Materials Science · Cross-listed from physics.app-ph
The effect of graphene orientation on permeability and corrosion initiation under composite coatings
Majid Shaker, Erfan Salahinejad, Weiqi Cao et al. (+3 more)
The unique anisotropic properties of
graphene, particularly impermeability, have made it a promising candidate for further advances in corrosion prevention applications. Despite the large number of experimental works divulging the use of
graphene in anticorrosion coatings, there is no report on the numerical modelling and simulation of the relationships between the orientation of
graphene sheets in composite coatings and the introduced corrosion protection efficiency, to our knowledge. Herein, it is tried to model the influence of the orientation of
graphene sheets dispersed in organic coatings on the diffusivity and flux of corrosive substances besides the corrosion initiation time of the protected substrates. To discover the relationship between the
graphene orientation and corrosion-related phenomena, this study introduces a novel model consisting of a trigonometric factor named unprotected projected surface area proportion, which calculates corrosion-related parameters based on the principal Fick's laws. The model reveals that the decrease in the angle between
graphene sheets and the substrate is highly beneficial for postponing the corrosion onset. It is accordingly estimated that a mismatch angle of 10 degree can slow down the
diffusion process significantly and delay the corrosion initiation by around 65 times in a 100 micron thick epoxy/
graphene composite coating in comparison to the counterpart with the perpendicular
alignment. The predicted corrosion parameters were in a good agreement with the experimental data, indicating the merit of the proposed model. Thus, this model can be further employed as the fundamental of future research on the optimum
graphene orientation in anticorrosion composite coatings.
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All authors Majid Shaker, Erfan Salahinejad, Weiqi Cao, Xiaomin Meng, Vahdat Zahedi Asl, Qi Ge
Materials Science
Origin of donor compensation in monoclinic (Al$_x$Ga$_{1{\rm -}x})_2$O$_3$ alloys
Sierra Seacat and Hartwin Peelaers
(Al$_x$Ga$_{1{\rm -}x})_2$O$_3$
alloys are frequently used in
heterostructures with monoclinic Ga$_2$O$_3$, resulting in a large conduction-band offset, which leads to charge carrier confinement, a property that is desirable for device applications. However, when (Al$_x$Ga$_{1{\rm -}x})_2$O$_3$
alloys are $n$-type doped with Si, the most efficient shallow donor, there is a significant reduction in the number of charge carriers when the Al content of the
alloys is greater than 26%, rendering intentional doping ineffective. Here we show that this compensation is due to cation vacancies forming in response to donor doping. We use density functional theory with the HSE06 hybrid functional to study cation vacancies in monoclinic AlGaO$_3$ and monoclinic Al$_2$O$_3$. We find that vacancies prefer to occupy split-vacancy configurations, similar to vacancies in Ga$_2$O$_3$. Furthermore, by comparing the formation energy of the vacancy with the formation energy of Si donors, we show that vacancies are lower in energy than Si donors, independent of the
Fermi level, as soon as the
alloys contain more than 16% Al. Therefore, cation vacancies will compensate the donor doping, explaining experimental observations.
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Materials Science
CVD Grown Hybrid MoSe$_2$-WSe$_2$ Lateral/Vertical Heterostructures with Strong Interlayer Exciton Emission
Md Tarik Hossain, Sai Shradha, Axel Printschler et al. (+14 more)
Lateral
heterostructures of 2D transition metal dichalcogenide offer a powerful platform to investigate photonic and electronic phenomena at atomically sharp interfaces. However, their controlled engineering, including tuning lateral domain size and integration into vertical van der Waals
heterostructures with other 2D materials, remains challenging. Here, we present a facile route for the synthesis of two types of
heterostructures consisting of monolayers of MoSe$_2$ and WSe$_2$ - purely lateral (HS I) and hybrid lateral/vertical (HS II) - using
liquid precursors of transition metal salts and chemical vapor deposition (CVD). Depending on the growth parameters, the
heterostructure type and their lateral dimensions can be adjusted. We characterized properties of the HS I and HS II by complementary spectroscopic and microscopic techniques including Raman and photoluminescence spectroscopy, and optical and atomic force microscopy, and scanning electron and transmission electron microscopy. The photoluminescence measurements reveal strong interlayer
exciton emission in the MoSe$_2$/WSe$_2$ region of HS II, which dominates the spectrum at 4 K and persisting up to room temperature. These results demonstrate high optical quality of the grown
heterostructures which in combination with scalability of the developed approach paves the way for fundamental studies and device applications based on these unique 2D
quantum materials.
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All authors Md Tarik Hossain, Sai Shradha, Axel Printschler, Julian Picker, Luc F. Oswald, Julian Fuehrer, Nicole Engel, Honey J. Shah, Christof Neumann, Daria I. Markina, Moritz Quincke, Johannes Biskupek, Kenji Watanabe, Takashi Taniguchi, Ute Kaiser, Bernhard Urbaszek, Andrey Turchanin
Materials Science
Revealing Short- and Long-range Li-ion diffusion in Li$_2$MnO$_3$ from finite-temperature dynamical mean field theory
Alex Taekyung Lee, Kristin A. Persson and Anh T. Ngo
Li$_2$MnO$_3$ is a key component of Li-excess layered cathodes of the form $(1-x),\mathrm{LiMO_2} + x,\mathrm{Li_2MnO_3}$ ($M$ = Mn, Ni, Co, \dots), yet its role in setting Li-ion transport limitations remains under debate. Here we combine DFT+$U$, finite-temperature DFT+DMFT with a continuous-time
quantum Monte Carlo
impurity solver, and nudged-elastic-band (NEB) calculations to study Li$^{+}$ migration in paramagnetic Li$_2$MnO$_3$ in the presence of a single Li vacancy. Evaluating DMFT total energies along the DFT+$U$ NEB geometries reveals that dynamical correlations strongly renormalize the lowest-barrier processes, reducing the activation energies to $E_a = 0.18$ eV for the shortest-range hop and $E_a = 0.50$ eV for the next-lowest (transport-controlling) step. The 0.18 eV barrier quantitatively reproduces the short-range activation energy from $\mu^{+}$SR, while the 0.50 eV barrier is consistent with the long-range transport scale extracted from ac-impedance measurements. This single-vacancy, paramagnetic DMFT description thus provides a unified interpretation of local and macroscopic probes without invoking clustered vacancy configurations or strong extrinsic disorder, consistent with nearly stoichiometric Li$_2$MnO$_3$ powders. More broadly, our results highlight finite-temperature dynamical correlations as an essential ingredient for predicting ionic migration energetics in correlated
oxide electrodes.
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Materials Science
Phonon assisted absorption in Transition Metal Dichalcogenide heterostructures
Yifan Liu, Robert Dawson, Nathaniel Gabor et al. (+1 more)
The coupling of atomic vibrations to electronic excitations - traditionally understood to be a source of energy loss in
semiconductors - has recently been explored in photosynthetic light harvesting as a means to circumvent dissipation by harnessing
quantum vibronic coherence. Motivated by recent photocurrent measurements of vibronic sidebands in WSe$_2$/MoSe$_2$ optoelectronic devices, we present a nonperturbative theoretical framework for
phonon-assisted absorption in van der Waals
heterostructures. Using a polaron transformation, a closed-form expression for the optical absorption spectrum at arbitrary temperatures is presented. Our model includes both intraband and interband electron-
phonon coupling. Detailed analysis shows that the observed periodic sidebands originate from the strong coupling between interlayer
excitons and nearly dispersionless optical
phonon modes. Comparing two limiting cases - one involving only intraband couplings, and another incorporating coherent interband processes - we show that interband
phonon-assisted transitions are needed to account for the observed data. Beyond enabling the direct estimation of vibronic coupling strengths from spectroscopic data, these findings have profound consequences for our understanding of optical and optoelectronic responses: coherent interband coupling of atomic vibrations to
excitons is essential to quantifying photoresponse in transition metal dichalcogenide
heterostructures.
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All authors Yifan Liu, Robert Dawson, Nathaniel Gabor, Vivek Aji
Materials Science · Cross-listed from cond-mat.mes-hall
Single-Emitter Spectra from an Ensemble
Jonah R. Horowitz, Oliver J. Tye, Oliver M. Nix et al. (+5 more)
The heterogeneity in nanoscale emitters hinders efforts to understand their basic photophysics and limits their use in practical applications. Existing methods have difficulty accurately characterizing single-emitter spectra and optical heterogeneity on a statistical scale. Here, we introduce SPICEE (SPectrally Imbalanced Correlations from Ensemble Emission), a spectrally filtered
photon-correlation technique that recovers single-particle emission lineshapes from an ensemble sample. Analytical derivations, numerical modeling, and experiments on a solution ensemble of emitters validate the technique. We apply SPICEE to blue-emitting ZnSeTe
semiconductor nanocrystals relevant to display applications and find that the low color purity in the ensemble spectrum is primarily caused by a small subpopulation of nanocrystals with a distinct emission mechanism. This work demonstrates that SPICEE is a powerful high-throughput tool for accurately characterizing the single-emitter properties of nanoscale systems.
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All authors Jonah R. Horowitz, Oliver J. Tye, Oliver M. Nix, Shaun Tan, Hogeun Chang, Ji Hyun Min, Taehyung Kim, Moungi G. Bawendi
Materials Science · Cross-listed from physics.optics
Gear-based 3D-printed Micromachines Actuated by Optical Tweezers
Alaa M. Ali, Gwenn Ulliac, Edison Gerena et al. (+4 more)
The miniaturization of mechanical mechanisms is crucial to enable the development of compact, high-performance micromachines. However, the downscaling actuation of conventional gears and micromotors has remained limited by the inherent challenges of implementing mechanical/electrical powering. Here, we present the design, fabrication, and characterization of an optomechanical, gear-driven micromachine realized through two-
photon polymerization 3D printing. The actuation is achieved using optical tweezers. The device integrates a microgear transmission system with an optically actuated part, enabling light-controlled micromachines. When illuminated by a highly focused
laser source, the first gear generates rotational torque within the gear assembly, converting optical energy into directional mechanical work that can be transmitted to the coupled gear. We demonstrate the fabrication of micromachines using two-
photon polymerization (2PP)
laser writing, enabling the fabrication of spur gear trains and bevel gears that can produce out-of-plane rotations, which is not achievable with traditional micromachining fabrication techniques. The micromachines are composed of a single gear or a train of two or three gears without any unwanted adhesion between the components, leading to functioning systems. Experimentally, the fabricated micromachines were actuated using optical tweezers, demonstrating continuous gear rotation, effective motion transmission in gear trains, out-of-plane rotations, and the ability to amplify velocity or torque. Optical-tweezer actuation broadens the potential applications of these micromachines, particularly in biomedical and lab-on-a-chip systems, where precise, minimally invasive control at the microscale is essential.
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All authors Alaa M. Ali, Gwenn Ulliac, Edison Gerena, Abdenbi Mohand-Ousaid, Sinan Haliyo, Aude Bolopion, Muamer Kadic
Materials Science · Cross-listed from physics.optics
Numerically optimized FROG results for the study of red-shifted spectra in multi-frequency Raman generation
Sakthi Priya Amirtharaj, Zujun Xu, Donna Strickland et al. (+7 more)
When multifrequency Raman scattering is driven in the transient regime by two chirped pump pulses, the resulting anti-Stokes orders exhibit asymmetric spectral broadening toward lower frequencies, leading to a characteristic double-peaked structure in each order. In this Letter, frequency-resolved optical gating (FROG) is used to investigate the spectral
evolution of the first anti-Stokes Raman component. To interpret the observed features, we introduce a double-pulse interference model and employ an adaptive learning-based reconstruction
algorithm using the Adam optimizer to retrieve the temporal field
evolution. The simulation results show good agreement with the experimental measurements. Our analysis indicates that the observed red-shifted spectral component originates from linear Raman processes within the two-
photon dressed-state framework.
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All authors Sakthi Priya Amirtharaj, Zujun Xu, Donna Strickland, Borun Chowdhury, Sagnik Acharya, Priyam Samantray, Anil Prabhakar, Kisor Kumar Sahu, Franz Bamer, S. Swayamjyoti
Materials Science
Unbounded Systematic Error in Thin Film Conductivity Measurements
Yongyi Gao, Hio-Ieng Un, Yuxuan Huang et al. (+2 more)
Electrical conductivity is the most fundamental charge transport parameter, and measurements of conductivity are a basic part of materials characterization for nearly all conducting materials. In thin films, conductivity is often measured in four bar architectures in which the current source and voltage measurement are spatially separated to eliminate systematic error due to contact resistance. Despite the apparent simplicity of these measurements, we demonstrate here that the four bar architecture is subject to significant systematic error arising from the finite conductivity of the metal electrodes. Remarkably, these systematic errors can in some cases become unbounded, producing arbitrarily high measured conductivity at modest true film conductivities, within the range relevant to emerging thin film thermoelectric materials such as conducting
polymers. These unbounded errors, which can occur even in properly conducted four-point measurements of patterned films, likely explain literature reports of extremely high conductivities in conducting
polymers, and can lead to anomalous scaling in temperature dependent studies, potentially leading to incorrect interpretation of the relevant charge transport mechanism. We characterize the device
geometric factors that control these errors, which stand partially at odds with those required for accurate Seebeck coefficient measurements. Our analyses allow us to identify device architectures that provide small systematic errors for conductivity and Seebeck coefficient while still providing a low measurement resistance, critical to reducing noise in thermal voltage measurements. These findings provide important guidelines for accurate measurements in the growing field of thin-film thermoelectric materials.
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All authors Yongyi Gao, Hio-Ieng Un, Yuxuan Huang, Henning Sirringhaus, Ian E. Jacobs
Materials Science
Mechanics of incompatible asymmetric grain boundary migration
Brandon Runnels
Grain boundary (GB) migration governs microstructure
evolution and can mediate plastic deformation through sliding or shear coupling. Numerous experimental and numerical studies have reported a wide range of behaviors associated with boundary migration, such as defect emission or mode switching. Notably, recent studies have reported directionally asymmetric migration rates under symmetric loading, attributing this behavior to intrinsically asymmetric mobility; however, a mechanistic mesoscale explanation for this behavior remains lacking. In this work, we introduce a constitutive flow rule for grain-boundary eigendeformation within a multiphase-field framework, in which interfacial shear evolves in response to its mechanically conjugate driving force through the phase field Allen-Cahn equations. The formulation systematically employs regularized grain boundary shear kinematics informed by crystallography, and enables elastic compatibility to modulate boundary motion. Migration thresholds, residual back-stress, and apparent directional asymmetry appear naturally as emergent mechanical behavior. Simulations of symmetric and asymmetric tilt grain boundaries under mechanical, synthetic, and
curvature-driven loading reveal persistent defect-like residuals following incompatible migration, transitions from planar motion to lamination at large inclinations, and even "ratcheting" behavior. These results provide a mechanically transparent explanation for behaviors such as effective mobility asymmetry and establish elastic compatibility as a constitutive mechanism in mesoscale models of boundary-mediated plasticity.
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Materials Science
Energy-Transfer-Enhanced Emission and Quantum Sensing of VB- Defects in hBN-PbI2 Heterostructures
Eveline Mayner, Yaroslav Zhumagulov, Cristian de Giorgio et al. (+6 more)
Spin defects in two-dimensional materials hold significant potential for
quantum information technologies and sensing applications. The negatively charged boron vacancy (VB-) in hexagonal boron nitride (hBN) has attracted considerable
attention as a
quantum sensor due to its demonstrated sensitivity to temperature,
magnetic fields, and pressure.1 However, its applications have thus far been limited by inherently dim photoluminescence (PL). By fabricating a van der Waals
heterostructure with a sensitizing donor layer, lead iodide (PbI2), we effectively enhance the PL intensity from the VB- by 5-45x, while maintaining compatibility with other
heterostructures and vdW optoelectronic platforms. The type-I band
alignment at the heterojunction enables efficient
exciton migration while suppressing back-electron transfer, and the strong spectral overlap between the PbI2 emission and defect absorption supports efficient fluorescence resonance energy transfer. Ab initio density functional theory (DFT) predicts a
photon-ratcheting mechanism that boosts absorption and emission while maintaining
magnetic resonance (ODMR) contrast through minimal hybridization. Experimentally, the
heterostructure exhibits enhanced continuous-wave ODMR sensitivity and functions as a precise probe of external
magnetic fields. This work establishes a proof-of-concept for amplifying weak defect signals in nanomaterials, highlighting a new strategy for engineering their optical and
magnetic responses.
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All authors Eveline Mayner, Yaroslav Zhumagulov, Cristian de Giorgio, Feihong Chu, Prabhu Swain, Georg Fantner, Andras Kis, Oleg Yazyev, Aleksandra Radenovic
Materials Science
Symmetry-restricted energy landscapes as a benchmark for machine learned interatomic potentials
Abhijith S Parackal, Rickard Armiento and Florian Trybel
Machine learned interatomic potentials (MLIPs) are becoming a standard method for DFT-level accurate molecular dynamics simulation and large-scale studies of
crystal energetics. Increasingly popular are universal pre-trained potentials, also called foundation models, based one, e.g. the MACE, CHGNet, M3GNet, ORB, and SevenNet architectures. While there are many
benchmarks of these models using validation errors and materials discovery tasks, their fidelity in reproducing the detailed features of potential energy surfaces (PES) is not understood to the same degree. We evaluate the accuracy of these potentials by systematically probing their predicted energy landscapes. Two-dimensional slices of the potential energy surface are constructed where the atomic positions are varied along selected Wyckoff degrees of freedom within a fixed
crystal symmetry. This approach enables a direct, visual comparison of the interatomic potentials and DFT-calculated surfaces which reveals potential artifacts e.g., arising from unique local environments. Our analysis highlights the strengths and limitations of different potentials in capturing local minima, saddle points, and overall PES
topology, offering insights into the physical accuracy of current pre-trained IAPs and providing
benchmarks for future model development.
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Materials Science
Triplet Envelope Functions for increasing machine learning interatomic potential efficiency and stability
Emil Annevelink and Varun Shankar
Central to interatomic potential efficiency is the radial envelope function that enables linear scaling with computational cost by defining a local neighborhood of atoms. This has enabled MLIPs to revolutionize materials science over the past decade by providing DFT accuracy with linear scaling computational cost in molecular dynamics workflows. However, MLIPs still have a relatively high computational cost compared to empirical interatomic potentials, preventing them from transforming molecular dynamics workflows. A central issue is that MLIPs use relatively large cutoff radii, converging to 6A over the last few years. The large cutoffs prioritize accuracy of any material over efficiency in any particular region of phase space, capturing dispersion effects and low density materials at the expense of increased computational cost in higher density materials. Past work has aimed to address this with KNN graph sparsification, which, while significantly reducing cost, has the drawback of breaking energy conservation. In this work, we propose higher-order envelope functions that prune local atomic neighborhoods through physically inspired
geometric functions to provide the
memory and efficiency benefits of KNN graph sparsification while eliminating non-conservative energy dynamics. Through numerical experiments on solids and
liquids with 5-8A cutoffs, we show that triplet envelope functions complement radial envelope functions by doubling training and inference speed, tripling
memory efficiency, and increasing simulation stability while not impacting accuracy or data efficiency for the most common 6A cutoff. Moreover, experiments with 8A radial cutoffs show triplet envelope functions create a pathway to larger cutoff radii for efficiently and accurately modeling open structures with large interatomic distances, showing a promising new direction for engineering MLIP efficiency.
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Materials Science · Cross-listed from cond-mat.supr-con
Direct Observation of Unidirectional Density Wave and Band splitting in a Single-Domain Trilayer Nickelate Pr$_4$Ni$_3$O$_{10}$
Zhicheng Jiang, Enkang Zhang, Yuxin Wang et al. (+12 more)
Unraveling the interplay between density-wave (DW) instabilities and multi-orbital physics is critical for understanding superconductivity in Ruddlesden-Popper nickelates, yet intrinsic electronic features have been persistently obscured by material inhomogeneity and thus the multi-domain averaging effect. Here, we employ micro-focused angle-resolved photoemission spectroscopy ($\mu$-ARPES) on single-domain Pr$_4$Ni$_3$O$_{10}$ to disentangle the complex hierarchy of intrinsic and back-folded bands, explicitly identifying the electronic states driving the DW phase transition. We provide decisive spectroscopic evidence that the low-energy reconstruction is governed by inter-orbital nesting between the $\alpha$ and $\beta$ bands. Specifically, we resolve a orbital-dependent gap of $\sim44$ meV on the $\alpha$ pocket, a value quantitatively consistent with prior measurements, unifying previously conflicting experimental reports regarding the locus and magnitude of the DW gap. Furthermore, we reveal strong orbital-selective mass renormalization in the $d_{z^2}$ states and successfully resolve the long-sought intrinsic trilayer $\beta$-band splitting, establishing a critical lower bound for the outer-layer hopping. These results define a coherent microscopic fingerprint for the trilayer nickelates, identifying the specific nesting channels and correlation effects that underpin the phase diagram.
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All authors Zhicheng Jiang, Enkang Zhang, Yuxin Wang, Zhengtai Liu, Jishan Liu, Runfeng Zhang, Xinnuo Zhang, Wenchuan Jing, Yu Huang, Qi Jiang, Mao Ye, Kun Jiang, Jun Zhao, Dawei Shen, Donglai Feng
Materials Science · Cross-listed from cond-mat.mes-hall
Intersubband electric dipole spin resonance in transition metal dichalcogenide heterobilayers
K.K. Grigoryan and M.M. Glazov
The theory of inter-
spin-subband electric dipole
spin resonance in transition metal dichalcogenide heterobilayers is proposed. Our
symmetry analysis demonstrates that, in contrast to monolayers, the reduced
symmetry of heterobilayers enables coupling between conduction band
spin subbands by an electric field. We establish the optical selection rules for all six high-
symmetry stacking configurations. The microscopic mechanism of the effect is identified as the
spin-orbit coupling induced mixing of Bloch states from different conduction bands, which generates a non-zero momentum
matrix element between the
spin-split states. It also leads to the linear-in-wavevector
spin-dependent terms in the effective
Hamiltonian, i.e., the Rashba effect. Our estimates show that the rate of electric-dipole
spin-flip transitions exceeds by far that of the
magnetic-dipole transitions in transition metal dichalcogenide heterobilayers.
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Materials Science
Optical properties of Fermi polarons in a GaInP/MoSe2 monolayer heterostructure
Hangyong Shan, Max Waldherr, Diksha Diksha et al. (+15 more)
Engineering optical properties, such as luminescence purity and charge transfer, is crucial for harnessing the application potential of atomically thin transition metal dichalcogenides (TMDCs). While electrostatic gating is widely applied to gain charge control in TMDC monolayers, charge transfer can also be engineered via coupling of TMDC monolayers at
semiconductor III/V, organic, or van der Waals interfaces. This confers great advantages, such as ease in implementation and compatibility in device integration. Here, we shed light on the optical properties of many-particle complexes emerging at the GaInP/MoSe2 interface as a highly relevant material combination to manipulate the optical properties of TMDCs in integrated photonic devices. Our study verifies its nature as a type II hetero-interface, which bears the feasibility to display disorder-free photoluminescence. Through optical absorption measurements, we verify that the charged complexes acquire substantial oscillator strength. Furthermore, temperature-dependent photoluminescence, supported by a microscopic theory framework, evidences the suppression of the characteristic carrier
recoil effect that was previously observed in the photoluminescence of trions in TMDCs. These phenomena allow us to identify the optical signatures at the TMDC-GaInP interface as
Fermi polaron quasiparticle resonances, which are of high importance in researching Bose-
Fermi mixtures in condensed matter systems.
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All authors Hangyong Shan, Max Waldherr, Diksha Diksha, Ghada Missaoui, Seyma Esra Atalay, Martin Zinner, Ana Maria Valencia, Kenji Watanabe, Takashi Taniguchi, Seth Ariel Tongay, Caterina Cocchi, Brendan C. Mulkerin, Jesper Levinsen, Francesca Maria Marchetti, Meera M. Parish, Niklas Nilius, Christian Schneider, Sven Höfling
Materials Science
FluxNet: Learning Capacity-Constrained Local Transport Operators for Conservative and Bounded PDE Surrogates
Zishuo Lan, Junjie Li, Lei Wang et al. (+1 more)
Autoregressive learning of time-stepping operators provides an effective approach to data-driven partial differential equation (PDE) simulation, yet for conservation laws, they face a fundamental challenge: learned updates may violate global conservation over long rollouts. For the important subclass of mass-conservation-type equations, the problem is compounded by inherent physical bounds (e.g., nonnegativity or concentrations in [0,1]) whose violation further destabilizes predictions. We introduce FluxNet, which learns cumulative transport amounts representing the total conserved quantity redistributed between each
cell and a configurable neighborhood over the full surrogate interval. A conservative update guarantees exact discrete conservation by construction; modular capacity-constrained transport heads (L, U, and D) enforce lower bounds, upper bounds, or near-zero dual-bound violations through architectural design. Unlike flux-rate surrogates that require temporal integration and thus inherit CFL constraints, FluxNet involves no such integration; configurable transport neighborhoods enable large-timestep prediction at full spatial resolution. Ghost
cells extend the framework to non-periodic boundaries. Experiments on four
benchmarks (1D convection–
diffusion, 2D shallow water, 1D traffic flow, 2D Cahn–Hilliard) demonstrate exact conservation, structural bound preservation, architecture modularity, and superior stability over flux-rate surrogates at large temporal strides. The code is publicly available at: https://github.com/Lan-zs/FluxNet.
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All authors Zishuo Lan, Junjie Li, Lei Wang, Jincheng Wang
Materials Science
Fe-DCA Metal-Organic Frameworks on the Bi2Se3(0001) Topological Insulator Surface
Anna Kurowská, Jakub Planer, Pavel Procházka et al. (+6 more)
The formation of two-dimensional metal-organic frameworks (MOFs) on an inert surface of a topological
insulator (TI) is a pathway to engineer
quantum materials with exotic properties. MOFs featuring ferromagnetically coupled metal atoms are theoretically predicted to induce an exchange gap in the TI surface band structure, potentially leading to a
quantum anomalous
Hall effect. However, achieving ordered MOFs on TI surfaces remains challenging due to the limited knowledge of self-assembly on these substrates. In this paper, we demonstrate self-assembly of Fe atoms and dicyanoanthracene (DCA) molecules into 2D MOFs on the Bi2Se3(0001) surface at room temperature, investigated via a combination of low-energy electron microscopy and diffraction (LEEM/LEED), scanning tunneling microscopy (STM), and ab initio calculations based on density functional theory (DFT). Two competing Fe-DCA phases form. The first phase corresponds to a close-packed Fe1DCA3 structure. In contrast, the second phase exhibits a larger unit
cell with no match to either known or DFT-calculated systems, indicating a more complex bonding environment. These findings advance the understanding of the growth of MOFs on a strong topological
insulator surface and provide insights for designing MOFs/TI interfaces with tailored electronic and
magnetic properties.
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All authors Anna Kurowská, Jakub Planer, Pavel Procházka, Veronika Stará, Elena Vaníčková, Zdeněk Endstrasser, Matthias Blatnik, Čestmír Drašar, Jan Čechal
Materials Science
Thermophysical properties of spark plasma sintered UCo: a comparison with machine learning predictions
Yifan Sun, Hironobu Nakamura, Masaya Kumagai et al. (+2 more)
Uranium dioxide has been widely used as a
nuclear fuel in commercial light water reactors due to its high uranium density and chemical stability. However, its relatively low thermal conductivity is not optimal from the viewpoints of fuel integrity and safety margins, particularly during loss-of-coolant accidents. Although the development of accident-tolerant fuels with higher thermal conductivity is strongly desired, many potential uranium compounds remain unexplored due to constraints associated with handling radioactive materials. To efficiently screen promising uranium compounds with high thermal conductivity, past studies have leveraged machine-learning models to accelerate the discovery process. In this study, we experimentally examine the model's predictions by fabricating UCo and measuring its high-temperature thermophysical properties. Our results show that the thermal conductivity of UCo predicted by machine learning is in good agreement with the experimental measurements. Despite slight discrepancies, additional SHAP analysis suggests that the model's decision logic is consistent with known physical trends. Overall, this study fills a gap in reported thermophysical properties of UCo and provides experimental support for machine-learning-assisted screening of uranium compounds relevant to advanced fuel development.
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All authors Yifan Sun, Hironobu Nakamura, Masaya Kumagai, Yuji Ohishi, Ken Kurosaki
Materials Science
Bayesian Parameter Estimation for Predictive Modeling of Illumination-Dependent Current-Voltage Curves
Eunchi Kim and Thomas Kirchartz
Machine learning enables rapid estimation of material parameters in
solar cells via neural-network-based surrogate models. However, the reliability of extracted parameters depends on underlying assumptions such as the choice of one-dimensional drift-
diffusion model and selection of free material parameters. To validate the inferred parameters, we perform predictive modeling of light-intensity-dependent current-voltage (JV) characteristics. Well-known physical effects, including the influence of external resistance and recombination dynamics on illumination-dependent device performance, are reflected in parameter estimation and prediction workflow. We show that correct treatment of dark shunt resistance and emphasizing shifted current (J + Jsc) during fitting enhances prediction accuracy at low to intermediate illumination level. Additionally, we analyze the information content of various input JV curve combinations, demonstrating that including at least one illuminated JV, preferably not under high illumination due to series resistance effects, is critical for reliable parameter estimation and device performance prediction.
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Materials Science · Cross-listed from cond-mat.mes-hall
Weyl-Dirac nodal line phonons with type-selective surface states
Le Du, Zeling Li, Jiabing Chen et al. (+3 more)
The band complex formed by multiple topological states has attracted extensive
attention for the emergent properties produced by the interplay among the constituent states. Here, based on group theory analysis, we present a scheme for rapidly identifying the Weyl-Dirac nodal lines (a complex of Weyl and Dirac nodal lines) in bosonic systems. We find only 5 of the 230 space groups host Weyl-Dirac nodal line
phonons. Notably, the Dirac nodal line resides along the high-
symmetry line, whereas the Weyl nodal line is distributed on the high-
symmetry plane and is interconnected with the Dirac nodal line, jointly forming a composite nodal network structure. Unlike traditional nodal nets, this nodal network exhibits markedly distinct surface states on different surfaces, which can be attributed to the fundamental differences in the topological properties between the Weyl and Dirac nodal lines. This unique property thus allows the material to present distinct surface states in a termination-selective manner. Furthermore, by first-principles calculations, we identify the materials NdRhO$_{3}$ and ZnSe$_{2}$O$_{5}$ as candidate examples to elaborate the Weyl-Dirac nodal line and their related topological features. Our work provides an insight for exploring and leveraging topological properties in systems with coexisting multiple topological states.
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All authors Le Du, Zeling Li, Jiabing Chen, Dongliang Mao, Lei Wang, Xiao-Ping Li
Materials Science
Facilitating electrical and laser-induced skyrmion nucleation with a dipolar-field enhanced effective DMI
Mark C. H. de Jong, Dinar Khusyainov, Julian Hintermayr et al. (+6 more)
We demonstrate experimentally how the nucleation of skyrmions in an Ir, Co, and Pt based
magnetic multilayer is affected by introducing a layer dependent sign for the Dzyaloshinskii-Moriya interaction (DMI). In one stack, the bottom half of the stack is given a positive DMI and the top half a negative DMI, and as a result, the in-plane component of the dipolar field is aligned parallel to the effective field of the DMI in every layer, enhancing the effective DMI. We show that this enhanced DMI facilitates the nucleation and stability of skyrmions using both current-driven and
laser-induced skyrmion nucleation. In the devices with an enhanced effective DMI, the density of nucleated skyrmions is greater by up to a factor 20 and skyrmions can be observed in stronger
magnetic fields - suggesting that their stability is also improved. These results show that skyrmion nucleation depends strongly on the magnitude of the effective DMI in a
magnetic multilayer and that the dipolar field within such a multilayer presents an effective route towards controlling the effective DMI, and thereby, the nucleation of
chiral magnetic textures.
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All authors Mark C. H. de Jong, Dinar Khusyainov, Julian Hintermayr, Bart Sanders, Dmitry Kozodaev, Aleksei V. Kimel, Bert Koopmans, Theo H. M. Rasing, Reinoud Lavrijsen
Materials Science
Morphological Evolution of Nickel-Fullerene Thin Film Mixtures
Giovanni Ceccio, Kazumasa Takahashi, Romana Miksova et al. (+5 more)
Hybrid systems consisting of metal-fullerene composites exhibit intriguing properties but often suffer from thermal instability. With proper control, such instability can be harnessed to enable the formation of sophisticated nanostructures with nanometric precision. These self-organization phenomena are not limited to thermal stimulation alone but can also be triggered by other external stimuli. In this work, we investigate the morphological
evolution of thin films composed of evaporated C60 and sputtered nickel mixtures, focusing on how external stimuli influence both their structural and electrical properties. Thin films were prepared under controlled deposition conditions, and their surface morphology was analyzed using advanced characterization techniques. Progressive changes in film morphology were observed as a function of composition and external treatment, highlighting the interplay between metallic and molecular components. In particular, it was observed that, due to the annealing treatment, the sample undergoes strong phase separation, with the formation of structures tens of microns in diameter and an increase in electrical resistance, exhibiting insulating behavior. These findings provide insights into the mechanisms governing hybrid thin film formation and suggest potential applications in electronic, optoelectronic, and energy-related devices.
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All authors Giovanni Ceccio, Kazumasa Takahashi, Romana Miksova, Yuto Kondo, Eva Stepanovska, Josef Novak, Sebastiano Vasi, Jiri Vacik
Materials Science
Degenerate Soft Modes and Selective Condensation in BaAl$_2$O$_4$ via Inelastic X-ray Scattering
Yui Ishii, Arisa Yamamoto, Alfred Q. R. Baron et al. (+2 more)
BaAl$_2$O$_4$ is a ferroelectric material that exhibits structural
quantum criticality through chemical composition tuning. Although theoretical calculations and several diffraction experiments have suggested the involvement of a soft mode in its ferroelectric structural phase transition, direct experimental verification is still lacking. In this study, we successfully observed two soft modes of BaAl$_2$O$_4$ using x-ray inelastic scattering, providing direct experimental evidence for their role in the structural phase transition. Furthermore, we reveal that the soft modes at the M and K points are nearly degenerate in energy, indicating a delicate balance in which either mode could potentially freeze. The K-point mode simultaneously softens toward the transition temperature ($T_{\rm C}$) in a manner nearly identical to the M-point mode. However, the phase transition condenses only at the M point, with the M-point mode stabilizing as an acoustic mode in the low-temperature structure and the K-point mode hardening as temperature decreases.
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All authors Yui Ishii, Arisa Yamamoto, Alfred Q. R. Baron, Hiroshi Uchiyama, Naoki Sato