Materials Science
Structural effects of liquid infiltration of 3Y-Zirconia with Sc, Mg and Y
Asbjoern Slagtern Fjellvaag, Oystein Slagtern Fjellvaag and Amund Ruud
The current work has investigated the effect of co-doping 3Y-Zirconia (3YSZ) with Sc, Mg and Y by wet infiltration. Pre-sintered discs of 3YSZ were immersed in diluted nitric acid solutions containing Sc, Mg or Y, and combinations of the three, trapping
liquid within the porosities of the samples. Upon drying, the cations are maintained inside the pellet, making the basis for the co-doping. After sintering, mass increase confirms the co-doping effect and X-ray diffraction analysis show clear variations in atomic structure depending on the doping element. Rietveld refinements show that the wet-infiltrated samples contain the tetragonal t, t double
prime and cubic c-phase in various fractions depending on the doping elements. Sc-infiltrated samples show a tendency to higher tetragonality, while the Mg-infiltrated sample obtained a single cubic phase. The multi-phase wet-infiltrated samples have a similar phase separation after sintering as 5Y-Zirconia (5YSZ), as calculated by the tetragonality deviation parameter. 3YSZ and 5YSZ sintered for 0 hours and 2 hours at 1500 degrees C show the effect of sintering time on the phase segregation. To evaluate the material properties in an application-based perspective, the Knoop hardness, translucency and grain size was measured. We conclude that
liquid infiltration is a viable route to perform co-doping of Zirconia with various co-doping elements.
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Materials Science
From Bulk to Surface: Structure and Dynamics of Amorphous Alumina from Deep Potential Molecular Dynamics
Zheng Yu, Jiayan Xu, Abhirup Patra et al. (+3 more)
Understanding the atomic-scale structure and dynamics of amorphous
oxide surfaces is essential for interpreting their chemical reactivity, mechanical stability, and interfacial behavior, yet direct experimental characterization remains challenging. We employ Deep Potential (DP) molecular dynamics to generate large-scale, ab initio-quality models of amorphous Al$_2$O$_3$ bulk glasses and melt-quenched free surfaces, enabling a quantitative analysis of both structure and relaxation dynamics with statistical confidence inaccessible to direct ab initio simulation. The trained DP model reproduces experimental
liquid and glass structure, captures the cooling-rate dependence of the bulk glass transition, and corrects systematic biases in the polyhedral populations predicted by widely used classical force fields. At the free surface, mass density recovers to bulk values over ~10 $\unicode{x212B}$, while local coordination requires a slightly wider subsurface region to fully converge. The outermost layer is oxygen-enriched, exhibits altered polyhedral connectivity with contracted Al-O bonds, and hosts a broad population of under-coordinated motifs (notably AlO$_3$ and OAl$_2$) whose abundances are governed by glass stability. These reactive Lewis acid and Br$\unicode{x00F8}$nsted base sites are locally paired in a manner consistent with bond-valence compensation, yet remain spatially dispersed rather than aggregating into extended clusters. Despite this pronounced structural heterogeneity, the surface relaxes on the same timescale as the bulk and exhibits a comparable glass transition temperature, suggesting that the disordered surface is kinetically stable once formed. Together, these results establish a molecular-level picture of amorphous alumina surfaces and demonstrate the capability of machine-learned potentials to resolve structure-property relationships in disordered
oxide interfaces.
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All authors Zheng Yu, Jiayan Xu, Abhirup Patra, Sharan Shetty, Detlef Hohl, Roberto Car
Materials Science
Light-Induced Even-Wave Spin Splittings in Nonmagnetic Centrosymmetric Systems with Spin-Orbit Coupling
Xiao-Jiao Wang, Dongling Liu, Di Zhu et al. (+2 more)
Spin splitting underpins a vast range of
spin-dependent phenomena. Traditionally, two primary mechanisms generate such splitting: relativistic
spin-orbit coupling (SOC) and nonrelativistic
magnetic exchange coupling (MEC). Governed by distinct
symmetry constraints, they produce splittings of opposite parity – odd for SOC and even for MEC – a dichotomy that underpins the distinct
spin physics of nonmagnetic and
magnetic systems. In this work, we break this dichotomy by demonstrating the dynamic generation of even-parity
spin splitting in centrosymmetric, nonmagnetic systems driven by circularly polarized light. We show that the
symmetry of the induced splitting is controlled by the angular character of the underlying orbitals, enabling the realization of s-wave, d-wave, and g-wave
spin-split band structures identical to those of ferromagnets and altermagnets. Furthermore, we find that these
spin-split bands can naturally host a Chern
insulator phase. We also discuss the associated
spin and orbital magnetization. Our results establish a direct and previously unrecognized conceptual link between the two fundamental mechanisms of
spin splitting.
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All authors Xiao-Jiao Wang, Dongling Liu, Di Zhu, Zheng-Yang Zhuang, Zhongbo Yan
Materials Science · Cross-listed from q-bio.BM
Enhancing Cryo-EM Density Map Segmentation in Phenix for Improved Atomic Model Building
Chenwei Zhang
We introduce PhenixCraft, a fully automated pipeline for building atomic models from cryo-EM density maps. By integrating AlphaFold predictions, we enhance the map-
segmentation step in Phenix during model building, addressing challenges posed by noise and artifacts that traditionally hinder this step. Our results demonstrate PhenixCraft's superior performance in TM-scores and sequence accuracy, significantly improving upon the limitations and inefficiencies of traditional model building using Phenix.
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Materials Science
Diversity-Aware Active Learning Builds Materials Datasets for Current and Future Objectives
Rafael Espinosa Castañeda, Ashley Dale, Hongchen Wang et al. (+6 more)
Materials science data collection can be expensive, making
dataset reuse and long-term utility important for future discovery. In practice, data collection often prioritizes properties of current interest while other properties are excluded from the acquisition process. This can produce
datasets that are well suited for current objectives but lose information needed for properties of future interest. Here, we present how to construct
datasets that remain informative for both. We develop and evaluate acquisition frameworks that combine predictive disagreement with diversity in material features, predicted outcomes, or both. We test these approaches across four DFT
datasets and an experimental thermoelectric
dataset. Diversity inclusion in
dataset construction can reduce present and future objectives trade-off by preserving a broader range of materials and property behavior during acquisition. Across all
datasets, the Non-dominated Sorting Genetic
Algorithm II with disagreements and feature diversity (NSGA-II Dis. + diversity) framework developed in this work provides the most robust balance between current and future objectives. It maintains prediction performance above random sampling for current objectives while mitigating bias on excluded properties and, in many cases, improving their performance beyond random sampling. This diversity-aware acquisition framework provides a practical route to building materials
datasets with unbiased quality entries and mitigating cold-start limitations in subsequent modeling and discovery campaigns.
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All authors Rafael Espinosa Castañeda, Ashley Dale, Hongchen Wang, Yonatan Kurniawan, Hao Wan, Runze Zhang, Adji Bousso Dieng, Kangming Li, Jason Hattrick-Simpers
Materials Science · Cross-listed from physics.optics
Planar chiral nanoantenna for excitation-chirality-controlled hot spot modulation and emitter-coupled circularly polarized emission
Abhik Chakraborty, Xiaofei Wu, Ankit Kumar Singh et al. (+5 more)
A planar
chiral plasmonic nanoantenna exhibiting an excitation-chirality-dependent hot spot in a nanogap is numerically investigated. Additionally, the underlying design principles are examined, providing a broadly applicable framework for engineering
chiral nanoantennas through controlled geometrical or modal asymmetry. The hot spot can be turned on and off by changing the handedness of the exciting circularly polarized light (CPL). This effect stems from the rationally designed interference of plasmonic modes excited by the linearly polarized orthogonal components of CPL. The hot spot exhibits maximal near-field dissymmetry factor (about -2) at a wavelength of 842 nm. The intensity at the hot spot can also be continuously modulated by varying the excitation ellipticity and handedness, approaching a modulation depth of 100%. These attributes enable chirality- and ellipticity-dependent switching and dynamic modulation of the plasmonic near field. Moreover, placing a
quantum emitter in the gap generates almost perfectly circularly polarized emission, offering a simple yet effective avenue to realize nanoscale circularly polarized single-
photon sources.
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All authors Abhik Chakraborty, Xiaofei Wu, Ankit Kumar Singh, Fabian Scheidler, Min Jiang, Jürgen Popp, Bert Hecht, Jer-Shing Huang
Materials Science
Uncovering hidden bias in neutron diffraction residual strain measurements
Cole Franz, Michael B. Prime, Jeffrey Bunn et al. (+2 more)
When calculating residual strain via
neutron or X-ray diffraction, uncertainties propagated from the peak fit are often inadequate to describe the true scatter of measurements about a singular strain state, such as one that should describe a macroscopic continuum. Because diffraction is inherently a selective process, orientation dependent scatter arises from the sub-sampling of strong microstructure and strain gradients. This paper investigates the appropriateness of propagated uncertainties with reference to their original intention, i.e., noise about a mean value. Thirty-six unique orientations of strain measurements are taken at multiple locations within an additive friction-stir deposition component with fine-scale gradients (~200 um) of plastic strain, texture, and residual elastic strain. Multiple strain and stress calculation pathways are compared: direct substitution of three measurements into Hooke's law, direct inversion of any six unique orientations into the strain state tensor, and thirty-six measurement least-squares estimation. For the latter two cases, the appropriateness of the uncertainty interval is statistically evaluated based on a physical constraint: common agreement under the strain transformation law. For this sample, the direct inversion of six measurements retains a conservative estimate of the uncertainty. However, propagated uncertainties in the least-squares solution greatly underestimate the true experimental scatter. A simple pathway to estimate appropriate uncertainty intervals is suggested. These results demonstrate that interpretation of uncertainty in residual strain is strongly dependent on intrinsic, sample-dependent effects, and that oversampling orientations and statistical analysis can give more accurate results with realistic uncertainties.
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All authors Cole Franz, Michael B. Prime, Jeffrey Bunn, Andrew Payzant, Katharine Page
Materials Science · Cross-listed from cond-mat.soft
Nonlinear phonon dispersion in disordered solids and non-Debye vibrational spectra
Edan Lerner and Eran Bouchbinder
All solids, whether crystalline or disordered, support elastic wave propagation with a linear dispersion relation in the long-wavelength limit. These waves, corresponding to low-frequency
phonons, feature a vibrational density of states that follows Debye's classical model. Deviations from Debye's predictions with increasing frequency can emerge from
phonon dispersion nonlinearity and from non-phononic vibrational modes, which exist in non-crystalline solids due to structural disorder. Both nonlinear
phonon dispersion in disordered solids and its relative contribution to non-Debye anomalies, most notably manifested by the controversial
boson peak, remain poorly understood. Here we show that nonlinear
phonon dispersion in a broad range of disordered solids, including elastic networks and various glasses, emerge from a mesoscopic, disorder-induced lengthscale, which also controls wave attenuation. We subsequently use analysis and large-scale computer simulations to quantitatively determine the relative contributions of nonlinear
phonon softening and non-phononic vibrations to the onset of non-Debye anomalies and to the
boson peak. We show that the relative magnitude of the two contributions strongly depends on the strength of disorder of the solid, e.g., controlled by the thermal history upon glass formation, and that for realistic laboratory glasses both pieces of physics significantly contribute to the
boson peak. These findings constitute basic progress in understanding disordered solids.
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Materials Science
Temperature dependence of the Gibbs energies of formation of point defects in B2 MoTa from ab initio calculations
Xiang Xu, Fritz Körmann, Sergiy Divinski et al. (+2 more)
Using B2 MoTa, the strongest B2 former among group V/VI refractory binaries, as a model system, we compute temperature-dependent Gibbs energies of formation of vacancies and antisites from ab initio calculations up to 3000 K at the stoichiometric composition. We explicitly account for thermal electronic excitations, vibrational anharmonicity, and electron-vibration coupling. The key finding is that the temperature dependence of the Gibbs energies of vacancy formation exhibits a pronounced sublattice asymmetry. Specifically, the Gibbs energy of formation of a Mo-site vacancy decreases by 1.1 eV from 0 to 3000 K, whereas the decrease for a Ta-site vacancy amounts to 2.1 eV, almost a factor of two larger. Two contributions of distinct origin govern the temperature dependence of this asymmetry: a quasiharmonic contribution associated with the chemical-potential imbalance set by the two antisite structures and an anharmonic contribution associated with the local vibrational response of the vacancy structures. The asymmetry in anharmonic vibrations is traced back to an enlarged local vibrational distribution of the first-nearest neighbors around the Ta-site vacancy. In contrast to the vacancies, the Gibbs energies of antisite formation vary only weakly with temperature.
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All authors Xiang Xu, Fritz Körmann, Sergiy Divinski, Blazej Grabowski, Xi Zhang
Materials Science
From Defects to Devices: Design Guidelines for High-Performance Diamond-Based Solar Cells and Single-Dopant Diodes
Matúš Kaintz and Antonio Cammarata
This work establishes key technological guidelines for designing diamond-based optoelectronic devices, derived from a first-principles investigation of two architectures: a PIN junction with a boron-vacancy-boron (BVB) intermediate-band absorber, and a PN junction based on phosphorus-vacancy (PV) defects. For the PIN
solar cell, practical design principles include: i) aligning incident light in the xz-plane to exploit anisotropic absorption; ii) using graded junctions to mitigate tunnelling losses at abrupt interfaces; iii) targeting an absorber thickness of ~500 nm to balance absorption and carrier extraction; and iv) leveraging the high transparency of both contact layers for bifacial device configurations. For the PN diode, the PV-doped diamond operates via
impurity-band conduction, making it suitable for degenerate p-type applications such as tunnel diodes or asymmetric junctions, while its temperature-dependent Seebeck anisotropy and sign-reversal offer opportunities for thermal management applications. When paired with phosphorus-doped n-type regions, these defects enable single-dopant junctions that significantly simplify device manufacturing. Using density functional theory with GW corrections, Bethe-Salpeter equation calculations and carrier transport modelling coupled to device electrostatics via a Poisson solver, we show that the BVB defect introduces intermediate bands without degrading diamond's high carrier mobility or thermal conductivity, while PV-doping provides high conductivity at room temperature through
impurity-band transport. Overall, both defect-engineered systems preserve diamond's superior transport and thermal properties even after doping, offering viable pathways for high-performance diamond optoelectronics. These guidelines provide a practical foundation for fabricating efficient diamond-based photovoltaic and diode devices.
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Materials Science
Efficient Quasi-Resonant, Polarization-Selective Excitation of GaN Quantum Emitters
Nilesh Dalla, Paweł Kulboka, Michał Kobecki et al. (+6 more)
Defect centers in GaN emerge as bright sources of single-
photons which recently have been demonstrated to optically interface a localized
spin. However, the structure and composition of these defects as well as their efficient excitation techniques were not a subject of thorough studies. This work presents evidence that by tuning the excitation
laser energy to specific resonance values the excitation efficiency can be enhanced, resulting in relative increase of photoluminescence intensity by up to an order of magnitude. The resonances can be selectively addressed with linearly polarized light, while the emission dipole remains unchanged, enabling polarization-controlled enhancement. These results establish an efficient way of excitation for GaN-based emitters, thereby increasing the generation rate of
photons. The data is consistent with excitation via localized vibrational modes associated with point-defect complexes, establishing a practical quasi-resonant route to brighter, polarization-addressable operation of GaN defect emitters and clarifying their energy-level structure.
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All authors Nilesh Dalla, Paweł Kulboka, Michał Kobecki, Jan Misiak, Paweł Prystawko, Tomasz Kazimierczuk, Piotr Kossacki, Henryk Turski, Tomasz Jakubczyk
Materials Science · Cross-listed from cond-mat.mes-hall
Guidelines for band gap opening in graphene superlattices with periodic {\pi}-vacancy distribution
Diyan Unmu Dzujah, Hongde Yu and Thomas Heine
Periodic $\pi$-vacancies in
graphene superlattices (GSLs) provide a
symmetry-based route to band-gap opening in
graphene by modifying the $\pi$-band dispersion. However, the
symmetry conditions that determine whether a vacancy motif can open a band gap remain unclear. Here, we investigate periodic $\pi$-vacancy GSLs using a nearest-neighbor tight-binding model with one $p_z$ orbital per carbon site to identify the
symmetry requirements for gap opening. $\pi$-vacancies, representing functionalized, substituted, or missing carbon sites, are modeled as site deletions in the $\pi$ basis, with all hopping
matrix elements to and from the deleted sites set to zero. We focus on $\pi$-vacancy motifs with $C_2$ and $C_3$ point-group
symmetry. A $3n \times 3n$ GSL, where $n=1,2,3,\ldots$ is the integer scaling factor multiplying the honeycomb primitive-
cell vectors, folds $K$ and $K'$ to $\Gamma$ and can therefore open a band gap. For $C_3$-type vacancies, the Dirac cones remain pinned at high-
symmetry points and thus stay at $\Gamma$ in folded $3n$ GSLs. In contrast, $C_2$-type vacancies that reduce the global point group of the GSL to $D_{2h}$ by preserving a pair of perpendicular mirror
symmetries, $\sigma_v \perp \sigma_d$, can also constrain the Dirac cones to $\Gamma$. When the $\sigma_v$ and $\sigma_d$ mirror planes are absent, the cones are allowed to shift away from $\Gamma$ to $(\pm \Delta q,\pm \Delta q)$ in the $3n$ superlattice.
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Materials Science · Cross-listed from cond-mat.mes-hall
Magnetic Brightening and Nanoscale Imaging of Spin-Polarized Helical Edge Modes
Samuel Haeuser, Richard H. J. Kim, Lin-Lin Wang et al. (+9 more)
Efficient sub-10 nm electric transport remains a major challenge for nanoelectronics due to high losses and impedance mismatches in conventional Drude metals. Despite their promise of dissipationless, reflection-free conduction, topologically protected
chiral edge modes remain little explored in their nanoscale
spin polarized transport-particularly regarding real-space visualization,
magnetic field tunability, and high-frequency edge conductivity. Here, we report
magnetic brightening and nanoscale visualization of highly
spin-polarizable infrared helical edge states using cryogenic magneto-infrared scattering-type scanning near-field optical microscopy (cm-IR-sSNOM). Our measurements reveal
magnetic field-induced near-field conductivity at step edges, uncovering
quantum spin Hall spin-splitting modes with enhanced infrared polarizability and slightly narrowed near-field profiles. In addition, the infrared edge electrodynamic response scales nearly linearly with atomic layer number, providing compelling evidence that
magnetic-field-induced gaps do not disrupt individual-layer edge states at energies of around 100 meV. These results sharply contrast with microwave and DC transport, where even small magnetically induced gaps decrease edge conduction. Magnetically tunable, topologically robust high-frequency edge modes open a pathway toward ultralow-loss nanoscale interconnects and
quantum logic architectures for next-generation microelectronics, spintronics and
quantum information science.
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All authors Samuel Haeuser, Richard H. J. Kim, Lin-Lin Wang, Thomas Koschny, Pedro M. Lozano, Genda Gu, Randall K. Chan, Joong-Mok Park, Martin Mootz, Liang Luo, Qiang Li, Jigang Wang
Materials Science
A Two-Step Chemical Vapor Deposition Process for the Synthesis of an Ir(111)/Borophene/2D-Hexagonal Boron Nitride Heterostructure by Intrinsic Segregation
Marko A. Kriegel, Karim M. Omambac, Smruti R. Mohanty et al. (+10 more)
We report on a two-step ultrahigh
vacuum chemical vapor deposition synthesis of a vertical Ir(111)/borophene/hexagonal boron nitride
heterostructure, using borazine as a single-source precursor. The process takes advantage of the finite solubility of boron in Ir: low precursor pressure at high temperature first establishes a boron reservoir in the near-surface region of the substrate, whereas subsequent growth at higher precursor pressure promotes the formation of a closed hexagonal boron nitride monolayer. During cooldown, the reduced boron solubility drives segregation to the surface, resulting in the formation of a borophene monolayer beneath the hexagonal boron nitride overlayer. The
heterostructure, with micron sized grains, homogeneously covers the entire Ir substrate. The study is performed by complementary spot profile analysis low-energy electron diffraction, low-energy electron microscopy, and scanning tunneling microscopy measurements. This intrinsic segregation-assisted growth concept provides a promising route toward scalable synthesis of high-quality, vertical
heterostructures of two-dimensional materials.
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All authors Marko A. Kriegel, Karim M. Omambac, Smruti R. Mohanty, Tobias Hartl, Stefan Schulte, Niels Ganser, Pascal Dreher, Alexandra Rödl, Steffen Franzka, Germán Sciaini, Thomas Michely, Frank-J. Meyer zu Heringdorf, Michael Horn-von Hoegen
Materials Science · Cross-listed from physics.optics
Unraveling the Defect Physics of SiC Micropipe Sidewalls by Non-Line-of-Sight Confocal Spectromicroscopy: Amphoteric Giant Traps
Irwan Saleh Kurniawan, Russel Cruz Sevilla, Ruth Jeane Soebroto et al. (+6 more)
Micropipes are among the most detrimental defects in SiC wafer and are closely linked to catastrophic device failure. However, the microscopic defect nature of their internal sidewalls and the mechanism of the associated leakage current remain poorly understood, because their high-aspect-ratio geometry severely restricts direct optical probing. Here, we develop a non-line-of-sight confocal multiple-reflection spectromicroscopy technique combined with direct defect photoionization to unravel the defect physics of micropipe sidewalls. We show that these sidewalls host a high density of donor-like and acceptor-like deep-level states, giving rise to ultrabroad emission bands composed of intrinsic DAP-like recombination and detrapping-mediated free-to-bound transitions. Unlike conventional defect luminescence, the DAP-like emission remains dominant even at room temperature across all excitation powers. This behavior is attributed to rapid carrier capture by the sidewall defects, as evidenced by fast-rising and nanosecond-scale decay dynamics, along with coupled carrier kinetics. These results suggest that micropipe sidewalls can serve as extended amphoteric
giant traps and carrier reservoirs, facilitating leakage current through trap-assisted transport. Our work provides a nondestructive optical approach for directly probing high-aspect-ratio extended defects and offers deep mechanistic insight into their defect physics and leakage mechanisms.
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All authors Irwan Saleh Kurniawan, Russel Cruz Sevilla, Ruth Jeane Soebroto, Hsiu-Ying Huang, Hsiu-Ming Hsu, Ji-Lin Shen, Sheng Hsiung Chang, Wen-Chung Li, Chi-Tsu Yuan
Materials Science · Cross-listed from physics.optics
Emergence of Localized Surface Plasmons in Unpatterned Hyperdoped Polycrystalline Silicon
Mohamad Bahsoun, Jesse Groenen, Gonzague Agez et al. (+7 more)
The ability to engineer localized surface plasmon resonances at large scale usually relies on precise nanoscale patterning. Here, we demonstrate that mid-infrared plasmonic responses can instead emerge in unpatterned polysilicon films composed of nanometric (5-50 nm) grains, challenging established design paradigms and eliminating the need for external nanostructuring. Using tailored out-of-
equilibrium annealing conditions, we show that hyperdoped polysilicon layers exhibit enhanced light-matter interactions that can be tuned across the mid-infrared range. By combining advanced electron microscopy, infrared spectroscopy and finite-difference time-domain electrodynamic simulations, we demonstrate that these remarkable optical properties originate from naturally formed metal-dielectric interfaces at grain boundaries, which support localized surface plasmon resonances. Importantly, this result is universal and can be extended to any doped
semiconductor system, regardless of the synthesis technique, provided that the grain size remains in the nanometric range. This work opens up a new field in plasmonics centered on polycrystalline
semiconductors, paving the way for cost-effective systems that are fully compatible with microelectronic and photovoltaic technologies, and capable of significantly reshaping light-matter interactions in the infrared range.
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All authors Mohamad Bahsoun, Jesse Groenen, Gonzague Agez, Sébastien Joulié, Cécile Marcelot, Robin Cours, Sébastien Kerdiles, Mathieu Opprecht, Caroline Bonafos, Jean-Marie Poumirol
Materials Science · Cross-listed from cond-mat.mes-hall
Spin-wave bandgap engineering via mode hybridization in dipolar-coupled YIG film/CoFeB nanodisk magnonic crystals
Junyoung Hyun, Krzysztof Szulc, Mateusz Zelent et al. (+5 more)
We investigate
spin-wave transport in hybrid two-dimensional magnonic
crystals comprising a low-damping yttrium iron garnet (YIG) film coupled to a periodic array of CoFeB nanodisks. Using propagating
spin-wave spectroscopy, super-Nyquist magneto-optical Kerr effect microscopy, and micromagnetic simulations, we demonstrate the formation of pronounced and tunable bandgaps that do not originate from conventional Bragg scattering. Instead, these gaps arise from hybridization between the fundamental magnonic-
crystal mode and in-plane transverse standing modes induced by the periodic nanodisk array. The spectral position and width of these gaps are controlled by
geometric parameters and by the
magnetic state of the nanodisks, including their
vortex configuration, which governs both static and dynamic dipolar coupling. For larger
lattice periods, additional gaps emerge through hybridization with modes quantized both transverse and parallel to the
spin-wave propagation direction, reflecting dispersion folding in two dimensions. Our results establish mode hybridization as a versatile mechanism for engineering
spin-wave band structures beyond the constraints of Bragg scattering and provide a pathway toward reconfigurable magnonic devices based on dipolar-coupled hybrid architectures.
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All authors Junyoung Hyun, Krzysztof Szulc, Mateusz Zelent, Nikolai Kuznetsov, Lukáš Flajšman, Maciej Krawczyk, Paweł Gruszecki, Sebastiaan van Dijken
Materials Science · Cross-listed from cond-mat.soft
Predicting the Brittle-to-Ductile Transition in Amorphous Polymers
Valeriy V. Ginzburg, Oleg Gendelman and Alessio Zaccone
Brittle-ductile transition (BDT) is an important characteristic of amorphous (and semicrystalline)
polymers. For a given strain rate, at temperatures above BDT, the
polymers exhibit strain softening followed by yield and strain hardening, while at temperatures below BDT, the same materials exhibit brittle failure at relatively low strains. Surprisingly, today there is no simple model describing BDT as a function of
polymer chemistry, sample history, deformation type, and strain rate. Experimental data suggest that BDT is often, though not always, associated with the beta-transition. We formulate a simple scalar model to describe the visco-elasto-plastic shear stress-strain curves as functions of temperature and strain rate. We also show that within this model, there is always an upper bound on the strain rate where the material can have a uniform viscoplastic flow; this upper bound is taken to represent the BDT. We stipulate that this upper bound is inversely proportional to the Johari-Goldstein beta-relaxation time. Using our "general" Sanchez-Lacombe "two-state, two-(time)scale" (SL-TS2) model, we compute the BDT for three
polymers (polystyrene, poly(methylmethacrylate), and poly(vinylchloride)) and found a good agreement with experimental data.
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Materials Science
Dynamical pseudopotentials
Matteo Quinzi, Tommaso Chiarotti and Nicola Marzari
Pseudopotential theory has greatly driven first-principles calculations in materials, replacing the explicit treatment of the chemically inert core electrons with an effective potential acting only on the valence states. This is inherently an
embedding problem, where tracing out the core electrons can be formulated in terms of a dynamical
embedding potential. Motivated by this perspective, we first introduce a framework for dynamical (i.e., energy-dependent) pseudopotentials, showing how this leads to generalized norm-conservation conditions. Then, adopting a sum-over-poles representation, we disentangle the number of reference energies from the number of projectors; this allows to reproduce all-electron scattering at many reference energies with great accuracy and over very extended energy ranges. We further show that these pseudopotentials enter naturally into many-body total energy functionals, leading for the first time to a consistent and unified treatment of the all-electron atom, the pseudo-atom, and the solid within the same electronic-structure theory.
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Materials Science
Plastic Deformation of B19' Martensite: Where it Matters in NiTi Technology
Petr Šittner, Hanuš. Seiner, Petr Sedlák et al. (+5 more)
Nitinol technology, besides utilizing the functional thermomechanical properties derived from the B2 cubic to B19' monoclinic martensitic transformation, also exploits the excellent plastic deformability of NiTi in the martensite state. It originates from the unique mechanism of plastic deformation of the B19' martensite by kwinking involving dislocation slip based kinking assisted by deformation twinning. Although the mechanism of plastic deformation of martensite by kwinking was revealed only very recently, various unusual phenomena that can only be rationalized by kwinking, have been reported in literature in the last 50 years. These phenomena include: 1) cold working with a high degree of reduction without introducing cracks, 2) excellent plastic deformability in the martensite state (plastic deformation up to~80% strain at stresses >1GPa), 3) refinement of austenitic microstructure to a quasi-amorphous state by tensile deformation, 4) observation of high density of {114} deformation bands in austenitic microstructures, 5) systematic ruptures of strengthened NiTi wires in tensile tests via necking at the onset of plastic yielding, 6) localized plastic deformation in tensile tests via propagation of Lüders band fronts with very large localized strain (~40%), 7) unusually long upper stress plateaus in superelastic tensile tests (>8% strain), 8) large plastic strains (> 20 %) generated in a single closed-loop cooling/heating cycle under constant stress, 9) shape setting of already annealed NiTi by heating under external constraint. Finally, we discuss how kwinking deformation was considered in constitutive modelling of thermomechanical behaviors of NiTi and, particularly, what is the role of the kwinking deformation in NiTi technology.
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All authors Petr Šittner, Hanuš. Seiner, Petr Sedlák, Orsolya. Molnárová, Lukáš Kadeřávek, Ondřej Tyc, Elizaveta Iaparova, Luděk Heller
Materials Science
Effective long-range attraction of moiré excitons under the influence of atomic reconstructions and anisotropic screening
Nils-Erik Schütte, Carl Emil Mørch Nielsen, Niclas Götting et al. (+3 more)
The moiré pattern, which emerges due to a relative rotation between two monolayers of transition metal dichalcogenides, features a long
lattice period for small twist angles. The resulting band structure modulation acts as an effective potential for interlayer
excitons (IXs), which can realize correlated many-body phenomena. Here, we aim for a material-realistic modelling of the
exciton-
exciton interaction, taking into account
lattice reconstructions and an
exciton-
exciton potential that incorporates the highly anisotropic screening imposed by the two-dimensional
bilayer and the dielectric background. We find strong modifications of the on-site interaction induced by the change of the moiré potential during
lattice reconstructions, while for long-range interactions on the length scale of the moiré period, anisotropic dielectric screening leads to a crossover from a repulsive to an attractive interaction. The interaction potential and hopping amplitudes serve as parameters for a Bose-Hubbard model on the moiré
lattice, which we use to explain correlated behavior of interlayer
excitons.
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All authors Nils-Erik Schütte, Carl Emil Mørch Nielsen, Niclas Götting, Alexander Steinhoff, Gabriel Bester, Christopher Gies
Materials Science
Dielectric, magnetic, and magnetodielectric behaviors of BaFe12O19 hexaferrite modulated by Mn and Ti substitutions
Xiao-Fan Zhang, Yang Yang, Ze-Qing Guo et al. (+4 more)
We prepared Mn- and Ti mono-doped and co-doped BaFe12O19 hexaferrites via solid-state reaction to investigate the interplay between
magnetic and dielectric properties. Mn2+ ions preferentially occupy the 4f2 and 2b sites, while Ti4+ ions mainly substitute the Fe3+ ions at 4f1 and 12k sites as revealed by the Raman spectroscopy and formation energy. Pure BaFe12O19 exhibits ferrimagnetism. The hexaferrites related to Ti doping have noncollinear longitudinal conical
spin order at low temperatures, where BaFe6Mn3Ti3O19 retains this
spin order up to room temperature. Ti4+ substitution at 4f1 and 12k sites plays a pivotal role in stabilizing the noncollinear conical
spin order through adjusting the superexchange interactions and reducing the uniaxial magnetocrystalline anisotropy along the c-axis. The
magnetic response exhibits two distinct transition temperatures because Ti4+ ions interrupt the
magnetic superexchange interactions with two inequivalent exchange integrals. Pure BaFe12O19 presents a
quantum paraelectric behavior at low temperatures, which is disrupted by Mn-Ti co-doping due to the decoupling of electric dipoles within the triangular bipyramid. Electron hopping and polaronic effects dominate the dielectric response at 10-50 K, while Maxwell-Wagner interfacial polarization and electron hopping contribute to dielectric dispersion at higher temperatures. The negative MD effect of pure BaFe12O19 and BaFe6Mn3Ti3O19 at 10 K originates from
spin-
phonon coupling and electric polarization induced by noncollinear
spin order under
magnetic field, respectively. The Mn-Ti co-doped samples achieve relatively higher MD responses at low
magnetic fields. In higher temperatures, the MD effect arises mainly from the
magnetic field modulation of the electron hopping with non-intrinsic interfacial polarization.
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All authors Xiao-Fan Zhang, Yang Yang, Ze-Qing Guo, Li Lv, Can Gao, Jian-Ping Zhou, Xiao-ming Chen
Materials Science
Unveiling the Atomistic Mechanisms of Shear-Induced LDA$\leftrightarrow$HDA Transformations and Shear Banding in Amorphous Silicon under High Pressures
Hao Chen, Valery I. Levitas, Tengyi Liu et al. (+3 more)
Large-scale molecular dynamics simulations of shear deformation under constant pressures of amorphous silicon, PT from low-density-amorphous (LDA) to high-density-amorphous (HDA) Si, and formation of shear bands (SBs) are performed using the state-of-the-art Gaussian Approximation Potential. The simulations reveal that LDA$\leftrightarrow$HDA shear-induced PTs occur simultaneously until reaching steady state. The developed mechanism-based analytical model well describes shear-strain-governed kinetics and steady states at all pressures, independent of shear stresses. Shear reduces the pressure for initiation and completion of LDA$\rightarrow$HDA PT by $4.36$ and $5.10$ GPa, respectively. Without PT at low pressure, shear-banding occurs, which is partially suppressed by PT at higher pressure with uniform deformation-PT at $9.8$ GPa. Despite the much larger shear and expected fraction of HDA, surprising sharp drop in the HDA atomic fraction within the SB was discovered. In bulk, Si deforms by atomic rearrangement in localized shear transformation zones with high nonaffine displacements, which trigger nucleation of HDA clusters within LDA and, concurrently, of LDA clusters within HDA, without growth and coalescence. In SB, a turbulent-like flow with swirls is revealed, which promotes reverse PT from HDA$\rightarrow$LDA more effectively. Transformation-induced plasticity in amorphous Si is revealed. The findings open up basic research into the mechanisms and kinetics of plastic strain-induced PTs in amorphous materials under high pressure, with numerous important applications.
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All authors Hao Chen, Valery I. Levitas, Tengyi Liu, Jingyu Lu, Rui Zhu, Zhongqiang Zhang
Materials Science
Thermodynamics of stacking faults and phase stability in cobalt alloys: A combined computational and experimental study
Zheng Zhong, Ziqi Cui, Yu Zhuo et al. (+12 more)
Stacking fault energy dictates phase stability and deformation behavior in Co
alloys and WC-Co cemented carbides, yet a quantitative assessment of alloying effects at finite temperatures remains poorly established. By integrating first-principles thermodynamics with microstructural characterization, we provide a rigorous evaluation of these influences across atomic and macroscopic scales. We show that stacking fault energetics at 0K for transition metal solutes are primarily governed by atomic misfit volume. While 4d and 5d elements follow a consistent linear trend, specific 3d solutes exhibit significant deviations due to non-negligible
magnetic contributions. By incorporating
phonon, electronic, longitudinal
spin-fluctuation, and
magnetic free-energy contributions, the model accurately captures the fcc-hcp transformation and quantifies how diverse solutes modulate the phase landscape. We demonstrate that V, Ni, Fe, Mo, and W lower the transformation temperature by stabilizing fcc phase, while Cr and C exhibit the opposite effect, consistent with experimental phase diagrams. Furthermore, microscopic analysis confirms that higher W content dissolved in the Co suppresses stacking-fault formation by elevating the stacking fault energy at finite temperatures. This work clarifies the physical mechanisms by which alloying regulates stacking fault energy and phase stability in Co-based systems, providing guidance for the design of Co-based
alloys and WC-Co cemented carbides.
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All authors Zheng Zhong, Ziqi Cui, Yu Zhuo, Tianyu Yu, Jianfeng Cai, Kaibo Zou, Jiacheng Shen, Bowen Huang, Zhuoming Xie, Huiqiu Deng, Yang Yu, Hao Zhang, Wangyu Hu, Tengfei Yang, Jie Hou
Materials Science
Magnetic influence on ion transport in concentrated solid solutions: An analytic investigation
Timothy Carlson and Sanjay Govindjee
It is well established that
magnetic fields have a significant effect on transport in certain classes of electronic conductors. Less reported, however, are similar effects in solid ionic conductors. Despite the rarity of
Hall mobility measurements in ionic conductors, recent experimental work in batteries and other systems has demonstrated that an applied
magnetic field can significantly and beneficially alter ionic transport and electrochemical processes in solid materials in a way that would not be predicted from naïve
Hall coefficient estimates. In this work, the influence of a
magnetic field on ion transport in solids is investigated analytically, and general multi-component transport equations accounting for
magnetic effects are presented. Specific models are then derived for solid, isotropic binary and single ion conductors. Material property combinations for which
magnetic field influence may become significant are then computed for certain systems subject to compositional constraints. Finally, it is demonstrated that the derived model for binary conductors in a
magnetic field fits experimental magneto-resistance data well for the fluoride ion conducting solid Pb$_{0.66}$Cd$_{0.34}$F$_2$, provided an assumption of near degenerate multi-component transport.
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