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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Monday 10 November

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

Magnetic anisotropy and intermediate valence in CeCo$_5$ ferromagnet

Alexander B. Shick and Evgenia A. Tereshina-Chitrova

The intermediate valence of Ce in CeCo$_5$ challenges standard density functional theory (DFT) and static DFT+$U$ approaches, which fail to capture its magnetic properties. By combining DFT+$U$ with exact diagonalization of the Anderson impurity model for the Ce 4$f$ shell, we find a substantial reduction of Ce spin and orbital moments, consistent with DFT+DMFT, arising from Ce$^{4+}$ - Ce$^{3+}$ valence fluctuations. The total magnetic moment of 6.70 $\mu_B$ agrees with experiment, and the calculated $4f$ density of states reproduces photoemission and Bremsstrahlung isochromat spectra. The uniaxial magnetic anisotropy energy reaches 4.8 meV/f.u. when Coulomb correlations on both Ce 4$f$ and Co 3$d$ shells are included, in very good agreement with experimental data. These results highlight the importance of dynamical correlations and provide guidance for exploring high-performance, low-rare-earth-content permanent magnets.
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Materials Science

Designing new Zintl phases SrBaX (X = Si, Ge, Sn) for thermoelectric applications using ab initio techniques

Vivek Gusain, Mohd Zeeshan and B. K. Mani

Slack's phonon-glass and electron-crystal concept has been the guiding paradigm for designing new thermoelectric materials. Zintl phases, in principle, have been shown as great contenders of the concept and thereby good thermoelectric candidates. With this as motivation, we design new Zintl phases SrBaX (X = Si, Ge, Sn) using state-of-the-art computational methods. Herein, we use first-principles simulations to provide key theoretical insights to thermal and electrical transport properties. Some of the key findings of our work feature remarkably low lattice thermal conductivities ($<$~1~W~m$^{-1}$~K$^{-1}$), putting proposed materials among the well-known thermoelectric materials such as SnSe and other contemporary Zintl phases. We ascribe such low values to antibonding states induced weak bonding in the lattice and intrinsically weak phonon transport, resulting in low phonon velocities, short lifetimes, and considerable anharmonic scattering phase spaces. Besides, our results on electronic structure and transport properties reveal tremendous performance of SrBaGe ($ZT\sim$ 2.0 at 700~K), highlighting the relevance among state-of-the-art materials such as SnSe. Further, the similar performances for both $p$- and $n$-type dopings render these materials attractive from device fabrication perspective. We believe that our study would invite experimental investigations for realizing the true thermoelectric potential of SrBaX series.
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Materials Science

The Microscopic Structure of Stacking Faults in Sr$_2$NaNb$_5$O$_{15}$

Robin Sjökvist, Yining Xie, Zabeada Aslam et al. (+4 more)

Stacking faults and other topological defects in ferroics can have a significant influence on the electronic and mechanical properties of the material. Here, regular stacking faults in the tetragonal tungsten bronze material Sr$_2$NaNb$_5$O$_{15}$ are investigated through transmission electron microscopy, symmetry mode analysis and machine-learned force-field calculations. It is shown that the faults, with a fault vector of $\frac{1}{4}[\bar{2}12]_o$, annihilate in sets of four in the material, owing to the $\frac{1}{4}$ unit cell displacement along the b-axis. The four resulting domains emerge as four possible directions of the S$_3$ order parameter, related to NbO$_6$ octahedral tilts in the material. Force-field calculations reveal that the stacking faults are likely placed at positions where the octahedra in neighbouring domains have similar magnitudes of rotation, and that the estimated stacking fault energy is 46 mJ/m$^2$. The investigation shows that the stacking faults have a significant local effect on the polar modes present in the structure, and therefore could affect the ferroelectric properties.
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All authors Robin Sjökvist, Yining Xie, Zabeada Aslam, Andy P. Brown, Nicholas C. Bristowe, Mark S. Senn, Richard Beanland

Materials Science

Wafer-Scale Films of Two-Dimensional Materials via Roll-to-Roll Mechanical Exfoliation

Yigit Sozen, Thomas Pucher, Bhagyanath Paliyottil Kesavan et al. (+6 more)

In this study, we demonstrate an improved version of the roll-to-roll mechanical exfoliation method, incorporating a controlled sliding motion into the exfoliation process to achieve uniform nanosheet films of two-dimensional materials at wafer-scale. This scalable technique enables the fabrication of high-quality films suitable for electronic and optoelectronic applications. We validate the process by fabricating WSe2 phototransistors directly on the exfoliated films, achieving performance metrics comparable to the best reported devices based on electrochemically exfoliated material. The all-dry transfer method employed ensures minimal contamination and preserves the intrinsic properties of the material. This work highlights the potential of high-throughput mechanical exfoliation as a cost-effective and reliable route for large-scale production of 2D material-based devices.
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All authors Yigit Sozen, Thomas Pucher, Bhagyanath Paliyottil Kesavan, Nuria Jimenez-Arevalo, Julia Hernandez-Ruiz, Zdenek Sofer, Carmen Munuera, Juan J. Riquelme, Andres Castellanos-Gomez

Materials Science

Perspective on Moreau-Yosida Regularization in Density-Functional Theory

Markus Penz, Michael F. Herbst, Trygve Helgaker et al. (+1 more)

Within density-functional theory, Moreau-Yosida regularization enables both a reformulation of the theory and a mathematically well-defined definition of the Kohn-Sham approach. It is further employed in density-potential inversion schemes and, through the choice of topology for the density and potential space, can be directly linked to classical field theories. This perspective collects various appearances of the regularization technique within density-functional theory alongside possibilities for their future development.
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All authors Markus Penz, Michael F. Herbst, Trygve Helgaker, Andre Laestadius

Materials Science

Challenges in predicting positron annihilation lifetimes in lead halide perovskites: correlation functionals and polymorphism

Kajal Madaan, Guido Roma, Jasurbek Gulomov et al. (+3 more)

Halide perovskites have emerged in the last decade as a new important class of semiconductors for a variety of optoelectronic applications. A lot of previous studies were thus devoted to the characterisation of their point defects. Positron annihilation spectroscopy is a well recognized tool for probing vacancies in materials. Recent applications of this technique to APbX$_3$ halide perovskites are sparse, and the rare theoretical predictions of positron lifetimes in these materials, published in association with experiments, do not fully agree with each other. These works suggest that vacancies on the A site are not detected. In our theoretical study we focus on the role of the electron-positron correlation functional. We thoroughly revisit and compare several approximations when applied to methylammonium lead iodide (MAPbI$_3$) with or without vacancies, as well as inorganic perovskites CsPbI$_3$ and CsPbBr$_3$, in various phases. We show also the relationship between the size of the voids, through Voronoi volumes, and the calculated lifetimes. For the cubic phases we investigate in detail the role of polymorphism, including the distribution of vacancy formation energies and positron annihilation lifetimes. In our lifetimes calculations, apart from older and more recent semi-local approximations for the electron-positron correlation potential, we also consider the weighted density approximation (WDA), which is truly non-local and should better describe positron annihilation in regions with strong electronic density variations. We show that for this class of materials, and especially for cations vacancies, the influence of the chosen approximation is crucial, much stronger than in metals, alloys and conventional semiconductors. This influence may induce to reconsider the interpretation of experimentally determined lifetimes.
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All authors Kajal Madaan, Guido Roma, Jasurbek Gulomov, Pascal Pochet, Catherine Corbel, Ilja Makkonen

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

Ultra-long-range spin coupling in graphene revealed by atomically resolved spin excitations

Beatriz Viña-Bausá, Antonio. T. Costa, Joao Henriques et al. (+6 more)

Magnetic interactions between localized spins-1/2 play a central role in quantum magnetism, spin-based quantum computing, and quantum simulation. The range and strength of these interactions are key figures of merit. Here, we probe exchange interactions in pairs and trimers of spins-1/2 introduced by chemisorption of individual hydrogen atoms on graphene. Using scanning tunneling microscopy and inelastic electron tunneling spectroscopy, supported by large-scale mean-field Hubbard calculations, we demonstrate 3 meV exchange couplings at separations beyond 10 nm, surpassing all prior systems. The couplings can be ferro- or antiferromagnetic depending on the relative sublattice arrangement. Real-space mapping of spin excitation amplitudes enables characterization with atomic-resolution. Through atomic manipulation we extend this control to spin trimers, revealing collective spin excitations when pairwise exchange couplings are comparable.
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All authors Beatriz Viña-Bausá, Antonio. T. Costa, Joao Henriques, Eva Cortés-del Río, Roberto Carrasco, Pierre Mallet, Jean-Yves Veuillen, Joaquín Fernández-Rossier, Iván Brihuega

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

Beyond the tip: Lattice dynamics, seams, and the mechanism of microtubule fracture

Amir Zablotsky, Subham Biswas, Laura Schaedel et al. (+1 more)

The structural integrity of microtubules is paramount for cellular function. We present a theoretical analysis of their lattice fracture, focusing on the influence of multi-seam structures arising from monomer defects and aiming to provide a more accurate estimation of GDP lattice parameters. Our findings reveal that seams function as pre-existing pathways that accelerate damage propagation. Consequently, monomer vacancies destabilize the lattice due to the inherent structural loss of tubulin-tubulin contacts and the additive acceleration of fracture through multiple seams. Importantly, the comparison of our simulations with experiments on lattice fracture suggests that the intrinsic ratio of longitudinal to lateral binding energies is bounded at approximately 1.5, challenging previous predictions of lattice anisotropy from tip-growth models and highlighting the urgent need to incorporate into current growth models parameters obtained from lattice dynamics.
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All authors Amir Zablotsky, Subham Biswas, Laura Schaedel, Karin John

Materials Science

Density-dependent sodium-storage mechanisms in hard carbon materials

Alexis Front, Tapio Ala-Nissila and Miguel A. Caro

Understanding the sodium-storage mechanism in hard carbon (HC) anodes is crucial for advancing sodium-ion battery (SIB) technology. However, the intrinsic complexity of HC microstructures and their interactions with sodium remain not fully elucidated. We present a multiscale methodology that integrates grand-canonical Monte Carlo (GCMC) simulations with a machine-learning interatomic potential based on the Gaussian approximation potential (GAP) framework to investigate sodium insertion mechanisms in hard carbons with different levels of porosity, achieved by simulating structural models with densities ranging from 0.7 to 1.9 g cm$^{-3}$. Structural and thermodynamic analyses reveal the interplay between pore size and accessibility and the relative contributions of adsorption, intercalation, and pore filling to the overall storage capacity. Low-density carbons favor pore-filling, achieving extremely high capacities at near-zero voltages, whereas high-density carbons primarily store sodium through adsorption and intercalation, leading to lower but more stable capacities. Intermediate-density carbons ($1.3-1.6$ g cm$^{-3}$) provide the most balanced performance, combining moderate capacity (480 and 310 mAh g$^{-1}$), safe operating voltages, and minimal volume expansion ($<10$%). These findings establish a direct correlation between carbon density and electrochemical behavior, providing atomic-scale insight into how hard carbon morphology governs sodium-storage. The proposed framework offers a rational design principle for optimizing HC-based SIB anodes toward high energy density and long-term cycling stability.
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Materials Science

Physical properties and first-principles calculations of an altermagnet candidate Cs$_{1-\delta}$V$_2$Te$_2$O

Chang-Chao Liu, Jing Li, Ji-Yong Liu et al. (+4 more)

We report the crystal growth, structure, physical properties, and first-principles calculations of a vanadium-based oxytelluride Cs$_{1-\delta}$V$_2$Te$_2$O. The material possesses two-dimensional V$_2$O square nets sandwiched by tellurium layers, with local crystallographic symmetry satisfying the spin symmetry for a $d$-wave altermagnet. An antiferromagnetic transition at 293 K is unambiguously evidenced from the measurements of magnetic susceptibility and specific heat. In addition, a secondary transition at $\sim$70 K is also observed, possibly associated with a Lifshitz transition. The first-principles calculations indicate robust Néel-type collinear antiferromagnetism in the V$_2$O plane. Consequently, spin splittings show up in momentum space, in relation with the real-space mirror/rotation symmetry. Interestingly, the V-$d_{yz}/d_{xz}$ electrons, which primarily contribute the quasi-one-dimensional Fermi surface, turns out to be fully orbital- and spin-polarized, akin to the case of a half metal. Our work lays a solid foundation on the potential applications utilizing altermagnetic properties in vanadium-based oxychalcogenides.
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All authors Chang-Chao Liu, Jing Li, Ji-Yong Liu, Jia-Yi Lu, Hua-Xun Li, Yi Liu, Guang-Han Cao

Materials Science

Machine Learning Approach to Predict the Curie Temperature of Fe- and Pt-Based Alloys

Svitlana Ponomarova, Oleksandr Ponomarov and Yurii Koval

Various techniques can be employed to determine the temperature of magnetic transformation, whether it be the Curie or Neel temperature. The standard procedure typically involves creating alloys with defined compositions and performing measurements experimentally. Alternatively, these temperatures can be predicted based on a material known physical and chemical properties prior to experiments. We identified an optimal feature set and selected the most effective algorithm. Our findings show that the Voting Ensemble model, when combined with Monte Carlo cross-validation, achieves the highest prediction accuracy. The normalized root mean squared error serves as the primary performance metric. For implementation, we utilize the Azure Machine Learning framework for its robust computational and integration capabilities. This approach offers an efficient and reliable strategy for designing and predicting the Curie temperature of ternary alloys. The paper also highlights potential applications of the model and its extensions for other systems.
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Materials Science

Polarization-Magnetization Coupling in Visible Light Ferroelectric Double Perovskites

Sathiyamoorthy Buvaneswaran, Trilochan Sahoo and Saurabh Ghosh

The bulk photovoltaic effect (BPVE), arising from broken inversion symmetry in ferroelectrics, offers a distinct pathway toward high-efficiency next-generation photovoltaics. We propose and investigate A/A$^\prime$-ordered double perovskites KLaFeMoO$_6$ and NaLaFeMoO$_6$ as promising single-phase ferroelectric photovoltaic (FE-PV) materials. First-principles calculations reveal robust P2$_1$ symmetry with A-site layer and B-site rock-salt ordering, accompanied by hybrid improper ferroelectricity driven by $a^{-}a^{-}c^{+}$ octahedral tilts. Both compounds exhibit significant spontaneous polarization and indirect band gaps of $\sim$ 1.8 eV, well suited for visible-light absorption ($>$10$^5$ cm$^{-1}$). Low carrier effective masses along the polar axis indicate efficient charge transport. Ab initio molecular dynamics simulations (AIMD) show that polarization-coupled magnetization switching is feasible above room temperature, making these materials suitable for room-temperature applications.
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Materials Science · Cross-listed from physics.app-ph

Local metamaterials and transition layers

Kimya Yadollahpour, Hossein Khodavirdi and Ankit Srivastava

In this paper, we elucidate the concept of local acoustic metamaterials. These are composites which exhibit equi-frequency contours (EFC) which correspond to those expected of homogeneous local acoustic media. We show that EFCs for local acoustic media are conics in 2-dimension and quadrics in 3-dimension. In 2-D, the sure signature of negative properties is if the conic is a hyperbola and in 3-D, the sure signature is the presence of hyperboloids. We note that metamaterial coupling (Willis coupling) has the potential of translating these conics and quadrics in the wave-vector plane but that it does not fundamentally change the shape of these geometries. The local effective properties assigned to a composite in such cases are dispersive (frequency dependent) and they satisfy causality considerations. We finally also show that such properties truly characterize the composite in the sense that they can be used to solve scattering problems involving different samples of the composite. We show that this is made possible through the consideration of transition layers. While the sharp-interface model incurs scattering errors exceeding 20% at oblique angles, the Drude-layer model restores agreement to within 2% without requiring integral-equation or multi-mode expansions, thereby offering a simple yet highly efficient route to accurate scattering predictions in resonant local acoustic metamaterials.
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Materials Science · Cross-listed from cond-mat.soft

Shape-controlled growth of two-dimensional kagome-lattice colloidal crystals through nanoparticle capping

Rui Huang, Jordan Austin-Frank Wilson, Allen Sun et al. (+2 more)

Organic capping ligands can selectively bind to crystal facets to modulate growth kinetics and are important in chemical synthesis of inorganic nanocrystals. Using the capping ligands for shape-controlled growth of colloidal crystals is challenging due to the size mismatch of molecules and nanoparticle building blocks. In existing synthetic pathways, colloidal crystal shapes are determined by their thermodynamically favored phases yet controlling their shapes independent of lattice symmetry is vital to study many solid-state properties. Here, we develop a nanoparticle capping strategy to control colloidal crystal shapes and structural heterogeneity. Au bipyramids were used as building blocks and assembled into rhombohedral colloidal crystals driven by DNA hybridization. In (111) planes of the crystals, bipyramids assembled into kagome lattices, featuring structure cavities organized in a hexagonal lattice. The rhombohedral crystals have truncated tetrahedral crystal habits, and the degree of truncation defines the exposed facets and crystal shapes. Our surface capping strategy is to introduce DNA-modified nanospheres as effective capping agents, which selectively register on the surface vacancies of the kagome facets and resemble the role of organic ligands in classic nanocrystal growth. Such selective capping is driven by maximizing DNA hybridization and leads to slower growth of the (111) kagome facets, changing the crystal shape from three-dimensional truncated tetrahedra to two-dimensional layered microplates with structural heterogeneity and shape anisotropy. This study underpins the importance of capping agents in colloidal crystal growth and inspires effective ways to control the growth kinetics and heterostructures of colloidal crystals.
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All authors Rui Huang, Jordan Austin-Frank Wilson, Allen Sun, Artemis Harlow, Zhiwei Li

Sunday 9 November

Materials Science · Cross-listed from quant-ph

A Hierarchy of Fibonacci Forbidden-Word Hamiltonians: From the Golden Chain to the Plastic Chain and Aperiodic Order

Marcelo Maciel Amaral

We introduce an infinite, scale-aligned hierarchy of one-dimensional, frustration-free Hamiltonians by forbidding the minimal forbidden factors of the Fibonacci word up to length $F_K$, the $K$-th Fibonacci number. The ground-state languages have exponential growth constants $\lambda_K$ that decrease monotonically, starting from the value associated with the “golden chain” (approximately 1.618) and progressing toward 1. This process yields a staircase of topological-entropy plateaus that flows to an aperiodic fixed point, also known as the Fibonacci subshift. The first nontrivial rung ($K=4$) is the “Plastic chain,” which forbids SS and LLL. We prove its ground-state counts follow a specific four-term linear recurrence relation and provide a closed-form solution governed by the plastic constant $\rho\approx 1.3247$. We propose an energy-entropy scaling where the energy penalty for each new forbidden pattern is proportional to the logarithmic ratio of the growth constants from the previous and current rungs, turning the sequence of projectors into an explicit renormalization-group flow from the initial high-entropy phase to the zero-entropy aperiodic fixed point. Algebraically, exact Temperley-Lieb braiding compatibility holds only at the base rung, $K=3$ (which forbids only SS); higher rungs define constrained aperiodic Hamiltonian codes rather than Temperley-Lieb representations. Small instances realized on a D-Wave quantum annealer match these predictions: $K=3$ is trivial, $K=4$ resolves a unit gap with moderate success, and $K\ge 5$ instances require reverse annealing to exceed $99\%$ success, clarifying reduction penalties and embedding variability.
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Materials Science · Cross-listed from cond-mat.mes-hall

High-quality nanostructured diamond membranes for nanoscale quantum sensing

Alexander Pakpour Tabrizi, Artur Lozovoi, Sean Karg et al. (+4 more)

Deploying nitrogen vacancy (NV) centers in diamond as nanoscale quantum sensors for condensed matter and materials physics requires placing the NV centers close to the sensing target. One solution is to fabricate diamond nanostructures and integrate them with materials and devices. However, diamond etching and ion milling can introduce subsurface damage and surface defects that degrade the charge stability and spin coherence of NV centers near the surface. Here we report a procedure for fabricating low-damage nanostructured diamond membranes, and we show that this fabrication scheme preserves the optical and spin properties of state-of-the-art shallow NV center quantum sensors, within nanometers of the diamond surface, while providing significant photonic enhancement. Furthermore, we demonstrate a pick-and-place transfer method, which enables integration with diverse sensing targets.
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All authors Alexander Pakpour Tabrizi, Artur Lozovoi, Sean Karg, Tecla Bottinelli Mondandon, Melody Leung, Kai-Hung Cheng, Nathalie P. de Leon

Materials Science · Cross-listed from cond-mat.soft

Thermal conductivity of commodity polymers under high pressures

Otavio Higino Moura de Alencar, James Mu, Marcus Müller et al. (+1 more)

Understanding the thermal conductivity of polymers under high-pressure conditions is essential for a range of applications, from aerospace and deep-sea engineering to common lubricants. However, the complex relationship between pressure, $P$, the thermal transport coefficient, $\kappa$, and polymer architecture poses substantial challenges to both experimental and theoretical investigations. In this work, we study the pressur-dependent thermal transport properties of a widely used commodity polymer – poly(methyl methacrylate) (PMMA) – using a combination of all-atom molecular dynamics simulations and semi-analytical approaches. While we report both classical and quantum-corrected estimates of $\kappa$, the latter approach reveals that as the pressure increases from 1 atm to 10 GPa, $\kappa$ rises by up to a factor of four – from 0.21 W m$^{-1}$ K$^{-1}$ to 0.80 W m$^{-1}$ K$^{-1}$. To better understand the mechanisms behind this increase, we disentangle the contributions from bonded and nonbonded monomer interactions. Our analysis shows that nonbonded energy-transfer rates increase by a factor of six over the pressure range, while bonded interactions show a more modest increase – about a factor of three. This observation further consolidates the fact that the nonbonded interactions play the dominant role in dictating the microscopic heat flow in polymers. These individual energy-transfer rates are also incorporated into a simplified heat diffusion model to predict $\kappa$. The results obtained from different approaches show internal consistency and align well with available experimental data. Additionally, some data for polylactic acid (PLA) are presented.
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All authors Otavio Higino Moura de Alencar, James Mu, Marcus Müller, Debashish Mukherji

Materials Science · Cross-listed from cond-mat.dis-nn

Machine learning intermolecular transfer integrals with compact atomic cluster representations

Keerati Keeratikarn, Christoph Ortner and Jarvist Moore Frost

Calculating intermolecular charge transfer integrals in organic semiconductors requires substantial computer resource for each individual calculation. We might alternatively construct a machine learning model for transfer integrals, which model the full six-degrees of freedom for the relative position of dimer pairs, trained on representative calculations for the molecules of interest. Recent developments have produced effective machine learning force fields, which model the total energy of atomic assemblies. We extend the Atomic Cluster Expansion (ACE) with the correct symmetries for transfer (kinetic-energy) integrals. Combined with a spherical harmonic basis makes, this forms a strong inductive bias and makes for a data efficient model. We introduce coarse-grained and heavy-atom representations, and assess the methodology on representative conjugated semiconductors: ethylene, thiophene, and naphthalene.
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Materials Science · Cross-listed from cond-mat.mes-hall

Facile Salt-Assisted Hydrothermal Synthesis of Nanodiamonds from CHO Precursors: Atomic-Scale Mechanistic Insights

Soumya Pratap Tripathy, Sayan Saha, Saurabh Kumar Gupta et al. (+14 more)

Hydrothermal synthesis offers an economical and scalable way to produce nanodiamonds under relatively mild, low-pressure and low-temperature conditions. However,its sustainability and the detailed mechanisms behind diamond formation in such environments are still not fully understood. In this work, we designed ten hydrothermal synthesis protocols using different CHO-based molecular precursors containing COOH and OH groups, such as organic acids, polyols, sugars, and polysaccharides.The reactions were carried out at 190 degrees Centigrade in chlorinated, strongly alkaline aqueous solutions with alkali and alkaline-earth metal ions. Using high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy, we confirmed the presence of diamond-specific lattice planes and sp3-hybridized carbon structures. Our results show that the type of precursor, its molecular size, and the ionic composition of the solution play key roles in determining the defect patterns and polymorph distribution in the resulting nanodiamonds. Atomic-scale imaging showed both coherent and incoherent transitions from graphite to diamond, along with gradual lattice compression and complex twinning patterns. These observations provide direct insight into how interfacial crystallography and defect dynamics drive diamond formation in aqueous systems. Overall, the study positions hydrothermal synthesis as a sustainable, chemistry-driven, and tunable approach for creating nanodiamonds tailored for applications in quantum technologies, biomedicine, catalysis, and advanced materials.
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All authors Soumya Pratap Tripathy, Sayan Saha, Saurabh Kumar Gupta, Pallavee Das, Binay Priyadarsan Nayak, Anup Routray, Priya Choudhary, Srihari V, Bitop Maitra, Ashna Reyaz, Anushka Samant, Debopriya Sinha, Kritideepan Parida, Kuna Das, Abhijeet Sahoo, Kunal Pal, Sirsendu Sekhar Ray

Materials Science

Decoupling interface and thickness effects on hydrogen absorption in V/MgO: experiments and DFT

Qiuxiang Zhang, Yan Zhu, Xiaofang Peng et al. (+3 more)

We report combined experimental and first principles investigations of hydrogen absorption in epitaxial vanadium films on MgO(001) with nominal thicknesses of 10 nm and 50 nm. In - situ optical transmission and four - probe resistance isotherms show that the 50 nm film reproduces bulk like behavior with a clear first order alpha-beta hydride transition, the formation enthalpy and entropy gradually decrease with increasing hydrogen concentration. The 10 nm film, by contrast, displays continuous uptake without plateaus, with formation enthalpies H that are relatively close in magnitude to the 50 nm film (both exhibiting exothermic behavior in the range of approximately 0.5 to 0.3 eV/H), but with a more negative entropy change S (larger S) indicating reduced configurational freedom for hydrogen in the ultrathin limit; the critical temperature for phase coexistence is suppressed below 400 K. Density functional theory calculations on MgO V superlattices (Vn/(MgO)n, n = 3,5,7) reveal pronounced V 3d and O 2p hybridization and interfacial charge redistribution that weaken hydrogen binding near the interface and recover toward bulk values with increasing V thickness. These results indicate that interfacial electronic structure, in addition to finite size energetics, governs hydride stability in ultrathin V films and that layer - thickness and interface engineering can tune reversible hydrogen uptake.
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All authors Qiuxiang Zhang, Yan Zhu, Xiaofang Peng, Weiguang Yang, Yuping Le, Xiao Xin

Materials Science

Magnetic and structural properties of epitaxial Er-substituted yttrium iron garnet films grown by pulsed laser deposition

Lukas Flajsman, Lars Peeters, Armi Kosunen et al. (+3 more)

Er-substituted yttrium iron garnet (Er:YIG) holds the potential of combining the low magnetic damping of YIG with the telecom-band optical transitions of $\text{Er}^{3+}$ ions, making it a suitable material for hybrid optomagnonic devices and microwave-to-optical quantum transduction. We report the epitaxial growth of $\text{Er}_{x}\text{Y}_{3-x}\text{Fe}_{5}\text{O}_{12}$ films with $x=0.008-0.20$ on (111)-oriented gadolinium gallium garnet (GGG) substrates using pulsed laser deposition. X-ray diffraction, reciprocal space mapping, and scanning transmission electron microscopy confirm single-phase, fully coherent growth with atomically sharp interfaces across the entire substitution range. Magnetometry reveals a gradual decrease in saturation magnetization with increasing Er content, consistent with antiparallel coupling between Er$^{3+}$ spins and the net Fe$^{3+}$ moments, along with the emergence of an in-plane uniaxial magnetic anisotropy. The ferromagnetic resonance broadens with Er concentration due to increased Gilbert damping and inhomogeneous linewidth broadening. Films with low Er content ($x=0.008$), most relevant for optomagnonic applications, retain nearly isotropic magnetization and exhibit a damping parameter only slightly higher than that of undoped YIG. These results identify growth and substitution conditions that preserve YIG's low-loss magnetic properties while introducing optical functionality, establishing Er:YIG as a viable platform for hybrid quantum magnonics and microwave-to-optical transduction.
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All authors Lukas Flajsman, Lars Peeters, Armi Kosunen, Lide Yao, Ionela Vrejoiu, Sebastiaan van Dijken

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

Modeling the precipitation distribution by radius and pore size during drying of an impregnated sphere

N.V. Peskov

The process of preparing heterogeneous catalysts on porous supports includes a drying stage, in which the porous material, impregnated with an aqueous solution of the catalyst precursor, is dried, and the precursor is precipitated on the pore walls. The precipitate distribution throughout the support volume strongly influences the catalyst performance and durability within industrial reactors. This paper presents a mathematical model for simulating the precipitation distribution during the drying of a porous sphere. Examples of calculations are given demonstrating the influence of some parameters on the distribution by space and by pore size.17
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Materials Science

Phonon-Dominated Thermal Transport and Large Violation of the Wiedemann-Franz Law in Topological Semimetal CoSi

Luyao Zhong, Xin Jin, Mingquan He et al. (+4 more)

The Wiedemann-Franz (WF) law, relating the electronic thermal conductivity ($\kappa_{\rm e}$) to the electrical conductivity, is vital in numerous applications such as in the design of thermoelectric materials and in the experimental determination of the lattice thermal conductivity ($\kappa_{\rm L}$). While the WF law is generally robust, violations are frequently observed, typically manifesting in a reduced Lorenz number ($L$) relative to the Sommerfeld value ($L_0$) due to inelastic scattering. Here, we report a pronounced departure from the WF law in the topological semimetal CoSi, where the electronic Lorenz number ($L_{\rm e}$) instead rises up to $\sim40\%$ above $L_0$. We demonstrate that this anomaly arises from strong bipolar diffusive transport, enabled by topological band-induced electron-hole compensation, which allows electrons and holes to flow cooperatively and additively enhance the heat current. Concurrently, we unveil that the lattice contribution to thermal conductivity is anomalously large and becomes the dominant component below room temperature. As a result, if $\kappa_{\rm L}$ is assumed negligible – as conventional in metals, the resulting $L$ from the total thermal conductivity ($\kappa_{\rm tot}=\kappa_{\rm L}+\kappa_{\rm e}$) deviates from $L_0$ by more than a factor of three. Our work provides deeper insight into the unconventional thermal transport physics in topological semimetals.
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All authors Luyao Zhong, Xin Jin, Mingquan He, Rui Wang, Xiaoyuan Zhou, Tianqi Deng, Xiaolong Yang

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

Do Discrete Fine-Scale Mechanical Models with Rotational Degrees of Freedom Homogenize Into a Cosserat or a Cauchy Continuum?

Jan Eliáš and Gianluca Cusatis

This article answers the question of whether homogenization of discrete fine-scale mechanical models, such as particle or lattice models, gives rise to an equivalent continuum that is of Cauchy-type or Cosserat-type. The study employs the machinery of asymptotic expansion homogenization to analyze discrete mechanical models with rotational degrees of freedom commonly used to simulate the mechanical behavior of heterogeneous solids. The proposed derivation has general validity in both stationary (steady-state) and transient conditions (assuming wavelength much larger that particle size) and for arbitrary nonlinear, inelastic fine-scale constitutive equations. The results show that the unit cell problem is always stationary, and the only inertia term appears in the linear momentum balance equation at the coarse scale. Depending on the magnitude of the local bending stiffness, mathematical homogenization rigorously identifies two limiting conditions that correspond to the Cauchy continuum and the Cosserat continuum. A heuristic combination of these two limiting conditions provides very accurate results also in the transition from one limiting case to the other. Finally, the study demonstrates that cases for which the Cosserat character of the homogenized response is significant are associated with non-physically high fine-scale bending stiffness and, as such, are of no interest in practice.
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Materials Science · Cross-listed from math.DS

A Bilayer Cathode Design Procedure for Li ion Batteries Using the Multilayer Doyle-Fuller-Newman Model (M-DFN)

E. C. Tredenick, A. M. Boyce, R. Drummond et al. (+1 more)

Heterogeneities in lithium ion batteries can be significant factors in electrode under utilisation and degradation while charging. Bilayer electrodes have been proposed as a convenient and scalable way to homogenise the electrode response. In this paper, the design of a bilayer cathode for Li-ion batteries composed of separate layers of lithium nickel manganese cobalt oxide (NMC622) and lithium iron phosphate (LFP) is optimised using the multilayer Doyle-Fuller-Newman (M-DFN) model. Changes to the carbon binder domain, electrolyte volume fraction, and tortuosity provided the greatest control for improving Li-ion charge mobility. The optimised bilayer design was able to charge at 3C between 0-90% SOC in 18.6 minutes, achieving 4.4 mAh/cm2. Comparing the optimal bilayer to the LFP-only electrode, the bilayer achieved 41% higher capacity. Through mechanistic physics-based modelling, it was shown that the 3C charging improvement of the optimised bilayer was achieved by enabling a more homogeneous current density distribution through the thickness of the electrode and electrolyte depletion prevention. The findings were confirmed on a high-fidelity X-ray computed tomography (CT) based microstructural model. The results illustrate how modelling can be used to rapidly search novel electrode designs
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All authors E. C. Tredenick, A. M. Boyce, R. Drummond, S. R. Duncan

Saturday 8 November

Materials Science

Transition from MOS to Ideal Capacitor Behavior Triggered by Tunneling in the Inversion Population Regime

Pedro Pereyra

An analytical solution to the nonlinear Poisson equation governing the inversion layer in metal-oxide-semiconductor (MOS) structures has recently been obtained, resolving a fundamental challenge in semiconductor theory first identified in 1955. This breakthrough enables the derivation of explicit expressions for relevant physical quantities, such as the inversion-layer width, electric potential, and charge distribution, as functions of gate voltage $V_G$, distance from oxide-semiconductor interface and impurity concentration. These quantities exhibit rapid variation during early-stage inversion but saturate once the gate voltage exceeds the threshold voltage by a few tenths of a volt signaling a transition in the MOS response to $V_G$. The onset of tunneling through the Esaki barrier leads to increased charge accumulation near the interface, reshaping the charge distribution into a two-dimensional profile and shifting the potential drop from the semiconductor to the oxide layer. This reconfiguration resembles the behavior of an ideal parallel-plate capacitor, with charge confined at the interface and the voltage drop localized across the oxide. We analyze this mechanism in detail and demonstrate, through explicit calculations, that the tunneling current through the Esaki-like barrier formed during inversion becomes dominant, effectively superseding classical inversion behavior. These results offer a new analytical foundation for quantum-aware device modeling and inform the design of next-generation MOSFET and tunneling FET architectures.
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Materials Science

Targeted synthesis of polycrystalline vanadium dioxide thin films via post-deposition annealing

Kirill Trunov, Yuri Lebedinskii, Ilya Zavidovskiy et al. (+6 more)

Implementation of neuromorphic hardware is a promising way to improve the computing efficiency and decrease the energy consumption of artificial neural networks. For this purpose, electronic elements emulating the behavior of synapses and neurons have to be developed. In order to realize electronic artificial neurons, threshold resistive switches or memristors can be efficiently used. One of the most widespread materials for threshold switches is vanadium dioxide due to its property to demonstrate the metal-insulator transition at a temperature about 70 {\deg}C. However, the processes of VO$_{2}$ synthesis are quite restrictive in temperature and gas atmosphere conditions, which hinders its integration into CMOS fabrication. In this work, we propose a new method of VO$_{2}$ synthesis: reactive pulsed laser deposition from metallic V target in oxygen atmosphere at room temperature, followed by vacuum annealing. Our method enables target synthesis of an appropriate VO$_{2}$ phase in a polycrystalline thin film form by finely tuning oxygen pressure during room temperature deposition, which allows to relax the equipment demands, such as high temperature heating in oxygen. Successful targeted VO$_{2}$ synthesis under fabrication conditions close to back-end-of-line CMOS production, achieved in this work, show the way toward its large-scale microelectronic integration for neuromorphic hardware creation.
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All authors Kirill Trunov, Yuri Lebedinskii, Ilya Zavidovskiy, Sergey Novikov, Alexander Morozov, Petr Shvets, Ksenia Maksimova, Andrei Zenkevich, Anton Khanas

Materials Science

Strain-Tunable Spin Filtering and Valley Splitting Coexisting with Anomalous Hall Effect in 2D Half-Metallic VSe2/VN Heterostructure: Toward a Unified Spintronic-Valleytronic Platform

Vivek Chowdhury and Ahmed Zubair

Rapid progress in valleytronics and spintronics is limited by the scarcity of two-dimensional materials that simultaneously provide robust valley splitting and strong spin selectivity. Here we showed that a van der Waals heterostructure (VSe2/VN) built from hexagonal VSe2 and hexagonal VN addressed this gap. Using first-principles density functional theory, phonon, ab initio molecular dynamics stability tests, Bader charge analysis, and Wannier-based Berry-curvature calculations, we demonstrated an energetically and dynamically stable heterostructure that exhibited interlayer charge transfer and a work function intermediate between the constituent monolayers. The electronic structure showed small indirect PBE gap (108.9 meV), with HSE06 indicating a half-metallic tendency; a sizable conduction-band valley splitting (\Delta CKK' = 22.9 meV for spin-up and \Delta CKK' = 61.3 meV for spin-down); and pronounced spin asymmetry, where the spin-down channel showed a wide semiconducting gap (0.64 eV) while the spin-up channel was nearly gapless. These features yielded a high zero-strain spin-filter efficiency P = 75.4%, tunable to 82.5% under +4% biaxial tensile strain. The heterostructure also supported non-zero, valley-contrasting Berry curvature, and a large anomalous Hall conductivity (peak sigmaxy = 568.33 S/cm). Importantly, mean-field estimation placed the ferromagnetic Curie temperature near room temperature at zero strain (Tc = 284.04 K), while Tc decreased to 183.9 K at +4% strain, the magnetic order remained robust to cryogenic temperatures, providing a beneficial tuning knob to balance spin-filter performance with thermal stability in device-relevant regimes. These results identified VSe2/VN as a practical, strain-tunable platform for integrated valleytronic, spintronic devices, and for exploring anomalous Hall and valley-dependent transport phenomena.
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Materials Science · Cross-listed from physics.optics

Unveiling architectural and optoelectronic synergies in lead-free perovskite/perovskite/kesterite triple-junction monolithic tandem solar cells

Md. Faiaad Rahman, Md. Ashaduzzaman Niloy, Ehsanur Rahman et al. (+1 more)

The widespread use of lead-based materials in tandem solar cells raises critical environmental and health concerns due to their inherent toxicity and risk of contamination. To address this challenge, we focused on lead-free tandem architectures based on non-toxic, environmentally benign materials such as tin-based perovskites and kesterites, which are essential for advancing sustainable photovoltaic technologies. In this study, we present the proposition, design, and optimization of two distinct lead-free monolithic tandem solar cell architectures - an all-perovskite dual-junction device employing potassium tin iodide (KSnI3) and formamidinium tin triiodide (FASnI3) as absorbers for the top and bottom subcells, respectively, and a triple-junction monolithic tandem structure incorporating KSnI3, FASnI3, and Ag-doped copper zinc tin selenide (ACZTSe) as absorbers for the top, middle, and bottom subcells, respectively. We simulated the optical and electrical characteristics of these devices using the finite-difference time-domain and finite element methods, explicitly considering radiative, non-radiative, and surface recombination mechanisms. The optimized all-perovskite dual-junction solar cell achieved a power conversion efficiency (PCE) of 27.3%, with short-circuit current density (Jsc) of 14.74 mA/cm2, open-circuit voltage (Voc) of 2.227 V, and fill factor (FF) of 83.14%. Conversely, the optimized triple-junction hybrid perovskite-kesterite architecture secured an elevated PCE of 30.69%, along with Jsc of 13.184 mA/cm2, Voc of 2.766 V, and FF of 84.18%. These findings reveal the strong potential of lead-free perovskite and kesterite material based absorbers in promoting high-performance hybrid tandem solar cells, highlighting their importance in advancing sustainable and efficient photovoltaic technologies.
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All authors Md. Faiaad Rahman, Md. Ashaduzzaman Niloy, Ehsanur Rahman, Ahmed Zubair

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

Effects of crystal field and momentum-based frustrated exchange interactions on multiorbital square skyrmion lattice

Yan S. Zha and Satoru Hayami

Motivated by recent theoretical predictions of a square-shaped skyrmion lattice (S-SkL) in centrosymmetric tetragonal Ce-based magnets [Yan Zha and Satoru Hayami, Phys. Rev. B 111, 165155 (2025)], we perform a comprehensive theoretical investigation into the role of multiorbital effects and momentum-based frustrated exchange interactions in stabilizing such topologically nontrivial magnetic textures. By employing self-consistent mean-field calculations over a broad range of model parameters, we demonstrate that the cooperative interplay among interorbital coupling, frustrated exchange interactions at higher-harmonic wave vectors, and crystal-field-induced anisotropy is crucial for the stabilization of the S-SkL. Furthermore, the competition between the easy-plane intraorbital anisotropy and the easy-axis interorbital anisotropy leads to a significant enhancement of the S-SkL stability region. We also identify a rich variety of multi-$Q$ states, including a topologically nontrivial S-SkL state with a slight breaking of fourfold rotational symmetry (S-SkL$'$), magnetic bubble lattices (MBLs), and double-$Q$ phases with a local/net scalar chirality. Our findings elucidate the microscopic mechanism responsible for the emergence of S-SkLs in prototypical Ce-based magnets and provide a route toward realizing skyrmion lattices in a broader class of $f$-electron materials beyond conventional Gd- and Eu-based systems lacking orbital angular momentum.
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