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Tuesday 29 September

Applied Physics

Integrated assessment of tritium releases from fission and fusion energy systems and their environmental implications

Liliana Arias, Jeffrey Wang, Ate Visser et al. (+4 more)

Tritium is a naturally occurring radioactive isotope of hydrogen; a low-energy beta emitter with its health significance through internal exposure. The anticipated deployment of fusion energy systems is expected to increase tritium production significantly. Here we present an integrated assessment of tritium generation, release pathways, and resulting environmental concentrations across existing and emerging nuclear technologies. We first compile a comprehensive database of tritium production and releases from monitoring reports and literature. Analysis of light-water-reactor operating data shows that tritium discharge levels and release pathways are governed mainly by plant-specific strategies rather than reactor power or design parameters. This pattern reflects industry operating practices and efforts, with releases remaining well below regulatory limits. Our synthesis further indicates that FLiBe-based (Li2BeF4) systems may increase tritium production and mobility through enhanced permeation of tritiated hydrogen, although mitigation strategies are available to further limit emissions. Environmental transport modeling suggests that, under appropriate siting conditions, resulting tritium concentrations remain below regulatory thresholds. Furthermore, comparative risk analysis indicates that the associated carcinogenic impacts are expected to be lower than those from fossil-fuel-based power generation. Together, these findings demonstrate the importance of a comprehensive monitoring framework for contextualizing and managing routine effluent releases across energy systems.
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All authors Liliana Arias, Jeffrey Wang, Ate Visser, Naofumi Akata, Hideki Kakiuchi, Shinji Ueda, Haruko M. Wainwright

Monday 28 September

Applied Physics · Cross-listed from physics.optics

Asymmetric imaging: Reciprocity bounds and manifestations

Romil Audhkhasi, Anna Wirth-Singh, Rose Johnson et al. (+6 more)

Recent demonstrations of unidirectional imaging using diffractive multilayers have brought a concept akin to optical isolation to imaging, yet the fundamental limits of such asymmetry have remained unknown. Here we develop a general theory of asymmetric imaging in linear, passive, reciprocal optical systems and derive a fundamental bound on the achievable unidirectionality. Reciprocity requires the forward and reverse transmission operators to have identical singular values, a wave-optical analogue of étendue equality, with a simple consequence: perfect asymmetry is attainable only for sets of $M \leq N/2$ orthogonal object patterns, where $N$ is the number of available object/image modes; for $M > N/2$, the average power asymmetry is bounded by $(N-M)/M$. Guided by this result, we present two complementary realizations: refractive imaging systems formed by bulk lenses and stops that attain the half-occupation limit, and a 1 cm-diameter all-silicon metasurface doublet that exhibits asymmetric focusing at 4 $\mu$m while fully complying with Lorentz reciprocity. We fabricate the doublet by direct laser writing and experimentally demonstrate its focusing asymmetry. By establishing mechanism-independent limits, our results provide a benchmark and design principle for asymmetric imaging across platforms, with implications for defense, surveillance and secure communications.
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All authors Romil Audhkhasi, Anna Wirth-Singh, Rose Johnson, Maksym Zhelyeznyakov, Vladimir Yarmolik, Rafael Piestun, Andrea Alù, Arka Majumdar, Owen Miller

Applied Physics · Cross-listed from cs.NE

Massively Parallel Reinforcement Learning with a Chaotic Reconfigurable Clockless Chip

Eric Oliveira-Gomes and Damien Rontani

Hardware accelerators based on physical dynamical systems offer an attractive route toward energy-efficient reinforcement learning applications. However, their scalability is challenging because it requires many statistically independent entropy sources. Here, we introduce a quasi-analog decision-making architecture based on asynchronous Boolean networks (or lattices) implemented on a clockless reconfigurable chip. Each node in the network consists of a single logic element that acts as an autonomous entropy source. This architecture gives rise to distributed Boolean chaos, in which a spatially coupled network generates parallel streams of chaotic Boolean transitions with very low statistical dependence between nodes. We experimentally demonstrate parallel decision-making on a 1024-armed bandit problem, which is beyond the scale of previous hardware implementations, while significantly improving power-law scaling performance. Separately, we scale the proposed entropy source to 5120 parallel channels, yielding an aggregate sample generation rate of 2.14 TS/s. Our solution is implemented on a commercial reconfigurable CMOS chip and offers high integration density and ease of programmability. Our results pave the way for using distributed Boolean chaos as a valuable hardware substrate for large-scale reinforcement learning and for the development of fully integrated, high-throughput decision-making accelerators.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci

Directional strain control of magnetism in MnBi$_2$Se$_4$, MnSb$_2$Se$_4$, and MnSb$_2$Te$_4$ freestanding monolayers

Swarnava Ghosh, Tanvir Sohail and Markus Eisenbach

MnBi$_2$Se$_4$, MnSb$_2$Se$_4$, and MnSb$_2$Te$4$ are layered magnetic quantum materials of interest for spintronic and topological electronic applications, where control of magnetic order at the atomic scale is essential. These materials are particularly sensitive to strain. We investigate their strain-dependent magnetism in the monolayer limit using first-principles calculations across the full two-dimensional strain space spanned by independent variations of the two in-plane strain components. Our results show that the Mn-projected local moments depend primarily on the volumetric strain, whereas the magnetic ground state, exchange interactions, magnetocrystalline anisotropy, and ordering temperature show pronounced directional and composition-dependent responses. We also observe strain-induced competition between the phases, with MnBi$_2$Se$_4$, and MnSb$_2$Se$_4$ monolayers exhibiting a more diverse range of competing magnetic states, while MnSb$_2$Te$_4$ monolayer remains ferromagnetic over a larger portion of strain space. MnSb$_2$Te$_4$ also exhibits a substantially larger out-of-plane magnetocrystalline anisotropy, while showing a weaker dependence on strain than the Se-based materials. The calculated magnetic ordering temperature maps further highlight the role of two-dimensional strain to tune thermal magnetic stability in these materials. These results establish magnetoelastic trends across this family of Mn-based chalcogenide monolayers.
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Applied Physics · Cross-listed from cond-mat.mes-hall

Capacitance sensing in bilayer graphene with gate reflectometry

Tamás Kalmár, Gergő Fülöp, Bálint Szentpéteri et al. (+5 more)

In the search for topological states in bilayer graphene, capacitance measurement methods are widely utilized in bridge type readouts or source-drain reflectometry setups. In this paper we demonstrate an alternative readout method based on gate reflectometry. We probe the capacitance of a BLG flake encapsulated between hBN and WSe$_2$ through a lumped-element LC resonator coupled to the top gate electrode of the heterostructure. The microwave readout reliably tracks the opening of a displacement field-induced band gap in the device. Compared to simultaneous DC transport measurements, the RF signal proves to be less affected by the percolating transport channels caused by sample disorder. Furthermore, we use the gate based readout to identify a small-angle alignment between the hBN and BLG flake. From the fixed frequency microwave readout, we extract the device capacitance change between the insulating and metallic state of the bilayer and utilize a comprehensive capacitance network model to explain its origin. Finally, we propose an advanced, multiplexed double-resonator readout scheme capable of simultaneously measuring top and bottom gate capacitances to extract the layer polarizability of the system. This work establishes gate reflectometry as a highly scalable and powerful methodology for exploring topological phases and internal charge dynamics in van der Waals heterostructures.
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All authors Tamás Kalmár, Gergő Fülöp, Bálint Szentpéteri, Olivér Kürtössy, Kenji Watanabe, Takashi Taniguchi, Szabolcs Csonka, Péter Makk

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

Low-Temperature Stabilization of $\delta$-NbN Superconducting Thin Films through Energy-Selective Ion Beam Sputtering

Yifan Liu, Junwoo Lee, Mingyu Xu et al. (+3 more)

Achieving high-quality superconducting thin films at low temperatures is a central challenge for scalable quantum device integration and Complementary Metal-Oxide-Semiconductor (CMOS)-compatible fabrication. Here, we demonstrate a room-temperature magnetron sputtering approach for synthesizing niobium nitride (NbN) thin films using a novel energy-selective ion source that enables independent control of ion energy and ion flux. This capability provides a powerful route to precisely tailor surface kinetics and crystallization pathways, overcoming longstanding limitations in stabilizing high-quality NbN at reduced temperatures. The resulting films were characterized by superconducting transport measurements, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Compared with conventional reactive sputtering, ion beam-assisted growth yields a substantial narrowing of the transition width at the superconducting temperature, indicating improved phase purity and electronic homogeneity. Furthermore, this work introduces energy-selective ion control as a general, non-equilibrium route to stabilize metastable superconducting phases at low temperatures, offering a new design paradigm for thin-film quantum materials.
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All authors Yifan Liu, Junwoo Lee, Mingyu Xu, Weiwei Xie, Robert J. Cava, Qi Hua Fan

Applied Physics

Far-field excitation of symmetry-protected bound states in the continuum by nonlinear virtual sources

Marc Martí-Sabaté, Yijie Zhang, Shengming Sun et al. (+4 more)

Bound states in the continuum (BICs) enable complete wave confinement within open systems through destructive interference or symmetry protection, giving rise to ideally infinite quality factors and extreme field enhancement. Their practical exploitation, however, is hindered by a fundamental paradox: the same mechanism that suppresses radiation also prevents efficient excitation from the far field. Existing experimental approaches typically overcome this limitation by introducing external coupling channels that inevitably perturb the protected state and reduce its confinement. Here we demonstrate the non-invasive excitation of a symmetry-protected acoustic BIC through nonlinear virtual sources generated directly at the surface of the structure. By focusing time-modulated ultrasonic beams onto a metamirror, nonlinear demodulation produces localized low-frequency sources whose spatial phase matches the symmetry of the target mode while avoiding any physical coupling to the resonator. This approach injects energy into the BIC without opening additional radiative channels, preserving its intrinsic non-radiative character. We develop a theoretical framework describing the formation and symmetry protection of the mode, realize a compact experimental implementation through symmetry reduction, and directly measure the confined pressure field and its quality factor. Our results establish nonlinear virtual sources as a route to accessing symmetry-protected states in open systems while maintaining their exceptional confinement properties, providing a general strategy for wave manipulation and high-sensitivity resonant devices across physical platforms.
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All authors Marc Martí-Sabaté, Yijie Zhang, Shengming Sun, Ruxin Li, Yabin Jin, Junfei Li, Daniel Torrent Martí

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

Phase-field simulation of interfacial stability in structured gas-liquid contactors: design rules for gas diffusion electrodes

Alexander J. Wagner, Hari Murali Krishna Varma Gottumukkala and Henning Bonart

Many process engineering applications hold a gas-liquid interface stationary inside a structured solid by a controlled pressure difference. Gas diffusion electrodes (GDEs) are one such case, where the interface separates the liquid electrolyte from the gaseous reactant. Maintaining it is particularly challenging in organic electrosynthesis, where low surface tensions lower the admissible pressures throughout and small contact angles leave the electrode with little margin against flooding. Here, we quantify how the shape, wettability, and three-dimensional topology of a structured medium set this window, using phase-field simulations of the Cahn-Hilliard-Navier-Stokes equations. Each geometry is characterised by its Laplace pressure curve, which yields both the maximum admissible pressure difference and the stiffness of the interface against pressure fluctuations. For single flat orifices at constant open area, elongating the opening from an aspect ratio of one to six raises the admissible pressure difference by 40 % and the stiffness by a factor of 3.3. Comparison with slits of equal width shows that this gain originates entirely from the reduced opening width. Sheared, diamond shaped openings are markedly less effective. In woven meshes, the wettability displaces the operating window several times as far as it stretches it. A less wetting surface therefore buys flooding margin largely at the expense of breakthrough margin, whereas the geometric route, established here for flat openings, widens the window itself. From these results we derive design rules for structured gas-liquid contactors and improved GDE architectures for organic electrosynthesis.
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Applied Physics

Adaptive metamaterial resonators: a discrete and continuous mechanism

Vanessa Cool, Elke Deckers and Frank Naets

Locally resonant metamaterials are an established route to lightweight attenuation of vibration and noise, but their performance is tied to a bandgap fixed at the design stage. In practice, excitation frequencies are rarely constant, as they can vary with operating conditions and loading, causing fixed-frequency resonators to lose effectiveness as conditions drift from their design point. Existing strategies to address this rely on active control, introducing sensors, actuators, and a continuous power supply, or on broadband and multi-resonator designs that trade attenuation depth for bandwidth. A passive alternative, capable of adapting its resonance characteristics directly within the operating environment, would remove this trade-off and open locally resonant metamaterials to a much wider range of real-world, time-varying applications. In this work, we present two adaptive resonator concepts that enable in-situ modification of local resonance characteristics through discrete and continuous adaptation mechanisms.
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Applied Physics · Cross-listed from quant-ph

Cavity magnonics and bound states in the continuum with Bragg and anti-Bragg mirrors

B.-Y. Wu, K.-P. Li, G. Chen et al. (+7 more)

A periodic resonant emitter array coupled to a one-dimensional waveguide can act as a mirror. A typical example is a Bragg mirror, where emitters are spaced by multiples of half wavelengths and collectively enhance light reflection. Two such mirrors form an effective cavity that hosts bound states in the continuum (BICs). However, generating and detecting the spatial profiles of such BICs has proven challenging. Here, we experimentally demonstrate BICs in cavity magnonics using two periodic ferrimagnetic-sphere arrays and a probe sphere in a dual-open-waveguide architecture. We realize both Bragg and anti-Bragg cavities, whose mirrors have different lattice constants. In the Bragg cavity, there are degenerate supermodes formed by mirror spheres. We show that a single dark supermode coherently couples to the probe magnon in the cavity region, forming two polaritons whose splitting scales with both the probe-sphere size and the number of mirror spheres. By contrast, the anti-Bragg cavity has bright and dark supermodes in a bandgap, substantially changing the magnon-cavity interaction. Moreover, by moving the probe sphere, we perform position-dependent detection of the cavity field, highlighting the role of BICs in these cavities. Our flexible experimental setup with a scanning probe opens possibilities to detect other exotic states created by light-matter interaction, to interface with superconducting circuits in hybrid quantum networks, and to study non-Hermitian physics with Bragg and anti-Bragg cavities.
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All authors B.-Y. Wu, K.-P. Li, G. Chen, W.-M. Zhou, C.-X. Run, K.-M. Hsieh, A. F. Kockum, Z.-R. Lin, W. Nie, I.-C. Hoi

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

Observing Colossal and Tunable Near-field Thermal Radiation with A Highly Sensitive Annular Micro-thermocouple Junction

Ken Araki, Wei Han Won and Liping Wang

Near-field radiative heat transfer between two objects has been theoretically predicted and experimentally demonstrated to exceed far-field blackbody limit across nanoscale vacuum gap distance enabled by evanescent surface waves coupling, while significant enhancement by more than 100 times usually requires sub-50-nm vacuum gaps around room temperature. This is challenging for parallel-plate configuration with millimeter sample sizes due to intrinsic wafer bow and contaminant particles. Sphere-plate configuration with a microsphere attached to bimaterial cantilevers or micro-thermocouple tips has been used to experimentally demonstrate near-field radiative heat transfer down to 30-nm gaps, but it is much less developed because of the challenges in the sophisticated sensor fabrication, low sensitivity and weak signals. In this work, we overcome these challenges by an annular micro-thermocouple junction fabricated at the end of a glass fiber with straightforward thin-film deposition to achieve high measurement accuracy with large Seebeck coefficient 25 uV/K and thermal resistance 8.7e6 K/W. With a silica microsphere attached underneath the micro-thermocouple junction, we report experimental observation of colossal near-field radiation heat transfer over blackbody limit down to 10-nm gap up to 2600 times with quartz and 900 times with doped silicon. Upon phase transition of VO2 thin film emitter, tunable near-field heat transfer up to 430-fold enhancement is experimentally demonstrated at 15-nm gap with 64% reduction. Experimental data agrees well with rigorous modeling based on fluctuational electrodynamics and Derjaguin approximation, and underlying mechanism is understood by energy transmission calculations. The results will advance the experimental study and fundamental understanding of energy transport at nanoscale gaps.
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Sunday 27 September

Applied Physics · Cross-listed from eess.SP

Wave-Domain Semantic Equalization Using a Practical Dynamic Metasurface Antenna with Strong Mutual Coupling

Yassine Sghaier, Emilio Calvanese Strinati and Philipp del Hougne

Semantic mismatch between independently trained AI-native agents in heterogeneous networks can impair semantic communications. Hybrid analog-digital semantic equalization can align the incompatible latent representations without retraining the semantic transceivers. We study a practical realization of this approach based on a fabricated dynamic metasurface antenna (DMA), an emerging low-cost, low-power, ultracompact technology for hybrid analog-digital beamforming. We model the DMA-assisted channel using multiport-network theory (MNT), accounting for mutual coupling (MC), structural scattering, and binary lossy tuning states. We use the experimentally estimated MNT parameters of our fabricated 19-GHz DMA prototype with strong MC. We jointly optimize digital pre- and post-equalizers and the DMA at a reference receiver geometry for latent-space alignment, then freeze the digital stages and adapt only the DMA after receiver motion. In our CIFAR-10 image-classification task at the receiver, the jointly optimized system achieves 94.5% accuracy, while DMA-only adaptation restores a median accuracy of 90.3% after receiver motion. Our semantic-aware wave-domain adaptation substantially outperforms semantic-unaware benchmarks. We further observe that varying the DMA configuration across channel uses provides little additional benefit for either semantic-aware or semantic-unaware optimization.
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Applied Physics · Cross-listed from cond-mat.mes-hall

Bare-Die Antiferromagnetic Computing

Yu Liu, Zhuoting Han, Zexin Feng et al. (+15 more)

Semiconductor electronic devices are increasingly constrained by fundamental quantum tunneling effects and charge-based mechanisms, which severely limit further miniaturization, write-speed scaling, and environmental robustness of silicon-based technologies. These limitations are particularly prohibitive for deep-space exploration, where extreme temperatures, ultra-strong magnetic fields, and intense radiation rapidly incapacitate conventional electronics without massive shielding. Here, we present an intrinsically resilient, strain-mediated antiferromagnetic MnIr/PMN-PT edge processor that operates reliably as a bare die under temperatures up to 500 K, magnetic fields of 55 T, and radiation doses of 1.5 Mrad. By exploiting an input-modulated in situ self-refreshing encoding mechanism, the device performs nonlinear feature extraction and classification directly from raw analog signals, enabling an analog computing architecture that requires no time-frequency transformation. This architecture achieves 99.8% accuracy in speech recognition without digital preprocessing and 100% accuracy in astronaut visual object recognition. Furthermore, an all-hardware integrated drone vision system demonstrates real-time in situ command execution and autonomous navigation, delivering a terahertz-level response frequency and an ultra-low energy consumption of approximately 0.2 fJ per operation. This work expands the functional scope of antiferromagnetic devices beyond memory and logic, establishing them as a promising materials platform for energy-efficient physical computing and autonomous intelligence in extreme environments.
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All authors Yu Liu, Zhuoting Han, Zexin Feng, Peixin Qin, Zhiyuan Duan, Yuhao Ye, Zengwei Zhu, Chengyan Zhong, Li Liu, Guojian Zhao, Wenbin Shen, Jingyu Li, Sixu Jiang, Xiaoyang Tan, Xiaoning Wang, Ziang Meng, Chengbao Jiang, Zhiqi Liu

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

Uncertainty Quantification for the Fission Matrix Method: A Rigorous Mathematical Framework and Computationally Efficient Alternatives

Valerio Mascolino

The fission matrix (FM) method recasts neutron transport in matrix form, enabling fast, interpolation-based reactor calculations from a pre-computed database of Monte Carlo-derived coefficients. Propagation of the underlying Monte Carlo statistical uncertainty to the FM eigenvalue and eigenvector is rarely rigorous: prior approaches assume independent coefficients without testing this against their actual covariance. This work derives a full-covariance Delta-method framework for propagating uncertainty to keff and the fission source, and evaluates it with two cheaper alternatives, a diagonal-covariance approximation and direct resampling of the FM coefficients, using an OpenMC model of the JSI TRIGA Mark-II reactor. For the all-rods-out case, these three estimators and an empirical benchmark of 100 independent Monte Carlo runs agree within 5.7% for keff and 1% for the fission source. The sign of the diagonal approximation's bias flips between the two statistics levels, so it must be checked case by case. With a global fixed-source FM generation strategy, the diagonal, resampling, and independent-run estimators agree within about 2% and lie roughly 10% below the full-covariance estimate, a gap attributed to covariance sampling noise. The large off-diagonal covariance is nearly symmetric and mostly cancels when propagated, rather than being small or negative as previously assumed. For the FM control-rod interpolation and combination strategy (FM-CRd), keff matches an exact perturbed reference within 60 pcm (about two standard deviations) and the fission source within 0.7%, while the diagonal and resampling estimators agree closely and are conservative by about a factor of two. Given this and the prohibitive memory cost of the full covariance, the diagonal Delta method is recommended as the practical default, with the full covariance reserved for one-time characterization of a system.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci

Unifying Magnetic, Electrical, and Thermoelectric Responses in a Non-Collinear Antiferromagnet

André José, Adrielson Dias, Carlos Eduardo et al. (+6 more)

Non-collinear antiferromagnets offer unconventional routes for controlling magnetic, electrical, and thermoelectric responses through their complex spin configurations and interfacial symmetry. Here, we detect exceptional interfacial properties arising from a non-collinear antiferromagnet by demonstrating a robust and quantitatively consistent exchange-bias response in an IrMn$_3$/Py heterostructure. The system consists of a 10 nm IrMn$_3$ layer coupled to a 5 nm permalloy (Py) film. Longitudinal magneto-optical Kerr effect (MOKE), anisotropic magnetoresistance (AMR), and anomalous Nernst effect (ANE) measurements independently reveal the same unidirectional field shift of approximately 50 Oe, together with a consistent cosine angular dependence. The simultaneous observation of these signatures establishes a direct correspondence between the interfacial magnetic symmetry imposed by the non-collinear antiferromagnet and the responses of the adjacent ferromagnet. This symmetry is manifested consistently in magnetization reversal, charge transport, and thermally driven voltage generation, demonstrating that the exchange-bias imprint is not restricted to a single experimental observable. Our results reveal a coherent multifunctional response of IrMn$_3$/Py and extend the conventional understanding of exchange bias beyond collinear antiferromagnetic systems. More broadly, they demonstrate the potential of non-collinear antiferromagnets as platforms for coupling magnetic, electrical, and thermoelectric functionalities in spintronic and spin-caloritronic devices.
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All authors André José, Adrielson Dias, Carlos Eduardo, Giovanna Celly, Luiza Paffer, José Araújo, José Laurentino, Monalisa Cavalcante, José Holanda

Saturday 26 September

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

Physics-based logarithmic description of electrostatic field enhancement in hemisphere-on-cylindrical-post structures for high-field applications

Thiago A. de Assis, Fernando F. Dall-Agnol and Richard G. Forbes

Electrostatic (ES) field enhancement at sharp conducting structures plays a central role in lightning protection, corona discharge, electrical breakdown in vacuum (for example in particle accelerators), and more generally in technological applications of field electron emitters. A canonical geometry for studying this ES effect is the hemisphere-on-cylindrical-post (HCP) model, in the regime where the structure stands on a planar conductor of large lateral extent, and a large gap exists between the structure and the counter-electrode. A parameter of major interest is the apex field enhancement factor (AFEF) (apex-ES-field/background-ES-field). For this (and other) structures, a formula for the AFEF can be written in the form AFEF = ASC x ASR, where the apex sharpness ratio (ASR) is given by the ratio (post-height/apex-radius-of-curvature), and the apex sharpness coefficient (ASC) depends on the post shape. For the HCP model, no exact analytical formulas for the ASC or the AFEF are currently known. (Quite possibly none exist.) This paper develops a compact analytical approximation for the ASC and hence for the AFEF. This compact formula has a logarithmic-style structure, rather than the power-style structure used in previous approximations. When compared with precise finite-element analyses of the HCP model, over the computationally accessible range 1 to 1000 for the ASR, this logarithmic-style formula has a maximum error-magnitude of 0.15 percent, which is significantly better than older approximations.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci

Composition-Driven Metal-to-Semiconductor Transition and Enhanced Phonon Transport in B-C substituted Clathrate

Ghulam Hussain, Dario Massa, Rajibul Islam et al. (+3 more)

Establishing chemical design rules that simultaneously control the electronic structure and thermal transport is a long-sought goal for heat-management and energy materials. Here, we demonstrate that a single B-to-C substitution changes the electron count and simultaneously reconstructs the bonding network and crystal structure, driving a metal-to-semiconductor transition while concurrently enhancing the lattice thermal conductivity. Using density-functional theory (DFT) and machine-learned interatomic potentials (MLIPs), we investigate the electronic structure, lattice dynamics, and phonon thermal transport in cubic BaB3C3 and its B-to-C-substituted tetragonal BaB2C4 structure. The substitution donates one electron per formula unit to the B-C framework, thereby triggering the formation of strong C-C bonds and opening a bandgap of 0.33 eV. The Message Passing Atomic Cluster Expansion (MACE) model reproduces DFT energies and forces, yielding phonon dispersion and lattice thermal conductivity in excellent agreement with DFT benchmarks. Thermodynamically stable cubic BaB3C3 possesses an isotropic lattice thermal conductivity of 7.6 W/mK at 300 K. Substituting B with C hardens the phonon dispersion (evidenced by a frequency upshift from ~800 to ~900 cm^-1) and simultaneously boosts both phonon group velocities and lifetimes. Consequently, the lattice thermal conductivity surges to 18.7 W/mK, representing a remarkable ~2.5-fold enhancement of the in-plane component and a transformation from isotropic to anisotropic behavior, characterized by kappa_x = kappa_y > kappa_z. Our results demonstrate that minimal B-to-C substitution provides a viable strategy to modulate the electronic structure, thereby transforming the crystal from a metal to a semiconductor and concomitantly enhancing phonon thermal transport.
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All authors Ghulam Hussain, Dario Massa, Rajibul Islam, Magdalena Birowska, Carmine Autieri, Xiaoguang Li

Applied Physics · Cross-listed from physics.optics

Reconfigurable Linear Optical Transformations in a Single Integrated Multimode Waveguide

Manoah van der Worp, Jonas Krimmer, Ivo M. Vellekoop et al. (+2 more)

Wavefront shaping enables control over optical fields for applications ranging from imaging to photonic information processing. While conventional wavefront shaping relies on free-space systems comprising bulk optical components, compact and fully integrated approaches are comparatively unexplored. Here, we introduce a concept based on a single multimode waveguide with distributed thermo-optic perturbations for controlling multimode propagation. We develop a differentiable physical model and numerically demonstrate shaping the outgoing wavefront and programmable linear optical transformations, using gradient-based optimization. We achieve diffraction-limited focusing with 20 spatial modes and show that the theoretical focusing limit can be retained while maintaining more than $99\%$ of the input optical power. We extend this approach to complete input–output transformations and implement Sylvester–Hadamard matrix operations with dimensions up to $32\times32$ with correlations exceeding $99\%$. Reducing the number of tunable elements requires stronger individual perturbations, resulting in stronger and broader mode coupling that extends beyond the target modes. To mitigate this effect, we consider ancillary modes and realize a $4\times4$ transformation that reaches $93.8\%\pm4.8\%$ correlation with only $5N^2$ tunable elements, where $N=4$ denotes the number of spatial modes. The best-performing realization reaches $98.3\%$ correlation with the target. Our results demonstrate that thermo-optic control of multimode waveguides offers an approach to fully-integrated wavefront shaping and programmable linear optical transformations, with potential applications in classical and quantum photonic processing
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All authors Manoah van der Worp, Jonas Krimmer, Ivo M. Vellekoop, Pepijn W. H. Pinkse, Stefan Rothe

Applied Physics · Cross-listed from physics.optics

Inverse-Designed Time-Varying Multilayers for Programmable Frequency-Momentum Light Scattering

Mohammad M. Asgari and Viktar Asadchy

Space-time-varying electromagnetic structures unlock wave-control mechanisms inaccessible to static media, including frequency conversion, harmonic generation, and joint control over frequency and momentum. Here, we introduce an inverse-design framework for multilayer space-time-periodic structures in which the spatial permittivity distribution and temporal modulation profile are optimized jointly. The proposed platform comprises multiple pixelated layers that are periodic along one or both transverse directions and harmonically modulated in time, enabling the direct synthesis of complex multichannel frequency-momentum scattering responses. We demonstrate two representative functionalities: independent control over the amplitudes and phases of three transmitted spatiotemporal channels and the generation of a frequency-momentum comb. Across these examples, we consider both continuous and binary permittivity distributions. To facilitate reproducibility and further development, we make the numerical implementation of the optimization framework freely available. These results demonstrate that inverse-designed time-varying multilayers provide a compact and versatile route toward programmable frequency-momentum multiplexing and the synthesis of space-time wave packets. The optimization code is made openly available to facilitate reproducibility and further development of the proposed inverse-design framework.
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Applied Physics

A 20-kV Optical-Injection-Enhanced 4H-SiC Reverse-Conducting IGBT With Snapback-Free Operation and Low On-State Voltage

Yujian Chen, Guoliang Zhang, Ruijun Zhang et al. (+4 more)

This letter proposes a 20-kV 4H-SiC optical-injection-enhanced reverse-conducting IGBT (OIE-RC-IGBT) with snapback-free operation and low on-state voltage. Light-emitting diodes (LEDs) are integrated into the gate structure to provide optical injection during forward conduction. The emitted light generates a high concentration of photogenerated carriers in the carrier-storage layer (CSL) and drift region, thereby reducing the resistance of the JFET and drift regions and increasing the device current. Consequently, the collector-side P+/N junction is turned on earlier, effectively suppressing the snapback effect and facilitating the transition to bipolar conduction. After bipolar conduction is established, the photogenerated carriers further enhance conductivity modulation, resulting in a reduced on-state voltage. TCAD simulation results show that, compared with the conventional RC-IGBT (C-RC-IGBT), the proposed device achieves snapback-free operation while reducing the required number of MOS cells from 25 to 5. Moreover, the on-state voltage, turn-off fall time, and turn-off energy loss are reduced by 22.37%, 25.06%, and 19.69%, respectively. These results demonstrate the potential of optical injection for improving the conduction and turn-off performance of ultrahigh-voltage SiC RC-IGBTs.
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All authors Yujian Chen, Guoliang Zhang, Ruijun Zhang, Liangxun Yue, Zhanwei Shen, Feng Zhang, Rong Zhang

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

In-Memory AM Demodulation Using an All-Silicon Independent-Dual-Gate Gain-Cell Memory with $<10^{-22}$ A Leakage Determined by Single-Electron Counting

Katsuhiko Nishiguchi, Toshiaki Hayashi, Kensaku Chida et al. (+3 more)

Ultra-low-leakage memories are attracting increasing attention for in-memory sensing and computing. However, achieving sufficiently long retention in silicon memories for analog signal processing remains challenging because of leakage through the access transistor. In this work, we demonstrate an all-silicon independent-dual-gate memory whose leakage current, inferred from single-electron counting statistics, is below $10^{-22}$ A, giving a measured retention time exceeding 1000 s. Owing to the extremely low leakage, the subthreshold nonlinearity of the access transistor can be exploited without disturbing the stored charge, enabling in-memory amplitude-modulation (AM) demodulation. The proposed memory provides a CMOS-compatible platform for ultra-low-power signal processing and in-memory sensing.
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All authors Katsuhiko Nishiguchi, Toshiaki Hayashi, Kensaku Chida, Takase Shimizu, Gento Yamahata, Seiya Kasai

Friday 25 September

Applied Physics

A reduced-order analysis for multi-reflection-driven laser absorptance in vaporization-induced cavities

Haolin Liu, Haoran Shi, Xuzhe Zeng et al. (+4 more)

Multiple internal reflections enhance laser absorption in vaporization-induced cavities, but connecting ray histories, cavity geometry, and absorptance typically requires full ray tracing. We develop a reduced-order framework based on Beer-Lambert-type attenuation governed by an effective per-reflection optical depth (EPROD). A power-weighted formulation defines an absorptance-equivalent interaction count under constant effective single-interaction absorptance, while a cumulant expansion separates the EPROD-independent mean interaction count from ray-path heterogeneity corrections. Across nine simulation groups spanning three alloys and three spot diameters, the mean interaction count follows a unit-intercept linear depth relation with R-squared values of 0.7824-0.9843. Its slope varies by only 3.4%-6.3% across alloys at fixed spot diameter and decreases with increasing spot diameter. Fixing this slope from ray statistics yields an absorptance-depth model with one fitted parameter and a median prediction error (MAPE) of 2.61%. An independent synchronized Ti-64 experiment yields model parameters within approximately 2.4% of corresponding simulation values. This framework separates geometric interaction accumulation from optical attenuation, enabling efficient energy-coupling prediction and absorptance-based keyhole characterization.
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All authors Haolin Liu, Haoran Shi, Xuzhe Zeng, Brian J. Simonds, Wenda Tan, Anthony D. Rollett, Levent Burak Kara

Applied Physics · Cross-listed from physics.optics

Discrete quality-factor control in a side-coupled photonic crystal microcavity: evanescent Bloch tunnelling and the finite-cell correction

Hasan Oguz

A point-defect cavity side-coupled to a line-defect waveguide in a two-dimensional photonic crystal of silicon rods in water is studied with plane-wave expansion and finite-difference time-domain computations. The defect-rod radius tunes the resonance continuously within the band gap, as first-order perturbation theory predicts, whereas the quality factor changes in discrete steps set by the number of lattice rows between cavity and guide; displacing the defect rod by up to a tenth of a period changes it by less than 7 percent. Each added row multiplies the quality factor by a factor that follows, without an adjustable parameter, from the decay of the evanescent Bloch channel of the bulk crystal that is phase-matched to the guided mode; the channel at zero wavevector along the guide predicts little more than half that factor. Two biases of a finite computational domain, leakage across the cladding and a standing wave set up by reflections at the ends of the truncated guide, lower the per-row factor and change the quality factor by up to a factor of two if left uncorrected. Scaled to 1550 nm the design gives a sensitivity of 634 nm per refractive index unit, which perturbation theory reproduces, and the linewidth agrees with that of a transmission spectrum normalized to a cavity-free reference. Absorption by water caps the quality factor near 9200 and limits the useful number of barrier rows. The guided mode lies inside the light cone, so a slab of finite height needs a different guide.
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Applied Physics

Depth-resolved elastic property tomography using higher-order shear-horizontal modes

Peter Huthwaite

Early material degradation can produce weak, local changes in elastic stiffness before a crack or void forms, but conventional ultrasonic measurements dilute these changes through path and thickness averaging. This paper introduces DEPTH (Depth-resolved Elastic Property Tomography using Higher-order modes), which uses mode-to-mode scattering among higher-order guided waves to reconstruct elastic-property variations as a function of axial position and depth through a plate. The formulation is developed using shear-horizontal (SH) modes, for which the reconstructed property is shear modulus. A Born formulation shows that each incident-received mode pair contains at most two cosine depth orders, allowing the through-thickness field to be recovered from diverse modal mixtures across mode pairs and frequency. The matrix-free regularised inverse is evaluated using direct two-dimensional modal data, practical single-surface excitation and reception, and full three-dimensional finite-element data. In a 10 mm plate, the ideal two-dimensional case gives a through-thickness point-spread FWHM of 0.84-1.03 mm, while the single-surface configuration recovers four compact targets at the correct depths. This provides the first demonstration of depth-resolved elastic-property tomography from multimode guided-wave transmission with excitation and reception confined to a single physical plate surface. With full three-dimensional propagation and finite-width transduction, the reconstruction retains the compact-target positions with a whole-image correlation of 0.899 against a matched acquisition-limited reconstruction. These simulation results demonstrate that higher-order guided-wave mode conversion can provide local depth-resolved elastic-property tomography from surface-access measurements, with potential for characterising early-stage damage such as fatigue.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci

Multiscale computational study of the dielectric response of semi-crystalline polyethylene with chemical defects

Roshal Perepadan Shaju, Guido Roma and Xavier Colin

Polymers are widely used as functional insulating materials, but predicting their dielectric behavior is challenging because multiple mechanisms, acting across different spatial and temporal scales, contribute to their response. In polyethylene (PE), one of the most common polymers, electronic, atomic, and mesoscale dynamics must all be considered. In this work, semicrystalline models of polyethylene were developed and investigated using a multiscale approach. Quantum simulations were employed to describe electronic and vibrational contributions to the dielectric response, while classical molecular dynamics simulations captured the behavior of polymer chains at room temperature and frequencies down to the 10-100 MHz range. The study focuses on the impact of radio-oxidation defects on the dielectric properties of polyethylene. Quantum calculations reveal how electronic and vibrational contributions depend on the local atomic environment surrounding these defects. Comparison with molecular dynamics results highlights the influence of temperature on the static dielectric constant. Structural analyses further assess the effect of each defect type on PE crystallinity. Analysis of dipolar correlation functions shows that different defects interact with one another and with the polymer matrix in distinct ways, affecting permittivity and dielectric loss peaks. For all defect types, defect-defect interactions provide the largest contribution to dielectric response. While most oxidized groups exhibit positive coupling with the PE matrix, alcohol defects display a negative cross-correlation, partially offsetting their impact on the dielectric properties. Our results also show that ketone groups produce the largest dielectric loss between the defects studied.
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Applied Physics · Cross-listed from quant-ph

Frequency- and Power-Dependent Optical Response of a Cesium Rydberg Microwave Receiver

Jure Pirman, Ema Stopar, Katja Gosar et al. (+2 more)

We show experimentally obtained frequency- and power-dependent optical response of a room-temperature cesium vapor cell used as a Rydberg microwave receiver based on electromagnetically induced transparency. An applied microwave field couples the ${70S_{1/2}}$ Rydberg state to the nearby ${70P_{1/2}}$, ${70P_{3/2}}$, ${69P_{1/2}}$, and ${69P_{3/2}}$ states, modifying the probe-transmission spectrum. Probe transmission is recorded over a 800 MHz range of coupling laser detunings. These EIT spectra are measured for RF frequencies from 9 to 13.5 GHz and over a 40 dB range of RF power. We analyze the RF induced splittings in the recorded EIT spectra. We observe both limiting cases, where the EIT peak separation is either dominated by the RF detuning or by the RF power. At higher powers we are also able to observe complex features due to coupling of multiple nearby Rydberg states. We further analyze the probe-transmission signal at zero coupling-laser detuning. Sigmoidal fits to the power-response curves are used to determine the midpoint power and the 10-90% transition interval as functions of RF frequency.
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All authors Jure Pirman, Ema Stopar, Katja Gosar, Erik Zupanič, Peter Jeglič

Applied Physics

Black silicon avalanche photodiode with dopant-free multiplication region achieves >98% EQE

O. Leiviskä, O. Setälä, A. Haarahiltunen et al. (+3 more)

Conventional silicon avalanche photodiodes (Si APDs) rely on highly doped regions to enable impact ionization and achieve internal gain. However, inefficient charge collection in these regions, combined with front surface reflection, degrades the external quantum efficiency (EQE) of these devices. In this work, we mitigate both loss mechanisms by integrating black silicon (b-Si) surface nanostructuring with Al2O3 induced carrier collection in an inverted-mesa Si APD architecture. This design confines the electric field and defines the multiplication region without requiring ion implantation. The resulting devices display near-ideal responsivity (at M = 1) across the UV-visible spectrum, with EQE exceeding 100% at 200-400 nm (peak ~130%) and exhibiting 92-100% at 400-700 nm. Avalanche gains of M ~ 4 at 80 V, M ~ 10 at 100 V, and M ~ 23 near breakdown at ~110 V are obtained. Dark current remains in the picoampere range up to ~80 V but rises to the nanoampere range near breakdown, narrowing the practical bias window. Capacitance-limited rise times of ~30-570 ns are measured for device diameters of 1-5 mm. The results demonstrate that the developed architecture enables APDs capable of detecting every single photon over wide range of wavelengths.
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All authors O. Leiviskä, O. Setälä, A. Haarahiltunen, J. Heinonen, V. Vähänissi, H. Savin

Applied Physics

FSSDataBase: a reconstructable dataset of simulated frequency-selective surface structures and scattering responses

Xinke Kuang, Shiyun Ma, Yuanyuan Wang et al. (+1 more)

Data-driven design of frequency-selective surfaces (FSSs) requires reusable datasets that link structural geometry to electromagnetic response under documented simulation conditions. Here we present FSSDataBase, an openly available collection of 5,000 procedurally generated single- and multilayer FSS unit cells simulated using Ansys HFSS. The dataset covers 10-20 GHz with transverse-electric and transverse-magnetic relfection and transmission responses, including magnitude and phase, for recorded incidence angles of $0^{\circ}$ and $30^{\circ}$. Each record links binary structural masks and JSON-based reconstruction metadata to raw response samples and derived magnitude labels. Structural descriptors, response-distance measures and task-oriented cost functions characterize geometric and electromagnetic variation and support screening for polarization stability, angular-selective bandwidth and matched-amplitude, 180{\deg} phase-separated structure pairs. Accompanying code supports model reconstruction, data processing and configuration-driven generation of additional samples. Beyond conditional forward modelling and response-based structure retrieval, FSSDataBase has the potential to serve as a reference dataset for deep-learning-based FSS inverse design, supporting fair comparisons across network architectures under shared data splits,input conditions and evaluation protocols.
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All authors Xinke Kuang, Shiyun Ma, Yuanyuan Wang, Jiang Wu

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

A hydrogen-informed Rice-Beltz model for crack-tip dislocation emission under mixed-mode loading

Kai Zhao

The fundamental competition between crack-tip cleavage and dislocation emission dictates the ductile-to-brittle transition in crystalline solids. In hydrogen-charged environments, this delicate balance is disrupted, yet existing models often struggle to self-consistently capture the atomic-scale thermomechanical modulation of the emission barrier. Here, we propose the hydrogen-informed Rice-Beltz framework to quantify the critical stress intensity factors (SIFs) required for initial dislocation nucleation under mixed-mode (I+II) loading. By integrating the elastic interaction of the dilatational field of interstitial hydrogen and the applied stress fields against the incipient dislocation core, the model recovers the non-monotonic relation between the most probable SIF and the hydrogen concentration. Unlike the classical pure mode-I (or mode-II) scenario, the minimization of the local strain energy density is employed to generate closed-form nominal driving forces, which are subsequently embedded into a transition-state-theory framework. This atomistically-informed approach yields the most probable SIF for the first dislocation emission event as a function of the loading rate, slip angle, and hydrogen concentration, providing a rigorous, parameter-free boundary condition for the onset of hydrogen-modulated crack-tip plasticity.
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Thursday 24 September

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

CTrex: A Research-Oriented Framework for Kernel- and Projection-Level Algorithm Development in CT Reconstruction

Karel Desplenter, Wannes Goethals, Thomas De Schryver et al. (+3 more)

Micro-computed tomography (micro-CT) is increasingly applied to imaging scenarios in which object motion, deformation, truncated fields of view, continuous rotation, or unconventional scanning protocols violate assumptions underlying classical reconstruction pipelines. Existing reconstruction frameworks efficiently support standard geometries and workflows but offer limited control over how projection operators are discretized and evaluated. This restricts methodological exploration when accuracy depends on ray sampling, interpolation, or operator coupling. We introduce CTrex, a research-oriented, GPU-accelerated iterative reconstruction framework that exposes the projection-correction-backprojection pipeline down to the kernel level. Rather than treating these operators as fixed black boxes, CTrex represents them as editable computational building blocks within a unified iterative structure. This allows non-ideal acquisition effects to be incorporated directly into the numerical operators rather than treated as external corrections. CTrex combines GPU-level accessibility with an extensible geometry formulation based on homogeneous-coordinate view matrices, allowing rigid and affine transformations, detector misalignments, and time-varying geometries to be expressed consistently. It supports circular, helical, offset, and conveyor-belt trajectories while keeping GPU kernels agnostic to the trajectory definition. Applications in motion- and deformation-aware reconstruction, event-based 4D imaging, cylindrical-coordinate reconstruction, and extended-field-of-view CT illustrate how operator-level adaptations enable strategies difficult to realize in conventional frameworks. CTrex provides a flexible platform for CT reconstruction research under realistic and unconventional imaging conditions.
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All authors Karel Desplenter, Wannes Goethals, Thomas De Schryver, Marjolein Heyndrickx, Jan Aelterman, Matthieu N. Boone