Materials Science
Materials Behavior as Mechanism Ensembles: A Probabilistic Framework for Emergent Behaviors
Brad L. Boyce, Mitchell A. Wood, Krishna Garikipati et al. (+16 more)
Materials behavior is often treated as a deterministic mapping from structure to properties, yet many important phenomena emerge from the conditional activation of multiple mechanisms across scales. This is especially evident in fatigue of metals, where crack growth is typically modeled as monotonic and irreversible process, despite evidence that local microstructure, loading history, and competing unit processes can shift the balance among propagation, arrest, and self-healing. Here we present a probabilistic framework that describes materials behavior as an ensemble of constituent mechanisms whose activation, interaction, and
evolution determine emergent outcomes. The framework connects mechanism activation, state
evolution, and macroscopic observables in a probabilistic way. In the case of fatigue crack propagation, it reframes damage tolerance as an inference problem over mechanism competition and provides a basis for integrating multiscale simulation,
multimodal characterization, and machine learning. The same logic extends to other physical and chemical systems suggesting a portable framework for any system in which emergent behavior reflects mechanism competition under changing conditions. The broader ambition of this perspective review is a shift from correlating structure and performance after the fact to identifying, in advance, the conditions that make desired emergent behavior probable.
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All authors Brad L. Boyce, Mitchell A. Wood, Krishna Garikipati, Andreas E. Robertson, Jeffrey Larson, Ishan Srivastava, Bert Debusschere, Saaketh Desai, Prasad Iyer, Pieterjan Robbe, Mathew Cherukara, Todd Munson, Ming Du, Trupti Mohanty, David J. Gardner, Laurent Capolungo, Benjamin A. Jasperson, Jingye Tan, Rémi Dingreville
Materials Science
Formation of $\mathrm{L}1_2$-ordered $\gamma'$-$\mathrm{Ni}_3\mathrm{Al}$ precipitates in ternary Cu-Ni-Al alloys modelled using an ab initio concentration wave theory and atomistic simulations
Christopher D. Woodgate, Hubert J. Naguszewski, Samuel L. Deacon et al. (+4 more)
Precipitation-strengthened Cu-Ni-Al
alloys are of interest for technological applications because coherent, $\mathrm{L}1_2$-ordered $\gamma'$-$\mathrm{Ni}_3\mathrm{Al}$ precipitates can confer high mechanical strength while allowing the material to retain many of the good transport properties characteristic of elemental Cu. In this work, we study the thermodynamics and phase stability of the pseudobinary $\textrm{Cu}_x (\textrm{Ni}_{3/4} \textrm{Al}_{1/4})_{1-x}$ system, $0 \leq x \leq 1$. We use a computational modelling framework combining first-principles electronic structure calculations with a concentration wave analysis from which atom-atom effective pair interactions are extracted for use in atomistic Monte Carlo simulations. Our modelling reveals three distinct, composition-dependent regimes of phase behaviour, in qualitative agreement with the experimentally determined phase diagram. At low Cu content, Cu is soluble in the $\mathrm{L}1_2$-ordered $\mathrm{Ni}_3\mathrm{Al}$ phase, with a single identifiable phase transition corresponding to chemical ordering between Ni and Al. At intermediate compositions, this high-temperature ordering is followed at lower temperatures by phase separation of Cu and $\mathrm{L}1_2$-ordered $\mathrm{Ni}_3\mathrm{Al}$. Finally, at high Cu content, $\mathrm{L}1_2$-ordered $\mathrm{Ni}_3\mathrm{Al}$ precipitates directly from the solid solution, with no clearly identifiable secondary transition. We relate these phase transformations to features of the underlying electronic structures of the considered
alloys. Overall, this work demonstrates a computationally efficient workflow capturing both chemical ordering and coherent precipitation in multicomponent substitutional
alloys, with relevance to the study of phenomena such as precipitation strengthening.
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All authors Christopher D. Woodgate, Hubert J. Naguszewski, Samuel L. Deacon, Mathys P. Potel, Ján Minár, David Quigley, Julie B. Staunton
Materials Science
No band gap, no problem: Defects in InAs using a band-avoiding occupation-constrained density functional theory
Peter A. Schultz, Arthur H. Edwards, Evan M. Anderson et al. (+2 more)
Density functional theory (DFT) underestimates the experimental band gap—the infamous band gap problem. As the band gap defines the energy scale of defect levels, this complicates computation of charge transition energies for atomic defects. In the extreme case of narrow-gap
semiconductors, the DFT band gap collapses to zero, seemingly precluding quantitative predictions of defect levels. We present a band-avoiding occupation-constrained DFT (ba-occ-DFT) approach that prevents spurious occupation of band-edge states and enables reliable total energy calculations of atomic defects. Application to indium arsenide (InAs) shows that ba-occ-DFT circumvents the band gap problem, separates band-edge errors from defect level calculations, and enables rigorous defect level predictions in a narrow-gap
semiconductor despite a zero DFT band gap.
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All authors Peter A. Schultz, Arthur H. Edwards, Evan M. Anderson, Anthony C. Knighton, Leopoldo Diaz
Materials Science · Cross-listed from cond-mat.mes-hall
Angular Momentum Transfer in Magnetic Weyl Semimetal Spheres
Adriano Biondo and Francesco M. D. Pellegrino
In this work, we investigate the problem of electromagnetic angular momentum within the framework of topological materials, described by
axion electrodynamics. Specifically, we calculate the electromagnetic angular momentum for a spherical sample of
magnetic Weyl semimetal in the presence of a point charge. We then analyze how, by moving the point charge quasi-statically, the angular momentum stored in the electromagnetic field can be converted into mechanical angular momentum of the sphere. Finally, we derive analytical expressions for the resulting angular velocity and angular displacement, demonstrating that the effect is enhanced in the Weyl semimetal compared with a topological
insulator.
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Materials Science
Generation of representative powder particle packing in 2D/3D: which tool for which application?
Antoine Tainturier, Louis Lemarquis, Victor Szczepan et al. (+1 more)
Although dense sphere packings serve as the initial state for simulations in powder metallurgy, additive manufacturing and granular physics, the choice of a packing generator is rarely guided by a systematic
benchmark. A representative packing must be (i)-(ii) physically admissible (non-overlapping particles in gravitational
equilibrium); (iii) faithful to the target particle size distribution (PSD); (iv) representative in relative density Phi; and (v) computationally affordable. Four open-source tools have been benchmarked, meeting (i)-(ii) by construction: the sequential DR (dropping-and-rolling) and its densified variant DR-ME, and the discrete element method (DEM) codes LAMMPS (
gravity) and dp3D (isostatic compression). Across four configurations (2D/3D lognormal, 3D bimodal, and a 3D domain-size study), they are compared against an industrial MIM-grade powder, with PSD fidelity measured by the bin-width-independent Hellinger distance and Phi against the feedstock solid loading (phi_exp = 0.62, by Archimedes' method). In 3D, the DEM codes reach the densest packings but run more than three orders of magnitude slower: for approximatively 20 000 particles, DR shows a 9% phi shortfall relative to dp3D while running 1800x faster. These idealised model packings yield application-driven tool-selection guidelines.
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All authors Antoine Tainturier, Louis Lemarquis, Victor Szczepan, Marc Bernacki
Materials Science
Theory of phonon-magnon hybridization and angular momentum in CrI$_3$ and CrBr$_3$
Maxime Mignolet, Miquel Royo, Massimiliano Stengel et al. (+1 more)
In
magnetic materials angular momentum can be mediated by different carriers, including electrons,
magnons, and
phonons. The
magnons can interact with circularly polarized
phonons which are close in energy, provided specific
symmetry conditions are met. If the interaction is strong enough the
phonons and
magnons shift in frequency and start to mix to form hybrid magneto-elastic quasi-particles. In this paper, we develop a constrained
Hamiltonian framework which incorporates hybrid stiffness
matrices and Berry
curvatures. We quantify the degree of hybridization between
phonons and
magnons (up to 8% in CrI$_3$ and 25% in CrBr$_3$) using a decomposition of the total energy, which is a generalization of the norm decomposition for atomic contributions to
phonons used in the literature. We also explore how the total angular momentum is conserved but shared between the phononic and magnonic subsystems upon hybridization.
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All authors Maxime Mignolet, Miquel Royo, Massimiliano Stengel, Matthieu J. Verstraete
Materials Science · Cross-listed from cond-mat.mes-hall
Two-magnon scattering in the framework of the Lippmann-Schwinger equation
Jorge Marquez Chavez, Ondřej Wojewoda, Yixuan Song et al. (+2 more)
Controlling
magnetic losses requires identifying the microscopic origin of extrinsic linewidth broadening. We introduce a Lippmann–Schwinger framework for two-
magnon scattering from weak defect potentials, showing that scattering is set by the overlap between the perturbation of the effective field and degenerate
spin-wave states. Applied to iron garnet films, YIG/GGG(111) and YIG/GGG(110), we identify crystallographic directions along which these perturbation are elongated. This approach provides a link between the crystallography, effective field on the sample scale and two-
magnon scattering.
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All authors Jorge Marquez Chavez, Ondřej Wojewoda, Yixuan Song, Geoffrey S. D. Beach, Caroline A. Ross
Materials Science
Ferroelectric switchable altermagnetic-like compensated ferrimagnets with charge ordering
Xinyu Yang and Shuai Dong
Unconventional collinear magnets with almost zero magnetization but prominent nonrelativistic
spin-splitting, such as altermagnets, can inherit the advantages of both ferromagnets and antiferromagnets. By incorporating more degrees of freedom such as ferroelectricity and charge ordering, these unconventional magnets can be even more interesting and functionalized. With this design principle, the Fe$_3$O$_5$ monolayer is predicted to exhibit a hybrid
spin-splitting mechanism, with the superposition of the altermagnetic-like $k$-path alternating splitting and ferrimagnet-like Zeeman splitting. Benefiting from the hidden magnetoelectricity based on the
spin-charge coupling, such
spin-splitting can be fully switched by an electric field. Its conductivity is highly
spin-polarized, with a polarization ratio above $99\%$, comparable to half-metals but with zero magnetization.
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Materials Science · Cross-listed from cond-mat.mes-hall
Depth-Resolved Lattice Distortions in a Silicon-Germanium Qubit Host
Jonathan C. Marcks, E. S. Joseph, J. Reily et al. (+6 more)
Semiconductor qubits, promising for
quantum computation, inherit properties from their host
lattice.
Quantum dot
spins, occupying the local lowest energy states in the conduction band, necessarily couple to structural disorder and interfaces. While silicon-based systems promise low noise alongside industrially compatible manufacturing, the growth of SiGe—a leading platform—unavoidably introduces
lattice dislocations, inhomogeneous strain, and crosshatch patterns, expected to cause fluctuations between devices,
qubit failure, and subsequently higher operational overhead. Through X-ray nano-structural mapping of an Intel Si/SiGe chip, we reveal, with 30$~$nm lateral and 200$~$nm functional depth resolution, how extended
lattice defects introduced during growth propagate through the
heterostructure, creating permanently distorted
lattice planes and strain. We correlate these at the $\approx1~\mu$m scale of a
quantum dot device and calculate the impact on
qubit energy spectra. We observe crosshatch fine structure and find that substrate miscut and growth correlate with the final crosshatch pattern.
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All authors Jonathan C. Marcks, E. S. Joseph, J. Reily, Talise Oh, Abigail Postlewaite, Tao Zhou, M. A. Eriksson, Mark Friesen, Martin V. Holt
Materials Science · Cross-listed from cond-mat.soft
Instability-induced bistable shape-morphing kirigami structures
Xiaoyuan Ying and Marcelo A. Dias
Deployable shape-morphing structures that transform from flat sheets into stable three-dimensional configurations are highly desirable for applications ranging from soft robotics and biomedical devices to adaptive architecture and aerospace systems. Existing kirigami-based morphing systems primarily rely on isotropic deployment, compliant soft materials, or external constraints to maintain deployed shapes, which limits
geometric programmability, structural integrity, and applicability in rigid-material systems. Here, we present an inverse design framework for anisotropic bistable kirigami structures that enables programmable shape morphing through controlled
geometric frustration and instability-induced deployment. The framework combines a semi-analytical mechanical model with geometry to establish a direct connection between
geometric transformation and the underlying energy landscape. We show that instability-induced shape morphing leads to tunable bistability and directional deployment in anisotropic kirigami structures. The results are validated through finite element simulations and experiments, demonstrating stable deployed configurations and programmable anisotropic morphing. The proposed framework further provides a general design strategy that can be integrated with various active actuation systems, enabling broader engineering applications.
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Materials Science · Cross-listed from cond-mat.str-el
The electric field gradient tensor as a symmetry-adapted order parameter in Landau theory
L. Scalise and A. W. Carbonari
Quadrupolar hyperfine spectroscopies, including
Nuclear Quadrupole Resonance (NQR),
Nuclear Magnetic Resonance (NMR), Time-Differential Perturbed Angular Correlations (TDPAC), and Mössbauer spectroscopy, have long used the electric field gradient (EFG) at a
nuclear site as an empirical proxy for order parameters in structural and electronic phase transitions, yet the EFG has never been systematically incorporated into Landau theory. Here we provide that framework. The EFG is an exactly traceless, symmetric rank-2 tensor defined at a crystallographic site. Decomposing it under the site-
symmetry group and inducing over the Wyckoff orbit determines its irreducible representation content in the parent space group. Whenever the representation of a zone-center transition is present,
symmetry requires the corresponding EFG combination to vanish above the transition and grow linearly with the order parameter below it, inheriting its critical exponent, sign, and domain structure.
Symmetry-orthogonal channels are quadratic, recovering the classic empirical relations. This yields a falsifiable classification of primary, secondary, and forbidden EFG responses. The framework is validated against five decades of quadrupolar experiments, reproducing critical exponents, first-order discontinuities, and a null result, and by first-principles calculations satisfying the predicted parity and zero
theorems. All-electron calculations for $\alpha$-quartz confirm the orbit-selection rule: only the EFG combination transforming as the soft-mode irreducible representation varies linearly with distortion amplitude, while the orthogonal combination remains suppressed by two orders of magnitude. A proposed study of the $^{75}$As site across the nematic transition in BaFe$_2$As$_2$ provides five falsifiable predictions, including a previously unstated null result.
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Materials Science
Structure-Property Correlation of Cr/Cu-MnFeCoNi High-Entropy Alloys for Alkaline Water Electrolysis
Shreyasi Chattopadhyaya, Raphael B. de Oliveira, Deepti Gangwar et al. (+10 more)
High-
entropy alloys (HEAs), with their unique compositional-complexity and tunable surface chemistry, have emerged as promising electrocatalysts for energy conversion. The catalytic activity of HEA often arises from the interplay between the intrinsic activity of the individual elements and the synergistic effects generated at the interfaces. Even a single-element substitution in a multicomponent HEA can substantially alter the surface-chemistry and electrochemical kinetics of the active surface. Here we investigated the structure-property relationship of CrMnFeCoNi (HEA-Cr) and MnFeCoNiCu (HEA-Cu) HEAs by comparing the alkaline hydrogen
evolution reaction (HER) and oxygen
evolution reaction (OER) activity. Under the same experimental condition, HEA-Cu outperforms HEA-Cr towards both HER and OER. Substituting Cr with Cu significantly enhances the bifunctional activity, where HEA-Cu achieved a lower overpotential (538 mV) and Tafel slope (165 mVdec-1) when compared with HEA-Cr. Computational analysis corroborates these findings, showing that Cu substitution modulates the electronic-structure to provide favorable binding energies for reaction intermediates (H*, O*, OH*, and OOH*). Interestingly, unlike HER, recovered HEA-Cu after OER showed migration of Cu forming a Cu-rich outer layer shell with a multimetallic core. These findings demonstrate the potential of single-element substitution in HEAs as a strategy for designing high-performance, cost-effective catalysts for efficient water electrolysis.
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All authors Shreyasi Chattopadhyaya, Raphael B. de Oliveira, Deepti Gangwar, Tymofii S Pieshkov, Marcelo L. Pereira Junior, Dhiman Banik, Astrid Campos-Mata, Atin Pramanik, Soumyabrata Roy, Douglas S. Galvão, Chandra Sekhar Tiwary, Krishanu Biswas, Pulickel M Ajayana
Materials Science
Crystal forming ability of amorphous refractory metals under nanoindentation: a molecular dynamics study
Prashant Dwivedi, Alberto Fraile and Tomas Polcar
Amorphous refractory metal coatings combine high hardness with chemical inertness, yet their metastability makes them prone to mechanically induced crystallisation (devitrification) under contact loading, and how readily such a glass re-orders to its parent body centred cubic (bcc)
crystal is unknown across the refractory series. We prepared amorphous V, Nb, Mo, Ta and W by melt quenching to 300 K, validated each interatomic potential against ab initio
liquid radial distribution functions, and probed them by large scale molecular dynamics nanoindentation. Indentation drives a localised amorphous to bcc transformation by bulk nucleation, growth and coalescence. A
crystal forming ability (CFA), the maximum slope of the sigmoidal bcc fraction versus depth curve, spans about a factor of four and decreases as V > Mo > Nb > Ta > W; it falls with indenter velocity as CFA $\propto v^{-m}$ with a mean exponent of 1.08, so CFA$\cdot v$ is nearly constant and the transformation rate is almost velocity independent. Transforming atoms carry excess non affine displacement and local shear strain, not hydrostatic pressure, marking a shear associated displacive pathway; the bulk driving force is largest for the most resistant element, W, so resistance tracks cohesive bond strength rather than the thermodynamic driving force. Early bcc like order sets the sharpness and depth of the transition, whereas the mechanical work to half transformation sets the persistent
nucleus density. A grain population balance links nucleation, growth and coalescence to a terminal microstructure whose completeness does not follow the CFA order.
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Materials Science
Magnetic hopfions at room temperature
Kaixin Zhu, Wenli Gao, Zhan Wang et al. (+12 more)
Hopfions are three-dimensional (3D) topological
solitons predicted to exist in diverse
magnetic systems, yet their practical utility has been largely restricted to cryogenic environments. Here, we overcome this temperature constraint by demonstrating stable
magnetic hopfions in the
chiral magnet Co8Zn8Mn4 at and above room temperature. Using a transmission electron microscope equipped for in situ optical excitation, we generate
magnetic hopfions with femtosecond
laser pulses. Long-term observations further reveal Brownian-like motion at room temperature and thermally activated collapse upon approaching the high-temperature regime. Together with micromagnetic simulations and homotopy group analysis, our experimental observations uncover the hopfion formation mechanism through the fusion of bimeron pairs. These findings establish room-temperature
magnetic hopfions and provide a framework for their further studies under technologically relevant conditions.
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All authors Kaixin Zhu, Wenli Gao, Zhan Wang, Shuaishuai Sun, Siyuan Huang, Junxi Tong, Jun Li, Huanfang Tian, Zian Li, Huaixin Yang, Ying Zhang, Olle Eriksson, Filipp N. Rybakov, Nikolai S. Kiselev, Jianqi Li
Materials Science
Inferring Magnetic Material Parameters from Statistical Measures in Strongly Fluctuating Magnetization Dynamics
Kübra Kalkan, Atreya Majumdar, Ross Knapman et al. (+5 more)
Magnetic material parameters such as the exchange stiffness and
magnetic anisotropy govern the behavior and functionality of
magnetic systems, yet their local inference from magnetization data remains challenging, particularly in strongly fluctuating regimes with polycrystalline or multiphase microstructure, where conventional texture-based methods become unreliable. We introduce a magnetization-only framework for inferring material parameters from thermally driven magnetization dynamics. Using micromagnetic simulations, we extract statistical quantities such as temporal mean and latent
entropy from the magnetization dynamics, fit models to these descriptors, and invert the models to infer material parameters. We show that this framework enables material-parameter inference as well as grain-boundary detection in a heterogeneous sample. Among the descriptors considered, latent
entropy yields more accurate parameter estimates than the temporal mean. Our results establish latent
entropy as an efficient descriptor for inferring
magnetic material parameters from dynamical magnetization data and point toward its use for experimental parameter extraction at high temperatures and, more broadly, under strongly fluctuating conditions.
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All authors Kübra Kalkan, Atreya Majumdar, Ross Knapman, Omer Fetai, Franziska Scheibel, Sabrina Disch, Illia Horenko, Karin Everschor-Sitte
Materials Science
End-to-End Modeling of a Volatile TiO2 Memristor for Neuromorphic Circuit Simulation
Lukas Endres, Hannes Töpfer, Michaela Blum et al. (+2 more)
Memristors are promising devices for applications such as non-volatile
memory, neuromorphic computing, logic
circuits, and analog signal processing. The development of such systems requires accurate simulations based on models that reproduce the electrical behavior of real devices under both continuous and pulsed excitation. This work presents the development of a simulation environment for a volatile TiO2-based memristor. Experimental measurement data are analyzed to verify the memristive behavior of the device and to identify a suitable model. The model parameters are then optimized to match the measured characteristics. The resulting model is implemented in SPICE and validated by comparing simulation results with measurement data. The comparison shows a good agreement between simulation and experiment, demonstrating that the developed model is suitable for reproducing the electrical behavior of the investigated memristor and can be applied in
circuit-level simulations, as demonstrated by a leaky integrate-and-fire
neuron.
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All authors Lukas Endres, Hannes Töpfer, Michaela Blum, Hauke Honig, Peter Schaaf
Materials Science · Cross-listed from cond-mat.str-el
Disentangling bulk and surface states in the electronic structure of PtBi$_2$(0001)
Stefanie Suzanne Brinkman, Xin Liang Tan, Anders Christian Mathisen et al. (+13 more)
Recent reports of surface-localized topological superconductivity in trigonal PtBi$_2$ highlight the importance of understanding its surface electronic structure. We investigate the bulk and surface band structure of PtBi$_2$ using angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations. Through
photon-energy- and polarization-dependent measurements, we disentangle bulk dispersions from surface states on the two distinct surface terminations of PtBi$_2$(0001). For both terminations, we assign several different surface states and find good agreement between experiment and calculations. Based on our calculations, we analyze the orbital composition in the surface and bulk bands and compare the results to polarization-dependent ARPES measurements. Together, our results provide a coherent picture of the surface electronic structure of PtBi$_2$ across both surface terminations.
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All authors Stefanie Suzanne Brinkman, Xin Liang Tan, Anders Christian Mathisen, Fabian Göhler, Øyvind Finnseth, Chul-Hee Min, Grigory Shipunov, Falk Pabst, Manuel Alonso Lemos, Balasubramanian Thiagarajan, Craig Polley, Masashi Arita, Kenya Shimada, Anna Isaeva, Jorge I. Facio, Hendrik Bentmann
Materials Science · Cross-listed from cond-mat.dis-nn
Quenched fluctuation-induced force arising from polarization disorder
Bing-Sui Lu
We investigate the zero-temperature behavior of the fluctuation force induced by the quenched disorder of electric dipoles frozen randomly into a material. Examples of such materials include relaxor ferroelectrics. In terms of the setup and geometry, we focus on a layered system comprising two coplanar semi-infinite slabs separated by a distance $\ell$ as well as a system comprising a neutral atom in the
vacuum located at a distance $\ell$ above the surface of a semi-infinite slab. For both systems, we consider the cases where the quenched random dipolar disorder occurs inside the bulk as well as on the surface of the slabs. In all of these cases, we find that the bulk (surface) dipolar disorder-induced force grows with the mean square quenched electric dipole moment per unit volume (area). The bulk (surface) dipolar disorder-induced pressure between two semi-infinite single-layered slabs decays with $\ell^{-3}$ ($\ell^{-4}$), whereas the bulk (surface) dipolar disorder-induced force on an atom in the
vacuum near a slab containing the disorder decays with $\ell^{-4}$ ($\ell^{-5}$). We also find that the quenched dipolar disorder-induced force between two coplanar slabs can be repulsive in a three-layered dielectric system that obeys a zero-frequency analogue of the Dzyaloshinskii-Lifshitz-Pitaevskii condition, and serve to enhance the “nanolevitation effect" if the latter is present in the disorder-free system.
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Materials Science · Cross-listed from cond-mat.supr-con
Electronically Inactive Intercalated La$_2$NiO$_4$ Layer in Superconducting La$_5$Ni$_3$O$_{11}$
Tianyang Xie, Yuxin Wang, Zhan Wang et al. (+2 more)
The recent discovery of superconductivity in La$_5$Ni$_3$O$_{11}$ extends the family of superconducting Ruddlesden–Popper nickelates beyond La$_3$Ni$_2$O$_7$. Unlike conventional members of a single Ruddlesden–Popper series, La$_5$Ni$_3$O$_{11}$ contains an intercalated La$_2$NiO$_4$ layer between La$_3$Ni$_2$O$_7$ blocks, raising the question of whether this additional layer participates in the low-energy electronic structure. Here, we combine density functional theory, Wannier-based tight-binding modeling, and rotationally invariant slave-
boson calculations to investigate the electronic role of the intercalated layer. We find that realistic electronic parameters place the La$_2$NiO$_4$ layer in gapped insulating regimes rather than a paramagnetic metallic state. Furthermore, realistic interlayer hybridization fails to generate any appreciable La$_2$NiO$_4$-derived spectral weight at the
Fermi level. Our results demonstrate that the low-energy electronic structure of La$_5$Ni$_3$O$_{11}$ is governed primarily by the La$_3$Ni$_2$O$_7$ block, with the intercalated La$_2$NiO$_4$ layer remaining electronically inactive. This establishes a minimal low-energy description of La$_5$Ni$_3$O$_{11}$ and provides a unified framework for understanding superconductivity in intercalated Ruddlesden–Popper nickelates.
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All authors Tianyang Xie, Yuxin Wang, Zhan Wang, Kun Jiang, Jiangping Hu
Materials Science
Computational Study of Water Adsorption and Dissociative Mechanisms Impacting g-C3N4's Optical and Electronic Properties
Amil Aligayev, Ulkar Jabbarli, F. Javier Dom{\i}nguez-Gutierrez et al. (+4 more)
In the quest for sustainable energy solutions, water splitting emerges as a crucial process for generating clean hydrogen a versatile and renewable fuel essential for energy storage, emissions reduction, and achieving sustainability goals. This study employs a comprehensive computational approach, utilizing atomistic simulations to systematically investigate the effects of water absorption on the electronic and optical properties of g-C3N4 nanosheets. Our methodology integrates ab initio computations grounded in density functional theory (DFT), which allows for a detailed characterization of the nanosheet and serves as a
benchmark for self-consistent charge density functional tight binding (SCC-DFTB) simulations. This approach provides valuable insights into the behavior of the nanosheet under the influence of absorbed OH and H2O molecules by considering calculated parameters for photocatalytic efficiency. Additionally, we extend our investigation to classical molecular dynamics simulations within the ReaxFF framework, modeling the emission of multiple H2O molecules and assessing the subsequent rate of H2
evolution. A key finding of our study reveals that the dissociation of H2O into HO and O molecules significantly enhances both the optical absorbance and conductance of the nanosheet compared to its pristine state. These results underscore the potential of g-C3N4 nanosheets as effective materials for water splitting applications.
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All authors Amil Aligayev, Ulkar Jabbarli, F. Javier Dom{\i}nguez-Gutierrez, Ulkar Samadova, Jialin Li, Stefanos Papanikolaou, Qing Huang
Materials Science
Transient Detour and Cooperative Oxygen Exchange in the Polarization Switching of Ferroelectric Hf0.5Zr0.5O2
Ryotaro Sahashi, Po-Yen Chen and Teruyasu Mizoguchi
Hafnium zirconium
oxide (HZO) has attracted significant
attention as a core material for next-generation non-volatile
memories due to its excellent ferroelectricity in the ultra-thin film regime and its CMOS process compatibility. However, the exploration of its polarization switching mechanism has predominantly relied on static energy barrier analyses, leaving the transient bond formation and cooperative dynamic mechanisms under actual electric field driving unresolved. In this study, we performed Electric-Field-Induced MD simulations on a defect-free ideal HZO
lattice using a fine-tuned machine learning force field (MACEField). As a result, we successfully reproduced the P-E hysteresis loop dynamically and demonstrated that the polarization switching in HZO is driven not by conventional simple displacement models (S:N/S:T models), but by the dynamic mutual exchange of 3-coordinated oxygen (O3c) and 4-coordinated oxygen (O4c). Analysis of the oxygen atom displacement trajectories revealed that this pathway is accompanied by a unique "detour" behavior originating from transient cation-oxygen bond formation. Furthermore, we identified an "internal self-compensation mechanism" in which the local volumetric expansion and contraction accompanying the coordination number changes are effectively offset within the
cell. These findings provide, from a dynamic perspective, a microscopic physical origin of for HZO's exceptional ability to sustain stable polarization switching without macroscopic strain, a property that has long distinguished HZO from conventional perovskite ferroelectrics yet lacked atomistic explanation. These findings suggest that preserving the integrity of cooperative O3c/O4c exchange pathways, rather than minimizing individual atomic displacements, is the key design principle for endurance and scalability in next-generation ferroelectric
memories.
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Materials Science
Percolating Multifractal Domains at a Polymorphic Phase Boundary
Yuan-Jinsheng Liu, Xu Tian, Jiahui Zhai et al. (+1 more)
Giant piezoelectricity in ferroelectrics is commonly associated with phase-boundary instabilities, among which the polymorphic phase boundary (PPB) is a prominent example conventionally attributed to the coexistence of ferroelectric phases. Here, using large-scale molecular dynamics simulations of the lead-free (K,Na)NbO3-(Bi,Na)ZrO3 solid solutions, we show that the PPB hosts a percolating multifractal polar domain which governs the dielectric and piezoelectric responses. By quantifying the global fractal dimension and multifractal spectrum width of this polar network, we identify fractal connectivity and multiscale heterogeneity as microstructural order parameters for the PPB. The maximum reversible piezoelectric response occurs when the fractal-domain volume fraction approaches the three-dimensional percolation threshold, suggesting that near-critical polar connectivity enables
giant reversible electromechanical coupling. In this mechanism, the fractal backbone preserves polar
memory and provides the restoring force required for reversibility, while the surrounding nonfractal regions supply the polar compliance needed for large polarization rotation and strain. These results establish percolating multifractal polar domains as a microscopic mechanism for PPB-enhanced piezoelectricity and suggest fractal connectivity as a design parameter for high-performance piezoelectrics.
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All authors Yuan-Jinsheng Liu, Xu Tian, Jiahui Zhai, Shi Liu
Materials Science · Cross-listed from cond-mat.str-el
Quantum Geometry-Driven RKKY: From Flat to Dispersive Bands
Zhenggang Zhou, Chuang Li and Lun-Hui Hu
In flat-band systems,
quantum metric bounds physical observables like superfluid weight and coherence length, suggesting a single
geometric scale for spatial correlations. Here, we show that the RKKY exchange in an isolated filled flat band can violate this expectation. With the intraband channel absent, the exchange proceeds via virtual interband transitions across the gap; the kernel becomes the inverse-gap-weighted trace product of the real-space flat-band projector and empty-band projectors. Because the corresponding momentum-space projectors are analytic, the kernel decays exponentially, with a decay length $\xi_\text{RKKY}$ set by the closest singularities of the analytically continued projectors in the complex momentum plane. Thus, this length depends on both the flat-band geometry and the band gap. Applying this formalism to Chern flat-band systems, we find that for small gaps, $\xi_\text{RKKY}$ depends non-monotonically on the
quantum metric length: it first decreases, then increases, revealing that stronger
quantum geometry can shorten the
magnetic exchange range. Upon restoring dispersion, a nontrivial inversion representation can force the overlap between Bloch states at antipodal
Fermi points to vanish under gate tuning, producing a $1/R^3$ RKKY tail instead of the conventional $1/R^2$—a
geometric selection effect.
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Materials Science
Nanoscale Imaging of Strain-Controlled Altermagnetic Domains in {\alpha}-MnTe
Alex L. Melendez, Sijie Xu, Liangbo Liang et al. (+6 more)
Altermagnets combine compensated
magnetic order with momentum-dependent
spin splitting, offering a route to spintronic functionality without the stray fields of conventional ferromagnets. Mechanical strain provides a promising means of controlling their Néel order, yet the microscopic pathway by which strain reorganizes an altermagnetic texture remains unresolved. Here, we combine scanning nitrogen-vacancy magnetometry with a piezo-driven uniaxial strain
cell to directly image the strain-driven
evolution of
magnetic domains in bulk {\alpha}-MnTe at room temperature. By applying uniaxial stress along the nearest-neighbor Mn-Mn bond direction, we find that compressive strain reorganizes the
magnetic texture through domain coalescence, increasing the size of the largest connected domain while reducing the domain-wall density. On sweeping toward tensile strain direction, however, the domain network follows a distinct trajectory from that observed during the compressive sweep. Instead, the large connected regions fragment into a new metastable configuration, producing pronounced hysteresis in the maximum domain size and stray-field distribution. These results identify domain connectivity and
topology as key carriers of strain-induced
magnetic memory. Our work reveals domain coalescence and hysteretic fragmentation as the microscopic pathway of strain control in {\alpha}-MnTe and establishes a route toward strain-programmable altermagnetic textures and reconfigurable spintronic devices.
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All authors Alex L. Melendez, Sijie Xu, Liangbo Liang, Rong-Zhu Lin, An-Ping Li, Pengcheng Dai, Hu Miao, Zhaoyu Liu, Huan Zhao
Materials Science
PUDA: An AI-Native Hardware Harness for Self-Driving Laboratories
Zekun Ren, Hongzhao Tan, Jiaen Yee et al. (+1 more)
Physical Unified Device Architecture (PUDA) is an AI-native hardware harness for self-driving laboratories (SDLs). Rather than building a human-centered graphical user interface (GUI) orchestration layer, PUDA creates a command-line runtime environment that lets
agents observe, orient, decide, and act over experiments while hardware execution remains deterministic, atomic, and auditable. Headless by design, devices appear through discoverable command-line interfaces, JSON protocols are routed through a distributed messaging system, and command responses, data products, and reports are preserved as structured records. PUDA organizes protocols, runs, samples, measurements, and command logs into an AI-native data structure linked by run identifiers and timestamps, preserving provenance from submitted protocol through hardware response to resulting data products. PUDA separates scientific orchestration from physical operation and data telemetry:
agents choose experiments, while PUDA executes validated commands and captures provenance-linked state, responses, and data. The contribution is not another optimizer, orchestrator, or recipe
language. It is a practical execution and data environment for agentic SDLs; the broader physical AI implication is that PUDA provides an AI-native hardware harness for AI systems to interact with physical tools.
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All authors Zekun Ren, Hongzhao Tan, Jiaen Yee, Kedar Hippalgaonkar
Materials Science
Physics-informed Machine Learning Prediction of Hubbard Interaction Parameters
Jiyeon Kim, Indukuru Ramesh Reddy, Bongjae Kim et al. (+1 more)
Accurate determination of Hubbard interaction parameters is essential for beyond-DFT approaches such as DFT+$U$, DFT+DMFT, and DFT+$U$+$V$ in correlated materials. In practice, however, these parameters are often chosen empirically, limiting their transferability across materials. Advanced computational approaches such as the constrained random-phase approximation (cRPA) provide a rigorous route for evaluating Hubbard interactions, but their computational cost remains a bottleneck for large-scale materials screening. Here, we present machine-learning (ML) models for predicting cRPA-derived Hubbard interaction parameters: effective on-site $U_{\rm eff}$, inter-site $V$, and Hund's coupling $J$ for transition-metal
oxides (TMOs). We combine ensemble-learning models with a regression-based brute-force search (BFS) approach to achieve both predictive accuracy and explicit analytical expressions. We construct features that capture electronic, structural, and atomic properties, including the TM-$d$ bandwidth and TM-$d$/O-$p$ band-center separation, as physically motivated descriptors of localization and screening. Our ensemble models achieve RMSEs of 0.148 eV, 0.062 eV, and 0.007 eV for $U_{\rm eff}$, $V$, and $J$, respectively. The derived analytical forms directly relate $U_{\rm eff}$ to electron localization and TM-$d$/O-$p$ hybridization, suggest the importance of hybridization and structural compactness in determining $V$, and indicate that $J$ is governed primarily by elemental descriptors of the TM ion. Together, the present study provides an efficient approach for predicting cRPA-derived $U_{\rm eff}$, $V$, and $J$, while offering physical insight into the factors underlying these Hubbard interactions.
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All authors Jiyeon Kim, Indukuru Ramesh Reddy, Bongjae Kim, Sooran Kim