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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Tuesday 30 June

Materials Science · Cross-listed from physics.optics

Plasmonic-cavity Modulator for the Mid-IR with a Semi-transparent and Nonlinear Heavily-doped Semiconductor Mirror

Tommaso Venanzi, Raffaella Polito, Andrea Rossetti et al. (+15 more)

We present a free-space plasmonic modulator based on a single heavily-doped semiconductor layer. We investigate its ability to modulate both the linear and nonlinear response at mid-infrared frequencies slightly below the plasma frequency of the semiconductor. We demonstrate electric control of the linear transmittance and reflectance, and of the efficiency of third-harmonic generation with a field-effect gate structure. We discuss further performance optimization of the device in terms of modulation speed and depth towards a fast modulator with very simple active material requirements. Our results establish a viable route toward practical plasmonic modulators and mixers operating in the mid-infrared atmospheric window available for free-space communications at wavelengths between 8 and 12 um.
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All authors Tommaso Venanzi, Raffaella Polito, Andrea Rossetti, Markus Ludwig, Daniele Brida, Adel Bousseksou, Isabelle Sagnes, Gregoire Beaudoin, Raffaele Colombelli, Antonio Valletta, Andrea Notargiacomo, Francesco Mattioli, Gonzalo Alvarez-Pérez, Cristian Ciracì, Valeria Giliberti, Marialilia Pea, Michele Ortolani, Huatian Hu

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

Fully compensated ferrimagnetic triferroics and multistate transport in hidden-phase wurtzite MnSe monolayer

Zhuang Ma, Hongfei Liang, Po Ma et al. (+5 more)

Fully compensated ferrimagnets (fFIMs) have attracted interest due to their compensated moments and nonrelativistic spin splitting across the Brillouin zone. Known fFIMs, however, are mostly restricted to complex three-dimensional (3D) systems or require external fields in two-dimensional (2D) heterostructures, leaving intrinsic fFIM monolayers unexplored. We identify a hidden-phase MnSe monolayer, derived from the (001) planes of wurtzite, as an intrinsic fFIM featuring inequivalent sublattices not linked by any symmetry. It is a unipolar magnetic semiconductor (UMS) with perpendicular magnetic anisotropy (528.60 * 10^-3 eV per unit cell) and simultaneously exhibits ferroelectricity (polarization 4.63 * 10^-10 C/m) and ferroelasticity (signal 61%), with barriers of 7.6 * 10^-3 and 0.10 eV/f.u., respectively, establishing a single-phase triferroic system. The ground fFIM UMS characteristics are robust against strain up to 3%. The In2Se3/MnSe heterostructure enables nonvolatile electrical control between semiconducting and metallic states. Constructed tunnel junctions exhibit giant tunneling magnetoresistance (2.98 * 10^5%), electroresistance (6.97 * 10^14%), elastoresistance (7.95 * 10^4%), and near-perfect spin filtering (~100%). Collectively, this spontaneous 2D fFIM with coexisting triferroic orders provides a promising platform for ultrahigh-density, low-power, and miniaturized memory devices.
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All authors Zhuang Ma, Hongfei Liang, Po Ma, Guangqian Ding, Xuehao Wu, Sikander Azam, Guoying Gao, Long Zhang

Materials Science

Side-Chain Tuning of Thermal-Expansion Crossover in Metal-Organic Frameworks

Wei Qiu and Penghua Ying

Achieving continuous control over macroscopic thermal expansion remains a fundamental challenge in solid-state physics. Using classical and path-integral molecular dynamics alongside lattice dynamics at near-ab initio accuracy, we report an entropy-driven thermal-expansion crossover from positive (PTE) to negative thermal expansion (NTE) in alkoxy-functionalized MOF-5, an archetypal metal-organic framework (MOF). We demonstrate that this non-linear response is continuously tunable via the alkoxy side-chain length, quantified by the number of carbon atoms $n$ grafted onto the archetypal cubic MOF-5 framework: systems with short chains ($n \le 2$) exhibit monotonic NTE, whereas longer chains ($n \ge 3$) trigger a pronounced PTE-to-NTE crossover. At low temperatures, thermal activation of longer side chains opens additional conformational states and generates steric pressure inside the pore, driving positive expansion through a gain in side-chain conformational entropy. Conversely, at elevated temperatures, the side chains enhance transverse linker fluctuations and strengthen the string-tension mechanism associated with low-frequency framework modes, causing structural contraction favored by framework vibrational entropy. Finally, by varying the concentration of side-chain-functionalized linkers, the thermal expansion coefficient can be continuously regulated to realize negative, near-zero, and positive thermal expansion within selected temperature windows. These results establish side-chain engineering as a practical route for programming macroscopic thermodynamic responses in MOFs.
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Materials Science · Cross-listed from cond-mat.mes-hall

Hodge Topology of Semiclassical Transport: A Coordinate-Free Geometric Framework for the Anomalous Hall Effect and Non-Linear Berry Dipole

Zhi-Wei Wang and Samuel L. Braunstein

We establish a coordinate-free differential geometric framework for anomalous transport in topological bands using the Hodge-de Rham decomposition of the Brillouin zone. Standard formulations face mathematical singularities (Dirac strings) when using the quantum Berry connection in bands with non-zero Chern numbers. Applying this decomposition to the Berry curvature 2-form isolates the quantized topological monopole flux from a globally smooth geometric 1-form proxy potential, $\mathcal{A}$. Substituting this regularized potential into semiclassical transport integrals yields distinct analytical advantages. For linear transverse transport, our cohomological decomposition enables an exact geometric derivation of Haldane's insight via the co-area formula, partitioning the response into a continuous Fermi sea topological background and a localized Fermi surface geometric line integral. For non-linear transport, this globally smooth proxy unifies the geometric description, reproducing the high numerical stability of scalar integration-by-parts techniques directly from its exact sector, accommodating arbitrary Chern numbers. By enforcing the continuous Coulomb-Hodge gauge ($\delta \mathcal{A} = 0$) alongside vanishing harmonic holonomies over fundamental 1-cycles ($\oint_{\gamma_i} \mathcal{A} = 0$), we map the Hodge potential $\mathcal{A}$ to the Maximally Localized Wannier Function (MLWF) gauge in trivial bands, providing a non-singular computational proxy for topologically obstructed bands. Finally, we analytically demonstrate that solving the Hodge Laplacian for $\mathcal{A}$ zeroes the macroscopic Brillouin zone average (uniform $\mathbf{R}=0$ zero-mode) topological divergence, yielding a mathematically consistent covariant formulation that matches the algorithmic robustness of standard methods against discrete $\mathbf{k}$-grid noise.
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Materials Science

From Materials Database to Materials Bank: Assetizing Data for AI Driven Materials Innovation

Chenyao Ma, Di Zhang, Weibo Gong et al. (+9 more)

Driven by high-throughput experimentation, computational modeling, and artificial intelligence (AI), materials data has expanded at an unprecedented rate. Conventional materials databases function only as passive repositories, archiving raw experimental records indiscriminately including both successful and failed data, without systematic value filtering or asset management. This creates a critical gap between massive data accumulation and actionable innovation, hindering the identification of high-potential materials and industrial translation. To address this bottleneck, we propose an industrialization-oriented Materials Bank, a dedicated valuefiltering and assetization layer that operates beyond traditional databases. It does not merely curate high-quality data but systematically elevates qualified candidates into standardized, upgradable materials assets via a multi-dimensional BankCard framework covering scientific validity, synthesis feasibility, application readiness, and industrial value. By unifying databases, AI models, automated experimentation, and multi-criteria assessment into a cohesive closed-loop ecosystem, the Materials Bank establishes a clear trajectory from data to knowledge, candidate, asset, and product. It serves not as an enhanced database or screening tool, but as a decision infrastructure bridging academic discovery and industrial demand, offering a scalable paradigm to accelerate AI-driven materials innovation and deliver tangible real-world impact.
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All authors Chenyao Ma, Di Zhang, Weibo Gong, Wei Du, Rui Su, Yuhang Chen, Kan Xu, Huan Gu, Limin Li, Piao Ma, Zhenghao Li, Hao Li

Materials Science

Photon Statistics from Yb3+-Doped CsPbCl3 are Inconsistent with Quantum Cutting

Vincent R.M. Benning, Faris Horani, Daniel R. Gamelin et al. (+1 more)

CsPb(Cl1-xBrx)3:Yb3+ has been widely reported as a broadband quantum-cutting material with a photoluminescence quantum yield exceeding 100%, making it a promising candidate for enhancing the blue-green spectral response of silicon photovoltaics. Many groups have reproduced absolute photoluminescence quantum yields over 100%, but others have struggled to obtain such high values. Here, we test the quantum-cutting capabilities of CsPbCl3:Yb3+ nanocrystals and bulk material using photon-correlation analysis. A quantum-cutting material is expected to exhibit photon bunching, but our experiments on CsPbCl3:Yb3+ show no such behavior. In fact, we observe the opposite – anti-bunching – under focused-excitation conditions. This observation can be explained with the previously established Auger-quenching pathway in CsPbCl3:Yb3+. Our results thus confirm high-power Auger quenching but question earlier descriptions of quantum cutting in CsPb(Cl1-xBrx)3:Yb3+.
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All authors Vincent R.M. Benning, Faris Horani, Daniel R. Gamelin, Freddy T. Rabouw

Materials Science

Ultrafast magnetization induced by linearly polarized pulses is widespread in nonmagnetic semiconductors

Xiangzhou Zhu, Junfeng Qiao, Nicola Marzari et al. (+1 more)

Ultrafast optical on-off switching of magnetic order promises near-petahertz information processing. Recently, it has been proposed that non-magnetic semiconductors with narrow band edges or strong exchange interactions could display ultrafast magnetization when photoexcited with linearly polarized femtoseconds pulses, but the experimental detection of this effect remains a challenge, mostly for the lack of suitable candidate compounds. Here, we present a high-throughput first-principles screening of the MC3D database of experimentally known inorganic crystals, identifying nearly 440 non-magnetic semiconductors that develop spin polarization under photoexcitation with linearly polarized pulses via a light-induced exchange-driven instability. We determine how the crystal field environment and band-edge orbital character govern the magnitude and the type of magnetic order of the photoinduced state and we unveil systematic chemical and periodic trends that provide intuitive guidance for materials selection. Our results argue that on-off switching of magnetization with linearly polarized femtosecond pulses is a widespread occurrence in non-magnetic semiconductors, opening novel avenues for experimental verification and application.
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All authors Xiangzhou Zhu, Junfeng Qiao, Nicola Marzari, Matteo Calandra

Materials Science

Three-phonon mixing as a source of light-induced chirality

Y . Zhu, A. Vanderhaegen, Z. Zeng et al. (+7 more)

Mid- and far-infrared optical pulses have found wide applicability in experiments in which collective modes of solids are driven nonlinearly, as a means to manipulate functional properties of materials on ultrafast time scales. In the illustrative case of boron phosphate (BPO$_4$), mid-infrared excitation has been used to induce chirality in an otherwise achiral crystal. The pump frequency dependence of photo-induced chirality reveals that, while on-resonance excitation is understood in terms of the well-documented phonon rectification from two-phonon mixing, additional pathways become relevant when the pump pulse is detuned from resonance. We find that a three-mode mixing mechanism becomes important in this case, whereas the contributions from other impulsive Raman terms are negligible. The results reported here provide a quantitative foundation for nonlinear phononic lineshapes in transparent materials, and open up new opportunities for lattice control.
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All authors Y . Zhu, A. Vanderhaegen, Z. Zeng, M. Först, M. Fechner, C. Putzke, P. J. W. Moll, D. Prabhakaran, P. Radaelli, A. Cavalleri

Materials Science · Cross-listed from cond-mat.str-el

Phonon-induced pseudogap phase in TiSe$_2$

Sotirios Fragkos, Nina Girotto Erhardt, Evgenia Symeonidou et al. (+9 more)

To comprehend quantum ordered states, such as charge density waves (CDW), in layered transition metal dichalcogenides (TMDCs), it is essential to uncover their underlying normal states. Here, we use time- and angle-resolved extreme ultraviolet photoemission spectroscopy and ab initio electron-phonon calculations to perform excited state band mapping of three prototypical 1T TMDCs, i.e., TiSe$_2$, HfTe$_2$, and ZrTe$_2$, at room temperature. The results reveal the profound impact of strong electron-phonon-induced thermal fluctuations on the normal-phase electronic structure. Specifically, in the moderate electron-phonon coupling regime, as in HfTe$_2$ and ZrTe$_2$, thermal fluctuations only lead to small spectral broadening and band renormalization. In the strongly coupled case, exemplified by TiSe$_2$, we observe soft-phonon-induced, momentum-dependent suppression of spectral weight, i.e., pseudogaps - extending up to 1 eV above the Fermi level. Our work establishes the normal phase of TiSe$_2$ as a phonon-induced pseudogap phase governed by strong CDW fluctuations, thereby uncovering previously missing aspects of the TiSe$_2$ phase diagram, with broader implications for other TMDCs in the strong electron-phonon coupling regime.
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All authors Sotirios Fragkos, Nina Girotto Erhardt, Evgenia Symeonidou, Hibiki Orio, Dominique Descamps, Stéphane Petit, Polychronis Tsipas, Kai Rossnagel, Jakub Schusser, Athanasios Dimoulas, Samuel Beaulieu, Dino Novko

Materials Science

Kinetic Monte Carlo-Ising Machine Optimization for Atomistic Inverse Design of Solid Electrolytes

Ai Koizumi, Tomofumi Tada and Ryo Tamura

Maximizing ionic conductivity remains a fundamental challenge in the atomistic design of solid electrolytes. To this end, we present a framework that combines kinetic Monte Carlo (KMC) and factorization machine with quadratic-optimization annealing (FMQA), an Ising-machine-based black-box optimization algorithm for large-scale combinatorial optimization. KMC evaluates the ionic conductivity for a given dopant configuration, whereas FMQA iteratively learns a surrogate model from a small configuration-conductivity dataset and proposes configurations expected to maximize conductivity. To address the severe combinatorial explosion in large KMC simulation cells, we partition the configuration space for parallel optimization. As a proof of concept, we apply this KMC-FMQA framework to bulk 8 mol % yttria-stabilized zirconia, identifying a dopant configuration with an order-of-magnitude higher conductivity than that of random configurations and the experimentally reported conductivity. Combined with experiments, this framework will enable the determination of microscopic structures from measured conductivity, providing insight into the underlying transport mechanisms.
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Materials Science

Symmetry-Enforced Ferroelectric Switching of Two-Dimensional Altermagnetism

Jiangyu Zhao, Yibo Liu, Guoli Wu et al. (+4 more)

Altermagnetism features strong momentum-dependent spin splitting despite zero net magnetization, offering a transformative platform for next-generation spintronics. However, the nonvolatile and deterministic switching between its two equivalent spin-splitting states remains a fundamental bottleneck. Here, we propose a universal layer-engineering paradigm to achieve symmetry-enforced ferroelectric switching of two-dimensional altermagnetism. By sandwiching a conventional antiferromagnetic monolayer between two identical ferroelectric layers, the out-of-plane polarization cleanly breaks the spatial symmetry to induce robust altermagnetic splitting. Crucially, the global combined parity-time symmetry dictates that reversing the ferroelectric polarization exactly inverts the altermagnetic spin-splitting pattern. We rigorously validate this mechanism in the In2Se3/MnPTe3/In2Se3 trilayer using first-principles calculations. As a direct consequence, the ferroelectrically driven spin-splitting reversal deterministically flips the anomalous Hall effect signal, providing an unambiguous transport fingerprint to electrically distinguish the two altermagnetic states. Unconstrained by the stringent symmetry requirements of intrinsic single-phase materials, our findings establish a versatile physical framework for electrically addressable altermagnetic spintronics.
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All authors Jiangyu Zhao, Yibo Liu, Guoli Wu, Xinru Li, Ying Dai, Baibiao Huang, Yandong Ma

Materials Science · Cross-listed from cond-mat.mes-hall

Observation of Intrinsic Anderson Localization in Few-Layer ReS$_2$

Shreya Paul, Pritam Das, Devarshi Chakrabarty et al. (+2 more)

Electron localization phenomena are expected to play an important role in the transport properties of two-dimensional materials. Rhenium disulfide (ReS$_2$), with its narrow conduction bandwidth, is uniquely susceptible to this effect. However, extrinsic disorder caused by fabrication methods obscures inherent localization behavior arising from reduced dimensionality and degrades transport properties. We report intrinsic Anderson localization in few-layer ReS$_2$ by eliminating extrinsic fabrication-induced disorder through all-dry van der Waals assembly and suppressing interface charge trapping through a hexagonal boron nitride (hBN) gate dielectric. Temperature-dependent transport reveals a crossover from nearest-neighbor hopping to two-dimensional (2D) Mott variable-range hopping (VRH). The non-monotonic gate-voltage dependence of activation energy provides direct access to the energy-resolved band-tail density of states of the ReS$_2$ conduction band. 2D Mott VRH yields a localization length of (3.5 $\pm$ 0.1) nm, an order of magnitude larger than disorder-dominated devices, providing a quantitative characterization of intrinsic Anderson localization in ReS$_2$.
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All authors Shreya Paul, Pritam Das, Devarshi Chakrabarty, Shamashis Sengupta, Sajal Dhara

Materials Science

High-Mobility and High-Reliability Top-Gate Oxide Semiconductor Transistors by Oxygen Engineering

Kai Jiang, Zhiyu Lin, Ziheng Wang et al. (+2 more)

In this work, we investigate the role of oxygen (O) on the performance of top-gate (TG) atomic-layer-deposited (ALD) oxide semiconductor transistors. The results reveal distinct defect characteristics and positive bias temperature instability (PBTI) degradation mechanisms between oxygen-rich (O-rich) and oxygen-deficient (O-poor) devices. It is found that an O-rich device fabrication process followed by O-free annealing can effectively achieve TG indium-rich (In-rich) oxide semiconductor transistors with high mobility, high reliability and high stability in hydrogen environment because O-rich process can suppress oxygen vacancies and their interaction with hydrogen, while O-free annealing plays a critical role in minimizing the formation of O-rich defects such as oxygen dimers (O-O bonds). Consequently, TG In-rich transistors with high mobility, steep subthreshold slope, and high PBTI reliability at high temperature are demonstrated. The understanding of O-rich defects provides a new insight to overcome the mobility-stability trade-off.
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All authors Kai Jiang, Zhiyu Lin, Ziheng Wang, Chen Wang, Mengwei Si

Materials Science · Cross-listed from quant-ph

Atom diffraction in the strong-coupling regime

Carina Kanitz, Jakob Bühler, François Aguillon et al. (+6 more)

Analytic methods based on matter-wave diffraction are a cornerstone in condensed-matter research, providing access to static and dynamic materials properties down to the atomic level. In these experiments, the shape of the diffraction pattern is largely determined by the lattice at equilibrium whereas vibrationally-induced distortions are treated perturbatively. Here, we show that the perturbative approach does not hold for helium diffracted at kiloelectronvolt energy through freestanding single-layer graphene. In this case, we enter a new regime of strong coupling where the projectile strongly interacts with the electron density of several lattice atoms simultaneously, leading to phase shifts of several radians. In consequence, lattice distortions introduce a significant phase spread that cannot be described by the typically employed Debye-Waller factor. We show that the weak-coupling regime is retained for atomic hydrogen diffraction. The experimental results are supported by simulations, providing a regime-independent approach to describe the influence of phonons on atom diffraction phenomena.
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All authors Carina Kanitz, Jakob Bühler, François Aguillon, Vladimír Zobač, Jaime Glerum, Toma Susi, Maxime Debiossac, Philippe Roncin, Christian Brand

Materials Science

Hidden ordered compound-layer and its tailoring of the electronic/optical property in Ge2Sb2SexTe5-x alloys

Chenxu Yu, Linggang Zhu, Hanyu Liu et al. (+4 more)

Ge2Sb2SexTe5-x (GSST) alloys represent an emerging class of phase-change materials for integrated photonics. However, the microscopic origins underlying their superior performance compared to the parent compound Ge2Sb2Te5 remain elusive. By using atomic simulations, this work elucidates that the thermal stability and low optical loss of GSST are fundamentally governed by the formation of an in-layer compound-like structure with SeTe2 or Se2Te stoichiometry depending on the Se content, contrasting to the previously believed pure-element-layered model where Se and Te atoms occupy separate layers inside GSST. The newly identified compound-layered structures maintaining stability at temperature above 370 K, yield an enlarged bandgap, weakened antibonding character, and more importantly, a moderate refractive index as well as decreased extinction coefficient which align better with the experiment compared to the previously believed model. The present findings not only help bridge the long-standing theory-experiment gap regarding the optical properties of GSST by redefining its atomic structure, but also establish local chemical ordering as a critical materials design principle for high-performance photonics.
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All authors Chenxu Yu, Linggang Zhu, Hanyu Liu, Xianyao Huan, Naihua Miao, Jian Zhou, Zhimei Sun

Monday 29 June

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

An Enhanced RPA-LDA Model for Ion Stopping Power from Cold Matter to High-Energy Density Plasmas: A Unified, Open-Source Framework

Thomas A. Mehlhorn, Ming Feng Gu and Igor Golovkin

We present an enhanced random-phase-approximation–local-density-approximation (e-RPA-LDA) model for the stopping power of ions that is valid over a wide range of conditions, from cold solids through warm dense matter to high-energy-density plasmas. The electronic stopping is computed from the RPA dielectric response in the local-density approximation over an average-atom electron density obtained in a muffin-tin potential with the Flexible Atomic Code, augmented by four corrections to the earlier RPA-LDA model of Wang et al.: a strong-collision correction for large-momentum-transfer events, a static local-field correction for electron correlations, an electron-binding correction, and the higher-order Barkas and Bloch terms. The resulting proton stopping powers agree with the NIST PSTAR and IAEA databases across the periodic table and for compounds – providing a physics-based alternative to semi-empirical codes such as SRIM – and reproduce the limited published plasma data, including charged-particle transport-workshop benchmarks, time-dependent DFT calculations, and the first measurements of enhanced light-ion stopping in plasmas. We further extend the model to a complete total stopping power for protons and alpha particles by adding nuclear and ionic (elastic ion-ion) stopping to the electronic term, yielding a continuous, self-consistent description of energy deposition from cold matter to hot dense plasmas. Because the average-atom treatment includes contributions from all electrons – unlike Kohn-Sham DFT – while remaining computationally efficient and applicable to low- and high-Z targets at arbitrary temperature and degeneracy, the model is well suited to inertial fusion and high-energy-density science. The computational framework is available on GitHub (https://github.com/dedx-erpa/dedx), with tabulated stopping powers and ranges in the data/ subdirectory.
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Materials Science

Computed materials proposals depart from the structural memory of experimental discovery

Dan Nguyen, Karen Cao, Brian Chu et al. (+3 more)

Generative AI and high-throughput DFT pipelines propose millions of inorganic crystal structures, but lack a calibrated reference frame against experimentally realized chemistry. Here we embed 167,500 Inorganic Crystal Structure Database entries in a continuous structural-similarity space, partition it into graph communities, and replay them in time. Experimental discovery shows strong structural memory: 82.9% of new formulas enter pre-existing communities; new-community formation falls from 40.2% (1930s) to 2.6% (2010s). The communities are chemically meaningful, positively identifying nine textbook field-defining renaissances, including cuprates, colossal-magnetoresistance manganites, MAX phases, and Li-ion battery cathodes. Projecting GNoME, MatterGen-public, Materials Project, JARVIS-DFT, and Alexandria-PBE into frozen historical maps yields a cutoff-robust ordering: held-out ICSD > MatterGen > {GNoME ~ MP-theoretical} > JARVIS > Alexandria. Structural departure from experimental basins is not specific to generative AI but general across the tested computed sets. Combining structural proximity with reduced-formula precedent defines a historical synthesizability prior for triaging computed materials.
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All authors Dan Nguyen, Karen Cao, Brian Chu, Nick Lemoff, Paul Kienzle, William Ratcliff II

2606.30967 · 29 Jun · 20 pp main text, 10 pp Extended Data, 51 pp Supporting Information; 4 main + 5 ED figures, 3 ED tables. Joint first authors: D. Nguyen and K. Cao. Submitted to npj Comput. Mater. Derived artifacts: Zenodo doi:10.5281/zenodo.20046302. Code: github.com/scattering/crystal-communities-paper. Dashboard: crystalcommunities.org

Abstract PDF $MEM ×2$XTAL ×2

Materials Science

Prebiotic Chemistry Assemblies of L-Cysteine on Defect-Free Pyrite Terraces

Adriana E. Candia, Sindy J. Rodríguez, Vanina G. Franco et al. (+3 more)

Wächtershäuser's theory proposes iron-sulfur minerals as key platforms for molecular synthesis and supramolecular organization in prebiotic environments. However, defects have been traditionally considered at the center of such assemblies, thereby underestimating the contributions of regular and pristine interfaces. Here, we combine scanning tunneling microscopy and spectroscopy (STM/STS) with density functional theory (DFT) to investigate the fundamental prebiotic chemistry system of L-Cysteine (L-Cys) on defectless FeS$_2$(100) terraces. To do so, we first achieved atomically ordered, defect-free terraces that act as support of two distinct supramolecular phases of L-Cys: one compact, highly ordered supramolecular network and another less packed, labile supramolecular network. We unveil trimer-based intermolecular interactions to be at the origin of these pattern formations. These results demonstrate that L-Cys self-assemblies can be hosted on flawless FeS$_2$ terraces due to the cooperative interplay between substrate electronic structure and intermolecular interactions, without the participation of dominant defects. Therefore, the autocatalytic activity of pyrite could have triggered the on-surface polymerization process of these non-static self-assembled structures under primordial conditions, thereby endorsing Wächtershäuser's postulates on the origin of life.
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All authors Adriana E. Candia, Sindy J. Rodríguez, Vanina G. Franco, Mario C. G. Passeggi, Jorge Lobo-Checa, Myriam H. Aguirre

Materials Science

Role of polarity in the growth of cubic GaN within silicon inverted pyramids

David Lister, Melissa Radford, Sara Fortin et al. (+4 more)

A lack of spontaneous internal polarization makes cubic GaN (c-GaN) a well-suited material for emerging micro-LED-based short-range communication, where c-GaN promises increased speed over conventional hexagonal GaN (h-GaN). Although c-GaN is metastable, there are well-established methods for growing it in Si V- or U-grooves; the logical step is to truncate these grooves to wedges or inverted pyramids for small devices. There are limited reports of GaN grown in inverted pyramid templates, and the results are contradictory. To study this process, we perform selective area growth of GaN using organometallic vapor phase epitaxy (OMVPE) on Si inverted pyramidal templates and analyze our samples by cross-sectional TEM. We find that polarity is critical to understanding the growth of c-GaN in this four-fold geometry, in contrast to the growth in long grooves. This effect fits within the broader set of challenges of polar-on-nonpolar heteroepitaxy; the c-GaN inside the four-fold symmetric template has its symmetry reduced by polarity to be two-fold. In typical growth conditions – where the underlying h-GaN polarity is uniform – we find this implies that two h-GaN to c-GaN grain boundaries will have a polarity inversion. We observe two different structures at these inverting boundaries, including a previously unreported inversion domain boundary along the basal plane of the undoped h-GaN. These findings show that for small devices – such as micro-LEDs – the polarity-inverting interfaces must be prevented, for example by suppressing the growth of h-GaN on two facets of the template or by locally controlling the h-GaN polarity.
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All authors David Lister, Melissa Radford, Sara Fortin, Bilal Janjua, Mohsen Asad, Karen Kavanagh, Simon Watkins

Materials Science · Cross-listed from cond-mat.mes-hall

Topological random alloy

Subrata Pachhal, Aziz Hasan and Adhip Agarwala

Topological phases of matter are often realized in crystalline materials. To extend their understanding beyond perfect stoichiometry, we introduce a minimal model of a topological random binary alloy and show that the system realizes an exotic form of impurity-band engineering. We reveal that, in contrast to Wannier charge centers pinned by impurities in conventional semiconductors, doping a proximate quantum anomalous Hall insulator results in dopant-centric chiral current loops. The nature of such current loops is intrinsically tied to the properties of both the host and the dopant. We demonstrate that, even at dilute dopant density, these current loops can form topological domains in an otherwise trivial host and trigger a topological phase transition. On the other hand, doping a topological host having chirality opposite to that of the dopants can unexpectedly stabilize a metallic phase in which bulk transport is mediated by inter-domain edge modes.
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Materials Science

Family of (NxH)-polytypes with La2WO6-related stoichiometry

E. Pospíšilová, M. Mihalkovič, N. Beronská et al. (+1 more)

Structure and chemical composition of non-stoichiometric $\mathrm{(N \times H)}$-polytypes, $\mathrm{N} \in \{3,\,4,\,5,\,6,\,7\}$, belonging to the family of La2WO6-related tungstates, are presented and the basic rules behind their construction are formulated. The polytypes are validated from the point of view of the internal energy per atom against all the competing La-O-W compounds by means of the ternary convex hull computed by DFT. According to DFT, the ground state of the La2WO6 family surprisingly turned out to be the as-yet hypothetical tungstate La2WO6.oP36, isostructural with the known compound Gd2WO6, closely related to the basic building H-block of the polytypes. One more candidate for an experimentally accessible low-energy structure, La2WO6.mC72, derived from the already observed Sm2MoO6, has been identified to lie only $\Delta E \approx 5\:\mathrm{meV/at.} \cong 60\:\mathrm{K}$ above the convex envelope.
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All authors E. Pospíšilová, M. Mihalkovič, N. Beronská, M. Gebura

Materials Science · Cross-listed from cond-mat.mes-hall

Quantum sensing of nanoscale electronic phase segregation

Izidor Benedičič, J. Paul Attfield and Denis Arčon

Doping of transition metal oxides such as CaFe$_3$O$_5$ offers a controlled way to tune the interplay of charge, spin, and lattice degrees of freedom, yet local-probe studies remain difficult because strong correlations and dynamic charge-spin fluctuations obscure fine spectroscopic features in powder samples. Here, we employ quantum magnetometry based on nitrogen-vacancy (NV) centers in nanodiamonds impressed into an Mn-doped CaFe$_3$O$_5$ powder pellet to probe static and dynamic magnetic fields at the nanoscale across the weak ferromagnetic transition. The splitting and broadening of the optically detected magnetic resonance (ODMR) spectra exhibit an order-parameter-like increase by ~ 15 MHz upon cooling below the critical temperature, T$_{\rm c}$. Concomitantly, the spin-lattice relaxation rate, 1/T$_1$, exhibits a pronounced, divergence-like enhancement at T$_{\rm c}$, increasing by about one order of magnitude from its high-temperature value. Moreover, detailed lineshape fits of ODMR spectra together with the stretched-exponential NV magnetization recovery curves corroborate the proposed electronic phase segregation in charge-ordered and charge-averaged phases at the nanometric scales. The presented study demonstrates the viability of using nanodiamonds as a platform for nanoscale magnetic probing of strongly correlated matter, including phenomena such as electronic phase separation.
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Materials Science

Bridging electrode preparation and electrocatalyst performance with physics-based causal AI

Evelyna Wang, Linda Hung, Sam Witty et al. (+2 more)

State-of-the-art artificial intelligence (AI) and Machine-Learning (ML) tools have not yet enabled rapid design of next-generation materials. Detailed physical understanding of how material properties affect device performance is required to advance materials development. For example, optimization of ink parameters for electrocatalysts has no known physical mathematical model and thus insights are difficult to translate from material studies to device studies. Herein, we demonstrate how to use the emerging AI tool, physics-based structural causal models (SCMs), to extract quantitative causative insights from complex heterogeneous electrochemical systems with small (n < 10), but multi-modal datasets (modes > 10). Our SCM quantitatively separates the role that varying the support-to-catalyst ratios and total material loadings plays on catalytic performance. The proof of concept model developed in this work enables root-cause-analysis on the cyclic voltammograms of manganese-antimony oxide oxygen reduction electrocatalysts on Vulcan carbon supports tested in alkaline media using a rotating disc electrode device configuration. Our preliminary causal analyses quantitatively disentangle how the catalyst performance is affected by the number of active sites versus the thickness of the electrode. To the best of our knowledge, this is the first demonstration of physics-based SCMs applied to electrochemical materials and their performance.
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All authors Evelyna Wang, Linda Hung, Sam Witty, Michaela Burke Stevens, Kevin Tran

Materials Science

Adaptive fine-tuning of foundation models for crystal structure prediction: Discovery of high-pressure phases in the CaFeNi system

N.M. Chtchelkatchev, M.V. Magnitskaya and R.E. Ryltsev

The prediction of crystal structures is a key challenge in chemistry and materials science, but evolutionary crystal structure prediction (CSP) remains computationally expensive because it relies on repeated ab initio relaxations and energy ranking. Machine learning interatomic potentials (MLIPs) can accelerate CSP, yet their use is limited by the need for large training sets and by the difficulty of choosing which candidate structures should be labeled by density functional theory (DFT). Here we introduce a self-consistent, foundation-model-assisted CSP workflow that combines evolutionary search with adaptive data selection and fine-tuning. Starting from a pretrained MLIP, the algorithm rapidly explores configuration space while iteratively selecting compact, representative, and physically relevant subsets of structures for DFT labeling, thereby reducing redundant calculations and improving a system-specific potential. We apply the method to the chemically complex Ca–Fe–Ni ternary system. The workflow reproduces the known low-pressure convex hull and enables efficient high-pressure exploration. It predicts a previously unreported compound, Ca$_6$FeNi, which becomes thermodynamically stable above 100~GPa. These results show that foundation-model-based, data-efficient CSP can greatly reduce computational cost while preserving accuracy and enabling the discovery of new materials in complex multicomponent systems.
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Materials Science

Atomic-Scale Characterization of Oxide Interfaces and Superlattices Using Scanning Transmission Electron Microscopy

Steven R. Spurgeon and Renae N. Gannon

Scanning transmission electron microscopy (STEM) is a cornerstone of our understanding of oxide interfaces and superlattices. No other technique provides the same level of insight into structure, chemistry, composition, and dynamics across as wide a variety of material systems. STEM imaging and diffraction, coupled with electron energy loss (EELS) and energy-dispersive X-ray (EDS) spectroscopies, offer unparalleled, high-resolution analysis of structure–property relationships. In this chapter we highlight investigations into key phenomena, including interfacial conductivity in oxide superlattices, charge screening effects in magnetoelectric heterostructures, interface engineering in iron oxides, and the complex physics governing atomic-scale chemical mapping. We also discuss emerging plasma preparation techniques and artificial intelligence-guided approaches to both ex situ and in situ microscopy. These studies illustrate how unique insights from STEM characterization can be integrated with other techniques and theory calculations to develop more predictive models for the behavior of functional oxides.
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Materials Science · Cross-listed from cond-mat.mes-hall

Experimental Realization of Synthetic Magnonic Lattice via Floquet Engineering

Amin Pishehvar, Jayakrishnan M. P. Nair, Zhaoyou Wang et al. (+5 more)

Magnonic systems, which exploit spin-wave excitations in magnetic materials, offer a promising platform for coherent information processing due to their low dissipation, strong nonlinearities, and intrinsic nonreciprocity. However, scaling magnonic circuits remains challenging, particularly with low-loss insulators such as yttrium iron garnet (YIG), which are difficult to pattern. Here, we experimentally realize a synthetic dimension in a magnonic system by coupling multimode magnon resonances in the frequency domain using time-periodic Floquet modulation. This approach enables electronically tunable interactions between discrete modes within a single YIG device, forming a reconfigurable mode-space lattice that supports functionalities such as Bloch oscillation. Our results demonstrate that high-dimensional magnonic dynamics can be achieved without increasing device footprint, establishing synthetic dimensions as a scalable and programmable route for integrated magnonic technologies. This advancement positions magnonic systems as promising platforms for engineering emergent phenomena that are inaccessible at equilibrium.
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All authors Amin Pishehvar, Jayakrishnan M. P. Nair, Zhaoyou Wang, Zixin Yan, Yu Jiang, Liang Jiang, Benedetta Flebus, Xufeng Zhang

Materials Science

Excitons in Large Disordered Boron-Nitride Layer using Linear-Scaling Bethe-Salpeter Simulations

Thomas Galvani, Lorenzo Sponza, Hakim Amara et al. (+2 more)

We introduce a real-space, linear-scaling Bethe-Salpeter framework that enables excitonic spectroscopy in large and possibly disordered boron-nitride-derived systems. Thanks to the use of a sublattice-resolved perturbative decoupling that maps localized electron-hole pairs onto a sparse tight-binding model, we implement the Kernel Polynomial Method to compute absorption spectra with O(N) cost. To illustrate the capabilities of our method, we apply it to Anderson-disordered monolayer hexagonal boron nitride with up to $10^{5}$ orbitals. The method reveals a disorder-induced asymmetric broadening of bright excitons, a crossover from quadratic to linear redshift of the main absorption peak, and Anderson localization of the exciton center of mass. This approach extends excitonic calculations beyond the reach of conventional ab initio Green's function methods (GW approximation and Bethe-Salpeter equation), opening optical spectroscopy to large-scale, disordered, moiré, quasicrystalline, and structurally complex quantum materials.
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All authors Thomas Galvani, Lorenzo Sponza, Hakim Amara, Sylvain Latil, Stephan Roche

Materials Science

Synthesizability and Mechanical Properties of High-Entropy Borides: First-Principles and Machine Learning Studies

Luke Moore, Ethan Fox, Bria Storr et al. (+4 more)

We perform density functional theory (DFT) calculations to investigate five-metal high-entropy borides (HEBs) in the hexagonal AlB$_2$ structure, considering all 126 possible elemental combinations among the nine group 4-6 transition metals (Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W). The entropy forming ability (EFA) descriptor is employed to evaluate their single-phase synthesizability, and the resulting EFA predictions show good agreement with the experimental data for selected HEBs. Mechanical properties are computed using special quasi-random structures. Several mechanically unstable compounds – primarily those containing Cr – are also predicted to be less synthesizable. Machine learning (ML) models are developed to analyze the results. This combined ab initio and ML study provides a systematic roadmap for identifying mechanically superior single-phase HEBs.
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All authors Luke Moore, Ethan Fox, Bria Storr, Jayden R. Palomino, Shane A. Catledge, Yogesh K. Vohra, Cheng-Chien Chen

Materials Science

Spontaneous Symmetry Breaking and Emergent Helicity in Achiral D4h-Symmetric Zinc Phthalocyanine Condensates

Bruno S. Zanatta, Giovani B. de Oliveira, Marcos E. G. Carmo et al. (+7 more)

Herein it is shown spontaneous symmetry breaking in supramolecular aggregates of D4h-symmetric zinc phthalocyanine (ZnPc). Ab initio density functional theory calculations at the M06/DGDZVP level reveal that intermolecular interactions induce a subtle relaxation of the macrocyclic framework, producing a characteristic red shift of the aza-bridge (C-N-C) stretching mode and symmetric stretching of the pyrrole ring. Confocal Raman Optical Activity measurements further reveal a negative Cotton effect at 1505 cm^-1 and 1338 cm^-1, providing evidence of emergent supramolecular chirality. Our findings identify pristine ZnPc as a model system for spontaneous self-assembled chiral symmetry breaking in molecular condensates and suggest new opportunities for chiroptical, spin-selective, and quantum functional materials.
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All authors Bruno S. Zanatta, Giovani B. de Oliveira, Marcos E. G. Carmo, Antonio Eduardo H. Machado, Thiago F. Silva, Guilherme F. S. Miguel, Antonio Otavio T. Patrocinio, Raigna A. da Silva, Erick Piovesan, Alexandre Marletta

Materials Science

Mechanical Manipulation of Graphene Auto-Kirigami with an AFM tip

Pierce C. Sinnott, Majid Fazeli Jadidi and Graham L. W. Cross

Graphene auto-kirigami describes the thermodynamically self-driven tearing, sliding and folding of graphene sheets to form micrometre-scale, folded ribbons. However, this process typically requires specialised multi-axial nanoindentation systems or highly laborious AFM-based scratching methods. We here introduce a novel, scalable, wholly AFM-based method to nucleate high yields of ribbons in comparable timeframes to previous multi-axial indentation methods, by AFM-based indentation and "hard tapping", whereby high setpoint AFM imaging can nucleate, manipulate and dynamically image the auto-kirigami ribbons. This can be performed with any conventional AFM, enabling extensional growth, rotation and reversal of ribbons towards potential applications as NEMS devices.
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