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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Thursday 8 January

Materials Science · Cross-listed from quant-ph

Quantum Elastic Network Models and their Application to Graphene

Ioannis Kolotouros, Adithya Sireesh, Stuart Ferguson et al. (+3 more)

Molecular dynamics simulations are a central computational methodology in materials design for relating atomic composition to mechanical properties. However, simulating materials with atomic-level resolution on a macroscopic scale is infeasible on current classical hardware, even when using the simplest elastic network models (ENMs) that represent molecular vibrations as a network of coupled oscillators. To address this issue, we introduce Quantum Elastic Network Models (QENMs) and utilize the quantum algorithm of Babbush et al. (PRX, 2023), which offers an exponential advantage when simulating systems of coupled oscillators. Here, we extend their algorithm in 2D systems and demonstrate how our method enables the efficient simulation of planar materials. As an example, we apply our algorithm to the task of simulating a 2D graphene sheet. We analyze the complexity for initial-state preparation, Hamiltonian simulation, and measurement of this material, and provide two real-world applications: heat transfer and the out-of-plane rippling effect. We estimate that an atomistic simulation of a graphene sheet on the centimeter scale, classically requiring hundreds of petabytes of memory and prohibitive runtimes, could be encoded and simulated with as few as $\sim 160$ logical qubits.
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All authors Ioannis Kolotouros, Adithya Sireesh, Stuart Ferguson, Sean Thrasher, Petros Wallden, Julien Michel

Materials Science

Prediction of Magnetic Topological Materials Combining Spin and Magnetic Space Groups

Liangliang Huang, Yuanze Song, Houhao Wang et al. (+3 more)

Recent developments in spin space groups (SSGs) have led to a new classification of magnetic order and, with it, the emergence of altermagnetism. However, an efficient and routine approach that predicts electronic band topology in magnetic materials by SSGs, and especially the evolution of band topology from negligible spinorbit coupling (SOC) to finite SOC with the symmetry lowering from SSGs to magnetic space groups (MSGs) determined by magnetic-moment directions, has not yet been established. Here, we propose a scheme combining SSG and its MSG subgroups to diagnose band topology in collinear magnets using symmetry indicators of electronic band topology, established for all the 1,421 SSGs and 3,420 MSG subgroups. Specifically, the compatibility relations from SSG to the MSG subgroups can enable a complete topological classification for all possible magnetic-moment directions from the first-principles calculated numbers of occurrences of irreducible (co-)representations at high-symmetry points without SOC with respect to SSG. This scheme can be directly applied to collinear magnets whose magnetic structures have already been determined experimentally or theoretically. Applying it to 488 collinear magnets from MAGNDATA with experimentally determined magnetic structures, we identify 26 materials that are trivial by MSG but are expected to inherit topology protected by SSG symmetry. We showcase Dirac nodal lines and boundary states predicted by SSG but invisible to MSG in FePSe$_3$. Our work demonstrates the predictive power of the approach combining SSG and MSG over the approaches based on either group alone. The results of high-throughput calculations are expected to extend the magnetic topological materials pool, facilitating future experimental realizations of more magnetic topological materials.
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All authors Liangliang Huang, Yuanze Song, Houhao Wang, Zhixian Yu, Xiangang Wan, Feng Tang

Materials Science

A First-principles Study of Weyl Nodal Loop and Multiple Sets of Weyl Points in Trigonal PtBi$_2$

Lin-Lin Wang

Coexistence of surface superconductivity and Fermi arcs in trigonal $\gamma$-PtBi$_2$ has recently attracted attention for possible realization of topological superconductivity. The Fermi arcs on the two different (0001) surface terminations have been associated with the set of Weyl points just above the Fermi energy (E$_F$). Here using first-principles calculations to explore the band crossings over the full Brillouin zone between the nominally highest valence and lowest conduction bands in $\gamma$-PtBi$_2$, we study the Weyl nodal loop (WNL) and multiple sets of Weyl points (WPs). The main difference between the two reported experimental structural parameters is the magnitude of Bi-layer buckling. While the WNL, bulk gap region and the set of Weyl points just above the E$_F$ are robust, the number and location of the other sets of WPs depend sensitively on the structural parameters with different magnitude of Bi-layer buckling. Besides calculating the 2D Fermi surface with Fermi arcs and quasi-particle interference (QPI) around the E$_F$ in good agreements with ARPES and experimental QPI, we also predict new Fermi arc features at higher energy.
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Materials Science · Cross-listed from cond-mat.mes-hall

Quantum Spin Transfer of Spin-Correlated Electron Pairs

Seongmun Hwang, Jung Hyun Oh, Paul M. Haney et al. (+2 more)

We theoretically investigate quantum spin transfer from spin-correlated conduction-electron pairs to localized spins in a ferromagnet, given that electrons are correlated intrinsically. We show that even spin-singlet pairs and triplet pairs with $m=0$, both carrying no net spin, can transfer finite angular momentum through the quantum fluctuation term inherent to the $sd$ exchange interaction. The amount of transferred spin differs between the singlet and triplet $m=0$ states due to quantum interference. The difference is such that the independent-electron approximation remains valid for spin transfer when injected spin currents are completely incoherent. However, in partially coherent systems, like superconductor/ferromagnet junctions, coherent spin-singlet currents can directly convert into equal-spin triplet currents in generic ferromagnets, without requiring magnetic inhomogeniety or spin-orbit coupling.
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All authors Seongmun Hwang, Jung Hyun Oh, Paul M. Haney, Mark D. Stiles, Kyung-Jin Lee

Materials Science

Hierarchical Crystal Structure Prediction of Zeolitic Imidazolate Frameworks Using DFT and Machine-Learned Interatomic Potentials

Yizhi Xu, Jordan Dorrell, Katarina Lisac et al. (+4 more)

Crystal structure prediction (CSP) is emerging as a powerful method for the computational design of metal-organic frameworks (MOFs). In this article we employ CSP to perform high-throughput exploration of the crystal energy landscape of zinc imidazolate (ZnIm2). As the most polymorphic member of the zeolitic imidazolate framework (ZIF) family, ZnIm2 has at least 24 reported structural and topological forms, and new polymorphs still being regularly discovered. With the aid of custom-trained machine-learned interatomic potentials (MLIPs) we have performed a high-throughput sampling of over 3 million randomly-generated crystal packing arrangements and identified 9609 energy minima characterized by 1484 network topologies, including 855 topologies that have not been reported before. All but one experimentally-reported structures of ZnIm2, falling within the search boundaries, were ultimately matched with the predicted structures, demonstrating the power of the CSP method in sampling experimentally-relevant ZIF structures. Finally, through a combination of topological analysis, density and porosity considerations, we have identified a set of structures representing promising targets for future experimental screening. as well as demonstrated how structures of mechanochemically-synthesized MOFs could be identified via matching experimental powder diffraction patterns with simulated patterns from the predicted structures.
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All authors Yizhi Xu, Jordan Dorrell, Katarina Lisac, Ivana Brekalo, James P. Darby, Andrew J. Morris, Mihails Arhangelskis

Materials Science

Electrically Controllable Flat Band in Two-Dimensional Electron Gases under Nonuniform Magnetic Fields

You-Ting Huang, Chao-Cheng Kaun and Ching-Hao Chang

Flat bands underlie a diverse range of quantum phenomena, from strongly correlated phases to superconductivity. We theoretically establish that a two-dimensional electron gas under a linear magnetic-field gradient and a transverse electric field exhibits electrically tunable flat bands. When the electric field magnitude is tuned to a value within a discrete sequence, these bands become strictly dispersionless. By providing exact classical and quantum solutions, we demonstrate that these states are high-order Landau levels associated with drift-compensated cyclotron orbits of carriers arising from the synergy between the magnetic-field gradient and the electric field. These electrically controllable Landau levels exhibit quantized Hall conductance and a strongly enhanced density of states. Our results provide a new route for flat-band creation, magnetoelectric band engineering, and quantized Hall currents controlled via source-drain voltage.
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Materials Science

Electronic structure of Sn(1-x)Mn(x)Te semiconducting solid solution: a resonant photoemission study

Elzbieta Guziewicz, Bronislaw A. Orlowski and Bogdan J. Kowalski

Manganese-doped tin telluride, Sn(1-x)Mn(x)Te, initially investigated as diluted magnetic semiconductor, has recently attracted considerable attention as a prospective thermoelectric material. The introduction of Mn was found to modify the valence band electronic structure, resulting in an improvement in the Seebeck coefficient and thus, the figure of merit (ZT). In the paper, we present a synchrotron radiation study of the electronic band structure of Sn(0.9)Mn(0.1)Te by resonant photoemission. The contribution of the Mn3d electrons to the valence band (VB), calculated as the difference between the Energy Distribution Curves (EDCs) taken at the maximum and minimum of the Fano resonance for the Mn3p - Mn3d absorption threshold, shows a contribution at the VB edge, a dominant maximum at 4 eV, as well as a wide structure between 7 and 11 eV. Moreover, comparison with undoped SnTe reveals strong renormalization of the Sn5p and Te5p electronic states, which certainly influences the shape of the upper part of the valence band and electron effective mass.
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Materials Science

Correlative Ultrafast Imaging of a Propagating Photo-Driven Phase Transition Using 4D STEM

Arthur Niedermayr, Jianyu Wu, Bertina Fisher et al. (+2 more)

Oxides exhibiting insulator-metal transitions are promising candidates for next generation ultrafast electronic switching devices. However, critical gaps remain in understanding the onset of strain and its dynamics as these materials undergo structural transitions, particularly in nanostructured configurations. Here, we present ultrafast four-dimensional scanning transmission electron microscopy enabling virtual imaging and strain mapping at every point in space and time. Using this technique, we directly probe a laser-excited phase transition in the prototypical material vanadium dioxide (VO2), recording its spatiotemporal propagation. This direct imaging capability reveals the dynamics of the structural phase transition and connects it to the resulting strain formation on picosecond timescales. This correlation reveals how atomic-scale symmetry breaking inherently generates lattice distortions, which then propagate to govern macroscopic property changes. Our findings provide new insights into the coupling between electronic, structural, and mechanical responses in correlated oxides under non-equilibrium conditions.
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All authors Arthur Niedermayr, Jianyu Wu, Bertina Fisher, Ido Kaminer, Jonas Weissenrieder

Materials Science

Stable Machine Learning Potentials for Liquid Metals via Dataset Engineering

Alex Tai, Jason Ogbebor and Rodrigo Freitas

Liquid metals are central to energy-storage and nuclear technologies, yet quantitative knowledge of their thermophysical properties remains limited. While atomistic simulations offer a route to computing liquid properties directly from atomic motion, the most accurate approach, ab initio molecular dynamics (AIMD), is computationally costly and restricted to short time and length scales. Machine learning interatomic potentials (MLPs) offer AIMD accuracy at far lower cost, but their application to liquids is limited by training datasets that inadequately sample atomic configurations, leading to unphysical force predictions and unstable trajectories. Here we introduce a physically motivated dataset-engineering strategy that constructs liquidlike training data synthetically rather than relying on AIMD configurations. The method exploits the established icosahedral short-range order of metallic liquids, twelvefold, near-close-packed local coordination, and generates "synthetic-liquid" structures by systematic perturbation of crystalline references. MLPs trained on these datasets close the sampling gaps that lead to unphysical predictions, remain numerically stable across temperatures, and reproduce experimental liquid densities, diffusivities, and melting temperatures for multiple elemental metals. The framework links atomic-scale sampling to long-term MD stability and provides a practical route to predictive modeling of liquid-phase thermophysical behavior beyond the limits of direct AIMD.
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Materials Science · Cross-listed from cond-mat.str-el

Kitaev interactions in the van der Waals antiferromagnet VBr3

Zeyu Kao, Yimeng Gu, Yiqing Gu et al. (+5 more)

Van der Waals materials hosting Kitaev interactions are promising platforms for exploring exotic quantum phenomena. Here, we report inelastic neutron scattering investigations of the van der Waals antiferromagnet VBr3, which forms a honeycomb lattice structure at room temperature and exhibits zigzag-type magnetic order below 26.5 K. Our observations reveal distinctive low-energy spin excitations arising from gamma, gamma', and M' points, each featuring a spin gap of around 2.5 meV. The overall spin excitation spectra can be effectively described by a spin Hamiltonian incorporating substantial nearest-neighbor Kitaev and biquadratic interactions, along with Heisenberg interactions. Our findings not only establish VBr3 as a new Kitaev magnet but also suggest that ligand engineering may provide a promising strategy to modulate Kitaev interactions, offering new opportunities for designing Kitaev materials with tailored quantum properties.
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All authors Zeyu Kao, Yimeng Gu, Yiqing Gu, Hao Zhang, Shiyi Zheng, Naoki Murai, Seiko Ohira-Kawamura, Jun Zhao

Materials Science

Three-dimensional Moiré crystallography

Ilya Popov and Elena Besley

Moiré materials, typically confined to stacking atomically thin, two - dimensional (2D) layers such as graphene or transition metal dichalcogenides, have transformed our understanding of strongly correlated and topological quantum phenomena. The lattice mismatch and relative twist angle between 2D layers have shown to result in Moiré patterns associated with widely tunable electronic properties, ranging from Mott and Chern insulators to semi- and super-conductors. Extended to three-dimensional (3D) structures, Moiré materials unlock an entirely new crystallographic space defined by the elements of the 3D rotation group and translational symmetry of the constituent lattices. 3D Moiré crystals exhibit fascinating novel properties, often not found in the individual components, yet the general construction principles of 3D Moiré crystals remain largely unknown. Here we establish fundamental mathematical principles of 3D Moiré crystallography and propose a general method of 3D Moiré crystal construction using Clifford algebras over the field of rational numbers. We illustrate several examples of 3D Moiré structures representing realistic chemical frameworks and highlight their potential applications in condensed matter physics and solid-state chemistry.
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Materials Science

Goldene monolayer as a highly effective catalyst for polysulfide anchoring and conversion: A theoretical study

Nicolas F. Martins, José A. dos S. Laranjeira, Bill D. A. Huacarpuma et al. (+3 more)

We use first-principles density functional theory to investigate how lithium sulfide and polysulfide clusters (Li2S, Li2S2, Li2S4, Li2S6, Li2S8, and S8) bind to Goldene, a new two-dimensional gold allotrope. All Li-S species exhibit robust binding to Goldene. The adsorption energies range from -4.29 to -1.90 eV. S8 that is alone interacts much less strongly. Charge density difference and Bader analyses indicate that substantial charge is transferred to the substrate, with a maximum 0.92 e for Li-rich clusters. This transfer induces polarization at the interface and shifts the work function to 5.30-5.52 eV. Projected density-of-states calculations indicate that Au-d and S-p states strongly mix near the Fermi level. This hybridization indicates that the electronic coupling is strong. Based on these results, the reaction free-energy profile for the stepwise conversion of S8 to Li2S on Goldene is thermodynamically favorable. The overall stabilization is -3.64 eV, and the rate-determining barrier for the Li2S2 -> Li2S step is 0.47 eV. This shows that Goldene is an effective surface for anchoring and mediating lithium polysulfide reactions.
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All authors Nicolas F. Martins, José A. dos S. Laranjeira, Bill D. A. Huacarpuma, Kleuton A. L. Lima, Luiz A. Ribeiro Jr, Julio R. Sambrano

Materials Science

Exploring the Potential of Two-dimensional Borospherene for Toxic Gas Sensing and Capture: A DFT Study

Nicolas F. Martins, José A. dos S. Laranjeira, Kleuton A. L. Lima et al. (+2 more)

Two-dimensional (2D) boron-based materials have gained increasing interest due to their exceptional physicochemical properties and potential technological applications. In this way, borospherenes, a 2D Boron-based fullerene-like lattice (2D-B40), are explored due to their potential for capturing and detecting toxic gases, such as CO, NO, NH3, and SO2. Therefore, density functional theory simulations were carried out to explore the adsorption energy and the distinct interaction regimes, where CO exhibits weak physisorption (-0.16 eV), while NO (-2.24 eV), NH3 (-1.47 eV), and SO2 (-1.51 eV) undergo strong chemisorption. Bader charge analysis reveals significant electron donation from 2D-B40 to NO and electron acceptance from SO2. These interactions cause measurable shifts in work function, with SO2 producing the most significant modulation (14.6%). Remarkably, ab initio molecular dynamics simulations (AIMD) reveal spontaneous SO2 decomposition at room temperature, indicating dual functionality for both sensing and environmental remediation. Compared to other boron-based materials, such as chi3-borophene, beta12-borophene, and B40 fullerene, 2D-B40 exhibits superior gas affinity, positioning it as a versatile platform for the detection and capture of toxic gases.
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All authors Nicolas F. Martins, José A. dos S. Laranjeira, Kleuton A. L. Lima, Luiz A. Ribeiro Jr, Julio R. Sambrano

Materials Science

Discovery of a new weberite-type antiferroelectric: La3NbO7

Louis Alaerts, Jesse Schimpf, Xinyan Li et al. (+7 more)

Antiferroelectrics are antipolar materials which possess an electric field-induced phase transition to a polar, ferroelectric phase and offer significant potential for sensing/actuation and energy-storage applications. Known antiferroelectrics are relatively scarce and mainly based on a limited set of perovskite materials and their alloys (e.g., PbZrO$_3$, AgNbO$_3$, NaNbO$_3$). Here, a new family of lead-free, weberite-type antiferroelectrics, identified through a large-scale, first-principles computational search is introduced. The screening methodology, which connects lattice dynamics to antipolar distortions, predicted that La$_3$NbO$_7$ could exhibit antiferroelectricity. We confirm the prediction through the synthesis and characterization of epitaxial La$_3$NbO$_7$ thin films, which display the signature double hysteresis loops of an antiferroelectric material as well as clear evidence of an antipolar ground state structure from transmission electron microscopy. The antiferroelectricity in La$_3$NbO$_7$ is simpler than most known antiferroelectrics and can be explained by a Kittel-type mechanism involving the movement of niobium atoms in an oxygen octahedron through a single phonon mode which results in a smaller change in the volume during the field-induced phase transition. Additionally, it is found that La$_3$NbO$_7$ combines a high threshold field with a high breakdown field ($\approx$ 6MV/cm) - which opens up opportunities for energy-storage applications. This new weberite-type family of materials offers many opportunities to tune electrical and temperature response especially through substitutions on the rare-earth site. Ultimately, this work demonstrates a successful data-driven theory-to-experiment discovery of an entirely new family of antiferroelectrics and provides a blueprint for the future design of ferroic materials.
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All authors Louis Alaerts, Jesse Schimpf, Xinyan Li, Jiongzhi Zheng, Ella Banyas, Jeffrey B. Neaton, Sinéad M. Griffin, Yimo Han, Lane W. Martin, Geoffroy Hautier

Materials Science · Cross-listed from physics.comp-ph

A joint voxel flow-phase field framework for ultra-long microstructure evolution prediction with physical regularization

Ao Zhou, Salma Zahran, Chi Chen et al. (+2 more)

Phase-field (PF) modeling is a powerful tool for simulating microstructure evolution. To accelerate the simulation of PF models governed by complex PDEs, machine learning methods such as PINNs and ConvLSTM have been introduced. However, current machine-learning-based approaches still suffer from limited flexibility, poor generalization, and short prediction horizons. To address these challenges, we present a joint framework that couples a voxel-flow network (VFN) with PF simulations in an alternating manner for long-horizon prediction of microstructure evolution with substantial computational acceleration. The VFN iteratively predicts future evolution by generating the next snapshot from the previous two snapshots. Periodic PF simulations suppress nonphysical artifacts, reduce accumulated error, and extend the reliable prediction horizon. The VFN was validated using a grain-growth example, and its accuracy outperforms that of similar prediction methods while preserving topological grain details. For an ultra-long grain-growth prediction of 82 frames from 2 input frames, the grain number decreases from 600 to 29 while the NMSE of the average grain area remains 1.64%. The framework also exhibits good generalizability across different PF models. Overall, this joint framework enables rapid, flexible, generalizable, and physically consistent microstructure forecasting from image-based data over ultra-long time scales.
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All authors Ao Zhou, Salma Zahran, Chi Chen, Zhengyang Zhang, Yanming Wang

Materials Science · Cross-listed from cs.AI

Higher-Order Knowledge Representations for Agentic Scientific Reasoning

Isabella A. Stewart and Markus J. Buehler

Scientific inquiry requires systems-level reasoning that integrates heterogeneous experimental data, cross-domain knowledge, and mechanistic evidence into coherent explanations. While Large Language Models (LLMs) offer inferential capabilities, they often depend on retrieval-augmented contexts that lack structural depth. Traditional Knowledge Graphs (KGs) attempt to bridge this gap, yet their pairwise constraints fail to capture the irreducible higher-order interactions that govern emergent physical behavior. To address this, we introduce a methodology for constructing hypergraph-based knowledge representations that faithfully encode multi-entity relationships. Applied to a corpus of ~1,100 manuscripts on biocomposite scaffolds, our framework constructs a global hypergraph of 161,172 nodes and 320,201 hyperedges, revealing a scale-free topology (power law exponent ~1.23) organized around highly connected conceptual hubs. This representation prevents the combinatorial explosion typical of pairwise expansions and explicitly preserves the co-occurrence context of scientific formulations. We further demonstrate that equipping agentic systems with hypergraph traversal tools, specifically using node-intersection constraints, enables them to bridge semantically distant concepts. By exploiting these higher-order pathways, the system successfully generates grounded mechanistic hypotheses for novel composite materials, such as linking cerium oxide to PCL scaffolds via chitosan intermediates. This work establishes a "teacherless" agentic reasoning system where hypergraph topology acts as a verifiable guardrail, accelerating scientific discovery by uncovering relationships obscured by traditional graph methods.
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Materials Science

Triple-well ferroelectricity and kagome-like Chern flat band in two-dimensional multiferroic CuVP$_2$Se$_6$

Brian Anchico, Jingyi Duan, Haojie Sun et al. (+3 more)

Two-dimensional multiferroics that host nontrivial topological bands offer a rich platform for correlated and tunable quantum phenomena, yet such materials remain rare. Here, using first-principles calculations, we reveal that monolayer CuVP$_2$Se$_6$ unites a tunable triple-well ferroelectric transition with a spin-polarized Chern flat band. The ferroelectric and paraelectric phases are close in energy and can be reversibly switched by moderate strain or an electric field. During the transition, a kagome-like flat band emerges near the Fermi level, which we describe via a minimal three-orbital tight-binding model on a triangular lattice. Furthermore, the system exhibits sizable magnetic anisotropy and a magnetization-dependent Chern insulating state: the Chern number is $C = \pm 1$ for out-of-plane magnetization but becomes trivial when the moments rotate in-plane. These findings establish CuVP$_2$Se$_6$ as a promising candidate for exploring electrically tunable flat-band correlations and topological magnetism in a multiferroic monolayer.
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All authors Brian Anchico, Jingyi Duan, Haojie Sun, Minjun Wang, Mikhail Talanov, Wei Jiang

Materials Science

Lateral Graphene-Metallene Interfaces at the Nanoscale

Mohammad Bagheri and Pekka Koskinen

Metallenes are atomically thin, nonlayered two-dimensional materials. While they have appealing properties, their isotropic metallic bonding makes their stabilization difficult and presents considerable challenges to their synthesis and practical applications. However, their stabilization can still be achieved by suspending them in the pores of two-dimensional template materials, making the properties of lateral interfaces of metallenes scientifically relevant. Here, we combined density-functional theory and universal machine-learning interatomic potentials to study lateral interfaces between graphene and 45 metallenes with various profiles. We optimized the interfaces and analyzed their energies, electronic structures, and stabilities at room temperature, defect formations, and structural deformations. While broad trends were identified using machine-learning analysis of all interfaces, density-functional theory was the main tool for studying the microscopic properties of selected elements. We found that the interfaces are the most stable energetically and with respect to lattice mismatch, defect formation, and lateral strain when their profiles were geometrically smooth. The most stable interfaces are found for transition metals. In addition, we demonstrate how universal machine-learning interatomic potentials now offer the accuracy required for the modeling of graphene-metallene interfaces. By systematically expanding the understanding of metallenes' interface properties, we hope these results guide and accelerate their synthesis to enable future applications and benefit from metallenes' appealing properties.
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Materials Science

Electric-Field Modulated Optical Transitions in Monolayer CrI3 and Its Nanoribbons

Xianzhe Zhu, Pu Liu, Wence Ding et al. (+3 more)

The successful synthesis of few-layer CrI3 has opened new avenues for research in two-dimensional magnetic materials. Owing to its simple crystal structure and excellent physical properties, layered CrI3 has been extensively studied in magneto-optical effects, excitons, tunneling transport, and novel memory devices. However, the most current theoretical studies rely heavily on the first-principles calculations, and a general analytical theoretical framework, particularly for electric-field modulation and transport properties, is still lacking. In this work, using a 28-band tight-binding model combined with linear response theory, we systematically investigate the optoelectronic response for monolayer CrI3 and its nanoribbons. The results demonstrate that: (1) a vertical electric field can selectively close the band gap of one spin channel while the other remains insulating, resulting a transition to an half-metallic state; (2) the electric field dynamically shifts the optical transition peaks, providing a theoretical basis for extracting band parameters from experimental photoconductivity spectra; (3) nanoribbons with different edge morphologies exhibit distinct edge-state distributions and electronic properties, indicating that optical transition can be dynamically modualted through edge design. The theoretical model developed in this study, which can describe external electric field effect, offers an efficient and flexible approach for analytically investigating the CrI3 family and related materials. This model overcomes the limitations of first-principles methods and provides a solid foundation for designing spintronic and optoelectronic devices controlled by electric fields and edge effect.
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All authors Xianzhe Zhu, Pu Liu, Wence Ding, Benhu Zhou, Xiaoying Zhou, Guanghui Zhou

Materials Science

Tuning Excitonic Properties and Charge Carrier Dynamics by Halide Alloying in Cs3Bi2(Br1-xIx)9 semiconductors

He Zhao and Eline M. Hutter

The perovskite-inspired bismuth halide semiconductor Cs3Bi2Br9 is widely investigated as photoactive material for light-conversion applications. However, charge generation and separation are inherently limited by its modest sunlight absorption and strong exciton binding energy, respectively. Here, we demonstrate that both the light absorption and exciton dissociation are improved by controlled substitution of Br with I via mechanochemical synthesis of Cs3Bi2(Br1-xIx)9. X-ray diffraction and Raman analyses confirm atomic-level halide mixing and reveal a crystallographic phase transition near x = 0.8. From absorption measurements on thin films, we determine the absorption coefficient, Urbach tail, and exciton binding energy for several Cs3Bi2(Br1-xIx)9 compositions. From here, we find that the band gap can be tuned from 2.59 to 1.93 eV (for x = 0.9), while exciton binding energies reach a minimum at x = 0.6. Finally, transient absorption spectroscopy measurements suggest a weak correlation between recombination lifetime and Urbach energy, where the longest lifetimes are observed for the materials with lowest disorder. These results offer valuable insights for designing stable bismuth halide semiconductors with favorable light absorption properties and charge carrier dynamics.
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Materials Science

Berry Phase of Bloch States through Modular Symmetries

Emanuele Maggio

The theoretical identification of crystalline topological materials has enjoyed sustained success in simplified materials models, often by singling out discrete symmetry operations protecting the topological phase. When band structure calculations of realistic materials are considered, complications often arise owing to the requirement of a consistent gauge in the Brillouin zone, or down to the fineness of its sampling. Yet, the Berry phase, acting as topological label, encodes geometrical properties of the system, and it should be easily accessible. Here, an expression for the Berry phase is obtained, thanks to analytical Bloch states constructed from an infinite series of $s$-type Gaussian orbitals. Two contributions in the Berry phase are identified, with one having an immediate geometric interpretation, being equal to the Zak phase. Eigenvalues of a modular symmetry, considered here for the first time in the context of crystalline solid state systems, are put in correspondence with the Zak phase: modular symmetries allow to define a non-trivial action for the spatial inversion also when the system does not have an inversion centre, as for the considered case of space group no. 22 ($F222$), which is known to host symmetry equivalent Bloch states distinguishable by their Berry phase.
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Materials Science

Scalable Dielectric Tensor Predictions for Inorganic Materials using Equivariant Graph Neural Networks

Haowei Hua, Chen Liang, Ding Pan et al. (+4 more)

Accurate prediction of dielectric tensors is essential for accelerating the discovery of next-generation inorganic dielectric materials. Existing machine learning approaches, such as equivariant graph neural networks, typically rely on specially-designed network architectures to enforce O(3) equivariance. However, to preserve equivariance, these specially-designed models restrict the update of equivariant features during message passing to linear transformations or gated equivariant nonlinearities. The inability to implicitly characterize more complex nonlinear structures may reduce the predictive accuracy of the model. In this study, we introduce a frame-averaging-based approach to achieve equivariant dielectric tensor prediction. We propose GoeCTP, an O(3)-equivariant framework that predicts dielectric tensors without imposing any structural restrictions on the backbone network. We benchmark its performance against several state-of-the-art models and further employ it for large-scale virtual screening of thermodynamically stable materials from the Materials Project database. GoeCTP successfully identifies various promising candidates, such as Zr(InBr$_3$)$_2$ (band gap $E_g = 2.41$ eV, dielectric constant $\overline{\varepsilon} = 194.72$) and SeI$_2$ (anisotropy ratio $\alpha_r = 96.763$), demonstrating its accuracy and efficiency in accelerating the discovery of advanced inorganic dielectric materials.
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All authors Haowei Hua, Chen Liang, Ding Pan, Irwin King, Shengchao Liu, Koji Tsuda, Wanyu Lin

Materials Science

Towards understanding the defect properties in the multivalent A-site Na$_{0.5}$Bi$_{0.5}$TiO$_3$-based perovskite ceramics

Pengcheng Hu, Chinmay Chandan Parhi, Jurij Koruza et al. (+1 more)

A defect model involving cation and anion vacancies and anti-site defects is proposed that accounts for the non-stoichiometry of multi-valent $A$-site Na$_{0.5}$Bi$_{0.5}$TiO$_3$ based perovskite oxides with $ABO_3$ composition. A series of samples with varying $A$-site non-stoichiometry and $A$:$B$ ratios were prepared to investigate their electrical conductivity. The oxygen partial pressure and temperature dependent conductivities where studied with direct current (dc) and alternating current (ac) techniques, enabling to separate between ionic and electronic conduction. The Na-excess samples, regardless of the $A$:$B$ ratio, exhibit dominant ionic conductivity and $p$-type electronic conduction, with the highest total conductivity reaching $4 \times 10^{-4}$ S/cm at 450$^\circ$C. In contrast, the Bi-excess samples display more insulating characteristics and $n$-type electronic conductivity, with conductivity values within the 10$^{-8}$ S/cm range at 450$^\circ$C. These conductivity results strongly support the proposed defect model, which offers a straightforward description of defect chemistry in NBT-based ceramics and serves as a valuable guide for optimizing sample processing to achieve tailored properties.
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All authors Pengcheng Hu, Chinmay Chandan Parhi, Jurij Koruza, Andreas Klein

Materials Science

Nanoscale resistive switching in electrodeposited MOF Prussian blue analogs driven by K-ion intercalation probed by C-AFM

L. B. Avila, O. de Leuze, M. Pohlitz et al. (+12 more)

K-ion intercalation in Prussian blue analogs (PBAs) is a well-established charge storage mechanism in potassium-ion batteries; here, we demonstrate that this same ion intercalation process is the basis for nanoscale resistive switching behavior in PBA-base memristive devices. Using C-AFM, we directly visualize and electrically control this intercalation process within sub-100 nm volumes, revealing reversible, localized conductance modulation driven by K-ion intercalation and Fe^(2+)/Fe^(3+) redox reconfiguration. This nanoscale operability highlights the exceptional potential of PBAs for high-scalable and low-dimension memristor-based devices integration. Due to their modular composition, PBAs constitute a chemically rich, earth-abundant materials platform whose electronic and ionic properties can be precisely tuned for specific device functions. K-ion intercalation PBA-based memristor devices, with their single-step, aqueous, and room-temperature fabrication, enable low-cost, large-scale processing compatible with CMOS, without any additional post-fabrication processing. Our findings establish PBAs as a new class of intercalation memristors with scalable nanoscale switching and exceptional materials versatility, toward highly integrated neuromorphic and non-volatile memory technologies. This work provides the first demonstration of intercalation-driven resistive switching under ultrafast voltage sweeps, with PW operating up to 200 V/s and PB up to 50 V/s. This unprecedented speed establishes PBAs as a distinct, high-rate class of K-ion intercalation memristors suitable for fast, high-density neuromorphic and memory applications.
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All authors L. B. Avila, O. de Leuze, M. Pohlitz, M. A Villena, Ramon Torres-Cavanillas, C. Ducarme, A. Lopes Temporao, T. G. Coppée, A. Moureaux, S. Arib, Eugenio Coronado, C. K. Müller, J. B. Roldán, B. Hackens, F. Abreu Araujo

Materials Science

How semiconducting are ferroelectrics: The fundamental, optical and transport gaps of Na$_{0.5}$Bi$_{0.5}$TiO$_3$-BaTiO$_3$ and NaNbO$_{3}$

Pengcheng Hu, Nicole Bein, Chinmay Chandan Parhi et al. (+7 more)

The energy gap is a fundamental property of materials, directly related to their optical and electronic properties. The energy gap of ferroelectric compounds and its adjustment by compositional variation has particularly attracted attention in recent years due to potential application in energy conversion and/or catalytic devices. It is demonstrated that it is necessary to distinguish between the fundamental gap, $E_{\rm g}^{0}$, the optical gap, $E_{\rm g}^{\rm opt}$, and the transport gap, $E_{\rm g}^{\rm tr}$, of ferroelectrics, which can differ significantly. The situation is comparable to those in organic semiconductors and emerges from the presence of localized charges. The fundamental gap is a ground state property, i.e.\ the energy difference between the maximum of the fully occupied valence band and the minimum of the completely empty conduction band. In contrast, the optical and transport gaps are excited state properties involving localized (polaronic) electrons and/or holes at energies considerably different from the band edges. This work illustrates how the different energy gaps of ferroelectrics can be determined by combining optical measurements, X-ray photoelectron spectroscopy and temperature and oxygen partial pressure dependent electrical conductivity measurements. We determine fundamental gaps of $\approx 4.5\,$eV for both materials, optical gaps of $3.25-3.45\,$eV/$3.5\,$eV and electrical gaps of $\approx 1.4\,$eV/$3.3\,$eV for Na$_{0.5}$Bi$_{0.5}$TiO$_3$-BaTiO$_3$/NaNbO$_{3}$, respectively.
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All authors Pengcheng Hu, Nicole Bein, Chinmay Chandan Parhi, Tadej Rojac, Barbara Malič, Mohammad Amirabbasi, Anton Volodin, Karsten Albe, Jurij Koruza, Andreas Klein

Materials Science · Cross-listed from cond-mat.supr-con

Condensation mechanism of high-$T_c$ cuprates: the key role of pairon excitations

Yves Noat, Alain Mauger and William Sacks

In this article we show that the condensation mechanism in cuprates involves the strong coupling of the condensate to pairon excited states. We present an accessible formalism that significantly extends our previous work, providing a theoretical basis for the energy-dependent gap function $\Delta(E)$. The latter is proportional to the effective spin exchange energy, $J_{eff}$, with no retardation effects, such as the case of spin-fluctuation or phonon mediated couplings. The fundamental parameters of the superconducting (SC) state are the condensation energy per pair, $\beta_c$, and the antinodal energy gap, $\Delta_p$, which are quantitatively extracted by fitting the cuprate quasiparticle spectrum from tunneling experiments. An explicit formula for the critical temperature is also derived in the model. Valid for any doping, we find $T_c$ to be proportional to $\beta_c$, and not the gap $\Delta_p$, in sharp contrast to conventional SC. The numerical factor $\beta_c/k_BT_c\simeq 2.24$ originates from pair excitations of the condensate, following Bose statistics, with a mini-gap $\delta_M \simeq 1\,$meV in the excitation spectrum. These results strongly suggest that the same `all-electron' mechanism is at work all along the $T_c$-dome.
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Materials Science

High mobility holes at germanane/Ge(111) allotropic cross-dimensional heterointerface

Yumiko Katayama, Daiki Kobayashi, Hikaru Okuma et al. (+3 more)

Germanane (GeH) is essentially a hydrogen-terminated Ge analog of graphene with a direct gap (~1.6 eV). Record hole mobility mu_h~67,000 cm2/Vs is found at 15 K for a single allotropic cross-dimensional(D) heterointerface. This is enabled by making topotactically-transformed 2D GeH layers meet the 3D bulk Ge(111). Temperature dependence of mu_h implies metallic conduction without ionized impurity scattering between 20 K and 250 K. Sheet hole density for a Fermi sphere n_S=2.8x10^11 /cm2 agrees well with 3.0x10^11 /cm2 of Hall measurements. A 6,500% magnetoresistance at 7 T accompanies Shubnikov-de Haas oscillations visible even at 15 K. These imply single-band conduction of holes with small effective mass in the in-plane directions, invoking a 2D hole gas (2DHG) picture that allotropic cross-D heterointerface between 2D GeH and 3D Ge harbors 2D-confined high-mobility holes. Even without elaborate heteroepitaxy and modulation doping, allotropic cross-D heterostructures pave the way toward facile 2DHG creation.
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All authors Yumiko Katayama, Daiki Kobayashi, Hikaru Okuma, Yuhsuke Yasutake, Susumu Fukatsu, Kazunori Ueno

Materials Science

Crystal Generation using the Fully Differentiable Pipeline and Latent Space Optimization

Osman Goni Ridwan, Gilles Frapper, Hongfei Xue et al. (+1 more)

We present a materials generation framework that couples a symmetry-conditioned variational autoencoder (CVAE) with a differentiable SO(3) power spectrum objective to steer candidates toward a specified local environment under the crystallographic constraints. In particular, we implement a fully differentiable pipeline to enable batch-wise optimization on both direct and latent crystallographic representations. Using the GPU acceleration, this implementation achieves about fivefold speed compared to our previous CPU workflow, while yielding comparable outcomes. In addition, we introduce the optimization strategy that alternatively performs optimization on the direct and latent crystal representations. This dual-level relaxation approach can effectively escape local minima defined by different objective gradients, thus increasing the success rate of generating complex structures satisfying the target local environments. This framework can be extended to systems consisting of multi-components and multi-environments, providing a scalable route to generate material structures with the target local environment.
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All authors Osman Goni Ridwan, Gilles Frapper, Hongfei Xue, Qiang Zhu

Materials Science

Spatial resolution(s) in atom probe tomography

Baptiste Gault, Frédéric De Geuser, Christoph Freysoldt et al. (+2 more)

Atom probe tomography (APT) is often quoted to provide "atomic-scale" analysis of materials in three dimensions. Despite efforts to quantify APT's spatial resolution, misunderstanding remain regarding its true spatial performance. If the depth resolution was once reported to be 20 pm, quoting this value outside of its specific context is misleading and should be avoided. The resolution achievable in pure metals, at one specific location within one reconstructed dataset, does not generally apply across materials or analysis conditions, or even throughout a single tomographic reconstruction. Here, we review various efforts at defining and measuring the spatial resolution in the study of single phase and single element materials - i.e. pure metals - in field-ion microscopy (FIM) and APT. We also report on the degradation of the resolution arising from ion optical devices used to improve the mass-resolution. We aim to offer some perspective as to how reported resolutions may be or may not be of any relevance to most of the materials characterisation efforts by APT, including cases of precipitates in a matrix that emphasise the need to consider an effective resolution. Finally, we discuss concepts to improve the spatial accuracy of the technique in a relatively distant future.
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All authors Baptiste Gault, Frédéric De Geuser, Christoph Freysoldt, Benjamin Klaes, François Vurpillot

Materials Science

Breaking Four-Point and Three-Point Bending Tests

Subhrangsu Saha, Jeffery R. Roesler and Oscar Lopez-Pamies

Since their initial standardizations in the 1930s and 1950s, the so-called four-point and three-point bending tests on unnotched beams have been embraced by practitioners as two popular methods to indirectly measure the tensile strength of concrete, ceramics, and other materials with a large compressive strength relative to their tensile strength. This is because of the ease that the tests afford in both the preparation of the specimen (a beam of rectangular cross section) and the application of the loads (simple supports pressing on the specimen). Yet, this practical advantage has to be tempered by the fact that the observations from both of these tests – being indirect experiments in the sense that they involve not uniform uniaxial tension but non-uniform triaxial stress states throughout the specimen – have to be appropriately interpreted to be useful. By making use of the phase-field fracture theory initiated by Kumar, Francfort, and Lopez-Pamies (2018), which has been recently established as a complete theory of fracture capable of accurately describing the nucleation and propagation of cracks in elastic brittle materials under arbitrary quasistatic loading conditions, the main objective of this paper is to carry out a thorough 3D quantitative analysis of when and where fracture nucleates and propagates in four-point and three-point bending tests and thereby establish how to appropriately interpret their results. As a corollary, the analysis provides an explanation for why four-point bending tests typically yield smaller flexural strengths than three-point bending tests, a source of constant headaches for practitioners who have been left to wonder which test – if any – would be more appropriate for their purposes.
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