Materials Science · Cross-listed from cs.LG
Learning ORDER-Aware Multimodal Representations for Composite Materials Design
Xinyao Li, Hangwei Qian, Jingjing Li et al. (+2 more)
Artificial intelligence has shown remarkable success in materials discovery and property prediction, particularly for crystalline and
polymer systems where material properties and structures are dominated by discrete graph representations. Such graph-central paradigm breaks down on composite materials, which possess continuous and nonlinear design spaces. General composite descriptors, e.g., fiber volume and misalignment angle, cannot fully capture the fiber distributions that determine microstructural characteristics, necessitating the integration of heterogeneous data sources through
multimodal learning. Existing
alignment-oriented frameworks have proven effective on abundant
crystal or
polymer data under discrete, unique graph-property mapping assumptions, but fail to address the highly continuous composite design space under extreme data scarcity. In this work we introduce ORDinal-aware imagE-tabulaR
alignment (ORDER), a
multimodal pretraining framework that establishes ordinality as a core principle for material representations. ORDER ensures that materials with similar target properties occupy nearby regions in the latent space, which effectively preserves the continuous nature of composite properties and enables meaningful interpolation between sparsely observed designs. We evaluate ORDER on a Nanofiber-reinforced composite
dataset and a carbon fiber T700
dataset. ORDER and its variants outperform both
alignment-oriented and customized property-aware contrastive baselines across property prediction, cross-modal
retrieval, and microstructure generation tasks. We further introduce physics-based ordinal surrogate signals avoiding the need for full property annotation during pretrain. Our work demonstrates learning continuous
multimodal features are fundamental for composite materials, and provides a reliable pathway toward data-efficient universal
multimodal intelligent systems.
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All authors Xinyao Li, Hangwei Qian, Jingjing Li, Lei Zhu, Ivor Tsang
Materials Science · Cross-listed from physics.chem-ph
A combined criterion of surface free energy and roughness to predict the wettability of non-ideal low-energy surfaces
Majid Shaker and Erfan Salahinejad
The significance of wettability between solid and
liquid substances in different fields encourages scientists to develop accurate models to estimate the resultant apparent contact angles. Surface free energy (SFE), which is principally defined for ideal (flat) surfaces, is not applicable to predict the wettability of real (rough) surfaces. This paper introduces a new parameter, namely normalized surface free energy (NSFE) as a combination of SFE and roughness, to predict the contact angle of
liquids on non-ideal low-energy surfaces. The remarkable consistency of the predicted and measured contact angles of
liquids on some rough surfaces also confirm the validity of the approach.
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Materials Science
Symmetry-protected topological polarons
Kaifa Luo, Jon Lafuente-Bartolome and Feliciano Giustino
Emergent quasiparticles in solids often exhibit unique topological properties as a result of the complex interplay between charge, orbital,
spin and
lattice degrees of freedom. Among these quasiparticles, the polaron occupies a special place as the first known manifestation of the interaction between a
fermion and a
boson field. While polarons have been investigated for almost a century, whether these quasiparticles exhibit topological properties and why remain open questions. Here, we establish the universal
symmetry principles governing the
topology of polar textures in large polarons. Using a group-theoretic analysis, we identify four distinct classes of polar textures in time-reversal-invariant systems, and we show that they carry integer topological charges. We validate this classfication by performing state-of-the-art first-principles calculations of materials representative of each class. For these materials, we compute the fingerprints of polaron
topology in Huang diffuse scattering, and propose ultrafast electron and X-ray scattering experiments to detect these quasiparticles.
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Mesoscale and Nanoscale Physics
Geometry-Induced Skin Effect in Electron Hydrodynamics
Jarosław Pawłowski, Piotr Surówka and Konstantin Zarembo
In ultra-clean 2d materials electron viscosity is as important as Ohmic dissipation and electron transport exhibits hydrodynamic features. Using a simple framework of Brinkman equations we find that hydrodynamic electron flows give rise to a
geometric skin effect: sharp obstacles locally enhance the current suppressing it far from the edges where the flow is unobstructed. This effect arises within hydrodynamic transport with finite momentum relaxation and does not rely on ballistic dynamics. Our results provide a natural hydrodynamic interpretation of edge-enhanced and double-bump current profiles observed in constricted geometries. By comparing with recent scanning NV magnetometry experiments on gated
graphene, we demonstrate that such flow patterns are consistent with viscous hydrodynamics shaped by geometry, clarifying the role of
geometric effects in the interpretation of electronic flow experiments.
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Materials Science
Embedded Ferroelectric Nanoclusters can drive Polarization Reversal in a Non-Ferroelectric Polar Film via the Proximity Effect
Anna N. Morozovska, Eugene A. Eliseev, Sergei V. Kalinin et al. (+3 more)
Heterogeneous nucleation from defects dominates the electric field required for polarization switching of ferroelectrics. Here, we consider the switching of a nominally non-switchable polar thin film of AlN due to the proximity effect arising from embedded ferroelectric nanoclusters of Al1-xScxN. Using a Landau-Ginzburg-Devonshire thermodynamic approach and finite element modeling, we study the influence of nanocluster shape on polarization switching and domain nucleation emerging in AlN. The ferroelectric nanocluster boundary is modeled as a thin layer transitioning from Al1-xScxN to AlN. We analyze the conditions under which polarization switching in the AlN film occurs at coercive fields significantly lower than its dielectric breakdown field. In the presence of spike-like Al1-xScxN nanoclusters, the proximity effect enables switching of the spontaneous polarization in AlN and significantly reduces the corresponding coercive field. The internal field, which is depolarizing inside the AlN (due to its larger spontaneous polarization) and polarizing within the ferroelectric Al1-xScxN nanoclusters (due to its smaller spontaneous polarization), lowers the potential barrier in the clusters and nucleates nanodomains at the Al1-xScxN-AlN interface, forming localized regions of reversed polarization. Proximity effect can thus provide a pathway towards "thawing" previously "frozen" ferroelectrics through engineered nucleation for
memory, actuation and optical technologies.
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All authors Anna N. Morozovska, Eugene A. Eliseev, Sergei V. Kalinin, Long-Qing Chen, Dean R. Evans, Venkatraman Gopalan
Materials Science
Minimal model for vortex nucleation and reversal in spherical magnetic nanoparticles
Michael P. Adams and Andreas Michels
Magnetic nanoparticles beyond the single-domain limit often develop
vortex-like magnetization textures arising from the competition between exchange and magnetostatic energies. While such states are routinely studied using micromagnetic simulations, transparent analytical descriptions of
vortex-mediated hysteresis and nucleation remain scarce. Here, we develop a semi-analytical minimal framework for
vortex states in spherical
magnetic nanoparticles. Guided by micromagnetic simulations, we introduce a parametrized
vortex magnetization Ansatz based on
hyperbolic functions that continuously interpolates between uniform and
vortex states. In this way, we achieve a complexity reduction leading to a minimal
Hamiltonian, which enables the efficient computation of magnetization curves and provides insight into
vortex-mediated magnetization reversal. As an application, we derive analytical estimates for the critical
vortex nucleation radius and field, recovering the functional form of Brown's classic result and extending it within a variational framework.
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Materials Science
Materials design based on a material-motif network and heterogeneous graphs
Anoj Aryal, Weiyi Gong, Huta Banjade et al. (+1 more)
Machine learning models for functional materials design require precise and informative representations of material systems. Common representations encode atomic composition and bonding but often do not include local coordination environments across chemically diverse
crystals. Recurring structural motifs provide a motif level description of crystalline solids and can serve as interpretable descriptors for structure property learning. To analyze the motif connectivity in materials, we construct a bipartite material motif network from 131,548 Materials Project entries, with materials and motifs as the two node sets. Edges connect materials to their constituent motifs and are weighted by motif distortion, which quantifies the strength of each material motif association. Network connectivity is analyzed to identify motif-defined material clusters that capture recurring local geometries relevant to structure property trends. Most shared motifs act as hubs that connect otherwise disconnected regions of the network, enabling motif guided screening by expanding from known motifs to nearby materials in the same neighborhoods. A network
embedding step converts this weighted connectivity into vector representations of materials. Using these motif informed
embeddings, property prediction yields a formation energy mean absolute error (MAE) of 0.157 eV per atom and a bandgap MAE of 0.601 eV. These results indicate that motif connectivity provides a compact, interpretable representation that complements existing descriptors for scalable screening and structure property modeling.
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All authors Anoj Aryal, Weiyi Gong, Huta Banjade, Qimin Yan
Materials Science
Discontinuous character of the ultrafast exciton Mott transition in monolayer WS$_2$
Subhadra Mohapatra, Samuel Palato, Nicholas Olsen et al. (+2 more)
There are conflicting predictions and reports on the character of the
exciton Mott transition (EMT) in monolayer transition metal dichalcogenides. It could be either a discontinuous or a continuous transition from the excitonic to the
plasma phase, with important implications for devices such as photoswitches. To resolve the nature of the transition in monolayer WS$_2$, we study its ultrafast optical response upon resonant photoexcitation of the A
exciton across a broad range of photoexcitation densities. In agreement with previously reported measurements we observe that the A
exciton quenches gradually with increasing excitation density. However, a detailed lineshape analysis unveils an abrupt red shift in the transient peak positions of the A and B
exciton resonances above an excitation density threshold. This is attributed to band gap renormalization arising from the formation of free charge carrier
plasma, i.e., the EMT. The
plasma phase decays with a time constant of 0.65 ps back into the excitonic state. The abrupt appearance of the
plasma phase at the threshold density suggests that the EMT is a discontinuous and not a continuous transition. This work demonstrates how transient optical spectroscopy combined with lineshape analysis of two excitonic resonances simultaneously can be used to investigate the EMT in 2D materials.
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All authors Subhadra Mohapatra, Samuel Palato, Nicholas Olsen, Julia Stähler, Lukas Gierster
Strongly Correlated Electrons · Cross-listed from physics.chem-ph
Degenerate coupled-cluster theory
So Hirata
A size-extensive, converging, black-box, ab initio coupled-cluster ($\Delta$CC) ansatz is introduced that computes the energies and wave functions of states from any degenerate or nondegenerate Slater-determinant references with any numbers of $\alpha$- and $\beta$-
spin electrons, any patterns of orbital occupancy, any
spin multiplicities, and any spatial
symmetries. For a nondegenerate reference, it reduces to the single-reference coupled-cluster ansatz. For a degenerate multireference, it is a natural coupled-cluster extension of degenerate Moeller-Plesset perturbation ($\Delta$MP) theory. For ionized and electron-attached references, it is a coupled-cluster Green's function, although the present theory is convergent toward the full-configuration-interaction (FCI) limits, while Feynman-Dyson many-body Green's function (MBGF) theory generally is not. Its single-excitation instance is a projection Hartree-Fock theory as per the Thouless
theorem, which may be useful for core ionizations, high-
spin states, and possibly electron affinities. A new multireference coupled-cluster theory for a general model space is also developed. This quasidegenerate coupled-cluster (QCC) theory is exactly converging, but not black-box, and intended for strong correlation. Determinant-based, general-order
algorithms of $\Delta$CC and QCC theories are implemented and compared with configuration-interaction (CI) and equation-of-motion coupled-cluster (EOM-CC) theories through octuple excitations and with $\Delta$MP and MBGF theories up to the nineteenth order. An algebraic, optimal-scaling
algorithm of $\Delta$CC theory is computer-synthesized at the levels of single excitations ($\Delta$CCS) and of single and double excitations ($\Delta$CCSD). The order of performance is: QCC $\approx$ $\Delta$CC > EOM-CC > CI at the same order or QCC $\approx$ $\Delta$CC > $\Delta$MP > MBGF at the same cost scaling.
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Materials Science
Thermodynamics of Ferroelectric and Optical Properties in KNbO3
Aiden Ross, Venkatraman Gopalan and Long-Qing Chen
Potassium niobate (KNbO3) is a prototypical perovskite ferroelectric with large electro-optic and nonlinear optical responses, high optical damage thresholds and a rich sequence of temperature-driven phase transformations, making it a promising platform for tunable photonic devices. In this work, we develop a thermodynamic model for the coupled ferroelectric and optical properties of KNbO3. By separating the total polarization into
lattice and electronic contributions, the model provides a unified description of both the anisotropic ferroelectric and optical properties. The thermodynamic coefficients are determined by fitting to experimental measurements of the spontaneous polarization, dielectric susceptibilities,
lattice parameters, and refractive indices. Without any further fitting, the model quantitatively predicts the temperature dependence of the electro-optic and piezoelectric coefficients in close agreement with experimental measurements. By utilizing the electronic polarization equation of motion, the model further captures the optical dispersion in the near infrared to visible spectrum. This work provides the thermodynamic foundation for future studies of coupled ferroelectric and optical phenomena in KNbO3.
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Materials Science
On-the-Fly Machine-Learned Force Fields for High-Fidelity Polymer Glass Transition Simulations
Ashutosh Srivastava, Sakshi Agarwal, Shivank Shukla et al. (+2 more)
Predicting
polymer glass transition temperatures (Tg) with first-principles fidelity has long remained out of reach, as cooling multi-thousand-atom systems over a broad temperature range at acceptable rates exceeds the computational limits of ab initio molecular dynamics (AIMD). Here we employ a hybrid scheme that merges AIMD with accelerated on-the-fly (OTF) machine-learned force-field (MLFF) construction, enabling Tg prediction at
quantum-mechanical accuracy with near-classical computational cost. The OTF protocol to construct MLFFs adaptively triggers first-principles calculations only when newly encountered configurations lie outside the current model's domain of confidence, allowing robust, parameter-free MLFFs to be built from merely 1000 AIMD-sampled configurations per
polymer. These MLFFs are then utilized to perform long-time cooling simulations on amorphous supercells containing several thousand atoms. Applied across twelve
polymers spanning aromatic, aliphatic, heteroatomic, and branched chemistries, the method yields predictions in excellent accord with experiment while reducing computational cost by approximately six orders of magnitude relative to AIMD. This work establishes a new paradigm for predictive
polymer modeling, demonstrating that OTF-MLFFs provide a generalizable, accurate, and scalable route to simulating the thermophysical behavior of complex disordered materials at near
quantum-mechanical fidelity.
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All authors Ashutosh Srivastava, Sakshi Agarwal, Shivank Shukla, Harikrishna Sahu, Rampi Ramprasad
Strongly Correlated Electrons
Ferrichiral skyrmions with sublattice-resolved chirality in extended Kitaev model in triangular lattice
Bogeng Wen, Jiefu Cen and Hae-Young Kee
We study an extended Kitaev model on the triangular
lattice in a limit where the symmetric off-diagonal bond-dependent and Heisenberg interactions together map onto an XXZ model, in addition to the Kitaev interaction. Within the previously identified $\mathbb{Z}_2$
vortex regime, we uncover a ferrichiral skyrmion phase characterized by a sublattice-resolved scalar chirality: two of the three sublattices carry unit skyrmion charge, while the third remains nonchiral. Using classical Monte Carlo simulations, we show that this ferrichiral skyrmion phase emerges at zero temperature and in the absence of both an external
magnetic field and Dzyaloshinskii-Moriya interactions, in sharp contrast to conventional skyrmion-hosting systems. The phase is stable over a wide parameter window and persists to relatively high temperatures. Our results reveal an unconventional route to skyrmion physics driven purely by frustrated exchange interactions and highlight the emergence of rich topological structures. Since both XXZ anisotropy and Kitaev interactions originate from the same
spin-orbit-coupling mechanism, materials traditionally classified as XXZ magnets are expected to host finite Kitaev interactions as well. The potential for ferrichirality in these systems therefore warrants further investigation.
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Materials Science
Detecting the full photoemission cone from laser-based ARPES experiments by leveraging deflector technology
Nicolas Gauthier, Benson Kwaku Frimpong, Dario Armanno et al. (+8 more)
Angle-resolved photoemission spectroscopy (ARPES) provides a direct access to the electronic band structure of solid and molecular systems. The momentum range accessible by this technique depends directly on the
photon energy used, and low-
photon-energy sources are insufficient to photoemit electrons over the full Brillouin zone of most
quantum materials. In addition, while electrons are emitted over a 2$\pi$ solid angle, conventional hemispherical analyzers only collect a small subset of those electrons. A previous work [RSI 92, 123907 (2021)] demonstrated that electrons emitted over a larger field-of-view can be acquired in one fixed configuration by accelerating them towards the analyzer with a bias voltage. Here, we extend this work by leveraging the deflector technology of novel ARPES hemispherical analyzers. We demonstrate the ability to detect all $2\pi$ photoemitted electrons in a fixed configuration for various materials such as gold, cuprates and transition-metal dichalcogenides. This approach is especially advantageous for time-resolved ARPES, as electron dynamics over a large momentum range can be accessed with identical measurement conditions.
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All authors Nicolas Gauthier, Benson Kwaku Frimpong, Dario Armanno, Akib Jabed, Francesco Goto, Vicky Hasse, Claudia Felser, Genda Gu, Heide Ibrahim, Francois Légaré, Fabio Boschini
Materials Science
Tunable Edelstein effect in intrinsic two-dimensional ferroelectric metal PtBi$_{2}$
Weiyi Pan and Jaroslav Fabian
The Edelstein effect, which enables charge-to-
spin conversion and is therefore highly promising for future spintronic devices, can be realized and non-volatilely manipulated in ferroelectric materials owing to their broken inversion
symmetry and switchable polarization states. To date, most ferroelectric systems reported to exhibit the Edelstein effect are
semiconductors, requiring extrinsic doping for functionality. In contrast, the Edelstein effect has rarely been reported in metallic ferroelectric systems, where doping is unnecessary. Using first-principles calculations, we predict that a pronounced Edelstein effect can be realized in the recently proposed intrinsic two-dimensional ferroelectric metal PtBi$_{2}$ monolayer, where the sign of the Edelstein coefficient is coupled to the direction of ferroelectric polarization through the polarization-switching-induced reversal of
spin textures, thereby enabling non-volatile control of charge-
spin conversion. The Edelstein effect reaches a magnitude of $10^{11}~\hbar/(\textup{A} \cdot \textup{cm})$, which is sizable compared to previously reported ferroelectric systems. Microscopically, the Edelstein effect in a PtBi$_2$ monolayer originates from competing contributions of inner Rashba-like electron pockets and outer hole pockets with opposite signs; an upward shift of the
Fermi level alters their balance and can reverse the sign of the Edelstein effect. Upon applying biaxial strain, the
Fermi-surface electronic structure is strongly modified, resulting in a pronounced change of the Edelstein effect: a 2 % compressive strain suppresses the Edelstein effect by about 50 %. Our results not only identify a promising material platform for tunable charge-
spin conversion but also provide new insights into the functional potential of metallic ferroelectric systems.
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Disordered Systems and Neural Networks · Cross-listed from cs.LG
A Scalable Measure of Loss Landscape Curvature for Analyzing the Training Dynamics of LLMs
Dayal Singh Kalra, Jean-Christophe Gagnon-Audet, Andrey Gromov et al. (+4 more)
Understanding the
curvature evolution of the loss landscape is fundamental to analyzing the training dynamics of neural networks. The most commonly studied measure, Hessian sharpness ($\lambda_{\max}^H$) – the largest
eigenvalue of the loss Hessian – determines local training stability and interacts with the learning rate throughout training. Despite its significance in analyzing training dynamics, direct measurement of Hessian sharpness remains prohibitive for Large
Language Models (LLMs) due to high computational cost. We analyze $\textit{critical sharpness}$ ($\lambda_c$), a computationally efficient measure requiring fewer than $10$ forward passes given the update direction $\Delta \mathbf{\theta}$. Critically, this measure captures well-documented Hessian sharpness phenomena, including progressive sharpening and Edge of Stability. Using this measure, we provide the first demonstration of these sharpness phenomena at scale, up to $7$B parameters, spanning both pre-training and mid-training of OLMo-2 models. We further introduce $\textit{relative critical sharpness}$ ($\lambda_c^{1\to 2}$), which quantifies the
curvature of one loss landscape while optimizing another, to analyze the transition from pre-training to fine-tuning and guide data mixing strategies. Critical sharpness provides practitioners with a practical tool for diagnosing
curvature dynamics and informing data composition choices at scale. More broadly, our work shows that scalable
curvature measures can provide actionable insights for large-scale training.
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All authors Dayal Singh Kalra, Jean-Christophe Gagnon-Audet, Andrey Gromov, Ishita Mediratta, Kelvin Niu, Alexander H Miller, Michael Shvartsman
Statistical Mechanics · Cross-listed from hep-th
Constrained Symplectic Quantization I: the Quantum Harmonic Oscillator
Martina Giachello, Francesco Scardino and Giacomo Gradenigo
Symplectic quantization is a functional approach to
quantum field theory that allows sampling of
quantum fluctuations directly in Minkowski space-time by means of a generalized microcanonical ensemble similar to the one of the standard microcanonical approach to
lattice field theory. In a previous paper we showed that, for an interacting scalar field theory in 1+1-dimensions, this formalism allows to capture numerically some crucial real-time features inaccessible to any Euclidean approach to
lattice field theory. Yet, the new approach was plagued by two main limitations: an ill-defined non-interacting limit and the absence of a direct formal correspondence between its correlation functions and those generated by the Feynman path integral approach. In this paper, we introduce the new "constrained
symplectic quantization" approach, for which the perfect equivalence with the Feynman path integral is proved and which is perfectly well defined for the free theory. This new approach is characterized by the analytical continuation of all fields and of the action from $\mathbb{R}$ to $\mathbb{C}$ and the presence of some constraints which guarantee the stability of the generalized
Hamiltonian dynamics and the convergence of the corresponding generalized microcanonical partition function, hence the name of the theory. We show the application of this formalism to the
quantum harmonic oscillator on a Minkowskian-time
lattice, finding perfect agreement between one- and two-point numerical correlators and the exact
quantum-mechanical results. We observe genuine real-time features such as the oscillatory propagator and the discrete excited-state energy spectrum. Our results provide strong numerical evidence that constrained
symplectic quantization can sample real-time
quantum-mechanical observables, offering a concrete route to overcome the limitations of Euclidean-time importance sampling.
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Statistical Mechanics · Cross-listed from quant-ph
Engineering discrete local dynamics in globally driven dual-species atom arrays
Francesco Cesa, Andrea Di Fini, David Aram Korbany et al. (+4 more)
We introduce a method for engineering discrete local dynamics in globally-driven dual-species neutral atom experiments, allowing us to study emergent digital models through uniform analog controls. Leveraging the new opportunities offered by dual-species systems, such as species-alternated driving, our construction exploits simple Floquet protocols on static atom arrangements, and benefits of generalized blockade regimes (different inter- and intra-species interactions). We focus on discrete dynamical models that are special examples of
Quantum Cellular Automata (QCA), and explicitly consider a number of relevant examples, including the kicked-Ising model, the Floquet Kitaev honeycomb model, and the digitization of generic translation-invariant nearest-neighbor
Hamiltonians (e.g., for Trotterized
evolution). As an application, we study chaotic features of discretized many-body dynamics that can be detected by leveraging only demonstrated capabilities of globally-driven experiments, and
benchmark their ability to discriminate chaotic
evolution.
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All authors Francesco Cesa, Andrea Di Fini, David Aram Korbany, Roberto Tricarico, Hannes Bernien, Hannes Pichler, Lorenzo Piroli
Strongly Correlated Electrons
Boundary critical phenomena in the quantum Ashkin-Teller model
Yifan Liu, Natalia Chepiga, Yoshiki Fukusumi et al. (+1 more)
We investigate the boundary critical phenomena of the one-dimensional
quantum Ashkin-Teller model using boundary conformal field theory and density
matrix renormalization group (DMRG) simulations. Based on the $\mathbb{Z}_2$-orbifold of the $c=1$ compactified
boson boundary conformal field theory, we construct microscopic
lattice boundary terms that renormalize to the stable conformal boundary conditions, utilizing simple current extensions and the underlying $\mathrm{SU}(2)$
symmetry to explicitly characterize the four-state Potts point. We validate these theoretical identifications via finite-size spectroscopy of the
lattice energy spectra, confirming their consistency with $D_4$
symmetry and Kramers-Wannier duality. Finally, we discuss the boundary renormalization group flows among these identified fixed points to propose a global phase diagram for the boundary criticality.
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All authors Yifan Liu, Natalia Chepiga, Yoshiki Fukusumi, Masaki Oshikawa
Materials Science
Atomically Resolved Acoustic Dynamics Coupled with Magnetic Order in a van der Waals Antiferromagnet
Faran Zhou, Kyle Hwangbo, Sung Soo Ha et al. (+22 more)
Magnetoelastic coupling in van der Waals (vdW)
magnetic materials enables a unique interplay between the
spin and
lattice degrees of freedom. Characterizing the elastic responses with atomic and femtosecond resolution across the
magnetic transition is essential for guiding the design of magnetically tunable actuators and strain-mediated spintronic devices. Here, ultrafast x-ray diffraction employed at a free-electron
laser reveals that the atomic displacements, wave vectors, and dispersion relations of acoustic
phonon modes in a vdW antiferromagnet FePS$_3$ are coupled with the
magnetic order, by tracking both in-plane and out-of-plane Bragg peaks upon optical excitation across the Néel temperature (T$_N$). One transverse mode shows that a quasi-out-of-plane atomic displacement undergoes a significant directional change across T$_N$. Its quasi-in-plane wave vector is derived by the comparison between the measured sound velocity and the first-principles calculations. The other transverse mode is an interlayer shear acoustic mode whose amplitude is strongly enhanced in the
antiferromagnetic phase, exhibiting eight times stronger amplitude than the longitudinal acoustic mode below T$_N$. The atomically resolved characterization of acoustic
phonon dynamics that couple with
magnetic ordering opens opportunities for harnessing unique magnetoelastic coupling in vdW magnets on ultrafast timescales.
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All authors Faran Zhou, Kyle Hwangbo, Sung Soo Ha, Xiao-Wei Zhang, Sae Hwan Chun, Jaeku Park, Intae Eom, Qianni Jiang, Zekai Yang, Marc Zajac, Sungwon Kim, Sungwook Choi, Zhaodong Chu, Kyoung Hun Oh, Yifan Su, Alfred Zong, Elton J. G. Santos, Ting Cao, Jiun-Haw Chu, Stephan O. Hruszkewycz, Nuh Gedik, Di Xiao, Hyunjung Kim, Xiaodong Xu, Haidan Wen
Materials Science
Connecting bond switching to fracture toughness of calcium aluminosilicate glasses
Sidsel Mulvad Johansen, Tao Du, Johan F. S. Christensen et al. (+5 more)
Fracture toughness is a critical mechanical property of glasses, but a detailed understanding of its link to composition and structure is still missing. Here, focusing on the industrially important family of calcium aluminosilicate glasses, we measure the fracture toughness of two glass series using the single-edge precracked beam method, one based on tectosilicate compositions with varying silica contents and the other covering both percalcic and peraluminous compositions with varying Al/Ca ratio. To elucidate the structural origins of the variation in fracture toughness, we perform X-ray total scattering measurements and molecular dynamics simulations. Our findings show that local coordination changes of especially Al atoms, so-called bond switching, feature an overall positive correlation with fracture toughness. We also compare this variation with that in other mechanical properties, including elastic
moduli, hardness, and crack initiation resistance. We find that various structural aspects need to be considered to describe and understand the mechanical properties of calcium aluminosilicate glasses.
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All authors Sidsel Mulvad Johansen, Tao Du, Johan F. S. Christensen, Anders K. R. Christensen, Xuan Ge, Theany To, Lars R. Jensen, Morten M. Smedskjaer
Materials Science
Łucja Kipczak, Tomasz Woźniak, Chinmay K. Mohanty et al. (+10 more)
Understanding the coupling between
lattice vibrations and
magnetic order is crucial for controlling properties of two-dimensional
magnetic materials. Here, we investigate the vibrational properties of bulk and thick-flake CrCl$_\textrm{3}$ using polarization-resolved Raman spectroscopy, complemented by photoluminescence, photoluminescence excitation, and optical absorption measurements.
Symmetry analysis, supported by first-principles
phonon calculations, enables the unambiguous assignment of all eight Raman-active modes, four $\textrm{A}_\textrm{g}$ and four $\textrm{E}_\textrm{g}$, previously predicted only theoretically. Excitation-energy-dependent measurements reveal that the strong enhancement of selected
phonon modes originates primarily from interference effects rather than resonant Raman scattering. Temperature-dependent Raman spectroscopy further reveals pronounced signatures of
spin-
phonon coupling across the transition from a fully
antiferromagnetic phase, through an intermediate regime with local, domain-like
ferromagnetic order, to the paramagnetic phase, accompanied by a clear rhombohedral-to-monoclinic structural transition. Together, these results demonstrate how
lattice, electronic, and
magnetic degrees of freedom collectively govern the Raman response of CrCl$_\textrm{3}$.
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All authors Łucja Kipczak, Tomasz Woźniak, Chinmay K. Mohanty, Igor Antoniazzi, Jakub Iwański, Przemysław Oliwa, Jan Pawłowski, Meganathan Kalaiarasan, Zdeněk Sofer, Andrzej Wysmołek, Adam Babiński, Maciej Koperski, Maciej R. Molas
Strongly Correlated Electrons
Doping-dependent orbital magnetism in Chromium pnictides
Henri G. Mendonça, George B. Martins and Lauro B. Braz
We present results for the phase diagram of the parent compound LaCrAsO under electron doping using the
matrix random-phase approximation. At low doping levels, the system stabilizes an
antiferromagnetic state in which different Cr sublattices carry opposite
spins, consistent with experimental observations. As the doping concentration increases, a stripe-type
antiferromagnetic phase becomes favored. At even higher doping, the system repeats the two former
magnetic states, but with incommensurate
magnetic ordering vectors. The commensurate
magnetic phases are associated with more localized electrons in the Cr $d_{3z^2-r^2}$ orbital, whereas the incommensurate phases are linked to the $d_{xy}$ orbital, whose stronger overlap favors itinerant-electron magnetism.
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