a 128$^{\circ}$ Y-cut LiNbO$_3$ delay-line device resonantly excite magnetization dynamics in an adjacent Co film through magnetoelastic coupling. The enhancement of the transmitted acoustic signal occurs exclusively when the SAW frequency satisfies the ferromagnetic resonance condition predicted by the Kittel dispersion, providing a direct experimental fingerprint of resonant magnon-phonon coupling. A systematic comparison between the Co/LiNbO$_3$ bilayer and the bare LiNbO$_3$ substrate demonstrates that the observed transmission enhancement originates solely from the dynamic interaction between propagating phonons and coherent magnetization precession. Furthermore, measurements performed at different SAW harmonics reveal that only the harmonic satisfying the FMR condition produces a measurable enhancement, confirming the frequency-selective nature of the phenomenon. These findings establish an efficient mechanism for transferring energy from magnons to propagating phonons and provide a new strategy for actively controlling coherent acoustic transport in hybrid spintronic, straintronic, and quantum phononic platforms.
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All authors André José, Carlos Eduardo, Adrielson Dias, José Araújo, José Holanda

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

Investigation of Widefield NV-Center Magnetic Imaging for Non-Destructive Materials Testing

Niklas Mathes, Marvin Feuerhelm, Simon Philipp et al. (+7 more)

Due to progressing miniaturization, material fatigue is expected to gain importance on microscopic scales. Nevertheless, most non-destructive testing techniques are optimized for macroscopic scales. Therefore, new approaches applicable to miniaturized samples need to be explored. High spatial resolution imaging of a material's magnetic stray field enables sensitive detection of microstructural changes due to the local interplay of magnetic properties, strain, and defects. Up to now, this approach has rarely been used for materials testing since high-resolution magnetic sensing is traditionally challenging. Novel quantum sensing techniques offer the potential to close this gap. One of the most prominent quantum sensors, the nitrogen vacancy center in diamond, is investigated for non-destructive testing applications within the scope of this work. An experimental system based on a widefield sensing approach was developed to image magnetic stray field distributions within seconds to minutes over areas up to 1 x 1 $mm^2$. Magnetic sensitivities below 10 $\mu$T/$\sqrt{\text{Hz}}$ and a spatial resolution of 1-2 $\mu$m were achieved. The technique offers high mechanical stability, which is crucial for non-destructive testing applications. Comparison with magneto-optical Kerr effect measurements showed that the magnetic field maps are strongly correlated with the material's surface domains while containing additional information from deeper inside the sample. Characteristic changes in the magnetic stray field distribution were detected in an electrical steel sample after cyclic loading. A potential marker for early fatigue damage was deduced from the splitting gradient distribution, while 2D Fourier transform analysis provided additional insight.
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All authors Niklas Mathes, Marvin Feuerhelm, Simon Philipp, Ivan Soldatov, Philipp D'Astolfo, Peter Knittel, Thomas Straub, Jan Jeske, Rüdiger Quay, Xavier Vidal

Applied Physics

A Green's-function method for vertical thermal boundary conductance in anisotropic multilayers

Dihui Wang, Troy Munro and Heng Ban

Vertical thermal interfaces occur in both engineered and natural materials. Their vertical thermal boundary conductance can differ from the horizontal counterpart, requiring dedicated characterization. Yet current thermal metrology resolves vertical thermal boundary conductance only in restricted geometries such as two bulk media, for lack of an efficient forward solution that admits anisotropy, multilayers, and depth-dependent vertical thermal boundary conductance together. We present a Green's-function boundary integral equation (GBIE) method that couples transfer-matrix Green's functions to an interface-only integral equation for depth-dependent $G_v(z)$, supporting dissimilar orthotropic multilayers ($k_x\neq k_y\neq k_z$) on either side and horizontal conductance $G_h$. For anisotropic film-on-substrate multilayers with films from $1~\mu\mathrm{m}$ to $100~\mathrm{nm}$, the GBIE agrees with three-dimensional finite element method (FEM) predictions to within one percent mean normalized phase and amplitude error, while running $29\text{--}210\times$ faster and reducing peak memory by factors of $120\text{--}450$ in single-core tests; a JIT-compiled JAX implementation reaches up to $4100\times$ on a matched 16-core comparison. The GBIE further reproduces a continuous film over a buried interface, representative of a thermoreflectance measurement, and a finite-depth interface with depth-dependent $G_v(z)$. The GBIE accommodates lateral-to-film-thickness ratios above $10^{5}$, where volumetric FEM can become computationally prohibitive. These results establish an efficient forward solution for vertical-interface heat transport in systems ranging from microelectronic device sidewalls to grain boundaries in polycrystalline solids.
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Applied Physics · Cross-listed from cond-mat.soft

Viscous Dissipation Governs Bubble Morphology and Failure in Soft Matter

Sushma SP, Anshul Shrivastava, Imnatoshi Jamir et al. (+2 more)

Cavitation, the growth of bubbles in fluids and soft matter, plays a central role in tissue damage, ultrasound therapies, and material failure, yet the influence of viscoelastic dissipation on bubble dynamics remains unclear. Here, we investigate cavitation in polyacrylamide hydrogels with identical elastic moduli but different viscous dissipation. We observe a striking symmetry breaking transition: elastic gels rapidly develop ellipsoidal cavities before rupture, whereas viscoelastic gels sustain large, nearly spherical bubbles. A modified Rayleigh Plesset framework shows that viscous stresses suppress shape instabilities and delay symmetry breaking, whereas elastic stresses accelerate cavity deformation. Finite element simulations independently validate these findings. The Deborah number (De) further captures the competition between material relaxation and cavity growth, with higher De associated with predominantly elastic growth and lower De with greater relaxation. Together, our results establish viscous dissipation as a key stabilizing mechanism that governs bubble morphology and failure in soft materials. These results have direct implications for understanding cavitation-mediated damage in biological tissues, optimizing therapeutic ultrasound, and advancing mechanical characterization of hydrogels for engineering and food processing applications.
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All authors Sushma SP, Anshul Shrivastava, Imnatoshi Jamir, Aritra Chatterjee, Namrata Gundiah

Applied Physics

Evaluation of effective wave velocities in polycrystalline materials using the ultrasonic reflection matrix

Gatien Clément, Alexandre Aubry, Cécile Brütt et al. (+2 more)

In-depth characterization of heterogeneous materials has long been a challenge in non-destructive testing. Here, a method is proposed to determine the elastic constants of metallic polycrystalline materials using back-scattered ultrasound. The waves scattered by the microstructure are analyzed to image the effective bulk velocities. To this end, a reflection matrix is acquired with an array of transducers. The projection of this matrix onto a focused basis is used to estimate an average point spread function. Optimizing this function with respect to the propagation model leads to an estimation of the longitudinal velocity. Additional treatments are developed to adapt the method to map the shear wave velocity. The local Poisson's ratio is then deduced from the ratio between those two velocities. Young's modulus and shear modulus can also be obtained assuming known densities. This matrix approach is experimentally validated on different polycrystalline materials. A sample displaying heterogeneous mechanical properties is then simulated to assess the accuracy and the resolution of the method. Its strengths and limitations are discussed, demonstrating its potential for quantitative non-destructive material characterization.
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All authors Gatien Clément, Alexandre Aubry, Cécile Brütt, Benoît Gérardin, Claire Prada

Applied Physics · Cross-listed from physics.optics

Intra-bandgap Bound-State Magnonics in a Photonic Crystal Waveguide

Chong-Xin Run, Xue-Feng Pan, Bang-Yao Wu et al. (+5 more)

Cavity and waveguide magnonics have recently emerged as frontiers for investigating light-matter interactions. In these systems, coupling magnons into meticulously engineered photonic lattices with rich band structures provides a promising platform for tailoring magnon-photon interactions. However, how these hybrid interactions behave in the bandgaps of photonic lattices—specifically, the formation of magnon-photon bound states (MPBSs)—remains largely unaddressed. Crucially, these bound states arise through a mechanism that is fundamentally distinct from bound states in the continuum (BICs). Here, we experimentally demonstrate intra-bandgap bound-state magnonics by coupling yttrium iron garnet (YIG) spheres to a microwave photonic crystal waveguide. At room temperature, we observe MPBSs featuring highly tunable spatial localization, power-dependent interaction modulation under microwave pumping, and long-range magnon-magnon interactions mediated by mode overlap. These unique features bridge fundamental insights into intra-bandgap light-matter interactions with practical applications, offering an avenue for scaling up coherent networks and investigating many-body physics through engineered interactions.
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All authors Chong-Xin Run, Xue-Feng Pan, Bang-Yao Wu, Kai-Min Hsieh, Wei-Min Zhou, Anton Frisk Kockum, Peng-Bo Li, Io-Chun Hoi

Monday 21 September

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

Ultrafast Dissipative Localization of Electronic Energy in AuPt Superlattices

C. Walz, M. Mattern, J.-E. Pudell et al. (+15 more)

Controlling the spatial distribution of absorbed optical energy is central to nanoscale photothermal chemistry, plasmonics, and ultrafast materials control. Here, we show that a metallic AuPt superlattice concentrates electronic energy in Pt within a few hundred femtoseconds, regardless of the initial energy distribution between the two constituents. Ultrafast X-ray diffraction follows this energy redistribution through the amplitude of a coherent 570 GHz superlattice phonon driven by the stress imbalance at the AuPt interfaces. Despite the nearly homogeneous absorption at 400 nm, the observed lattice motion is identical to that produced by 800 nm excitation, which is absorbed predominantly in Pt. This dissipation driven localization of energy arises from the large electronic heat capacity of Pt and rapid electronic transport through the superlattice, providing a route to femtosecond control of nanoscale energy distributions.
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All authors C. Walz, M. Mattern, J.-E. Pudell, J. Jarecki, L. Mehner, F.-C. Weber, F. Baltrusch, S. P. Zeuschner, M. Herzog, B. Ahn, J. C. Ekström, D. Kroon, A. Jurgilaitis, J. Larsson, M. Kronseder, D. Schick, A. von Reppert, M. Bargheer

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

Silk-templated Nanostrips as Superprotonic Fibre Sensors

Jianhui Zhang, Ahmed Salem, Robert Tidswell et al. (+4 more)

Transforming textile fibres into sensors can facilitate continuous physiological monitoring for improving human healthcare. Coating fibres with electronic conductors can help detect physiological stimuli but their sensitivity scales with thickness and often lowers the fibre mechanical flexibility. Proton conductors are potential alternatives; however, they suffer from fragile physical interfaces, and sluggish kinetics. Here, we report a bio-templated, scalable strategy to create superprotonic interfaces using natural silk fibres. We exploit ordered nanofibrils on silk fibres to selectively grow continuous metal-organic framework (MOF) nanostrips. This patterned, ca. $10\,\mu\mathrm{m}$-diameter fibre-structure provides low-defect interfacial pathways for ultrafast proton transport, yielding conductivities up to 40 $S\,cm^{-1}$ - two orders of magnitude above the state of the art - with millisecond response and high mechanical robustness. The individual micro-thread sensors facilitate respiratory monitoring with a mean bias of 0.01 breaths $min^{-1}$ in volunteer testing, unaffected by human movement and readily capture breathing signature in high-flow oxygen therapy devices. We integrate arrays of micro-thread sensors in textiles and exploit deep learning to demonstrate high-resolution spatiotemporal humidity mapping in dynamic flow-fields and resolve asymmetric respiratory patterns that elude conventional single-point detectors. Our results should have broad-ranging implications, e.g. in wearable health monitoring, bioelectronics, and human-machine interfaces.
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All authors Jianhui Zhang, Ahmed Salem, Robert Tidswell, Haowei Wang, Vikramjeet Singh, Laurence B. Lovat, Manish K. Tiwari

Applied Physics

A State-Space Framework for trivial and Topological Metamaterial Stochastic Analysis

Luiz Henrique Marra da Silva Ribeiro, Abhilash Sreekumar, Vinícius Fonseca Dal Poggetto et al. (+4 more)

Topological phononic crystals and elastic metamaterials support edge states defined by global topological invariants, offering a route toward vibration-control and wave-guiding devices that remain functional in the presence of defects. However, manufacturing-induced spatial variability can perturb these invariants and compromise their robustness, making its quantification essential during design. In this work, we first demonstrate that a previously proposed linear time-varying (LTV) formulation is mathematically equivalent to the spectral element method based on transfer matrices for elementary rod, Saint-Venant shaft, and Euler-Bernoulli beam theories. The deterministic formulation is then extended to stochastic analyses through a stochastic linear time-varying (SLTV) framework. The proposed methodology combines Monte Carlo simulations with stochastic Fourier series and an analytical Karhunen–Loève expansion, providing closed-form stochastic fields and their derivatives required by the LTV formulation. The SLTV approach enables the computation of stochastic dispersion diagrams and forced responses of one-dimensional waveguides with arbitrarily varying geometry and mechanical properties. Because the LTV-based transition matrix isolates individual wavemodes without requiring the mode tracking needed by conventional eigenproblem-based formulations, the framework is particularly suited for evaluating topological invariants, specifically the Zak phase, and assessing the robustness of topological bands under spatial variability. Numerical results for rods, shafts, and Euler-Bernoulli beams demonstrate the applicability of the proposed framework as a unified methodology for deterministic and stochastic analyses of trivial and topological periodic waveguides under continuous spatial uncertainty.
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All authors Luiz Henrique Marra da Silva Ribeiro, Abhilash Sreekumar, Vinícius Fonseca Dal Poggetto, Vicent Romero-García, Dimitrios Chronopoulos, Carlos De Marqui Jr., José Roberto de França Arruda

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

III-V antiphase boundaries are not generated by Si or Ge substrate step edges

Charles Cornet, Sreejith Pallikkara Chandrasekharan, Audrey Gilbert et al. (+7 more)

We critically review recent experimental and theoretical advances on the valence- and structure-mismatched heteroepitaxy of III-V semiconductors on group-IV substrates. We examine key aspects including wetting behavior, atomic configurations at the hetero-interface, substrate passivation, and the stability of antiphase boundaries (APBs). By synthesizing these findings with pioneering studies, we propose a refined description of antiphase boundaries formation. Our analysis shows that hetero-interface formation is dictated by substrate terrace reconstruction, demonstrating that APBs are not generated at monoatomic step edges. This generalized III-V/IV growth framework provides new insights for the integration of III-V semiconductors on group-IV platforms and, more broadly, for valence-mismatched heteroepitaxy.
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All authors Charles Cornet, Sreejith Pallikkara Chandrasekharan, Audrey Gilbert, Milan Silvestre, Rozenn Bernard, Pascal Turban, Gilles Patriarche, Eric Tournie, Laurent Pedesseau, Jean-Baptiste Rodriguez

Applied Physics

Pendellösung length-scale neutron and X-ray interferometry

Owen Lailey, Alexandre Boutot, David G. Cory et al. (+12 more)

Neutron and X-ray perfect-crystal interferometers (PCIs) are powerful platforms for studies of fundamental physics and phase-contrast imaging. Further enhancing several PCI capabilities requires reducing crystal blade thickness to the micron scale, which minimizes dynamical-diffraction image blur, permits operation in the pendellösung regime where blade thickness controls beam splitting, and reduces absorption for simultaneous neutron and X-ray operation. However, fabricating multiple crystal blades with identical micrometer-scale thicknesses over centimeter-scale areas remains a major challenge. Here, using a non-etching sub-micron fabrication technique, we demonstrate silicon triple-Laue interferometers with equal-blade-thicknesses of 110 $\mu$m and 350 $\mu$m, operated with both neutrons and X-rays. These devices are the thinnest PCIs realized to date, enabling a factor-of-six reduction in dynamical-diffraction beam spreading for improved phase-contrast imaging, while reaching the single pendellösung length regime in which crystal thickness provides an experimentally accessible control parameter for engineered quantum-optical beam splitting of plane-wave inputs. These results motivate multi-blade PCI designs utilizing identical half-pendellösung crystal lamellae that are proposed for neutron spin–orbit and electric dipole moment measurements.
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All authors Owen Lailey, Alexandre Boutot, David G. Cory, Joseph P. Cotter, Vishal Dhamgaye, Tao Hong, Michael G. Huber, Young-June Kim, Winfried Kockelmann, Jeremy W. Paster, Dusan Sarenac, Kawal Sawhney, Naume Shentevski, Ivar Taminiau, Dmitry A. Pushin

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

Vector Measurements Using Integrated Radio Frequency Atomic Magnetometers

Ayse Marasli, Thomas W. Kornack, D. Casey Oware et al. (+1 more)

We demonstrate reconstruction of three-dimensional radio-frequency (RF) magnetic-field vectors using a pair of integrated RF atomic magnetometers operated with orthogonal bias-field orientations. A theoretical and experimental analysis identifies a phase-ambiguity dead band that limits reconstruction when the two sensor responses become nearly identical. Measurements performed in an unshielded laboratory environment demonstrate accurate reconstruction of RF magnetic-field orientations and validate the predicted dependence of reconstruction accuracy on signal imbalance. These results establish integrated RF atomic magnetometers as a compact and sensitive platform for directional RF magnetic-field sensing, particularly at low frequencies, and provide a foundation for portable source-localization and field-mapping applications.
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All authors Ayse Marasli, Thomas W. Kornack, D. Casey Oware, Karen L. Sauer

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

VNS Tokamak for Medical Isotope Production

Christopher Ehrich, Pavel Pereslavtsev, Christian Bachmann et al. (+1 more)

The Volumetric Neutron Source (VNS) tokamak is a proposed fusion reactor for testing components under fusion neutron irradiation, and has potential use for radioisotope production. The VNS geometry is modeled in the Serpent 2.2.2 and OpenMC 0.15.2 neutronics codes. Coupled neutron-photon simulations compared fluxes, spectra, and selected reaction rates in the blanket and vacuum vessel. Good agreement was found overall, with the largest difference found in (n, 2n) reactions. On an HPC cluster, Serpent 2 was found to have shorter computation time in coupled simulations, while OpenMC was faster in neutron only simulations. Radioisotope production yields were simulated in Serpent 2.2.2 for capsule and Cobalt plate irradiation facilities. Results indicate potential for large volume production of 99Mo, 131I, 225Ac, 177Lu, 192Ir, 64Cu, 67Cu, 161Tb, and 153Sm while 203Pb indicates lower potential. 100Mo and LEU target heating was calculated, suggesting the LEU target mass or the cooling may need adjustment. Optimized 60Co production yielded 1.2 GBq/mg and 100,000 TBq after a 3-year irradiation period. Sensitivity to plant outage for 99Mo, 131I, 177Lu, and 60Co was simulated, suggesting irradiation can be restarted for the same isotope loading and demonstrated long-lived 60Co to be robust to long plant dwell-time.
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All authors Christopher Ehrich, Pavel Pereslavtsev, Christian Bachmann, Christian Reiter