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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Thursday 11 June

Materials Science

Symmetry-electronic fingerprints reveal competing magnetic phases in two-dimensional materials

Addis Fuhr, Zachary R. Fox, David Parker et al. (+1 more)

Two-dimensional magnets offer compelling platforms for spintronics and quantum technologies, yet predicting their magnetic ground states, moments, and anisotropy remains challenging. This limitation primarily arises because existing machine-learning representations encode chemical environments without capturing the symmetry or exchange physics that govern magnetism. In this work, we introduce the symmetry-electronic fingerprint (SEF), a physically interpretable representation that encodes crystallographic symmetry operations, Wyckoff-site geometry, together with site-resolved electronic structure. Combined with ensemble learning with random forests, the SEF accurately classifies magnetic ordering while regressing moments alongside anisotropy energies while simultaneously resolving the distinct regimes of itinerant Stoner ferromagnetism from localized superexchange. What sets the SEF-trained models apart is that regions of elevated model uncertainty are not a failure but a diagnostic, identifying materials where these mechanisms compete. First-principles calculations on Co- and Ni-based halides and oxides confirm that these regions correspond to genuine near-degenerate FM and AFM phases with magnetic frustration, suppressed anisotropy, and emergent non-collinear ordering. By encoding symmetry together with exchange physics directly into the representation unlike conventional descriptors, the SEF transforms model uncertainty into a compass pointing toward two-dimensional materials where small perturbations drive transitions between collinear, frustrated, or non-collinear magnetic phases.
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All authors Addis Fuhr, Zachary R. Fox, David Parker, Ayana Ghosh

Materials Science · Cross-listed from math.NA

Momentum Space Algorithm for Electronic Structure of Double-Incommensurate Trilayer Graphene

Ken Beard and Daniel Massatt

Numerical algorithms for computing electronic structure of incommensurate 2D materials using ab initio models is critical for predicting material properties and guiding experiment. For bilayers, momentum space and continuum models have been introduced to approximate observables of ab initio tight-binding models using a momenta description despite the lack of periodicity in the tight-binding model required for Bloch theory. A similar structure has been introduced for double-incommensurate trilayers using a continuum model, where the three lattices are all mutually incommensurate. However, this description leads to a four-dimensional lattice space, and numerical convergence of the density of states was observed to have poor convergence. In this work, we introduce a momentum space framework for double incommensurate trilayer graphene, and introduce an efficient truncation scheme of the four-dimensional lattice to drastically improve convergence of the density of states and momentum local density of states (a parallel object to classical band structure). We implement this algorithm on an ab initio model of twisted trilayer graphene and validate convergence estimates. We further verify numerically that the momentum space algorithm, inherently higher order than the continuum model as it is an exact transformation of the tight-binding model, captures altered band behavior near the flat bands at magic angles.
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Materials Science

Dopant-induced modifications of the optical properties of GaSe

Jakub Sójka, Katarzyna Olkowska-Pucko, Kacper Walczyk et al. (+5 more)

Doping plays a crucial role in tailoring the electronic, optical, and magnetic properties of semiconductors, enabling control of carrier dynamics and the formation of functional states for optoelectronic applications. We investigate the influence of Fe dopants on the optical properties of GaSe crystals using photoluminescence (PL) spectroscopy under varying excitation power, temperature, and magnetic field. Fe incorporation introduces multiple sharp emission lines in addition to intrinsic excitonic transitions, including free and localised excitons. Power- and temperature-dependent measurements indicate that these emission features are associated with Fe-related dopant centres (Fe-bound excitons). Magneto-PL measurements reveal two distinct families of $g$-factors, enabling the identification of intrinsic excitonic transitions and Fe-induced defect states. These results demonstrate that Fe doping creates optically and magnetically active centres in GaSe, providing insight into defect-related excitonic processes and their potential relevance for magneto-optoelectronic and quantum photonic applications.
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All authors Jakub Sójka, Katarzyna Olkowska-Pucko, Kacper Walczyk, Zakhar R. Kudrynskyi, Volodymyr Boledzjuk, Adam Babiński, Maciej R. Molas, Grzegorz Krasucki

Materials Science

The phase composition and physical properties of melt-quenched multicomponent alloy FeCoNiB0.7Si0.3Be

Oleksandr I. Kushnerov, Sergey I. Ryabtsev, Pavlo O. Galagan et al. (+1 more)

The structure and physical properties of the high-entropy multicomponent alloy FeCoNiB0.7Si0.3Be in the as-cast and melt-quenched states were studied. The cooling rate of the melt-quenched films was estimated to be approximately 10^6 K/s based on the film thickness. X-ray analysis revealed a multiphase structure, including a BCC-type ordered phase (structural type B2) and intermetallic compounds (Fe, Ni, Co)2B. In melt-quenched samples, the fraction of the B2 phase increased, leading to a decrease in microhardness from 10400 MPa in the as-cast state to 8900 MPa in the melt-quenched state. Magnetic studies confirmed the ferromagnetic nature of the FeCoNiB0.7Si0.3Be alloy. The coercive field of melt-quenched samples (17500 A/m) was significantly higher than that of the as-cast ones (5200 A/m), which is attributed to structure refinement and an increased level of microstresses.
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All authors Oleksandr I. Kushnerov, Sergey I. Ryabtsev, Pavlo O. Galagan, Valerij F. Bashev

Materials Science

Physics-informed time-series forecasting of perovskite photoluminescence stability

Alexander Wieczorek, Manuel Kober-Czerny, Fábio Lopes et al. (+5 more)

Accelerated ageing using elevated temperatures and illumination is one of the most common methods to rapidly study the stability of novel semiconductor materials. However, as the pace of materials discovery continues to accelerate, even faster stability evaluations are needed. A physics-informed time-series forecasting algorithm designed to predict the long-term photoluminescence stability of metal halide perovskites is presented. A diverse experimental dataset of 167 metal halide perovskites is collected, including different crystallinities and compositions. These are stressed using heat and light, while the photoluminescence (PL) is monitored. The >86k collected PL spectra are featurized using a physics-informed model, and a hybrid CNN-LSTM model is trained to forecast the PL intensity during degradation of samples unseen during model training. Notably, the approach generalizes across the material groups and outperforms baseline benchmarks. Furthermore, the physics-based featurization ensures explainability, enabling analysis to identify critical stability descriptors for given predictions. It is expected that this approach will be adapted to other types of time-series data and enables a pathway to significantly reduce experimental testing times.
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All authors Alexander Wieczorek, Manuel Kober-Czerny, Fábio Lopes, Austin George Kuba, Leon Müller, Christian M. Wolff, Jason Hattrick-Simpers, Sebastian Siol

Materials Science

Enhanced Photocurrent Response in Epitaxial 0.5PZT-0.5PFN Multiferroic Thin Films

Lucia Imhoff, Miguel A. Rengifo, Jose M. Caicedo Roque et al. (+4 more)

The exploration of novel multiferroic materials with strong coupling between ferroelectric polarization and photovoltaic effects is crucial for next-generation optoelectronic devices. In this study, we characterized highly oriented 0.5Pb(Zr0.52Ti0.48)O3-0.5Pb(Fe0.5Nb0.5)O3 multiferroic thin films grown by pulsed laser deposition on SrTiO3 (001) substrates with a SrRuO3 bottom electrode. The films exhibited excellent crystalline quality, with a single perovskite phase and (001) orientation. They displayed good ferroelectric properties (remanent polarization $\sim$17 $\mu$C/cm$^2$, PUND; coercive field $\sim$150 kV/cm), alongside weak ferromagnetic behavior at room temperature (remanence 1.30 emu/cm$^3$; coercive field 90 Oe). Photovoltaic measurements demonstrated a robust, polarization-dependent photoresponse under 403 nm monochromatic laser illumination, achieving Jsc values between $\pm$20 $\mu$A/cm$^2$. This compelling observation confirms the intrinsic coupling between ferroelectric polarization and photovoltaic effects, highlighting the considerable promise of these single-phase multiferroic thin films for advanced photovoltaic and optoelectronic memory applications.
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All authors Lucia Imhoff, Miguel A. Rengifo, Jose M. Caicedo Roque, Jessica Padilla-Pantoja, Jose Santiso, Marcelo G. Stachiotti, Myriam H. Aguirre

Materials Science

Polarizing ultrathin ferroelectric BaTiO3 films through interfacial layer polarization

Ipek Efe, Edith Simmen, Tobias Goldenberger et al. (+3 more)

An important requirement for the integration of ferroelectric thin films into devices is deterministic control of the polarization state in films of only a few unit cells in thickness. Here, we utilize the charged atomic planes of (001)-oriented SmNiO$_3$ (SNO) buffer layers as a polarizing template to stabilize the polarization in ferroelectric BaTiO$_3$ (BTO) model system thin films. We show that an upwards (downwards) oriented polarization is achieved by selection of the [SmO]$^+$ ([NiO$_2$]$^-$) buffer termination. Most importantly, the charged atomic planes of SNO suppress the depolarizing-field-induced critical thickness in BTO, and we record the emergence of a net polarization in our BTO films from the first unit cell deposited. Our experiments, guided by density-functional-theory (DFT) calculations, further highlight the impact of charged defects on the polarizing effectiveness of the SNO buffer. Specifically, oxygen vacancies counteract the polarizing field of the negatively charged, [NiO$_2$]$^-$-terminated surface of the SNO buffer. Our findings provide important insights into the interplay of defect chemistry and polarizing interfaces to stabilize ferroelectric polarization down to the single-unit-cell limit.
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All authors Ipek Efe, Edith Simmen, Tobias Goldenberger, Manfred Fiebig, Nicola A. Spaldin, Morgan Trassin

Materials Science

Thickness-Independent Quantum Geometric Responses Driven by Interlayer Antiferroic Coupling

Zhiming Xu and Huaqing Huang

Two-dimensional ferroic materials exhibit rich and intriguing physical phenomena, but their response properties generally depend sensitively on thickness, requiring precise layer-number control and thereby limiting practical applications. Here, we propose a general strategy for realizing thickness-independent quantum geometric responses through symmetry engineering induced by interlayer antiferroic coupling. Using spatial-dependent symmetry analysis, we show that thickness-independent behavior emerges when the symmetry breaking required for a given response is generated by interlayer antiferromagnetic (AFM) or antiferroelectric (AFE) coupling, without invoking topological mechanisms. Our first-principles calculations predict that multilayer MnS in the G-type AFM configuration exhibits a surface-dominated anomalous Hall effect, whose thickness-independent behavior can be significantly influenced by the stacking order. We further propose design principles for achieving thickness-independent anomalous and nonlinear Hall effects driven by interlayer AFE coupling, and suggest potential applications in distinguishing magnetic structures. Our findings open a new route towards robust functional devices based on antiferroic materials.
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Materials Science · Cross-listed from cond-mat.soft

Real-time quantification of fluid flows around bubbles during directional solidification

Bastien Isabella, Emma Houllegatte, Cécile Monteux et al. (+1 more)

Directional solidification of bubbly liquids plays a critical role in shaping the microstructure and properties of many materials, yet the fluid dynamics governing bubble behavior during solidification remain poorly understood. Using cryo-confocal microscopy and particle image velocimetry, we quantify fluid flows around bubbles during solidification of water containing surfactants and tracers. Our results reveal that volumetric expansion dominates fluid motion, with velocities scaling linearly with the solidification rate (1-20$~\mu m/s$), while Marangoni flows-hypothesized to play a key role-are negligible ($< 5~\mu m/s$) under our experimental conditions. Diffusiophoresis and thermophoresis also contribute minimally. These findings challenge existing theoretical models and provide a framework for controlling bubble distribution in solidified materials
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All authors Bastien Isabella, Emma Houllegatte, Cécile Monteux, Sylvain Deville

Materials Science

Decoding Crystallographic Surface Chirality from Real Space and Momentum Space Images by Machine Learning

Chetana Badala Viswanatha, Ka Man Yu, Benito Arnoldi et al. (+6 more)

Intrinsically chiral metal surfaces, where handedness arises from the asymmetric step-kink-terrace topology of high-Miller index planes, are model systems for enantiospecific catalysis, sensing, and spintronics. Yet no consistent method exists to classify their handedness directly from experimental observables, without prior knowledge of crystallographic indices. Here, we report a dual-domain machine learning framework that recognizes handedness in chiral metal surfaces from two independent image representations: atomic structure models in real space and simulated momentum-resolved photoemission maps of Fermi surface projections in reciprocal space. A ResNet18 model pretrained on general image data is fine-tuned for chirality classification independently on both image representations and achieves meaningful classification accuracy for both real space and reciprocal space images. However, the Fermi surface classifier significantly outperforms the real space classifier. Critically, the reciprocal space classifier, trained only on synthetic images, correctly identifies synchrotron-acquired experimental Angle-Resolved Photoemission Spectroscopy (ARPES) maps of Cu(643)$^R$ and Cu(643)$^S$. The stronger performance in momentum space, as well as the transfer to experimental data, shows that handedness is encoded more globally and robustly in the electronic structure than in the spatially localized kink-site geometry. These results establish ARPES as a quantitative readout of crystallographic surface chirality and suggest a scalable route to identify chiral metal surfaces relevant to spin-selective phenomena.
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All authors Chetana Badala Viswanatha, Ka Man Yu, Benito Arnoldi, Anagha Aravind, Aaruni Kaushik, Jannis Lessmeister, Martin Aeschlimann, Benjamin Stadtmüller, S. Harshini Tekur

Materials Science

A first-principles approach for predicting infrared optical properties of solids

Sreerag Sundaram, Ziqi Guo, Dudong Feng et al. (+2 more)

We present a simplified formalism for predicting infrared optical constants from first-principles calculations. Addressing limitations of the widely used four-parameter semi-quantum Lorentz model, the proposed approach bridges the gap between the harmonic three-parameter model and full self-energy-based methods. By incorporating essential anharmonic effects including four-phonon scattering and phonon renormalisation, the model provides an efficient and accurate alternative while maintaining low computational cost. The frequency-dependent refractive indices of MgO and rutile TiO$_2$ are computed and compared with experimental data, demonstrating good quantitative agreement. The framework offers a practical approach for predicting optical properties of materials across a wide range of materials.
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All authors Sreerag Sundaram, Ziqi Guo, Dudong Feng, Karthik Sasihithlu, Xiulin Ruan

Materials Science

Disentangling the origin of degradation in perovskite solar cells via optical imaging and Bayesian inference

Akash Dasgupta, Robert D. J. Oliver, Manuel Kober-Czerny et al. (+5 more)

Machine learning and computational inference, coupled with experimental data, promise to significantly accelerate our rate of learning in most scientific disciplines. In this study, we develop tools that connect microscopic observations to macroscopic device behaviour, a capability that is essential for accelerating the design of durable energy materials. To this end, we introduce a novel approach that integrates photoluminescence imaging with drift diffusion simulations to understand operation and degradation in fully fabricated perovskite solar cells. By employing Bayesian inference, we generate "inferred maps" of parameters that govern recombination processes present in devices. We track these parameter maps while the devices are aged (70 {\deg}C, full spectrum sunlight) to analyse their temporal evolution during degradation. Notably, our approach allows us to distinguish between degradation occurring at the hole or electron transporting layer interface, or within the bulk. Our analysis reveals pronounced spatially non-uniform degradation, with significant macroscopic heterogeneity observed in the optoelectronic parameter maps. We pinpoint the greatest degradation observed in specific regions to stem from the perovskite/transport layer interfaces. Finally, we demonstrate that an amino-silane molecular passivation treatment suppresses this degradation, highlighting its specific role in enhancing device stability. Our approach offers valuable insights for future device fabrication and is a clear exemplification of how advanced Bayesian inference can significantly increase the value of experimental data.
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All authors Akash Dasgupta, Robert D. J. Oliver, Manuel Kober-Czerny, Charlie H. G. Nicholls, Xueli Cao, Yen-Hung Lin, Alexandra J. Ramadan, Henry J. Snaith

Materials Science

Holonomy Analysis of Optical-polarization Temperature Trajectories in Stress-induced Ferroelectric SrTiO$_3$

Hirotaka Manaka, Kazuma Seike and Yoko Miura

We develop a data-induced geometric framework for temperature trajectories in optical-polarization data and apply it to temperature-dependent birefringence imaging of stress-induced ferroelectric SrTiO3. By treating the measured response as an observable projection of local material states, the optical-polarization response at each pixel is cast as a trajectory along the temperature axis. Singular value decomposition separates trajectory-induced geometric objects associated with optical-polarization-direction structure and temperature-evolution modes. Holonomies are then defined by transporting these objects around closed loops in real space. The resulting maps reveal spatially localized connection mismatches correlated with an enhanced ferroelectric transition temperature and stress-related optical anisotropy. Local order parameters and angular-gradient analyses confirm that these loop-level signals are distinct from orientational disorder and simple spatial variation. The signed holonomy of the temperature-evolution modes further resolves positive and negative connection structures under a fixed frame convention. These results demonstrate that the data-induced connection geometry of temperature trajectories provides an experimentally accessible diagnostic of electromechanical inhomogeneity in SrTiO3 under stress, without explicitly reconstructing hidden strain or electric-polarization fields.
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Materials Science

A Geometric Design Principle for $\mathbb{Z}_2$ Topological Phases in Twisted Triangular-Lattice Bilayers

Jiaheng Li, Jiaxuan Liu, Yan Zhang et al. (+3 more)

Twisted van der Waals bilayers provide a versatile platform for moiré electronic states, yet a transferable symmetry-based principle for time-reversal-invariant $\mathbb{Z}_2$ moiré bands has remained largely missing. Here we show that triangular-lattice bilayers with symmetry-related stacking minima provide a geometric route to an emergent honeycomb moiré lattice. Band-edge states derived from the untwisted $\Gamma$ valley are trapped by the reconstructed stacking landscape, forming A/B moiré orbitals whose inter-domain coupling generates Dirac crossings. Spin–orbit coupling opens a topological gap, yielding an effective Kane–Mele description and a quantum spin Hall phase characterized by a nontrivial $\mathbb{Z}_2$ invariant. First-principles calculations for Janus BiTeBr confirm the robustness of this phase over a broad twist-angle range and demonstrate an electric-field-driven topological transition. Representative triangular-lattice bilayers further establish this symmetry-based design principle as a broadly applicable route to tunable moiré quantum spin Hall materials.
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All authors Jiaheng Li, Jiaxuan Liu, Yan Zhang, Zhong Fang, Hongming Weng, Quansheng Wu

Materials Science

Observation of orbital-angular-momentum-driven temperature modulation via the spin Peltier effect

Sang J. Park, Tsuneyoshi Kan, Takamasa Hirai et al. (+1 more)

Angular-momentum transport provides a pathway for controlling energy flow in solids beyond conventional charge-based mechanisms. While spin currents are known to mediate spin-caloritronic phenomena such as the spin Peltier effect (SPE), the role of orbital angular momentum in heat transport remains largely unexplored. Here we demonstrate orbital-angular-momentum-driven temperature modulation via the SPE in yttrium iron garnet/Pt/CuOx heterostructures. Using wedge-shaped CuOx layers combined with spatially resolved active thermal measurement techniques, we map the continuous thickness dependence and quantitatively disentangle the spin- and orbital-current-mediated contributions within a single device. The orbital-mediated component exhibits a pronounced maximum at an intermediate thickness, revealing a characteristic length scale for interfacial orbital-angular-momentum generation and propagation at the Cu/CuOx interface. These results provide direct experimental evidence that charge-current-driven orbital angular momentum can drive SPE-induced temperature modulation, establishing interfacial orbital processes as an additional channel for heat transport and providing a pathway toward spin-orbit caloritronics.
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All authors Sang J. Park, Tsuneyoshi Kan, Takamasa Hirai, Ken-ichi Uchida

Materials Science

Conditional spinodal decomposition in Li-Mg anodes for lithium metal batteries

Leonardo Shoji Aota, Aubin Leray, Yuqi Liu et al. (+14 more)

The development of batteries with high energy density, short charging times and use of sustainable materials is critical for decarbonization. Magnesium (Mg)-based anodes for lithium (Li) metal batteries promote homogeneous Li plating, thereby avoiding the formation of Li dendrites that cause short circuits and battery failure. However, microstructural modifications induced by Li-alloying and their influence on battery operation remain elusive. Here, we unveil the previously unknown formation of an ordered B2 phase, which creates a conditional spinodal decomposition with the e̱ta}-body-centered cubic phase. Chemical fluctuations characteristic of spinodal decomposition give rise to uniformly dispersed Li-rich e̱ta}-BCC and Li-poor B2 continuous interconnected phases, with the former providing a fast diffusion pathway for Li diffusion towards the anode, hence decreasing the propensity for dendrite formation at elevated current density. This is achieved using Earth-abundant and inexpensive Mg.
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All authors Leonardo Shoji Aota, Aubin Leray, Yuqi Liu, Frederic de Geuser, Chanwon Jung, Shyam Katnagallu, Tim M. Schwarz, Alisson Kwiatkowski da Silva, Júlio César Pereira dos Santos, Eric Marchezini Mazzer, Poonam Yadav, Christoph Freysoldt, Frank Stein, Yug Joshi, Se-Ho Kim, Dierk Raabe, Baptiste Gault

Materials Science

Leveraging rapid sintering to retain metastable zirconia in copper

Wangshu Zheng, Xi Chen, Xuyang Feng et al. (+6 more)

Cermets combining metastable ceramics and ductile metals promise superior toughness and strength. However, retaining metastability often requires high-temperature sintering that coarsens microstructures and relaxes matrix constraint. Here we introduce an ultrafast high-temperature sintering (UHS) strategy to overcome this trade-off in zirconia-copper cermets. By applying Joule heating at around 100 degrees C per second to 900 degrees C with only a 20 second hold, we obtained cermets containing up to 50 weight percent of metastable austenite in zirconia at room temperature within a fine-grained and homogeneous microstructure. The rapid sintering kinetically favors semi-thermal austenite formation while suppressing copper grain growth and matrix relaxation, thereby stabilizing the high-temperature phase and simultaneously preserving microstructural refinement. This approach offers significant potential for copper-based composites in applications such as transformation toughening, self-healing, and crack detection.
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All authors Wangshu Zheng, Xi Chen, Xuyang Feng, Aiji Zou, Andrew Yun Ru Ng, Xiaoqing Wang, Zhili Dong, Qiang Guo, Chee Lip Gan

Materials Science

A wrong ground-state structure of HfO$_2$ predicted by machine-learning interatomic potentials based on the PBE functional

Shuqi Tang, Jinchen Wei, Kang Wang et al. (+4 more)

Machine-learning interatomic potentials (MLIPs) have become powerful tools for material simulations. Many MLIPs are trained based on density functional theory (DFT) datasets generated with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional. Using a PBE-based MLIP for HfO2, we identify a previously unreported low-energy I41/amd structure, which is predicted to be more stable than the well-known ground-state structure, the monoclinic P21/c structure. Since experiments show clearly that HfO2 takes the P21/c structure as the ground state, this is obviously a wrong prediction. Unfortunately, the same prediction is also made by widely used PBE-based foundation models such as NequIP-OAM-L and MatterSim-v1-5M. Comparisons among different DFT functionals show that this error originates from the PBE functional, which overstabilizes low-density structures containing sixfold Hf-O octahedral units, such as the I41/amd and Pbcn phases. The error also affects the calculated energy landscapes and barrier heights along ferroelectric HfO2 polarization switching paths when there are large lattice relaxations. Fortunately, the error can be largely suppressed by other functionals such as PBEsol and local density approximation. Our study serves as a warning about the impact of errors in exchange-correlation functional approximations on the reliability of MLIP simulations of crystal structures and phase transitions.
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All authors Shuqi Tang, Jinchen Wei, Kang Wang, Junjie Zhou, Yihan Zhang, Menglin Huang, Shiyou Chen

Materials Science

Molecular reference corrections for quantum Monte Carlo adsorption energies

Roman Fanta and Michal Bajdich

Accurate surface thermochemistry requires balanced error cancellation between extended slabs and molecular reference states. This balance can fail whenever the electronic-structure error is not transferable across the chemically distinct species entering a thermodynamic cycle. Here we examine this problem in single-determinant fixed-node diffusion Monte Carlo (SD-FNDMC) for oxygen-reduction intermediates on Pt(111) and selected CO-reduction intermediates on Cu(111). Gas-phase thermochemistry is used to diagnose the reference-state imbalance, and a hybrid cycle is introduced to separate slab–adsorbate binding from molecular formation. The hybrid cycle keeps the surface binding term at the SD-FNDMC level, where cancellation is expected to be most favorable, and replaces the molecular formation contribution with a benchmark coupled cluster reference. For Pt(111), the resulting correction is small for O and OH but larger for OOH, while the geometry-matched refinement gives only a secondary correction. Applying the same cycle to $^\ast$CHO and $^\ast$COH adsorption on Cu(111) gives corrections of opposite sign, showing that the bias is controlled primarily by the electronic structure of the corresponding HCO and COH molecular references rather than by adsorbate geometry alone. This decomposition identifies molecular reference imbalance as a separable source of error in SD-FNDMC surface thermochemistry and reduces the corresponding bias without modifying the SD-FNDMC slab-binding contribution.
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Wednesday 10 June

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

Effects of High-Temperature Preconditioning on Li Plating During Low-Temperature Cycling of the COTS LG Chem HG2 Cell

Lukas Lehnert, Keith B. Chin, Frederick C. Krause et al. (+7 more)

Commercial off-the-shelf~(COTS) Li ion cells offer an attractive and rechargeable power source for spacecraft applications. However, since these cells are typically designed for charging above 0\,\textdegree C, challenging sub-zero temperatures could inflict irreversible degradation and safety hazards during in-flight operation. To address these challenges, this work explores strategies affecting their low-temperature performance. Specifically, we investigate the Li plating behavior of the COTS~LG~Chem~18650~HG2 cell during galvanostatic cycling at $-20\,$\textdegree C and its dependence on prior high-temperature preconditioning protocols, involving either two-week galvanostatic cycling or storage at 30\,\textdegree C, as well as a reference case without preconditioning, i.e., direct cycling at $-20\,$\textdegree C. Experimental cycling tests reveal distinct differences in Li metal deposition between cells subjected to these conditions. To identify the origin of these discrepancies, we combine computed tomography of the electrode microstructure with three-dimensional, spatially resolved cell modeling and analyze the simulation results.
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All authors Lukas Lehnert, Keith B. Chin, Frederick C. Krause, John P. Ruiz, Simon Hein, John Bescup, Gil Garteiz, Arnulf Latz, Erik J. Brandon, Birger Horstmann

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

Polyconvexity does not imply true-stress-true-strain monotonicity in the incompressible three-dimensional case

Dominik K. Klein, Maximilian P. Wollner and Patrizio Neff

We study constitutive conditions of hyperelastic potentials for incompressible material behavior in three dimensions. By means of a counterexample, we show that polyconvexity does not imply true-stress-true-strain monotonicity. Thus, polyconvexity alone is not strong enough to guarantee a physically reasonable response for idealized elasticity.
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Materials Science

Intrinsic Ductility from Shear Amorphization: From Pure Metals to Multi-Principal-Element Alloys

Morgan R. Jones, Duane D. Johnson and Nicolas Argibay

Direct links between electronic structure and intrinsic ductility remain elusive for metals. A framework is proposed that reduces the complexities of valence charge distribution, band filling, and shear strain effects into structure-property relationships describing the intrinsic ductility of metals and alloys. Rather than relying on crystal cleavage and dislocation nucleation at preexisting crack tips, we show that a lower energy fracture criterion, i.e., the activation energy density for amorphization, enables accurate predictions of both intrinsic ductility and ductile-to-brittle transition temperatures. From analytical expressions and tabulated ab-initio stiffness constants, lattice parameters, and binary interaction energies, we present a unified theory that reconciles ductile flow in pure metals and solid-solution alloys. Phase diagrams generated for the Nb-Ta-V-Ti system simultaneously explain its high strength and room-temperature tensile ductility, validating this framework as a practical one for rapid design of structural multi-principal-element alloys.
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Materials Science

Water Flow Through Polar and Non-Polar Nanopores: Insights from Multiscale Simulations

Elizane E. de Moraes, João Victor Lemos Valle, Bruno H. S. Mendonça et al. (+3 more)

Global water stress has emerged as a critical challenge, driving the search for advanced membrane materials that enable efficient, selective water filtration and transport. In this context, two-dimensional nanoporous membranes provide an ideal platform to elucidate how atomic-scale structure and electronic polarization govern water flow under extreme confinement. In this study, we employ multiscale simulations to investigate the effect of water flow through nanopores in graphene and hexagonal boron nitride (hBN) membranes. Our results reveal significantly higher water flow in hBN membranes than in graphene. This enhanced flow is attributed to the asymmetry of the hBN pores, which induces an electric dipole moment, as confirmed by quantum-mechanical (QM) calculations. Classical molecular dynamics simulations further demonstrate that water molecules exhibit a random distribution with no preferential orientation near the graphene pores, whereas hBN induces strong structuring. Furthermore, hybrid quantum mechanics/molecular mechanics (QM/MM) simulations indicate that the dipole moment of the hBN pore increases in the presence of water, as evidenced by the average charge distribution. Conversely, the symmetric nature of graphene pores results in non-polar characteristics, as verified by both QM/MM and QM calculations. These findings provide valuable insights into the distinct water-transport properties when flowing through graphene and hBN nanopores, with potential implications for designing advanced nanofiltration membranes.
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All authors Elizane E. de Moraes, João Victor Lemos Valle, Bruno H. S. Mendonça, Ernane de Freitas Martins, Hélio Chacham, Pablo Ordejón

Materials Science

Extending the La Solubility Limit in Sr$_3$Ir$_2$O$_7$ through High-Pressure High-Temperature Synthesis

Cheng Peng and Weiwei Xie

La-doped bilayer iridates provide an important platform for studying the evolution of the spin-orbit-assisted Mott state under electron doping, but the La solubility achieved by conventional ambient-pressure synthesis is limited. Here, we report the synthesis and physical properties of nominally La-doped (Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$ (x = 0.05, 0.10, 0.15, and 0.20) prepared using high-pressure high-temperature techniques. Single-crystal X-ray diffraction refinements, supported by scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX), reveal significantly enhanced La incorporation, with nominal x = 0.05 and 0.15 corresponding to actual compositions of approximately (Sr$_{0.89}$La$_{0.11}$)$_3$Ir$_2$O$_7$ and (Sr$_{0.77}$La$_{0.23}$)$_3$Ir$_2$O$_7$, respectively. At nominal x = 0.20, the bilayer phase is no longer stabilized and instead transforms into cubic perovskite Sr$_{1-x}$La$_x$IrO$_3$. (Sr$_{0.89}$La$_{0.11}$)$_3$Ir$_2$O$_7$ exhibits a ferromagnetic-like transition near 186 K accompanied by magnetic hysteresis and subtle lattice anomalies indicative of spin-lattice coupling. Despite its high electron-doping level, the compound remains strongly insulating, consistent with a heavily doped localized magnetic insulating state distinct from both parent Sr$_3$Ir$_2$O$_7$ and ambient-pressure La-doped samples. In contrast, (Sr$_{0.77}$La$_{0.23}$)$_3$Ir$_2$O$_7$ displays metal-like electronic behavior, weakened magnetic order, and enhanced carrier delocalization, although disorder-driven localization persists at low temperatures. These results demonstrate that high-pressure synthesis substantially extends the accessible doping range of bilayer iridates and reveals electronic and magnetic states inaccessible through conventional synthesis routes.
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Materials Science

Site Preferences and "Coloring Problem" in Cu-doped BiMn$_7$O$_{12}$ Quadruple Perovskite

Cheng Peng, Mingyu Xu, Yang Zhang et al. (+3 more)

Lightly Cu-doped BiMn$_7$O$_{12}$ (x = 0.05, 0.10, and 0.15) was investigated using high-pressure synthesis, single-crystal X-ray diffraction, pair distribution function (PDF) analysis, STEM, magnetic measurements, and first-principles calculations. All compositions retain an average monoclinic $I$2/$m$ structure, while Cu substitution progressively suppresses the monoclinic distortion and drives the lattice toward a pseudo-cubic metric symmetry. PDF analysis reveals increasing local structural disorder and reduced medium-range coherence with increasing Cu concentration, despite preservation of the overall quadruple-perovskite framework. Single-crystal refinements indicate enhanced electron density at the octahedral Mn B sites, suggesting preferential Cu occupation within the MnO$_6$ network rather than the conventional square-planar sites expected for Cu$^{2+}$. Magnetic measurements reveal two characteristic anomalies near $T_1$ ~ 100-120 K and $T_2$ ~ 50-60 K, together with pronounced magnetic irreversibility, field-dependent hysteresis, and unsaturated magnetization. Increasing Cu concentration progressively suppresses the low-temperature magnetic state and weakens the field-induced moment. First-principles calculations favor Cu occupation at the square-planar sites, contrasting with the experimental refinements and highlighting strong competitions among local bonding, short-range disorder, and metastability in this highly frustrated quadruple perovskite system.
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All authors Cheng Peng, Mingyu Xu, Yang Zhang, Ismail El Baggari, Jie Li, Weiwei Xie

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

Fine-tuning MLIP foundation models: strategies for accuracy and transferability

Tamás Lajos Tompa, Eszter Varga-Umbrich, Ilyes Batatia et al. (+3 more)

Adapting machine-learned interatomic potential (MLIP) foundation models to specialised tasks through fine-tuning is an increasingly important practice, yet systematic guidance on when and how to fine-tune is currently limited. We evaluate seven fine-tuning strategies – naive full-parameter updates, two layer-freezing variants, Low-Rank Adaptation (LoRA), multihead replay, pseudolabelled replay, and replay combined with LoRA – across five chemically diverse benchmarks (aqueous NaCl, ice polymorphs, S$_\mathrm{N}$2 reactions, SPICE biomolecules, and lithium electrolytes), three generations of foundation models, and training sets spanning five orders of magnitude. To support this evaluation we implement three capabilities in the MACE codebase: LoRA adapted for equivariant message-passing architectures, including both scalar and equivariant linear layers; pseudolabelled replay, which decouples the replay data source from the original pretraining corpus; and model-aware atomic reference energy (E0) reestimation for fine-tuning workflows. We find that foundation model quality, correct E0 initialisation, and well-chosen hyperparameters are prerequisites whose impact routinely exceeds that of the fine-tuning strategy itself. Once these prerequisites are met, most strategies achieve strong target-task accuracy, consistently surpassing models trained from scratch. The practical distinction depends on deployment scope: naive fine-tuning offers the best convergence for single-system applications, while multihead replay – with either original or pseudolabelled data – is the only approach tested that consistently preserves out-of-distribution robustness, maintaining both pretraining-distribution accuracy for broader deployment and many-body short-range repulsion.
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All authors Tamás Lajos Tompa, Eszter Varga-Umbrich, Ilyes Batatia, Alin M. Elena, Noam Bernstein, Gábor Csányi

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

From Loss Diagnosis to Rational Design: A Unified Analytical Model for Photoelectrochemical Cells

Ziyan Pan and Giulia Tagliabue

Photoelectrochemical (PEC) cells are a compelling route to solar-driven chemical energy storage and feedstock synthesis, yet their deployment is hindered by coupled losses spanning light absorption, carrier transport, interfacial charge transfer, and semiconductor-electrolyte matching. Existing models address these losses in an architecture-specific manner and fall short of quantitative experimental diagnosis or actionable design guidance. Here, we introduce a unified loss-analysis framework applicable to both built-in junction (BIJ) and semiconductor-electrolyte junction (SEJ) photoelectrodes within a consistent set of physically meaningful parameters. The framework delivers current-voltage curves and efficiency metrics under ideal and real conditions, constructing efficiency maps to delineate theoretical limits and material-selection windows. Critically, by fitting experimental current-voltage data, it enables quantitative energy-loss decomposition into thermodynamic, optical, recombination, and interfacial contributions, pinpointing performance bottlenecks in real devices and mapping them directly onto optimization strategies such as co-catalyst integration or nanostructuring. Energy flows are visualized through Sankey diagrams, providing an intuitive picture of how incident solar energy is absorbed, dissipated, or converted into chemical output. Validated against state-of-the-art literature results spanning solar water splitting, CO2 reduction, NH3 synthesis, and solar redox flow batteries, the framework further enables systematic comparison of photovoltaic-grade absorbers (e.g., Si, perovskites) with intermediate-bandgap semiconductors (e.g., hematite, BiVO4), identifying key factors limiting each material class. Together, these capabilities support a paradigm shift from empirical optimization to mechanism-informed rational design of high-efficiency PEC energy-conversion systems.
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Materials Science

Lock-In Infrared Thermography: Phase Analysis for Rapid, Wide-Range Thermal Conductivity Measurements

Ethan A. Scott, Jeffrey L. Braun, Jessica Reyes et al. (+5 more)

We report on a phase-based lock-in thermography approach, combined with a multilayered thermal model (often employed in thermoreflectance analysis), to measure the thermal conductivity of bulk materials and layered structures. The spatial distribution of the material's thermal phase is monitored with an infrared camera, which is locked into the frequency of a modulated laser used to heat the material. This phase distribution is then fit with a thermal model, in which properties such as thermal conductivity are extracted as fit parameters. This approach enables non-contact, front-side measurements, which are insensitive to surface roughness. The technique does not strictly require the application of a transducer layer, but we highlight the practical benefits of applying a removable adhesive layer to serve as a near-surface absorber. We demonstrate the efficacy of the method by measuring materials with thermal conductivities that span over three orders of magnitude (approximately 1 W/m/K to > 2000 W/m/K).
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All authors Ethan A. Scott, Jeffrey L. Braun, Jessica Reyes, Bruce Bolliger, Terrence Soares, John T. Gaskins, Marko J. Tadjer, Patrick E. Hopkins

Materials Science

Resolving Finite-Size Errors in EOM-CCSD Band Gaps of Solids with Interacting-Bath Dynamical Embedding Theory

Jiachen Li, Christopher Hillenbrand, Christian Venturella et al. (+2 more)

Periodic equation-of-motion coupled-cluster theory with single and double excitations (EOM-CCSD) has shown promise for quantitative calculations of band structures in solids. However, its steep computational scaling has limited calculations to relatively coarse $k$-point meshes, leading to sizable finite-size errors and discrepant estimates of thermodynamic-limit band gaps in recent benchmarks. In this work, we revisit EOM-CCSD band gaps for ten semiconductors and insulators using interacting-bath dynamical embedding theory (ibDET), a systematically improvable Green's function embedding framework that enables dense Brillouin-zone sampling at modest computational cost. By pushing the $k$-point sampling up to $10\times10\times10$, well beyond the system sizes accessible in canonical periodic EOM-CCSD calculations, we significantly reduce finite-size errors and obtain stable thermodynamic-limit extrapolations. We further compare $G_0W_0$@PBE, $G_0W_0$@HF, and EOM-CCSD on an equal footing using the same numerical settings in PySCF. We find that EOM-CCSD yields a mean absolute error of 0.32 eV relative to experimental band gaps for a test set of ten semiconductors and insulators, lower than that of $G_0W_0$@PBE. For ZnO, EOM-CCSD also accurately describes the Zn $3d$-band binding energy, despite overestimating the band gap. These results demonstrate that ibDET offers a practical route to high-accuracy many-body electronic structure calculations in periodic systems.
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All authors Jiachen Li, Christopher Hillenbrand, Christian Venturella, Enzhi Chen, Tianyu Zhu

Materials Science

Computationally efficient method for determining limiting velocities of edge dislocations in anisotropic crystals

Daniel N. Blaschke

The continuum-limit theory of dislocations in crystals predicts divergences in the elastic energy at crystal-geometry dependent limiting velocities $v_L$. The $v_L$ separate subsonic, transonic, and supersonic dislocation glide regimes and are therefore important for material strength models at high strain rates. Although it is known how to calculate these limiting velocities, there is one special case - edge dislocations with reflection symmetry, but non-vanishing elastic constants $c'_{16}$ or $c'_{26}$ - where previous methods have been notoriously slow. In this letter, we address this deficiency by deriving a computationally efficient method for determining the $v_L$ of edge dislocations with reflection symmetry which is two orders of magnitude faster than the previous method.
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