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Monday 21 September

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

Ferroelectric switching of odd-parity magnon spin splitting

Yuhan Liang, Xingyu Yan, Bowen Hao et al. (+13 more)

Magnetic symmetry can lift spin degeneracy in momentum space without producing net magnetization, generating spin textures classified by their parity under momentum reversal. Even-parity textures have well established in altermagnets. Odd-parity spin textures have recently emerged in electronic bands of compensated magnets, but their counterpart in collective bosonic excitations remains experimentally unresolved. Magnons provide a natural setting for this extension because they carry spin angular momentum through insulating magnets without accompanying charge flow. Beyond realizing this missing state, a broader challenge is to program spin splitting with voltage at room temperature. Here we report room-temperature transport evidence for ferroelectric switching odd-parity magnon spin splitting in multiferroic BiFeO3. Symmetry analysis and spin-wave calculations reveal that the cycloidal chirality splits opposite-spin magnon branches with an odd-in-momentum dependence and sets the sign. Experimentally, an injected in-plane-polarized spin current generates an out-of-plane magnon spin component during propagation. This component exhibits the crystalline angular dependence predicted by theory and reverses upon ferroelectric switching, providing a transport fingerprint of the spin-split magnon state. We use the programmed magnon spin to drive deterministic field-free switching of a perpendicular ferromagnet and demonstrate XNOR logic-in-memory. Our results extend odd-parity spin splitting from fermionic electronic states to bosonic collective modes and establish nonvolatile electrical control at room temperature.
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All authors Yuhan Liang, Xingyu Yan, Bowen Hao, Ziye Zhu, Tianle Sui, Daniel Pharis, Xiaoxi Huang, Rakshit Jain, Tong Zhou, Di Yi, Wanjun Jiang, Pu Yu, Igor Žutić, Yuan-Hua Lin, Daniel C. Ralph, Tianxiang Nan

Applied Physics · Cross-listed from eess.AS

Performance Analysis and Design of an Optomechanical Microphone Using an Integrated Photonic Waveguide Interferometer

Xiaoyu Niu, Yuqi Meng, Zihuan Liu et al. (+2 more)

We present an optomechanical microphone based on a diaphragm-integrated photonic waveguide Mach-Zehnder interferometer. Acoustic pressure deforms the MEMS diaphragm, inducing strain in the sensing waveguide and changing its optical path length. We analytically evaluate the optical and mechanical transduction mechanisms and key figures of merit, including signal-to-noise ratio, dynamic range, acoustic overload pressure, and minimum detectable pressure. Two design cases are considered: a MEMS microphone and a measurement microphone. The results indicate competitive performance but no substantial overall advantage over state-of-the-art microphones in conventional applications. The architecture may nevertheless offer advantages for high-temperature and other harsh-environment sensing applications.
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All authors Xiaoyu Niu, Yuqi Meng, Zihuan Liu, Ehsan Vatankhah, Neal Hall

Applied Physics · Cross-listed from cond-mat.stat-mech

Exact Nonperturbative Equilibrium Mode Statistics in Nonlinear Wave and Lattice Systems

Jialin Zhang, Yong Zhang and Hong Zhao

We derive exact finite-size nonperturbative representations of equilibrium modal occupations and related statistics for three representative nonlinear systems: the Majda-McLaughlin-Tabak dispersive-wave model, the Fermi-Pasta-Ulam-Tsingou beta anharmonic chain, and the discrete nonlinear Schrodinger lattice field. Independent simulations confirm the predictions from weak to strong nonlinearity. For DNLS, the theory remains accurate across the weak-coupling quasicondensation crossover, where large low-mode occupations and long-range coherence amplify interaction effects even when the bare nonlinear coefficient is small. The finite-ring DNLS occupations are further resolved into a positive sum of Rayleigh-Jeans channels with distinct correlation lengths, explaining when a single Rayleigh-Jeans law applies and why it fails near quasicondensation. In MMT and DNLS, the exact occupations also determine the mean modal frequencies even when the dynamical spectra broaden or split. The nonperturbative results allow a direct assessment of two representative perturbative approaches. Treating the mean interaction appropriately yields accurate low-order approximations, including at strong nonlinearity. At higher orders, however, the corrections cease to decrease and successive approximations oscillate with increasing amplitude; both finite-order approaches also fail near weak-coupling quasicondensation. Thus neither low-order agreement nor a small bare coupling guarantees a reliable perturbative description. The results establish nonperturbative equilibrium theory for widely used nonlinear wave and lattice models and provide a quantitative basis for modal distributions of energy, particles, and optical power in nonlinear optics, dispersive waves, anharmonic lattices, and cold-atom systems.
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Sunday 20 September

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

AI-assisted analytical theory in soft matter and multiphysics: new results and lessons from diffusiophoresis and bipolar membranes

Ankur Gupta

We present a framework to advance analytical theory in the area of soft matter and multiphysics using assistance from AI. The framework emphasizes (i) setting "honesty rules", (ii) focusing on a few key papers that are used to formulate a problem of interest, (iii) specifying checks a priori, (iv) using only one task per session and keeping a running log of tasks, checks, corrections, and sessions so that a mistake is not propagated through a project, and (v) ensuring all decisions are approved by humans while AI focuses primarily on execution. The framework is applied to two distinct problems to create new knowledge, including (i) diffusiophoresis of a spherical particle in the presence of an arbitrary number of electrolytes at arbitrary Debye lengths, and (ii) analytical description of I-V curves, including overlimiting current, in bipolar membranes without including the water dissociation kinetics. Both of these problems are advanced analyses and would each typically require several months to a year's worth of effort, but were solved in a matter of a few days. However, the increased efficiency should be cautiously navigated to avoid cognitive offloading and ensure that AI-assisted results are used to extract human-readable insights instead of just reporting a new mathematical formula. The usage of AI is transparently presented. Finally, we also share brief thoughts on how to integrate AI tools in theoretical research during graduate education.
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Applied Physics

Quantitative Dried droplet Morphology and Image Analysis for Screening Adulteration in Milk

Neha Gautam, Sumita Mondal, Debanjan Das et al. (+1 more)

Adulteration of milk with water, urea, calcium compounds and starch is still a widespread food safety problem, especially in areas where there is no access to laboratory based chemical testing, and is a global threat to human food safety and security, especially for children and the elderly. We present the development of a reagent free screening method, based on droplet evaporative deposition method, optical microscopy, and quantitative image analysis, for consistent detection and classification of milk adulteration. Droplets of Single Toned ST, 3% fat, and Double Toned DT, 1.5% fat milk samples, adulterated with water, urea, calcium, and starch, respectively, at different concentrations were tested. Deposition patterns were characterized by image processing using radial intensity profile descriptors area under the curve, and edge decay slope and gray level co occurrence matrix GLCM texture features contrast, correlation, energy, homogeneity, and entropy. The descriptors exhibit consistent adulterant specific trends: water and urea adulteration resulted in increasingly smooth, more homogeneous deposits decreasing contrast, increasing homogeneity, while calcium and starch adulteration resulted in structurally rougher deposits increasing contrast, decreasing homogeneity. Urea was further distinguished in the two groups by a significant increase in homogeneity and entropy collapse at higher concentrations, whereas calcium and starch were distinguished by diverging area under curve AUC trends. Milk type ST vs. DT was resolved by a combined multivariate signature of the descriptors at baseline. Our findings show that a simple, two level feature based framework: first resolving milk type, then adulterant family, then specific adulterant identity can be realized entirely from optical microscopy data without additional chemical reagents.
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All authors Neha Gautam, Sumita Mondal, Debanjan Das, Purbarun Dhar

Applied Physics

Temporal Quadrupole Moments: Floquet Higher-Order Topology with Nonreciprocal Frequency-Converting Corner States

Sajjad Taravati and Jingbang Liu

We introduce the temporal quadrupole moment and leverage its nonreciprocal frequency-converting topological corner states to experimentally realize a magnet-free transceiving circulator in a topological time-modulated microwave metasurface. Under periodic driving, the temporal quadrupole moment evolves the corner charge of a bulk-gapped lattice over the drive cycle, generating two distinct families of topologically protected corner states: a corner mode at quasienergy $\varepsilon=0$ and a purely dynamical period-doubled mode at $\varepsilon=\pi/T$ that exists only under periodic driving. We show that the relative phase between the two time-modulated coupling channels that generate it acts as a synthetic gauge field, breaking time-reversal symmetry while leaving the corner-mode topological protection intact. Specifically, a signal launched into the metasurface at TX port at frequency is up-converted and radiated into free space, while a free-space wave at is preferentially captured and routed — at the same frequency, unconverted — to RX port rather than back to TX port; the reverse itinerary is forbidden by the same broken symmetry. We confirm the temporal quadrupole moment, its associated Floquet corner states, and the resulting nonreciprocal frequency conversion through spatial field-intensity and angle-resolved radiation measurements of the time-modulated array on a fabricated microwave prototype.
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Saturday 19 September

Applied Physics · Cross-listed from quant-ph

Deterministic synthesis and processing of frequency-bin qubits in a macroscopically coherent quantum memory

S.A.Moiseev

Quantum information processing requires efficient storage and manipulation of photonic states. In this work, we harness pre-created macroscopic spin coherence as an additional degree of freedom to control a cavity-assisted quantum memory. We derive equations of motion for such a memory that predict efficient emission and absorption of two-color fields under a generalized nonlocal spectral impedance-matching condition, which reduces to the well-known condition in the single-mode case. These equations reveal a new operating mechanism of cavity-assisted quantum memory wherein the controlled spin coherence couples the emitted spectral modes. As a result, our memory deterministically synthesizes arbitrary frequency-bin photonic qubits using simple radio-frequency rotations, while the temporal reversibility of the protocol provides perfect transformation of the qubit states. Our findings establish a unified platform bridging quantum storage with elementary signal processing for quantum networks based on spectral encoding of photonic qubits.
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Applied Physics

Magnetic Particle Magnetometer Based on Langevin Response of Superparamagnetic Nanoparticles for Remote Magnetic Field Sensing

M. Jurj, C. McDonough, C. Bastajian et al. (+1 more)

We demonstrate a novel magnetometer that utilizes the Langevin nonlinear magnetization of superparamagnetic nanoparticles as the sensing medium. The magnetic sensor exploits the even-order harmonics of the magnetization response, particularly the second harmonic, which is proportional to the local magnetic field component. By remotely detecting the magnetization response, the magnetometer enables non-invasive, localized, and distributed magnetic field sensing without requiring wired connections, with a small sensing volume, which can be used for in situ biomedical sensing, geomagnetic monitoring, smart diagnostics, and distributed industrial sensing. In the linear operating regime, the magnetometer provides a measurement range of $\pm$ 0.2 mT and a high sensitivity of 10 pT/$\sqrt{Hz}$, while an extended operating mode allows measurements over a range exceeding $\pm$ 0.5 mT. The sensor offers a dynamic bandwidth from dc up to a few kilohertz, determined by the excitation frequency.
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All authors M. Jurj, C. McDonough, C. Bastajian, A. Tonyushkin

Applied Physics

Understanding Ideality Factor in Wide-Band Gap Semiconductor Devices with Strong Recombination Planes

Iris Celupica-Liu, Tanay Tak, Yuh-Renn Wu et al. (+1 more)

Ideality factor of a diode will depend on the location of the plane of maximum recombination within the diode's depletion region. It will have a minimum of one, but can range up to infinity depending on placement of the plane. Case studies analyzed in this work demonstrate better agreement with experimental data from GaN-based p-i-n diodes.
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All authors Iris Celupica-Liu, Tanay Tak, Yuh-Renn Wu, James S. Speck

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

Three-dimensional atom-by-atom measurement of interface diffusion dynamics

Doojin Park, Hyesung Jo, Yongmin Kwon et al. (+7 more)

Diffusion at interfaces governs how materials and devices form, evolve and function. It is usually measured through smooth concentration profiles and bulk transport coefficients, which average over the discrete atomic rearrangements. At nanoscale interfaces only a few atomic layers wide, however, such coarse-graining obscures the local three-dimensional (3D) atomic transport, and scalar diffusion coefficients cannot fully describe species-, layer- and facet-resolved redistribution. The essential observable is the discrete 3D redistribution of atoms themselves, beyond an averaged profile. Here we combine micro-electro-mechanical systems (MEMS) pulse-quench heating with atomic electron tomography (AET) to reconstruct five 3D atomic configurations of the same coherent Pd@Pt core-shell nanoparticle, each corresponding to a well-defined thermal state. Species-conserving one-to-one assignment links neighbouring configurations, and labelled reference simulations correct the displacement bias caused by indistinguishable same-species atoms. The corrected Pd diffusivities follow Arrhenius behaviour, giving an apparent activation energy of 1.10 eV, consistent with migration-limited vacancy-mediated transport. Atomic-layer transition statistics further show that increasing 3D mobility can coexist with declining net chemical transfer and reveal facet-dependent pathways hidden by the scalar diffusivity. Together, these measurements establish a 3D atom-by-atom framework that connects identity-corrected mobility to species-, layer- and facet-resolved transport at buried nanointerfaces.
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All authors Doojin Park, Hyesung Jo, Yongmin Kwon, Seokjo Hong, Jaewhan Oh, Youngjoo Whang, Eunjik Lee, Gu-Gon Park, Sang Woo Han, Yongsoo Yang

Friday 18 September

Applied Physics

Dose-Insensitive Defect Engineering, Carrier Kinetics, and Reproducible Chromaticity Tuning in Ion-Implanted InGaN/GaN Quantum Wells

Quan-Shan Liu, Mason Adshead, Sadia Sheraz et al. (+3 more)

Post-growth defect engineering via ion implantation provides a powerful pathway for spatial optical profiling and colour patterning in III-V alloying photonic integration. However, the comprehensive recombination kinetics governing deep-level defect saturation and excitonic recovery under high-temperature annealing remain insufficiently understood. Here, we present a systematic study on the optical dynamics, rate-equation kinetics, and chromaticity evolution of indium-implanted InGaN/GaN multiple quantum wells (MQWs) across implantation doses (5E14 to 5E16 ions cm^-2) and subsequent thermal annealing stages (500 to 1100 deg C). Photoluminescence (PL) spectrum analysis reveals that a dose of <= 5E14 ions cm^-2 induces a modification of the optical response that does not further change upon high-dose implantation. A two-channel coupled rate-equation model is fitted to the data, optimised via differential evolution, allowing the extraction of transition rate constants. This demonstrates that thermal processing at 1000 deg C suppresses the carrier capture rate into deep-level states and also reduces its radiative recombination rate. This kinetic bottleneck drives an order-of-magnitude extension in the channel-specific radiative lifetime. Leveraging the excitation power density dependence of the differential recombination kinetics, where deep defects saturate whilst MQW emission scales near-linearly, we achieve a universal and power density-tunable chromaticity trajectory from warm yellow to cool white-blue emission. These insights enable microscopic defect physics to be linked to the macro-scale colour tailoring observed.
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All authors Quan-Shan Liu, Mason Adshead, Sadia Sheraz, Maddison Coke, Nicholas Lockyer, Richard J. Curry

Applied Physics

Boundary-condition identification from a scale-invariant frequency ratio in shear-deformable and nonlocal beams and plates

Ak{\i}n Oktav

The ratio of a structure's first two natural frequencies depends on its boundary conditions but not on its size, material density, or absolute stiffness, which multiply every frequency equally and cancel in the quotient. We use this to identify the boundary conditions of a small-scale beam or plate from two ratio measurements, without knowing its exact dimensions or material. The paper first establishes how the ratio $r=\omega_2/\omega_1$, and the fractional shift $\Delta r$ it undergoes when a boundary condition changes, respond to the two effects that matter at small scale: transverse shear deformation, through Timoshenko beam and Mindlin plate theory, and small-scale elasticity, through Eringen's nonlocal Timoshenko model. Using a locking-free Rayleigh-Ritz beam solver and a finite-element Mindlin plate solver, each checked against benchmarks, we find an asymmetry. The absolute ratio moves appreciably with thickness, by 12 to 14 per cent over the shear-deformable range, and with orthotropy, by 6 to 9 per cent, but only weakly with nonlocality; the shift $\Delta r$, by contrast, varies by less than 0.2 per cent over the full nonlocal range and by a few per cent under thickness change. Because $\Delta r$ is largely independent of these details, a measured shift identifies which boundary-condition transition a deliberate change of support has produced, with a resolution we quantify and verify against molecular-dynamics data. Two spring continua then extend the method to estimating support compliance, with the non-uniqueness of the tip-support case stated explicitly. The method needs no value of the small-scale parameter or the material constants.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci

Experiments and Modeling of Defect Dynamics and BTI Behavior in Doped InO TFTs during $400^\circ$C Post-Processing Forming Gas Annealing

Yu-Hsin Kuo, Chengyang Zhang, Priyankka Ravikumar et al. (+13 more)

We investigate the impact of a monolithic three-dimensional (M3D) integration process-critical $400^\circ$C post-processing forming gas anneal (FGA) on the electrical performance, reliability, and defect evolution of oxide-channel thin-film transistors (TFTs), combining systematic experiments with density-functional-theory (DFT)-based liquid-quench molecular-dynamics (MD) simulations. Indium tungsten oxide (IWO) TFTs are employed as a model system and encapsulated with a thin 3 nm Al$_2$O$_3$ / 3 nm HfO$_2$ hybrid layer that effectively suppresses external hydrogen ingress. We reveal a non-monotonic evolution of device behavior during FGA, governed by initial densification followed by partial crystallization. Short-duration FGA (10 min) induces channel densification and the formation of shallow, delocalized defect states, leading to pronounced positive bias temperature instability (PBTI) degradation and the emergence of a characteristic transfer-curve "kink." With prolonged annealing (>40 min), partial crystallization of the oxide channel occurs, stabilizing hydrogen in deep, localized defect states, suppressing hydrogen mobility, and restoring device reliability. As a result, the PBTI shift is reduced to 10.4 mV after 2000 seconds of stress, accompanied by complete elimination of the transfer-curve kink. These findings provide a mechanistic understanding of hydrogen-defect interactions during high-temperature post-processing FGA and demonstrate that appropriate hydrogen-blocking encapsulation enables oxide-channel TFT integration without compromising electrical performance or reliability.
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All authors Yu-Hsin Kuo, Chengyang Zhang, Priyankka Ravikumar, Sanghyun Kang, Taeyoung Song, Marco Villena, Luca Larcher, Hwan Kim, Minji Hong, Pilsang Yun, Gaurav Thareja, Shimeng Yu, Daewon Ha, Suman Datta, Julia Medvedeva, Asif Khan

Applied Physics

Liquid-Nitrogen Micropillar-Wick Cooling for Cryogenic Electronics: A Numerical Study of Thermal Performance and Capillary Dry-Out Limits

Felix Mende, Marcus Wislicenus, Dianping Jiang et al. (+2 more)

Cryogenic computing technologies are maturing rapidly, but heat removal remains a key challenge when increasing the device density and operating power. Two-phase evaporative cooling is a promising approach to solve this issue, because it can dissipate high heat fluxes while maintaining small temperature rises. Here, we numerically investigate liquid-$\mathrm{N_2}$-filled silicon micropillar wicks as a capillary-fed thin-film evaporation concept for cryogenic electronics. The model combines Young-Laplace meniscus calculations, Hertz-Knudsen-Schrage evaporation, unit-cell heat-transfer and liquid-flow simulations, and an array-level thermal and capillary-flow model. For a representative geometry with a pillar diameter of $10\,\mu\mathrm{m}$, pitch of $24\,\mu\mathrm{m}$, and pillar height of $75\,\mu\mathrm{m}$ at an applied heat flux of $20\,\mathrm{W\,cm^{-2}}$, the predicted chip-temperature rise is approximately $2.7\,\mathrm{K}$. This is substantially below the estimated temperature rises for representative conduction cooling through an indium-interlayered copper heat sink and direct liquid-$\mathrm{N_2}$ immersion. The corresponding predicted single-fed dry-out length is approximately $2.7\,\mathrm{mm}$, equivalent to an ideal double-fed coolable width of approximately $5.3\,\mathrm{mm}$. The results indicate that local thermal performance is favorable, whereas lateral scalability is primarily constrained by capillary dry-out. An approximate capillary-viscous scaling relation provides a compact framework for comparing dry-out limits across working fluids and related wick geometries and for identifying strategies to extend capillary-fed transport.
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All authors Felix Mende, Marcus Wislicenus, Dianping Jiang, Munehiro Tada, Lukas M. Eng

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

Single Best Fits Can Be Misleading: Resolving Common Trapping Signatures across FA–Cs Perovskites

Maxim Simmonds, Katarzyna Pydzińska-Białek, Thomas C. Rossi et al. (+6 more)

Identifying defects responsible for non-radiative recombination in metal-halide perovskites remains challenging, with no common defect signatures established across compositions. Here, we combine fluence-dependent time-resolved photoluminescence, full Shockley–Read–Hall modelling and Bayesian posterior inference across an FA$_{1-x}$Cs$_x$PbI$_3$ compositional series. We show that trap occupation governs carrier dynamics and defect-parameter identifiability in semiconducting materials: weakly occupied states exhibit electron-capture-coefficient–trap-density degeneracies, whereas trap filling lifts them. In our perovskite systems, a non-degenerate signature $T\beta$, characterized by a strongly asymmetric $\beta_p/\beta_n$ capture-coefficient ratio, occurs across all compositions, suggesting substantial trap filling is a general feature of perovskite carrier dynamics. We further identify $T\alpha$ as a shared, device-performance-limiting non-radiative recombination channel, while a shallow $T\epsilon$ signature unique to FAPbI$_3$ produces the largest steady-state non-radiative recombination rate and is consistent with the previously observed high stacking-fault density of this composition. This framework therefore provides a basis for comparing trapping signatures across different semiconducting materials at room temperature.
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All authors Maxim Simmonds, Katarzyna Pydzińska-Białek, Thomas C. Rossi, Mostafa Othman, Aïcha Hessler-Wyser, Christian Wolff, Christophe Ballif, Vincent M. Le Corre, Eva Unger

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

Predicting the Elastic Properties of a Cemented Granular Material during Chemical Damage (Debonding)

Alexandre Sac-Morane, Maria Olarte-Garzon, Philipp Braun et al. (+3 more)

While underground reservoirs emerge as essential elements to face global warming, these systems represent complex multi-physical and multiscale problems. The considered injection of fluids during hydrogen storage, carbon dioxide sequestration, or geothermal energy recovery involves a modification of the chemical equilibrium of the fluid in the porous reservoir. Chemical reactions can induce microstructural changes of the rock matrix, leading to a reduction of elastic properties of the material, and to potential settlement or stress redistribution. Consequently, it becomes pivotal to establish predictive behavior laws to describe the effect of chemical damage on elastic properties. Facing the difficulties to estimate experimentally the impact of chemical damage on mechanical properties, a Digital Rock Physics approach is proposed in this contribution. This numerical homogenization scheme is used to compare two distinct types of microstructure models: the first one consists in a Discrete Element Model, while the second one employs a continuous description. This continuous formulation is based on a Phase-Field description to predict the evolution of the microstructure subjected to chemical alterations and on the Fast Fourier Transform to estimate the macroscopic properties of the material. Finally, these frameworks establish different softening laws that can be used as constitutive ingredients for a cemented material during its weathering.
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All authors Alexandre Sac-Morane, Maria Olarte-Garzon, Philipp Braun, Jean-Michel Pereira, Manolis Veveakis, Hadrien Rattez

Applied Physics

Multiplexing approaches to thermoradiative signatureless communications

Valerii Radchenkov, Peter J. Reece, Stephen P. Bremner et al. (+2 more)

Using mid-infrared emission from semiconductor devices for covert communications remains a relatively unexplored and yet promising opportunity. The phenomenon of negative luminescence allows for a method of signatureless covert communications where the net infrared emission of an emitting optoelectronic device is balanced to be identical to the ambient thermal background. In this work we provide a practical demonstration of covert data transfer over a thermoradiative channel with data rates up to 100 kbps. In addition, we demonstrate several additional multiplexing techniques that make the proposed thermoradiative communications method more secure against interception by achieving zero instantaneous optical emission, while remaining detectable if a sufficiently spatially or spectrally discerning observation is utilised. Finally, we discuss various application scenarios in which the proposed methods can be used to achieve secure signatureless communications.
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All authors Valerii Radchenkov, Peter J. Reece, Stephen P. Bremner, Nicholas J. Ekins-Daukes, Michael P. Nielsen

Thursday 17 September

Applied Physics · Cross-listed from physics.optics

Volumetric Evanescent Edge Coupling for Fiber-to-Chip Optical I/O

Hamdy Elshehaby, Omar Bakheet, Mohamed A. Swillam et al. (+1 more)

Scaling optical input/output for co-packaged optics is limited by the fiber-to-chip interface. Conventional edge coupling offers low loss and broad bandwidth but confines channels to a single row along the chip facet. On the other hand, surface couplers are either narrowband or difficult to fabricate with high yield and, importantly, compete with back-end metal routing. In this work, we introduce volumetric edge coupling, in which the chip edge is structured in three dimensions so that optical coupling can occur over a two-dimensional region rather than along a single line, providing a route toward interfacing multiple waveguides with multiple cores of a multicore fiber while preserving optical access from the chip perimeter. We investigate a single-channel realization based on total-internal-reflection (TIR)-mediated evanescent coupling through the 54.7$^\circ$ sidewall of a KOH-etched silicon cavity, with the coupling profile shaped by a wedged buried-oxide ridge. Finite-difference time-domain simulations predict a peak coupling efficiency of 88% (-0.56 dB) at 1550 nm and a 1-dB bandwidth of 86.45 nm spanning the C-band. The design further exhibits a vertical alignment tolerance of approximately $\pm$2 $\mu$m, weak sensitivity to transverse offsets up to 5 $\mu$m, and a $\pm$0.8$^\circ$ 1-dB angular tolerance. The reflected optical field also provides a potential alignment signal, offering a path toward reduced active alignment overhead in future multicore implementations.
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All authors Hamdy Elshehaby, Omar Bakheet, Mohamed A. Swillam, Mohamed Elkabbash

Applied Physics

Three-dimensional vector waves in time-variant materials, with applications in time-reversed focusing and Green's function retrieval

Kees Wapenaar and Dirk-Jan van Manen

The behavior of wave propagation and scattering in time-variant materials has been studied by many authors, for electromagnetic as well as for mechanical waves. Most studies consider two-dimensional waves, governed by scalar wave equations. Here we introduce a unified wave equation for three-dimensional electromagnetic and elastodynamic vector-wave propagation and scattering in homogeneous, time-variant materials. Using the symmetry properties of this equation, we establish the conservation of net field-momentum density, and a reciprocity relation between causal and acausal Green's functions. The latter relation is exploited in the derivation of the counterparts of classical time-reversed focusing and Green's function retrieval for time-variant materials.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci

Divergent Solid-state Conversion Pathways in Evaporated All-perovskite Tandem Solar Cells

Huagui Lai, Amber Wright, Nick Huber et al. (+8 more)

Sequential thermal evaporation (sTE) is emerging as a solvent-free route to high-quality mid-bandgap perovskites, but its extension to mixed-halide wide-bandgap (WBG) and Sn-Pb narrow-bandgap (NBG) absorbers for all-perovskite tandem solar cells (TSCs) remains limited by an incomplete understanding of solid-state conversion. Here, using time-sliced ex situ analysis, we reveal divergent solid-state conversion mechanisms in sequentially evaporated WBG and NBG precursor stacks. In WBG stacks, formamidinium (FA)-containing species penetrate the inorganic template and Br/I redistribution precedes substantial three-dimensional perovskite formation. The photoactive phase then crystallizes from a chemically mixed reservoir, and absolute PbBr$_2$ thickness, rather than nominal PbBr$_2$/PbI$_2$ ratio, determines the final bandgap. In NBG stacks, by contrast, an early Pb-rich perovskite phase forms upon formamidinium iodide deposition, restricting further FA penetration into the buried SnI$_2$ precursor. Subsequent annealing promotes rapid lattice reorganization faster than Sn/Pb interdiffusion, leaving vertical compositional gradients. Guided by these insights, we develop sTE absorbers with bandgaps spanning 1.26-1.96 eV and demonstrate the first evaporated all-perovskite TSC, reaching a power conversion efficiency of 19.2%. Encapsulated tandems retain on average 80% of their initial efficiency after 1,200 h at 65 $^\circ$C (ISOS-D-2). These results establish bandgap-specific control of solid-state conversion as a design principle for sequentially evaporated perovskite tandem photovoltaics.
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All authors Huagui Lai, Amber Wright, Nick Huber, Niels Uythoven, Federico De Giorgi, Jincheng Luo, Tristan Sachsenweger, Sunil B. Shivarudraiah, Chih-Jen Shih, Wolfgang Tress, Fan Fu

Applied Physics

Energy Harvesting for Self-Powered Microsystems: A Critical Review of Materials, Power Management, and System Integration

Lyuye Lin, Feng Zhifu, Ermanno Miele et al. (+12 more)

The relentless proliferation of the Internet of Things (IoT), wearable bioelectronics, and cyber-physical infrastructure has rendered the conventional electrochemical battery the single most prohibitive bottleneck to long-term, maintenance-free autonomous microsystems. Energy harvesting, i.e. the conversion of ambient mechanical, thermal, and radiative energy into usable electrical power, has consequently emerged as a transformative paradigm to realize perpetual, battery-independent operation. This review critically synthesizes the most significant advances in energy harvesting technologies over the recent period, with a focus on triboelectric nanogenerators (TENGs), piezoelectric and pyroelectric transducers, indoor photovoltaics, radio-frequency (RF) rectennas, and their multi-source hybrid integrations. We highlight paradigm-shifting breakthroughs, including liquid-solid TENGs that eliminate mechanical wear, nonlinear piezoelectric oscillators that broaden operational bandwidth by over 300%, machine-learning-accelerated material discovery for high charge-density dielectrics, and multiband and broadband RF harvesting enabled by metamaterial architectures. Crucially, we move beyond conventional materials-centric narratives to critically interrogate the "unseen" system-level bottlenecks: ultra-low-voltage cold-start power management integrated circuits (PMICs), the impedance-matching challenges of hybrid energy sources, and the persistent degradation of micro-supercapacitors and thin-film batteries under realistic field conditions.
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All authors Lyuye Lin, Feng Zhifu, Ermanno Miele, Giuseppe Cantarella, Elena Degoli, Diego Angeli, Lethy Krishnan Jagadamma, Feng Gao, Michele Magno, Ivano Eligio Castelli, Tommaso Ongarello, Chunbo Liu, Roman Krahne, Denis Garoli, Remo Proietti Zaccaria

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

Anharmonic Phonon Renormalization and Defect Tolerance of the Thermoelectric Power Factor in Monolayer SnSe

Nguyen Tran Gia Bao, Thang Bach Phan, Vu Thi Hanh Thu et al. (+1 more)

Monolayer tin selenide (SnSe) exhibits phase-dependent anharmonic lattice dynamics, yet their consequences for the thermoelectric power factor (PF) and point-defect tolerance remain unresolved. We combine density functional theory, the stochastic self-consistent harmonic approximation (SSCHA), and Boltzmann transport calculations including electron-phonon and electron-defect scattering to investigate monolayer $\alpha$-SnSe (Pnma) and $\beta$-SnSe (Cmcm). In dynamically stable $\alpha$-SnSe, SSCHA renormalizes the finite-temperature phonons without changing the qualitative n-type transport picture. In $\beta$-SnSe, SSCHA removes the harmonic soft-mode instability of the Cmcm phase at 800-1000 K, and thereby enables high-temperature transport calculations; LO/TO-2 is the principal electron-scattering channel. In the lower-density window near $10^{12}$ cm$^{-2}$, the n-type PF reaches 15-19 $\mu\mathrm{W}/(\mathrm{K}^{2}\cdot\mathrm{cm})$ at 800-900 K and exceeds the p-type PF primarily because of the higher electrical conductivity. Se vacancies ($V_{\mathrm{Se}}$) produce weaker electron-defect scattering than Sn vacancies ($V_{\mathrm{Sn}}$), and p-type transport is less defect tolerant than n-type transport in both phases. We define an operational critical defect concentration, $C_{\mathrm{crit}}$, at which the PF decreases by 15% relative to the corresponding defect-free value. The lowest $C_{\mathrm{crit}}$ is $8.841\times10^{-5}$ (approximately 88 ppm) for p-type $\alpha$-SnSe with $V_{\mathrm{Sn}}$; for n-type $\beta$-SnSe with $V_{\mathrm{Se}}$, the 15% threshold is not reached up to $5\times10^{-3}$ (5000 ppm). These results distinguish finite-temperature phonon renormalization in stable $\alpha$-SnSe from anharmonic stabilization in $\beta$-SnSe and provide defect-concentration limits for preserving the PF.
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All authors Nguyen Tran Gia Bao, Thang Bach Phan, Vu Thi Hanh Thu, Nguyen Tuan Hung

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

Exergy-Anergy Representation of Turbomachine Performance Characteristics

Tihomir Varchev, Yiwen Yuan, Tobias Schateikis et al. (+1 more)

The performance synthesis calculation of aircraft engines relies on tabulated datasets for the simulation of the complex turbomachinery components at acceptable runtimes. Typically, these so-called performance maps express the change of the fluid's energetic state over the component in terms of the total pressure ratio and the isentropic efficiency of the process. However, the definitions of both parameters are different for compressors and turbines and the isentropic efficiency is in both cases not defined for a unity pressure ratio. Moreover, this parameter combination is not directly applicable when modelling the engine at the aircraft level, which is required for modern highly integrated aircraft design. As exergy analysis is an established tool for aircraft design asessment, novel performance maps are proposed that describe the change in exergy and anergy over a given turbomachine component. Both changes are expressed as non-dimensional parameters whose definition is consistent for compressors and turbines, and is compatible with a unity pressure ratio. It is shown that the presented exergy-anergy maps are obtainable on a standard turbomachine test bed or through transformation of existing maps. It is highlighted using examples, that the conversion between existing maps and exergy-anergy maps is completely lossless. The different operating regimes of the turbomachines are clearly distinguishable in the novel map representation, which allows an assessment of the map's physical consistency. It is therefore concluded, that the exergy-anergy maps are an important alternative to the performance map variants established today.
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All authors Tihomir Varchev, Yiwen Yuan, Tobias Schateikis, Stephan Staudacher

Applied Physics · Cross-listed from physics.optics

Voltage-Current-Emission Framework of Time-Resolved Electroluminescence

Hui Bao, Longjia Wu, Yanan Guo et al. (+3 more)

Time-resolved electroluminescence has been a central methodology in the development of LED devices. However, it still lacks quantitative theoretical descriptions of time-resolved electroluminescence. By combining the equivalent circuit models of semiconductor devices and the carrier dynamics of electroluminescence processes, we here developed a Voltage-Current-Emission framework to illustrate time-resolved electroluminescence from the pulse voltage as input, to injection current and finally generate electroluminescence as output. The features of different LED devices can be quantitatively interpreted, confirming the universal applicability across LEDs with different materials and device structures. Importantly, the curves of time-resolved electroluminescence can be simulated to quantitatively describe the dynamics of current and carriers of LED operation. In all, the Voltage-Current-Emission framework offers theoretical guidance for achieving advanced LED devices for AI technology.
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All authors Hui Bao, Longjia Wu, Yanan Guo, Jianchang Yan, Ying Wang, Haizheng Zhong

Wednesday 16 September

Applied Physics

Giant Resonant Reflection Gain from Injection-Induced Quenching in a Tunnel Diode

Darmindra Arumugam, Jack Bush and Brook Feyissa

Negative-resistance microwave oscillators can simultaneously sustain autonomous oscillations and coherently scatter electromagnetic waves, enabling active reflection beyond conventional linear amplification. Here we demonstrate giant resonant reflection gain from synchronization-induced phase localization in a self-sustained tunnel diode oscillator operating near 2.96 GHz. Weak resonant RF injection drives a transition from a broadband free running state to a phase localized narrowband reflected carrier. The resulting reflected enhancement reaches 83.1dB relative to the injected signal and is accompanied by greater than order of magnitude linewidth collapse, nonlinear injection pulling, and a synchronization bandwidth of 15.84 kHz. Time resolved spectrograms directly resolve injection locking and frequency entrainment, while noisy Stuart Landau simulations reproduce the observed spectral concentration and detuning dependent gain roll off near the Hopf instability. Artificially increasing phase diffusion with broadband bias noise suppresses the reflected enhancement, confirming synchronization-induced quenching of phase fluctuations as the origin of the giant coherent reflection gain.
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Applied Physics · Cross-listed from nlin.PS

The Origin of Imperfection Sensitivity in the Buckling of Cylindrical Shells

Tian Yang and Tobias M. Schneider

Buckling of thin cylindrical shells under axial compression, a classical example of a subcritical instability, is highly sensitive to small imperfections, with minute geometric variations causing large changes in buckling threshold. To uncover the origin of this sensitivity, we use numerical continuation and bifurcation analysis while systematically varying the depth and size of a single localized Gaussian defect. We show that the instabilities of the imperfect shell originate from localized equilibria already present in the perfect shell. By breaking translation symmetry, the defect pins these equilibria and changes how they connect to the imperfect base state. Small changes in defect geometry can thereby switch the bifurcation that triggers buckling, producing non-monotonic and discontinuous changes in buckling threshold and abrupt changes in buckling mode. Imperfection sensitivity is therefore not simply sensitivity to imperfection magnitude, but sensitivity of the underlying bifurcation structure to imperfection geometry.
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Applied Physics · Cross-listed from physics.ed-ph

From Prompts to Physical Laws: A Generative AI Workflow for Engineering Physics Education

Laura B. Alvarado-Cruz, Josep Ll. Suñer, Pedro Yuste et al. (+3 more)

This work explores the use of generative artificial intelligence (AI) as a source of synthetic experimental content for introductory physics courses in engineering education. Using PixVerse.ai, Grok Imagine, and Pippit, three video scenarios were generated to represent distinct resistive force regimes: constant friction, linear drag, and quadratic drag. Kinematic data were extracted from the generated videos using Tracker, an open-source video analysis tool, and subsequently fitted to the corresponding analytical models through non-linear least-squares regression in Microsoft Excel. The results show good agreement between the synthetic data and the classical kinematic equations derived from Newton's Second Law. From the fitted parameters, physically meaningful quantities were recovered in each case, with values broadly consistent with those reported in the literature under the assumed conditions. A recurring observation is that the physical plausibility of the generated motion depends on the level of detail included in the text description used to generate the videos. More specific descriptions tend to produce more coherent dynamical behaviour, suggesting that the formulation of input prompts plays a relevant role in shaping the resulting physical consistency and can be regarded as an integral component of the experimental design process. The integration of generative AI, video-based motion tracking, and curve fitting provides a complete workflow that mirrors key stages of experimental practice, from model construction to quantitative validation. The proposed methodology engages students in experimental design, data acquisition, parameter estimation, and model evaluation, promoting key engineering competencies in modelling of physical models using widely available tools. Overall, the proposed methodology demonstrates the potential of generative AI to support physics education
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All authors Laura B. Alvarado-Cruz, Josep Ll. Suñer, Pedro Yuste, Juan C. Castro-Palacio, Juan A. Monsoriu, Francisco M. Muñoz-Pérez

Applied Physics

Static-to-dynamic field conversion in a temporally switched Lorentz medium

Alazar G. Salfore and Mario J. Mencagli

We investigate static-to-dynamic electromagnetic field conversion in a temporally switched Lorentz medium initially subjected to an electrostatic field. An abrupt change of the oscillator strength drives the material away from its initial equilibrium, while the polarization retains memory of the pre-switch state and acts as the source of the resulting transient. We formulate the resulting initial-value problem in the Laplace domain and derive an analytical representation of the generated field in terms of the poles of the finite Lorentz slab. Material dispersion gives rise to a richer modal structure than in the nondispersive case, including families of slab-mode poles that accumulate toward the singularities associated with the Lorentz polarization dynamics. We further show that material memory governs the earliest stage of the transient, producing a smooth field onset and setting the velocity of the earliest propagating disturbance through the high-frequency permittivity. Because the temporal switch generates broadband spectral content, the transient samples positive-, near-zero-, and negative-permittivity regions of the post-switch material response, leading to qualitatively different spatial field distributions. These results reveal how material dispersion and memory fundamentally shape the generation and evolution of radiation produced from an initially static electromagnetic state.
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Applied Physics

Si- and C-Induced Modifications in Vapor-Solid-Grown InGaAs Nanowires: From Crystal Structure to Carrier Dynamics

Hamidreza Esmaielpour, Leopold Rothmayer, Thomas Trinkl et al. (+5 more)

Determining the impact of dopants in ternary III-V nanowires (NWs) is crucial for their applications in next-generation optoelectronic and photonic devices; however, the interplay between dopant species, crystal structure, and carrier dynamics in vapor-solid-grown InGaAs NWs remains underexplored. In this study, the influence of silicon (Si) and carbon (C) doping on the structural, morphological, and optical properties of catalyst-free, selective-area grown InGaAs NWs fabricated by molecular beam epitaxy is investigated. Scanning electron microscopy demonstrates that C-doping increases the NW aspect ratio by over 100% compared to undoped NWs, while a concomitant decrease in their planar defect density is observed, indicating enhanced crystal quality with C-doping. Despite their superior crystal quality, the C-doped NWs present a diminished photoluminescence intensity, due to point defects and increased surface recombination velocity. This is further supported by time-resolved photoluminescence spectroscopy, revealing accelerated non-radiative recombination in the C-doped NWs. Lastly, hot-carrier effects in these nanostructures are studied, and their signatures remain observable, albeit with reduced intensity in both Si- and C-doped NWs. This comprehensive study establishes clear correlations between doping parameters and the resulting material characteristics and carrier dynamics, offering valuable insights into the fundamental mechanisms governing the VS-grown InGaAs NWs and their implications in optoelectronic devices.
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All authors Hamidreza Esmaielpour, Leopold Rothmayer, Thomas Trinkl, Laura Niermann, Tore Niermann, Michael Lehmann, Jonathan J. Finley, Gregor Koblmüller

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

Encapsulation epitaxy of air-stable monolayer superconducting films for quantum circuits and qubits

Xudong Zheng, Sameia Zaman, Kenan Zhang et al. (+22 more)

Two-dimensional (2D) superconductors are an emerging platform for strongly correlated physics and quantum information science. Their reduced dimensionality, atomically flat interfaces, and high crystallinity are attractive for realizing compact lumped-element devices in superconducting circuits. However, synthesizing large-area, monolayer 2D superconductors remains challenging because of their susceptibility to oxidation. Here, we report an "encapsulation epitaxy" mechanism that enables the growth of large-area, air-stable, monolayer superconducting NbSe2 films and explore their use in superconducting quantum circuits. A 2D encapsulation layer, such as graphene or hexagonal boron nitride (hBN), pre-deposited on a 3D substrate (e.g., SiO2 or Si3N4), serves both as a template for epitaxial growth of monolayer NbSe2 (1L-NbSe2) underneath it and as a protective cover. This approach produces uniform, large-area (>1-inch) 1L-NbSe2 with greatly enhanced ambient stability, enabling device fabrication in air. The resulting 1L-graphene/NbSe2 heterostructures exhibit robust superconductivity (Tc ~ 1 K) and enhanced charge density wave order (TCDW ~ 177 K), indicative of high material quality. We further integrate 1L-NbSe2 into superconducting circuits using oxidation-free transfer and superconducting edge-contact techniques. The 1L-NbSe2 exhibits a measured kinetic inductance LK ~ 0.7 nH/square, making it suitable for quantum circuits requiring high-kinetic-inductance elements. Encapsulation epitaxy thus provides a route to air-stable 2D superconductors and van der Waals heterostructures, with potential for wafer-scale, monolithic fabrication of superconducting quantum circuitry.
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All authors Xudong Zheng, Sameia Zaman, Kenan Zhang, Connor A Occhialini, Haowei Xu, Zhien Wang, Fangyuan Liu, Luiz Gustavo Pimenta Martins, Sejoon Lim, Tianyi Zhang, Tilo H. Yang, Jiangtao Wang, Yunyue Zhu, Zachariah Hennighausen, Sein Park, Steven Vitale, Kevin Tibbetts, Stephen Margiotta, Phillip Kim, Cong Su, Ju Li, Riccardo Comin, William D. Oliver, Joel Î-j. Wang, Jing Kong