Applied Physics
Physical mechanisms of ohmic contact and tunnel diode: A novel explanation in terms of impurity-photovoltaic-effect resulting from infrared self-emission at room-temperature
Jianming Li
A mechanism of
quantum-mechanical tunneling is based on electron-wavefunction and is used to explain ohmic contact as well as tunnel and Zener diodes. Tunneling is the important example of wave-particle duality. In this study, an attempt is made to explain these devices in particle description. As is well known, any object at room-temperature emits infrared (IR)
photons due to blackbody radiation. The process of heavy doping can cause a lot of defects, e.g. vacancies and interstitials. The self-absorption of the IR emission could be achieved through sub-band-gap excitations due to defect-related levels in forbidden energy gap, creating carriers. In a heavily doped p-n junction diode, some of the IR-generated carriers diffuse into the junction which has a built-in field in a depletion layer. The built-in field then sweeps out the carriers, producing IR photocurrent. The IR photocurrent is regarded as the reverse current of the p-n junction according to the precedent where
impurity-photovoltaic-effect is used to explain
circuit devices (arXiv:2510.18226). Also, a reverse bias voltage increases depletion layer width, but carrier
diffusion length out of the depletion layer remains unchanged, and more IR-generated carriers created in and near the depletion layer can contribute to the IR current. In addition, heavy doping results in not only a great many IR-generated carriers but also avalanche effect at low voltage. As a result, total reverse current dramatically increases with voltage, thus a Schottky diode can be altered to create an ohmic contact and a p-n diode can become a tunnel diode. Considering the wave-particle duality, the combination of
quantum-mechanical and photovoltaic mechanisms is suggested to explain these devices. Each mechanism plays a big or small role in the explanation.
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Optics
Scalable optical neural network with nonlocally coupled coherent photonic processor
Chun Ren, Ryota Tanomura, Kazuki Ichinose et al. (+5 more)
Optical neural networks (ONNs) based on programmable photonic integrated
circuits (PICs) offer a promising route toward low-latency and energy-efficient deep learning. However, conventional photonic implementations of
matrix-vector multiplication (MVM) rely on locally connected architectures, such as Mach-Zehnder interferometer (MZI) meshes, whose number of active components scales quadratically with
matrix size, severely limiting scalability. Here, we present a scalable ONN that overcomes this limitation by exploiting the intrinsically diffractive and nonlocal nature of coherent light inside a silicon photonic chip. Our approach employs cascaded stages of multiport directional couplers (MDCs) interleaved with compact phase-shifter arrays, enabling strong nonlocal coupling among multiple optical modes. We show that an MDC-based optical
unitary converter (OUC) requires only $3N$ phase shifters to achieve uniform coverage over the $N$-dimensional complex
unitary group, in stark contrast to the $O(N^2)$ scaling of conventional MZI meshes. Based on the singular value decomposition, we demonstrate that an $N\times N$ MVM can be realized using only $7N$ phase shifters, breaking the traditional $O(N^2)$ scaling barrier. We experimentally implement a 32-input silicon photonic MVM chip with a tenfold reduction in active components and validate its performance on various classification tasks. Our results establish a practical pathway toward large-scale, energy-efficient, and reconfigurable photonic neural networks.
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All authors Chun Ren, Ryota Tanomura, Kazuki Ichinose, Keigo Mizukami, Yoshitaka Taguchi, Taichiro Fukui, Yoshiaki Nakano, Takuo Tanemura
Fluid Dynamics
Optimize discrete loss with finite-difference physics constraint and time-stepping for PDE solving
Yali Luo, Yiye Zou, Heng Zhang et al. (+4 more)
Computational Fluid Dynamics (CFD) is an important approach for analyzing flow phenomena and predicting engineering-relevant quantities. The governing physics is formulated as partial differential equations(PDEs) and solved numerically on computational grids. Physics-informed neural networks(PINNs) have emerged as a popular optimization-based approach for solving PDEs, but they often suffer from ill-conditioned objectives and the high cost of automatic differentiation. Optimization-based discretizations such as ODIL mitigate several PINN drawbacks by optimizing discrete variables directly, yet accuracy and efficiency remain limited on body-fitted geometries and for time-dependent problems. This paper proposes FDTO, a finite-difference time-stepping loss-optimization solver that defines physics losses from discrete residuals. FDTO couples curvilinear coordinate transforms with body-fitted structured grids and decomposes long-horizon
evolution into sequential, well-conditioned subproblems consistent with time marching. The method is primarily evaluated on incompressible Navier-Stokes flows, including lid-driven cavity
benchmarks, external airfoil aerodynamics (lift/drag consistency), and a cylinder case on a multi-block structured mesh with cross-block coherent solutions. Additional validations on
diffusion and flow-mixing problems further demonstrate generality. Compared with representative PINN-based solvers, FDTO reduces GPU
memory by about 82.6% on the lid-driven cavity case and achieves 3-5 times lower relative error on the flow-mixing problem. These results indicate that FDTO enables accurate, stable, and
memory-efficient discrete-loss optimization for incompressible-flow solutions, while remaining applicable to other PDE models.
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All authors Yali Luo, Yiye Zou, Heng Zhang, Mingjie Zhang, Gang Wei, Jingyu Wang, Xiaogang Deng
Fluid Dynamics
Topographic Effects on Steady-States of Non-Rotating Shallow Flows
Pierpaolo Bilotto and Roberto Verzicco
In this work, we discuss the long-time behavior of non-rotating quasi-2D viscous flows over topographies. We develop a novel theoretical and numerical framework for the analysis of these flows, derived as a dimensional reduction of the 3D Navier-Stokes equations in the limit of infinite Rossby number $\mathit{Ro}$. We numerically determine dynamical attractors for fixed kinetic energy, focusing on the dependence of the final state on the Reynolds number. Under turbulent conditions, the attractor is no longer unique but delocalized, spanning the lowest excited states of the deterministic system. Regardless of the realized stationary configuration, large-scale
vortices settle within topographic valleys, in contrast with the phenomenology of the rotating case. These findings have significant implications for understanding steady turbulent regimes in slowly rotating ($\mathit{Ro} \gg 1$) planetary environments.
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Applied Physics · Cross-listed from cond-mat.stat-mech
Harvest Ambient Heat via Constraint-Shaped Phase-Change Cycles: Micro $\Delta T$, Subcooled Liquid, and Liquid-Only Compression
Ting Peng
Conventional heat engines typically require two distinct thermal reservoirs, with their efficiency strictly bounded by the Carnot limit. We present a theoretical design for a phase-change heat engine that utilizes water as the working fluid undergoing state transitions within geometry-constrained flow paths. The proposed cycle operates under a micro-temperature difference (1–2\,$^\circ$C) and relies on
liquid-only compression. The system harvests thermal energy via an ambient micro-temperature difference relative to the environment ($q_{\mathrm{in}} \approx 8.37\,\mathrm{kJ}/\mathrm{kg}$ at 24–26\,$^\circ$C). Expansion work is recovered from the enthalpy drop during flash evaporation. Comprehensive numerical analysis using NIST property data confirms that, in the reversible limit, the cycle yields positive net work while maintaining standard thermodynamic consistency. This study illustrates the theoretical potential for ambient energy harvesting via low-pressure phase change, although the extremely small work output per cycle suggests that hardware realization will require exceptional mechanical precision to overcome parasitic losses.
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Optics
The Bragg Frequency Convertor: A Meeting Between Spatial and Temporal Periodicities For Selective Parametric Frequency Translation
Sajjad Taravati
This study introduces the Bragg Frequency Converter, a spatiotemporal-periodic grating concept that extends conventional Bragg gratings into the dynamic domain for pure parametric frequency conversion. By selectively time-modulating either the high-index or low-index layers of a quarter-wave stack, the structure achieves directional frequency conversion: high-index modulation yields efficient down-conversion, while low-index modulation produces up-conversion. This layer selectivity stems from the asymmetric Bloch mode distribution and associated phase-matching conditions. One practical realization, based on a silicon rib waveguide with periodic sidewall corrugations and selective doping of the high-index segments, is presented and analyzed. A coupled-mode theory is developed to explain the mechanism and validated through full-wave simulations. An experimental setup using optical pumping is also proposed for practical implementation. The theoretical and numerical results establish temporal Bragg gratings as a versatile, reconfigurable platform for spurious-free frequency conversion with applications in optical signal processing and integrated photonics.
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Physics and Society
Robustness and size-dependence of circadian rhythms in multiscale suprachiasmatic-nucleus networks
Youhao Zhuo, Yingpeng Liu, Jiao Wu et al. (+2 more)
Understanding how multi-scale network structure influences circadian rhythms in the suprachiasmatic
nucleus (SCN) is essential for uncovering the principles of rhythmic robustness and synchronization. Previous studies using synthetic SCN networks suggested a size-dependent phenomenon, in which rhythmic activity initially strengthens with network size and then saturates, but it remains unclear whether this occurs in real SCN networks. Here, we apply
geometric branch growth (GBG) and
geometric renormalization (GR) to generate self-similar scaled-up and scaled-down replicas from a single-scale functional mouse SCN network. Unlike synthetic models, these SCN replicas do not exhibit size-dependent rhythms: average period, amplitude, and synchronization remain stable across scales. By increasing the average degree with network size, we reproduce size-dependent rhythms and show that they arise from network connectivity, whereas low-degree networks fragment and fail to sustain oscillations. Disrupting clustering self-similarity slightly reduces synchronization, but circadian rhythms remain robust, indicating that average degree, rather than clustering, is the dominant structural driver. These results highlight the resilience of SCN rhythms to network scaling and provide a framework for linking multi-scale network structure to biological timekeeping.
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All authors Youhao Zhuo, Yingpeng Liu, Jiao Wu, Kesheng Xu, Muhua Zheng
Medical Physics
Ultra-Sharp Upright Photon Radiotherapy via Low Energy Extended Distance: An Alternative to FLASH for high flux Sources
Lloyd E Kamole Ghomsi, Clinton Gibson, Veng-Jean Heng et al. (+2 more)
Standard 6 megavolt (MV) radiotherapy is limited by source size and secondary electron range to minimum radiological penumbra widths of ~2-3 mm. This study investigates sharper beams via upright radiotherapy with lower energies and extended source-to-patient distances. A 2.5 MV beam from a clinical linac was delivered at a 4 m source-to-phantom distance (2.5 MV-ED). Lateral profiles and percent depth doses were measured in a solid water phantom with radiochromic film and an ion chamber. These single beam measurements were used to
benchmark TOPAS Monte Carlo simulations. The validated 2.5 MV-ED model was then used to simulate upright deliveries with a conical beam geometry. These simulations were compared against equivalent plans generated for standard 6 MV-FFF coplanar deliveries at 1 m from the source. The 2.5 MV-ED single 28x28 mm^2 beam produced a measured 80%-20% penumbra of 1.0 +-0.1 mm, compared to 2.4 mm Jaw-defined penumbra for a standard 6MV-FFF beam. The doses at 10 cm depth were 52% vs. 56%, and the surface doses were 22% vs. 38% for the 2.5MV-ED and standard 6 MV-FFF respectively. Conical geometry Monte-Carlo simulations using the 2.5 MV-ED beams demonstrated significantly sharper composite dose fall-off in all cardinal directions compared to coplanar 6MV-FFF plans. For a spatially fractionated
lattice example plan with 5 mm diameter high dose spheres, the 2.5 MV-ED conical approach achieved a peak-to-valley dose ratio of 4.5-5.2, compared to the 2.6-2.9 achievable with a standard 6 MV-FFF clinical system. Low-energy, extended-distance
photon beams can provide sharper penumbra and lower surface dose, while maintaining comparable depth-dose penetration as standard 6 MV setups. Combined with upright patient setups, ultra-sharp dose distributions with enhanced treatment conformity, reduced toxicity, and higher-fidelity dose modulation are possible.
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All authors Lloyd E Kamole Ghomsi, Clinton Gibson, Veng-Jean Heng, Ramish M Ashraf, Lawrie Skinner
Optics · Cross-listed from cond-mat.soft
Realizing microrheological response of configurable viscoelastic media with a dynamic optical trap
Sanatan Halder and Manas Khan
The local viscoelastic (VE) environment governs the motion of an embedded microsphere and consequently, pertinent dynamical phenomena. However, studying such phenomena with varying VE properties remains challenging for various reasons, including the strong coupling among the VE parameters and their dependence on experimental conditions, such as temperature. Here, we demonstrate the experimental realization of configurable VE media with broad variations, wherein the VE properties can be systematically and independently tuned, employing a dynamic optical trap. Specifically, the dynamics of a particle in a slowly diffusing optical trap provides the linear microrheological response of single-relaxation VE fluids, namely Jeffreys or Maxwell-Voigt (MV) fluids, where the trap strength and its
diffusion coefficient regulate the elastic response and the low-frequency viscosity, respectively. The characteristic features in the mean square displacement (MSD) of the trapped particle match those of a probe particle in real MV fluids, and the simulation results following harmonically bound Brownian particle with long-time
diffusion model describing single-relaxation complex fluids. Our scheme is further validated by demonstrating excellent quantitative agreement between the experimentally observed MSDs of the trapped bead and those from the corresponding analytical predictions. We extend the applicability of this scheme for realizing the microrheological response of double-relaxation VE media by incorporating appropriately correlated noise in the trap trajectory, signifying its validity for any linear VE media with multiple relaxations. Our scheme can be further extended to realize probe particle dynamics in an active VE environment, e.g., an entangled network of active
polymers, by translating the trap along an active Brownian trajectory.
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Optics
Impact of refractive index heterogeneity on stimulated Brillouin scattering microscopy: a quantitative analysis
Meng Xu, Zixuan Du, Yun Qi et al. (+4 more)
Stimulated Brillouin scattering (SBS) microscopy enables label-free biomechanical imaging, with Brillouin gain serving as a critical contrast parameter for quantitative analysis. However, the influence of sample-induced refractive index (RI) heterogeneity on gain measurements remains poorly understood. Here, we quantitatively investigate, how RI mismatch affects SBS microscopy using finite element simulations and experiments on a phantom sample comprising polydimethylsiloxane beads embedded in agarose gel. We demonstrate that RI heterogeneity induces focal field distortion that reduce pump-probe beam overlap, resulting in attenuated Brillouin gain and degraded shift precision at material interfaces. Crucially, we establish that fiber-coupling efficiency, commonly used for system
alignment, cannot serve as a linear proxy for Brillouin gain due to its heightened sensitivity to focal field distortion.
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All authors Meng Xu, Zixuan Du, Yun Qi, Jinrui Zhang, Shuai Yao, Robert Prevedel, Fan Yang
Chemical Physics
Ab Initio Adiabatic Potential Energy Surfaces and Non-adiabatic Couplings for O$_3$: Construction of Four State Diabatic Hamiltonian
Avik Guchait, Gourhari Jana, Satyam Ravi et al. (+2 more)
We compute highly accurate first principle based ab initio adiabatic potential energy surfaces (PESs) using State-Averaged Multi-Configurational Self-Consistent Field (SA-MCSCF) followed by internally contracted Multi-Reference Configuration Interaction method incorporating fixed-reference Davidson corrections [ic-MRCI(Q)], where a full valence active space of 18 electrons in 12 orbitals and aug-cc-pVQZ basis set are employed for the low-lying four singlet electronic states of ozone ($\tilde{X}^1A'$, $1~^1A''$, $1~^1A'$ and $2^1A''$). It accurately reproduces the dissociation energies of ozone (1.101 eV) as well as the molecular oxygen (5.106 eV) along with vibrational frequencies of O$_3$ in comparison with experimental data. To ensure appropriate accuracy and proper convergence in the interaction as well as asymptotic regions, we (a) extend the number of electronic states in SA-MCSCF calculation (singlet as well as triplet and quintet); (b) systematically expand the active space [(12e,9o) $\rightarrow$ (18e,12o) $\rightarrow$ (24e,15o)] and basis set size (AVDZ $\rightarrow$ AV6Z $\rightarrow$ Complete Basis Set limit); (c) incorporate multi-reference character along with Davidson correction. Conical intersections between the adjacent electronic states (1-2, 2-3 and 3-4) are located at C$_{2v}$, D$_{3h}$ as well as C$_{s}$ geometries through the four-state adiabatic-to-diabatic transformation of non-adiabatic coupling terms (NACTs) computed at Coupled-Perturbed Multi-Configurational Self-Consistent Field (CP-MCSCF) method along the circular contours. Finally, we present: (a) ic-MRCI(Q) calculated minimum energy path of incoming oxygen to the diatom (O$_2$) is devoid of any “reef” feature; (b) NACTs and diabatic PES
matrix elements as function of hyperangles ($\theta$,$\phi$) at a fixed hyperradius $\rho = 4$ Bohr for a four state sub-
Hilbert space.
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All authors Avik Guchait, Gourhari Jana, Satyam Ravi, Koushik Naskar, Satrajit Adhikari
Optics
Spatiotemporal Stabilization of Turbulence-Distorted Gaussian Beams via Waveguide Spatial Filtering
Shouvik Sadhukhan and C. S. Narayanamurthy
Optical beams propagating through atmospheric
turbulence undergo spatiotemporal intensity fluctuations that deviate significantly from an ideal Gaussian profile. In this work, we present a unified theoretical and experimental framework for quantifying and mitigating these
turbulence-induced distortions by coupling a higher-order statistical characterization technique with optical waveguide spatial filtering. The statistical characterization employs a Cholesky-whitened Gram–Charlier expansion that decomposes the two-dimensional beam intensity distribution into a Gaussian core augmented by third- and fourth-order cumulant corrections, thereby isolating skewness and excess kurtosis as quantitative non-Gaussianity indicators. Concurrently, the propagation of the distorted beam through a dielectric waveguide is analyzed to demonstrate that higher-order spatial modes, which carry the dominant share of
turbulence-induced structural distortions, encounter a cutoff condition governed by the normalized frequency parameter and subsequently undergo exponential attenuation along the propagation direction. The waveguide thus acts as a passive spatial mode filter that selectively transmits the fundamental guided mode while suppressing radiative higher-order modes. The fitted beam volume, derived from the Gram–Charlier intensity model, serves as a unified scalar diagnostic that tracks the frame-by-frame
evolution of
turbulence-induced structural changes. Experimental measurements validate the theoretical predictions, demonstrating a substantial reduction in intensity fluctuations and a recovery of Gaussian beam statistics after waveguide propagation.
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Optics
Vectorial Control of Scintillation in Kolmogorov Turbulence and Quality Parametrization
Shouvik Sadhukhan
Intensity scintillation limits free-space optical links in strong
turbulence. We examine experimentally how sequential linear polarization filtering modifies the scintillation of a
laser beam distorted by Kolmogorov-type
turbulence, and interpret the results with a vector-field and fourth-order-moment model. A collimated He–Ne beam (632.8~nm) crossed a rotating pseudo-random phase plate (Fried parameter $r_0\approx0.6$~mm) and zero to five co-aligned thin-film polarizers; 200 camera frames were recorded per configuration, together with a
turbulence-free reference. For fully developed speckle the model gives a total-field index $\sigma_I^2=(1+P^2)/2$ in terms of the degree of polarization $P$. From zero to five polarizers, the Gaussian-envelope scintillation index fell from 0.083 to 0.002 and the single-pixel index from 0.80 to 0.27 (about 66%), whereas beam wander remained comparable across configurations. As Gaussian statistics alone cannot explain this reduction, we attribute it to rejection of a depolarized, strongly fluctuating component and derive a quantitative criterion for this mechanism. Passive polarization filtering thus offers a simple, low-cost route to scintillation mitigation in free-space optical terminals.
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Fluid Dynamics
A semi-analytical pseudo-spectral method for 3D Boussinesq equations of rotating, stratified flows in unbounded cylindrical domains
Jinge Wang and Philip S. Marcus
We present a pseudo-spectral method for solving the three-dimensional Boussinesq equations in unbounded cylindrical domains, specifically tailored for rotating, stably stratified flows subject to strong azimuthal shear. To effectively capture the global geometry without sacrificing spectral accuracy, the spatial discretization employs
Fourier expansions in the azimuthal and axial directions alongside mapped associated Legendre
polynomials in the radial direction. This basis spans the semi-infinite domain while analytically resolving the coordinate singularity at the origin. While this spectral framework ensures high spatial fidelity, the temporal integration of these rotating shear flows presents a formidable computational challenge due to the numerical stiffness driven by fast restorative wave forces and rapid background advection. To circumvent this, we develop an exponential time differencing (ETD) scheme that analytically integrates the fully coupled linear operator, including the radially dependent advective cross terms. By encoding the physical resonance characteristics and stability limits of the background flow directly into the integration operators, the proposed ETD formulation removes the numerical stability constraints imposed by the background shear and stratification. This permits integration time steps scaled by the slow macroscopic
evolution of the physical instabilities rather than the fast background kinematics, offering significant performance gains over standard mixed implicit-explicit schemes. The method's accuracy and stability are validated through the precise conservation of energy and angular momentum, establishing a robust framework for simulating instabilities in astrophysical and geophysical
vortices.
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Computational Physics
Full-Scale GPU-Accelerated Transient EM-Thermal-Mechanical Co-Simulation for Early-Stage Design of Advanced Packages
Hongyang Liu, Tejas Kulkarni, Ganesh Subbarayan et al. (+2 more)
In the early-stage design of advanced electronic packages, designers face a critical trade-off between simulation fidelity and computational turnaround time. Conventional early-stage methodologies typically achieve speed by relying on steady-state assumptions and structural homogenization. While computationally efficient, these approximations fundamentally fail to capture dynamic thermal events and stress concentrations at fine-grained internal interfaces, effectively masking failure mechanisms driven by transient signal bursts. In this work, we present a GPU-accelerated transient coupled Electromagnetic-Thermal-Mechanical solver that resolves this bottleneck. The proposed solver enables full-scale, non-homogenized, time-domain simulation of large-scale packages with runtimes amenable for rapid design iteration. Simulation of a NEC SX-Aurora TSUBASA package demonstrates that the tool allows for the identification of signal-induced adiabatic stress that is typically invisible to steady-state and homogenized baselines. This capability brings sign-off level physics fidelity to the early design phase, facilitating the prevention of costly late-stage design failures and broader transient thermal performance degradation risks.
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All authors Hongyang Liu, Tejas Kulkarni, Ganesh Subbarayan, Cheng-Kok Koh, Dan Jiao
Applied Physics · Cross-listed from cond-mat.mes-hall
Pressure-Induced Metal-Insulator and Paramagnet-Altermagnet Transitions in Rutile OsO2 Single Crystals
Guojian Zhao, Ziang Meng, Wencheng Huang et al. (+19 more)
Altermagnets with compensated
spin structures and nonrelativistic
spin splitting have emerged as a new class of
magnetic materials. Rutile OsO2 has been theoretically predicted to be altermagnetic, but experimental studies have been limited by synthesis challenges. We have succeeded in synthesizing high-quality single
crystals of rutile OsO2. Electrical transport studies reveal that OsO2 is highly conductive and exhibits clear
Fermi liquid behavior, indicating strong electron-electron scattering.
Magnetic measurements show that the
crystals are isotropically paramagnetic. Density-functional theory calculations indicate that bulk OsO2 is semimetallic with coexisting electron and hole pockets, with its
magnetic ground state strongly dependent on the on-site Coulomb correlation U. Angle-resolved photoemission spectroscopy studies unveil that the bulk bands do not yet show altermagnetic
spin splitting. Interestingly, resistivity is rather pressure sensitive: at 44 GPa, a clear metal-
insulator transition occurs. Hybrid functional calculations reveal that applying pressure significantly increases the Hubbard U value, driving a phase transition from a paramagnetic metal to an altermagnetic metal, and eventually to an altermagnetic
insulator. These findings suggest that tuning external pressure effectively modulates the
magnetic ground state of OsO2, providing a pathway to realize altermagnetism in this material.
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All authors Guojian Zhao, Ziang Meng, Wencheng Huang, Peixin Qin, Shaoheng Ruan, Liang Ma, Lin Zhu, Yuzhou He, Li Liu, Zhiyuan Duan, Xiaoning Wang, Hongyu Chen, Sixu Jiang, Jingyu Li, Xiaoyang Tan, K. Ozawa, Bosen Wang, Jinguang Cheng, Qinghua Zhang, Jianfeng Wang, Chaoyu Chen, Zhiqi Liu
Optics · Cross-listed from cond-mat.mtrl-sci
Cooperative Quantum Optical Effects of Moiré Exciton Superlattices
Haowei Xu, Wang Yao and Ju Li
The unique properties of two-dimensional moiré systems have been widely studied from many perspectives. However, relatively little work has investigated how the real-space structure of moiré systems can directly engender novel properties and functionalities. In this Letter, we explore how intriguing cooperative optical effects can emerge from the real-space superlattice formed by moiré
excitons. Particularly, we show that the collective moiré
exciton states can have either strongly enhanced (superradiant) or suppressed (subradiant) radiative decay rates, depending on their in-plane wave vector. These super- and subradiant states can be efficiently switched by a gate-induced electric field gradient. Moreover, the cooperative transmittance T of the atomically thin moiré system can be switched from $T\approx 0$ (opaque) to $T \approx 1$ (transparent) with $\lesssim ~1\%$ heterostrain or a $1^{\circ}$ adjustment in the twist angle ${\theta}$. These features are robust against nonradiative losses and disorders, making the moiré system a highly versatile platform for cooperative
quantum optics with potential applications in, e.g., single
photon storage and switching.
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Atomic Physics
In situ magnetic-field stabilization for quantum-gas experiments
E. Gvozdiovas, A. Valdés-Curiel, Q.-Y. Liang et al. (+6 more)
We demonstrate a minimally-destructive in situ technique for measuring and stabilizing slowly-drifting
magnetic fields in ultracold-atom experiments. While conventional
magnetic-field sensors such as
Hall,
giant magnetoresistive, or fluxgate-based devices are broadly used, their accuracy, precision and dynamic range can be limited. In addition, these sensors are typically positioned at least several centimeters away from the in-
vacuum atomic system, as their operation creates perturbing
magnetic fields, and their placement is limited by
geometric constraints imposed by the
vacuum system. We overcome these issues by using the atomic system itself as a built-in magnetometer. To that end, we employ a pair of weak measurements to determine the Zeeman splitting – and thereby the
magnetic field – of a magnetically sensitive atomic transition. We provide closed-form expressions quantifying the trade-offs between measurement noise, dynamic range, and atom loss. This procedure is demonstrated with ultracold Rb-87, weakly measured using partial-transfer absorption imaging. We then incorporate a Kalman filter to stabilize the
magnetic field; this eliminated long-term drift in the ambient field (as high as ~70 nT/hr) in exchange for a modest increase in shot-to-shot variability from 1.8(2) nT to 2.0(2) nT.
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All authors E. Gvozdiovas, A. Valdés-Curiel, Q.-Y. Liang, E. D. Mercado-Gutierrez, A. M. Piñeiro, J. Tao, D. Trypogeorgos, M. Zhao, I. B. Spielman
Optics
Cavity enhanced UV combs generated by sum frequency mixing with near-IR chirped-pulse electro-optic combs for Rb atom sensing at 323 nm
Jasper R. Stroud and David F. Plusquellic
A chirped-pulse electro-optic (EO) dual comb system operating near 821 nm is used to generate cavity enhanced dual combs in the ultraviolet (UV) region near 323 nm with an optical bandwidth of up to 90 GHz. The UV combs result from intracavity sum frequency mixing of the non-resonant near-IR combs with a cavity enhanced field at 532 nm in a nonlinear
crystal. The cavity is pumped with 1 W at 532 nm and seeded with less than 10 mW in the near-IR region to generate a few uW of UV power within a detection bandwidth of < 20 MHz. The UV power is enhanced by 100-fold relative to single pass methods and is readily detectable using an avalanche photodiode. The system is used to measure the high-resolution UV comb spectra of Rb atoms near 323 nm (9 2P3/2 <- 5 2S1/2). This method is easily extendable across the 300 nm to 400 nm region using telecom and near-IR dual EO comb sources for seeding.
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Data Analysis and Statistics · Cross-listed from cond-mat.mtrl-sci
Electronic manifolds for extrapolative alloy discovery
Pranoy Ray, Sayan Bhowmik, Phanish Suryanarayana et al. (+2 more)
This study presents a computationally efficient framework for accelerated
alloy discovery that uses the non-interacting electron density to capture intrinsic structure-property relationships in refractory high-
entropy alloys (HEAs). Unlike state-of-the-art approaches relying on expensive, self-consistent density functional theory calculations, our method employs the non-interacting electron density as the primary structural descriptor. By extracting physical features through directionally resolved two-point spatial correlations and compressing them via Principal Component Analysis, we efficiently map the design space. Coupling these descriptors with
Bayesian active learning, we achieve a normalized mean absolute error (NMAE) of <2% for the bulk modulus of Al-Nb-Ti-Zr
alloys using only 10 training samples (<0.2% of the
dataset). Furthermore, we demonstrate that the model learns an electronic packing
manifold that is transferable within the refractory BCC
alloy family. Validated on a distinct 7-component refractory system (Mo-Nb-Ta-Ti-V-W-Zr) containing four elements entirely absent from the training data, the framework enables zero-shot transfer within the refractory BCC
alloy class. Moreover, by augmenting the base model with just 20 samples from the target domain, we achieve high-fidelity predictions (NMAE<3%) for 7-component
alloys, reducing data acquisition costs by orders of magnitude compared to standard workflows. A controlled comparison confirms that composition-based descriptors under the identical pipeline do not reach the same accuracy threshold within the same sample budget, establishing that the spatial autocorrelation encoding of the non-interacting electron density provides information beyond elemental composition statistics alone.
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All authors Pranoy Ray, Sayan Bhowmik, Phanish Suryanarayana, Surya R. Kalidindi, Andrew J. Medford