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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Tuesday 11 November

Materials Science

Sliding properties of Transition Metal Dichalcogenide bilayers

Pier Luigi Silvestrelli, S. Subashchandrabose, Alberto Ambrosetti et al. (+1 more)

Transition-metal dichalcogenides (TMDs) are valuable as solid lubricants because of their layered structure, which allows for easy shearing along the basal planes. Using Density Functional Theory (DFT) we conducted a first-principles study of the sliding properties of several TMD bilayers: MoS$_2$, MoTe$_2$, WS$_2$, WSe$_2$, VS$_2$, VSe$_2$, TaS$_2$, TaSe$_2$, TiS$_2$, TiSe$_2$, HfS$_2$, ZrS$_2$, MoS$_2$WS$_2$, MoS$_2$VS$_2$. Given the crucial role of van der Waals (vdW) interactions in accurately describing the interlayer interactions in TMD bilayers, we employed vdW-corrected DFT functionals. Our research confirms the dominance of vdW effects by estimating the fraction of interlayer binding energy attributable to these interactions. We also examined how the choice of different vdW-corrected DFT functionals might influence quantitative results. Using MoS$_2$ as a reference TMD bilayer system, we found that most other TMD bilayers studied exhibit stronger interlayer bonds and greater corrugation. However, TiSe$_2$ shows a profile similar to MoS$_2$, while, interestingly, TiS$_2$, VS$_2$, and ZrS$_2$ are characterized by weaker bonding and lower corrugation than MoS$_2$. We explored relationships between various properties of TMD bilayers, with a particular focus on potential connections between tribological and electronic properties often characteristic of solid interfaces. To this end, we evaluated adhesion energies, work of separation, charge density redistributions in interface regions, differential charge densities, and corrugation. While corrugation and thus resistance to sliding generally tends to increase with the size of the chalcogen element and is typically proportional to the adhesion energy, the relationships between other structural, energetic, and electronic properties do not follow a single, well-defined trend.
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All authors Pier Luigi Silvestrelli, S. Subashchandrabose, Alberto Ambrosetti, Maria Clelia Righi

Materials Science · Cross-listed from astro-ph.EP

Remanent crustal strain on Mars in non-poikilitic olivine of NWA 7721

Yaozhu Li, Szilvia Kalácska, Phil McCausland et al. (+5 more)

We present a multiscale microstructural analysis of olivine from the non-poikilitic lithology of the poikilitic shergottite NWA 7721, using dark-field X-ray microscopy (DFXM), electron backscatter diffraction (EBSD), and context in situ 2D micro-XRD. A single olivine crystal contains two distinct subgrain populations. Type 1 subgrains are fine (1-5 micrometers), randomly oriented, and nearly strain-free, whereas Type 2 subgrains are coarse (greater than 30 micrometers), aligned, and strongly strained. Layered DFXM data reveal slip-band features in Type 2 that are absent in Type 1. We interpret Type 1 as products of shock-induced recrystallization, whereas Type 2 preserves remnants of a highly deformed parent grain. This bimodal microstructure, not observed in other Martian meteorites including the paired NWA 1950 and ALH A77005, points to a heterogeneous response to impact influenced by pre-existing strain in the olivine grain. We propose that NWA 7721 olivine experienced substantial crustal or magmatic stress before impact. The subsequent shock wave imposed a rapid load-release cycle that mobilized dislocations and produced low-angle boundaries in Type 2, while driving recrystallization of Type 1. Grain-growth constraints limit the post-shock heating duration to approximately 2.3 s, consistent with rapid quenching. These results provide the first evidence that non-poikilitic olivine in NWA 7721 preserves dynamic crustal deformation on Mars in the Late Amazonian.
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All authors Yaozhu Li, Szilvia Kalácska, Phil McCausland, Roberta L. Flemming, Callum Hetherington, Bo Zhao, Can Yildirim, Carsten Detlefs

Materials Science

Effect of W in Cu-Zr-W thin films: Molecular dynamics simulations and experimental verification

Hassan Ataalite, Jiri Houska, Deepika Thakur et al. (+2 more)

We investigate the effects of W incorporation into Cu-Zr thin film metallic glasses using molecular dynamics (MD) simulations combined with magnetron sputtering. All studies are carried out in the whole range of W concentrations (0 to 100 at. %) and the MD studies also in a wide range of incident energies (1 to 500 eV) and deposition angles (0 to 60{\deg}). Calculated X-ray diffractograms, packing factor, short-range order (bonding fractions and coordination numbers), medium-range order (network ring and common neighbor statistics) and stress are correlated with measured X-ray diffractograms and properties (hardness, hardness/Young's modulus ratio and elastic recovery). The simulations explain the experimental results at the atomic level and provide a lot of information that is not available experimentally. Special attention is paid to non-monotonic dependencies on the elemental composition and incident energy. Collectively, the results explain the role of W in modifying the structure and improving the mechanical performance of Cu-Zr metallic glasses, predict optimum compositions which maximize some of the mechanical properties, and contribute to the development of advanced materials for various applications.
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All authors Hassan Ataalite, Jiri Houska, Deepika Thakur, Michaela Cervena, Petr Zeman

Materials Science

Ferroelectric Order and Enhanced Interfacial Superconductivity in Lightly-Doped Quantum Paraelectric KTa$_{1-x}$Nb$_x$O$_3$

F. Yang and L. Q. Chen

Ferroelectric quantum criticality in perovskite oxides offers a fertile ground for emergent collective phenomena. Here we develop a first-principles-inspired quantum-statistics-based theoretical analysis of the ferroelectric order and interfacial superconductivity in lightly-doped quantum paraelectric, niobium (Nb)-doped KTaO$_3$. We demonstrate that local distortions induced by the doped Nb atoms beyond its quantum critical composition induce a long-range ferroelectric order. The predicted dielectric properties quantitatively agree with the experimental measurements over the entire temperature range from the symmetry-broken ferroelectric phase across the phase transition to the paraelectric region. As the same soft phonon mode that governs dielectric behavior provides the essential pairing channel for interfacial superconductivity of KTaO$_3$, we predict a pronounced enhancement of this superconductivity on (111) surface when the system is tuned to its quantum-critical composition via Nb doping, providing a concrete avenue for experimental verification. This finding establishes ferroelectric quantum criticality as a unique design principle for engineering enhanced superconductivity and discovering emergent quantum phases in polar oxide heterostructures, explicitly suggesting that similar materials-tuning strategies (e.g., epitaxial strain) could be exploited to enhance superconductivity in quantum paraelectric systems.
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Materials Science

Self-induced marginality in plastically deformed crystals

Oguz Umut Salman, Aylin Ahadi and Lev Truskinovsky

Quasi-brittle plastic yielding is a salient feature of well-annealed glassy materials. Here we show that the same behavior is characteristic of perfect crystals after they experience mechanically driven elastic instability leading to massive nucleation of dislocations. We argue that such 'preparation' effectively converts an atomic configuration from crystalline to quasi-amorphous. To understand the nature of the subsequent intermittent mechanical response we study a model 2D crystal subjected to AQS driving and show that both pre- and post-yield dislocation avalanches exhibit power law statistics with similar exponents indicative of self-induced marginal stability.
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Materials Science

Excitonic shift current induced broadband THz pulse emission efficiency of layered MoS2 crystals

Neetesh Dhakar and Sunil Kumar

Following the ultrafast photoexcitation of a semiconductor, it embodies competing dynamics among photocarriers, many-body transient states of highly energetic excitons, and electron-hole liquid. Here, we show that femtosecond optical pulse excitation induces transient excitonic shift current contributing to stronger THz emission from a single crystalline bulk MoS2 at low temperatures. The control of dominating excitonic shift current is elucidated from excitation density dependent experiments at varying temperatures. A strong decrease in the excitonic contribution beyond a critical fluence of 150microJ/cm^2 is observed at a very low temperature of 20K. This behavior suggests the formation of a new quantum condensate, i.e., the electron-hole liquid, in the regime when the exciton density is overwhelmingly large that the average spacing between exciton pairs is comparable to the exciton radius. Furthermore, the exciton density dependent THz emission at varying temperatures is consistent with the Varshni model and the crystal Debye temperature of 260K.
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Materials Science

Suppression of magnetism in Co$_3$Sn$_2$S$_2$ under external pressure

A. Chmeruk, D. Jones, R. Balducci et al. (+13 more)

The ability to control the magnetic state provides a powerful means to tune the underlying band topology, enabling transitions between distinct electronic phases and the emergence of novel quantum phenomena. In this work, we address the evolution of ferromagnetic state upon applying external pressures up to 10.8~GPa using a combined experimental and theoretical study. The standard ab initio Density Functional Theory computation including ionic relaxations grossly overestimates the unit cell magnetization as a function of pressure. In our theoretical analysis we identify two possible mechanisms to remedy this shortcoming. Matching the experimental observations is achieved by a symmetry-preserving adjustment of the sulfur atoms position within the unit cell. Alternatively, we explore various combinations of the exchange and correlation parts of the effective potential which reproduce the experimental magnetization, the structural parameters and the measured optical conductivity spectra. Thus, the pressure-dependent behavior of magnetization demands a careful theoretical treatment and analysis of theoretical and experimental data.
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All authors A. Chmeruk, D. Jones, R. Balducci, J. Ebad-Allah, F. Beiuşeanu, F. Schilberth, M. A. Kassem, U. Schade, A. Veber, L. Puskar, Y. Tabata, T. Waki, H. Nakamura, C. A. Kuntscher, A. Östlin, L. Chioncel

Materials Science

On the Role of Interlayer Electrons on the Frictional Behavior of Two-Dimensional Electrides

Jingcheng Qi, Giuliana Materzanini, Gian-Marco Rignanese et al. (+2 more)

Friction accounts for up to 30% of global energy consumption, underscoring the urgent need for superlubricity in advanced materials. Two-dimensional (2D) electrides are layered materials with cationic layers separated by 2D confined electrons that act as anions. This study reveals the unique frictional properties of these compounds and the underlying mechanisms. We establish that interlayer friction correlates with the cationic charges and sliding-induced charge redistribution. Remarkably, the 2D electride Ba2N stands out for its lower interlayer friction than graphene, despite its stronger interlayer adhesion, defying conventional tribological understanding. This anomalous behavior arises from electron redistribution as the dominant energy dissipation pathway. Combining ab initio calculations and deep potential molecular dynamics (DPMD) simulations, we show that incommensurate twisted interfaces (2{\deg} < {\theta} < 58{\deg}) in Ba2N achieve structural superlubricity by suppressing out-of-plane buckling and energy corrugation. Notably, a critical normal load of 2.3 GPa enables barrier-free sliding in commensurate Ba2N ({\theta} = 0{\deg}), with an ultralow shear-to-load ratio of 0.001, suggesting the potential for superlubricity. Moreover, electron doping effectively reduces interlayer friction by controllably modulating stacking energies in 2D electrides. These findings establish 2D electrides as a transformative platform for energy-efficient tribology, enabling scalable superlubricity through twist engineering, load adaptation, or electrostatic gating. Our work advances the fundamental understanding of electron-mediated friction, with Ba2N serving a model system for cost-effective, high-performance material design.
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All authors Jingcheng Qi, Giuliana Materzanini, Gian-Marco Rignanese, Maria Clelia Righi, Junjie Wang

Materials Science

Non-destructive 3D characterization of microtextured regions in the bulk of Ti-6Al-4V alloy

Mads Carlsen, Xiaohan Zeng, Haixing Fang et al. (+4 more)

In this study we present spatially resolved texture and orientation maps from a cube-shaped sample of Ti-6Al-4V alloy, reconstructed by means of texture tomography (TT). Unlike grain resolved 3DXRD techniques which require "spotty" diffraction patterns, TT can reconstruct local (voxelized) orientation distribution function (ODFs) from continuous diffraction patterns collected in a 3D scanning procedure. Reconstructions of the same sample, scanned in two different settings and subsequent EBSD analysis parallel to one of the sample faces show excellent mutual agreement and validate the single-axis data collection and reconstruction procedure for this class of materials. The reconstruction reveals the presence and the 3D shape of several micro-textured regions, showing a sharp unimodal texture of the $\alpha$-phase with a clear link of the orientation and spatial alignment of these zones to the rolling, transverse and normal directions of the rolled material.
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All authors Mads Carlsen, Xiaohan Zeng, Haixing Fang, Moritz Frewein, Tilman A. Grünewald, Joao Quinta da Fonseca, Wolfgang Ludwig

Materials Science

Attosecond-resolved coherent control of zone-folded acoustic phonons in silicon carbide

Hiromu Matsumoto, Tsukasa Maruhashi, Yosuke Kayanuma et al. (+3 more)

Zone-folded acoustic phonons (6 THz) in 4H silicon carbide (SiC) have been coherently excited using a femtosecond near-infrared pulse and measured through transient reflectivity with a pump and probe protocol. Their amplitude is coherently controlled with 300-attoseconds precision and the results show interference fringe patterns due to electronic and phonon interference. The results are well reproduced by a model calculation with two electronic and phonon levels and an impulsive stimulated Raman process. Using the model, we obtain the analytical form of the coherent control scheme at an off-resonant condition.
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All authors Hiromu Matsumoto, Tsukasa Maruhashi, Yosuke Kayanuma, Yadong Han, Jianbo Hu, Kazutaka G. Nakamura

Materials Science

Tuning Stability of AB3-Type Alloys by Suppressing Magnetism

Hung Ba Tran, Toyoto Sato, Ryuhei Sato et al. (+3 more)

Hydrogen is a promising clean energy carrier, yet effective and reversible storage remains challenging. AB3-type intermetallic alloys are promising for solid-state hydrogen storage due to intermediate thermodynamic stability and rapid hydrogen uptake. Optimizing stability and gravimetric density is hindered by competing thermodynamic and magnetic effects. Here, we analyze AB3 compounds (A = Ca, Y, Mg; B = Co, Ni) and ternary alloys CaxYyMg1-x-yB3 using first-principles calculations and Monte Carlo simulations. We find a direct correlation between formation energy and total magnetic moment that dictates alloy stability, explaining the trade-off in hydrogen storage. In Co-rich systems with large lattice volumes, formation energy rises with magnetization, showing magnetism as the dominant factor. Mg-rich compositions achieve high gravimetric densities, but strong magnetism destabilizes the system, requiring Y substitution to suppress magnetic moments. Replacing Co with Ni weakens magnetism: YNi3 is nonmagnetic, while CaNi3 and MgNi3 are weakly polarized, allowing thermodynamic stability across compositions. Notably, CaMg2Ni9 combines high theoretical capacity (3.32 wt%) with good reversibility. Mg-rich Ni-based alloys are predicted to offer negative formation energies with the highest gravimetric densities (up to 3.40 wt%). These results show that controlling magnetism via transition-metal substitution is key to overcoming the stability-capacity trade-off in AB3 hydrogen storage materials.
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All authors Hung Ba Tran, Toyoto Sato, Ryuhei Sato, Hiroyuki Saitoh, Shin-ichi Orimo, Hao Li

Materials Science

Implementation and application of a DFT$+U$$+V$ approach within the all-electron FLAPW method

Wejdan Beida, Gustav Bihlmayer, Christoph Friedrich et al. (+3 more)

We present an implementation of the density-functional theory DFT$+U$$+V$ formalism within the all-electron full-potential linearized augmented-plane-wave (FLAPW) method as implemented in the FLEUR code. The DFT$+U$$+V$ formalism extends DFT, supplemented by the onsite Coulomb interaction $U$, to address local correlation effects in localized states by incorporating intersite Coulomb interaction terms $V$. It holds promise for improving charge and bond disproportionation, charge and orbital ordering, charge density wave formation, charge transfer, and the intersite correlation resulting from hybridization between states of neighboring sites in a solid. $U$ and $V$ parameters are obtained from first principles using the constrained random-phase approximation (cRPA) employing two different atom basis representations to project the screened Coulomb interaction: the Wannier and the muffin-tin basis functions. We investigate in detail the impact of the $V$ term for typical covalently bonded materials like graphene, for bulk semiconductors such as silicon and germanium, and for charge-transfer insulators like NiO. Our results demonstrate an improvement in accuracy of specific properties across these systems, providing a framework for describing materials with different interaction regimes. We compare our DFT$+U$$+V$ results using our cRPA parameter sets with (i) previous DFT$+U$$+V$ calculation employing pseudopotential approximations, (ii) with experimental results and (iii) with our $GW$ results.
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All authors Wejdan Beida, Gustav Bihlmayer, Christoph Friedrich, Gregor Michalicek, Daniel Wortmann, Stefan Blügel

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

High and Magnetic-field-dependent Surface Carriers Mobility in 3D Topological Insulators without Bulk States

M. V. Pugachev, A. E. Borisov, A. V. Shupletsov et al. (+3 more)

By applying the conventional two-liquid model to the magnetoresistivity tensor, we reveal a record-high carrier mobility for surface states in tetradymite topological insulators ($\sim$ 20000 cm$^2$/Vs) in both bulk crystals and thin flakes of Sn-Bi$_{1.1}$Sb$_{0.9}$Te$_2$S. Bulk crystals of this 3D topological insulator exhibit a transition from bulk to surface-dominated conductivity below 100 K, whereas in thin flakes, bulk conductivity is suppressed at even higher temperatures. Our data therefore suggest that a key ingredient for elevated mobility is the absence of bulk carriers at the Fermi level. A fingerprint of the high-mobility carriers, i.e a steep low-field magnetoresistance along with a strong Hall effect nonlinearity below 1 T, signifies the presence of at least two surface-related carrier species, even when bulk states are frozen out. To explain the magnetoresistance and the Hall effect in a wider range of magnetic fields ($>1$ T), one must assume that the carrier mobility drops with the field. The influence of Zeeman splitting on mobility and the contribution of anomalous Hall conductivity provide a much better description of the magnetoresistance and the nonlinearity of the Hall coefficient. Our data call for a revision of the surface state mobility in 3D topological insulators.
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All authors M. V. Pugachev, A. E. Borisov, A. V. Shupletsov, V. O. Sakhin, E. F. Kukovitsky, A. Yu. Kuntsevich

Materials Science

Inhomogeneous dynamic state in the double trillium lattice antiferromagnet KBaFe$_2$(PO$_4$)$_3$

S. J. Sebastian, S. S. Islam, R. Kolay et al. (+11 more)

The three-dimensional (3D) magnet KBaFe$_2$(PO$_4$)$_3$ hosts a double-trillium lattice of Fe$^{3+}$ (spin, $S=5/2$) ions offering a prototypical platform to study the frustration induced effects in 3D. Through magnetization, specific heat, $^{31}$P nuclear magnetic resonance (NMR), and muon spin relaxation ($\mu$SR) experiments, supported by first principles calculations, we uncover an unconventional ground state. Despite strong antiferromagnetic interactions with a large Curie-Weiss temperature $\theta_{\rm CW} = -70(2)$ K, no magnetic long-range order is observed down to 30 mK. Below $T^{\ast}\simeq 3.5$ K, the NMR linewidth becomes nearly field-independent and the spin-spin relaxation rate $1/T_2$ saturates, accompanied by an inhomogeneous distribution of transverse nuclear magnetization $M_{xy}$. The latter indicates the emergence of short-range dynamical correlations, which was further corroborated by a robust and field-insensitive broad maximum in specific heat. In $\mu$SR, we detect neither a static internal field nor spin freezing; instead the relaxation remains dynamic and is best described by two coexisting dynamic relaxation channels: a dominant fast (sporadic) channel and a slower Markovian component. Their differing weights and fluctuation rates suggest microscopic inhomogeneity in spin dynamics. Altogether, KBaFe$_2$(PO$_4$)$_3$ exemplifies a rare high-spin stochiometric 3D antiferromagnet that evades ordering and instead fosters a mosaic of spin dynamics driven by strong geometric frustration intrinsic to the trillium lattice.
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All authors S. J. Sebastian, S. S. Islam, R. Kolay, S. Mohanty, Q. P. Ding, Y. Skourski, J. Sichelschmidt, M. Baenitz, Jonas A. Krieger, T. J. Hicken, H. Luetkens, A. A. Tsirlin, Y. Furukawa, R. Nath

Materials Science

Short-range order influences H distribution in Fe-Ni-Cr austenitic stainless steels

Tianyu Su, Brian J. Blankenau, Namhoon Kim et al. (+4 more)

Hydrogen embrittlement (HE) in austenitic stainless steels is advanced by hydrogen enhanced localized plasticity (HELP), typically accompanied by a transition from homogeneous to localized slip. Short-range order (SRO) in face-centered cubic (FCC) alloys is known to promote slip planarity, and recent studies suggest that H may amplify this localization behavior linked to inherent SRO. However, the manner in which the introduction of H affects SRO properties and, conversely, the manner that pre-existing SRO may affect H behavior, are not fully understood. In this work, a spin cluster expansion model combined with Monte Carlo simulation is employed to study the interplay between H and SRO in Fe-Ni-Cr alloys. Chemical order is quantified using Warren-Cowley SRO parameters, and the model predictions are validated against experimental data. We find that the presence of H only slightly alters the intrinsic ordering preference of the Fe-Ni-Cr alloys. As temperature decreases and the alloy evolves from disordered to ordered thermodynamic states, distinct H-metal correlations emerge. In particular, H-Ni and H-Cr pairs exhibit stronger ordering tendencies than H-Fe pairs, suggesting a selective affinity of H for certain atomic environments. On the other hand, we also find that compared to random alloys, when pre-existing SRO is present, it significantly affects the resulting H distribution by promoting local H enrichment in SRO domains. Such SRO-driven local H accumulation may facilitate slip localization and contribute to the early onset of embrittlement. These findings provide thermodynamic and structural insights into the interaction between H and SRO in austenitic stainless steels, highlighting possible implications on how the interaction between HELP and SRO brings about hydrogen embrittlement in austenitic stainless steels.
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All authors Tianyu Su, Brian J. Blankenau, Namhoon Kim, Kshitij Vijayvargia, Petros Sofronis, Jessica A. Krogstad, Elif Ertekin

Materials Science · Cross-listed from eess.IV

Deep generative priors for robust and efficient electron ptychography

Arthur R. C. McCray, Stephanie M. Ribet, Georgios Varnavides et al. (+1 more)

Electron ptychography enables dose-efficient atomic-resolution imaging, but conventional reconstruction algorithms suffer from noise sensitivity, slow convergence, and extensive manual hyperparameter tuning for regularization, especially in three-dimensional multislice reconstructions. We introduce a deep generative prior (DGP) framework for electron ptychography that uses the implicit regularization of convolutional neural networks to address these challenges. Two DGPs parameterize the complex-valued sample and probe within an automatic-differentiation mixed-state multislice forward model. Compared to pixel-based reconstructions, DGPs offer four key advantages: (i) greater noise robustness and improved information limits at low dose; (ii) markedly faster convergence, especially at low spatial frequencies; (iii) improved depth regularization; and (iv) minimal user-specified regularization. The DGP framework promotes spatial coherence and suppresses high-frequency noise without extensive tuning, and a pre-training strategy stabilizes reconstructions. Our results establish DGP-enabled ptychography as a robust approach that reduces expertise barriers and computational cost, delivering robust, high-resolution imaging across diverse materials and biological systems.
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All authors Arthur R. C. McCray, Stephanie M. Ribet, Georgios Varnavides, Colin Ophus

Materials Science

Control of Spontaneous Orientation Polarization in Organic Semiconductors: The Role of Molecular Structure and Film Growth Conditions

Albin Cakaj, Markus Schmid, Alexander Hofmann et al. (+1 more)

Spontaneous orientation polarization (SOP) occurs when molecules with a finite permanent dipole moment are grown as thin films by physical vapor deposition and their alignment is such that a net non-zero polarization remains. We discuss how SOP in organic semiconductors can be controlled by the design of molecules as well as the film growth conditions and discuss its relevance in organic light-emitting devices.
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All authors Albin Cakaj, Markus Schmid, Alexander Hofmann, Wolfgang Brütting

Monday 10 November

Materials Science · Cross-listed from cs.CL

Large language models in materials science and the need for open-source approaches

Fengxu Yang, Weitong Chen and Jack D. Evans

Large language models (LLMs) are rapidly transforming materials science. This review examines recent LLM applications across the materials discovery pipeline, focusing on three key areas: mining scientific literature , predictive modelling, and multi-agent experimental systems. We highlight how LLMs extract valuable information such as synthesis conditions from text, learn structure-property relationships, and can coordinate agentic systems integrating computational tools and laboratory automation. While progress has been largely dependent on closed-source commercial models, our benchmark results demonstrate that open-source alternatives can match performance while offering greater transparency, reproducibility, cost-effectiveness, and data privacy. As open-source models continue to improve, we advocate their broader adoption to build accessible, flexible, and community-driven AI platforms for scientific discovery.
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Materials Science

Nanorod Pair Complexes Manipulated via Magnetic Casimir Forces

S Pal, L. M. Woods, C. Persson et al. (+3 more)

Controlling nanoscale interactions to suppress aggregation from short-range attractive forces is a key problem in nanoengineering. Here, we demonstrate a route to modulate Casmir-Lifshitz interactions between anisotropic nanoparticles with the magnetic fluids. By semi-classical quantum electrodynamics, we study ground state dispersion forces for cylindrical dielectric nanorods made of polystyrene (PS), and zinc oxide (ZnO) embedded in toluene-based host media with gold-coated magnetite nanoparticles and also predict magnetic contributions to the non-retarded excited state interaction. The variation in magnetic permeability enables tuning between repulsive and attractive interaction and a thermally unstable and measurable magnetic Casimir traps are predicted between a pair of ZnO-PS nanoparticles whose equilibrium position can be modulated over an order of magnitude with a small variation in the size of the magnetite nanoparticle. This provides an alternative magnetic Casimir-effect pathway to reversibly tune quantum electromagnetic forces at the nanoscale for assembly and enhancement of colloidal stability.
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All authors S Pal, L. M. Woods, C. Persson, I. Brevik, U. De Giovannini, M. Boström

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

Magnetic structure evolution and magnetoelastic coupling across the spin reorientation transition in TmCrO3

Vishesh Sharma, Gaurav Gautam, Poonam Yadav et al. (+5 more)

We present a comprehensive study of the magnetic structure evolution across the spin reorientation transition in orthorhombic (Pnma) TmCrO3. Magnetic susceptibility reveals canted antiferromagnetic (CAFM) ordering at T_N = 125 K, two compensation points (T_comp1 and T_comp2), followed by magnetization reversal with a magnetic susceptibility minimum between T_comp1 and T_comp2. Heat capacity shows a sharp lambda-type transition at T_N, associated with the long-range antiferromagnetic ordering of Cr, followed by a broad feature near 9 K. Neutron powder diffraction (NPD) establishes the Pn'm'a (Gamma2) magnetic structure below T_N. A gradual change in magnetic structure occurs during the spin-reorientation (SRO) transition below 30 K, where the magnetic symmetry transforms from Pn'm'a (Gamma2) to Pn'ma' (Gamma4) phase. However, below the SRO, neither Gamma2 nor Gamma4 alone adequately fit the intensity of magnetic reflections. A satisfactory refinement is achieved using the monoclinic subgroup P21'/c', derived from a combination of Gamma2 and Gamma4. The gradual SRO of Tm and Cr moments across the compensation regime is consistent with the magnetic symmetry P21'/c'. Furthermore, the ordered moments of Cr and Tm in TmCrO3 exhibit a complex, non-monotonic temperature dependence, with the Tm sublattice driving the spin-reorientation transition near the compensation point. Anomalies in the lattice parameters reveal strong magnetoelastic coupling, linking structural distortions to the SRO.
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All authors Vishesh Sharma, Gaurav Gautam, Poonam Yadav, Chin-Wei Wang, Kaya Wei, N. P. Lalla, Theo Siegrist, Shivani Sharma

Materials Science

Coexistence of Ferroelectric and Relaxor-like Phases in a Multiferroic Solid Solution (1-x)Pb(Fe$_{1/2}$Nb$_{1/2}$)O$_3$-xPbMnO$_3$

Anna N. Morozovska, Victor N. Pavlikov, Yuriy O. Zagorodniy et al. (+7 more)

Experimental and theoretical studies of unusual polar, dielectric and magnetic properties of room temperature multiferroics, such as perovskites Pb(Fe$_{1/2}$Nb$_{1/2}$)O$_3$ (PFN) and Pb(Fe$_{1/2}$Ta$_{1/2}$)O$_3$ (PFT), are very important. We study the phase composition, dielectric, ferroic properties of the solid solutions PFN and PFT substituted with 5, 10, 15, 20 and 30 % of Mn ions prepared by the solid-state synthesis. The XRD analysis confirmed the perovskite structure of sintered ceramics. Electric measurements revealed the ferroelectric-type hysteresis of electric charge in pure PFN ceramics and in PFN ceramics substituted with (10 - 30)% of Mn. At the same time, the PFN-5% Mn ceramics did not show any ferroelectric properties due to very high conductivity.Temperature dependences of the dielectric permittivity of PFN-10% Mn and PFN-15% Mn ceramics have two pronounced maxima, one of which is relatively sharp and has a weak frequency dispersion; another is diffuse and has a strong frequency dispersion. A further increase in the Mn content up to 20% leads to the right shift in the paraelectric-ferroelectric phase transition temperature, as well as to the strong suppression of the second wide maximum, which transforms into a small diffuse shoulder. An increase in the Mn substitution up to 30% leads to a significant decrease in the dielectric permittivity, left shift of its maximum, and induces a pronounced frequency dispersion of the paraelectric-ferroelectric transition temperature, which is inherent to relaxor-like ferroelectrics.Comparison of the model with experiments reveal the coexistence of the ordered ferroelectric-like and disordered relaxor-like phases in the multiferroic solid solutions PFN-Mn and PFT-Mn.
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All authors Anna N. Morozovska, Victor N. Pavlikov, Yuriy O. Zagorodniy, Iryna V. Kondakova, Oleksandr S. Pylypchuk, Andrii V. Bodnaruk, Oksana V. Leshchenko, Myroslav V. Karpets, Roman O. Kuzian, Eugene A. Eliseev

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

Effect of shape on void growth: A coupled Extended Finite Element Method (XFEM) and Discrete Dislocation Plasticity (DDP) study

Muhammad Usman, Sana Waheed and Aamir Mubashar

Voids are one of the many material defects present at the microscopic length scale. They are primarily responsible for the formation of cracks and hence contribute to ductile fracture. Circular voids tend to deform into elliptical voids just before their coalescence to form cracks. The principle aim of this study is to investigate the effect of void shape on the micro-mechanism of void growth by using Discrete Dislocation Plasticity simulations. For voided crystals, conventional DDP produces a continuous slip step throughout the material even if a dislocation escapes from a non-convex domain. To overcome this issue, the Extended Finite Element Method (XFEM) is used here to incorporate the displacement discontinuity. Different aspect ratios of elliptical voids are considered under uniaxial and biaxial deformation boundary conditions. The results suggest that voids having the largest surface area tend to have maximum growth rate as compared to void with lower surface area, i.e. "larger is faster". Under biaxial loading, a higher magnitude of strain hardening, and void growth rate are observed as compared to uniaxial loading. The results also suggest that the orientation of slip planes as well as voids, affect the overall plastic behavior of the voided-ductile material. Furthermore, circular void tends to induce minimum growth rate but have the maximum strain hardening effect as compared to other void shapes under both loading conditions. The results of this study provide a deeper understanding of ductile fracture with applications in manufacturing industry, aerospace industry and in the design of nano/micro-electromechanical devices i.e. NEMS/MEMS.
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Materials Science

Oxygen vacancies in vanadium dioxide: A DFT$+V$ study

Oskar Leibnitz, Peter Mlkvik, Nicola A. Spaldin et al. (+1 more)

We present a density-functional theory study of the effects of oxygen vacancies on the structural and electronic properties of vanadium dioxide (VO$_2$). Our motivation is the reported suppression of the metal-insulator transition by oxygen vacancies and the lack of a clear consensus on its origin. We use the DFT$+V$ method with a static intersite vanadium-vanadium interaction term, $V$, to calculate the properties of the oxygen-deficient metallic rutile and insulating monoclinic M1 phases of VO$_2$ on the same footing. We find that oxygen vacancies induce local distortions in the M1 phase, but do not destroy the dimerization usually associated with the insulating behavior. In spite of this, we find that the M1 phase becomes metallic as a result of the partial filling of the conduction band due to a rigid-band-like doping effect.
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All authors Oskar Leibnitz, Peter Mlkvik, Nicola A. Spaldin, Claude Ederer

Materials Science

A Linear-Scaling, Charge-Aware Foundation Potential for Atomistic Simulations

Tsz Wai Ko, Runze Liu, Adesh Rohan Mishra et al. (+3 more)

Electrostatics govern charge transfer and reactivity in materials. However, most foundation potentials (FPs) either neglect explicit electrostatic interactions or come at prohibitive computational cost. Here, we introduce charge-equilibrated TensorNet (QET), an equivariant, charge-aware architecture that achieves linear scaling with system size via an analytically solvable charge-equilibration scheme. We demonstrate that a trained QET FP matches state-of-the-art FPs on materials property benchmarks but delivers qualitatively different predictions in systems dominated by electrostatic interactions. The QET FP reproduces the correct structure and density of the NaCl-CaCl2 ionic liquid and the crystallization of Ge1Sb2Te4 phase change memory, which charge-agnostic FPs miss. We further show that a fine-tuned QET captures reactive processes at the Li/Li6PS5Cl solid-electrolyte interface and supports simulations under applied electrochemical potentials. These results remove a fundamental constraint in large-scale atomistic simulations of electrostatics and establish a general, data-driven framework for charge-aware FPs with transformative applications in energy storage, catalysis, and beyond.
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All authors Tsz Wai Ko, Runze Liu, Adesh Rohan Mishra, Zihan Yu, Ji Qi, Shyue Ping Ong

Materials Science

Domain Walls and Defects in Ferroelectric Inorganic Halide Perovskites CsGeX$_3$ (X = Cl, Br, I)

Kristoffer Eggestad, Benjamin A. D. Williamson and Sverre M. Selbach

Among all-inorganic halide perovskites, the only known ferroelectrics are the family of CsGeX$_3$ (X = Cl, Br, I). Here, we study their ferroelectric domain walls (DWs) and common point defects by density functional theory (DFT) calculations and investigate the interplay between DWs and defects. The most stable defects are V$_{\text{X}}$ and V$_{\text{Cs}}$ and the former shows low migration barriers and high mobility. In contrast to oxide ferroelectrics, the affinity between point defects and DWs is negligible, reflecting the subtle structural distortions at CsGeX$_3$ DWs. Concomitantly, the formation energies and migration energy barriers of CsGeX$_3$ DWs are small compared to oxides, and neither V$_{\text{X}}$ nor V$_{\text{Cs}}$ pin migrating DWs. The band gap invariance across DWs and the lack of affinity towards intrinsic charged point defects imply that conducting DWs for nanoelectronics may be challenging to realise in CsGeX$_3$. However, shallow $p$-type defect levels and low hole effective masses suggest that high $p$-type conductivity may be achievable in nominally ferroelectric CsGeX$_3$. The low DW migration energy barriers and insignificant DW pinning by point defects make CsGeX$_3$ promising materials as robust soft ferroelectrics for high-frequency switching applications with low energy dissipation.
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Materials Science

A Strain-Engineered 0D/1D Heterojunction of InVO4/Cu-TbFeO3 for High- Selectivity CO2 Photoreduction

Muneeb ur Rahman

The catalytic CO2 photoreduction to CO is significantly hindered by the pervasive kinetic bottleneck of *CO-desorption and inefficient charge separation. Surpassing the conventional single photocatalytic strategy, herein, a multi-synergetic 0D/1D S-scheme heterojunction by precisely assembling 0D InVO4 nanoparticles on 1D Cu-doped TbFeO3 (IVO/CTFO). This nano-heterojunction is rationally designed at multiple steps where Cu2+ substitution at the Fe3+ site induces a compression in lattice strain and oxygen vacancies (VO), acting as electron traps and CO2 chemisorption sites, which breaks spin-polarization of pristine TbFeO3 to facilitate multichannel charge flow. The 0D/1D strategy couples the maximum surface active-sites and short charge diffusion routes with directional charge migration. Moreover, a 0D/1D lattice mismatch creates a built-in electric field at the interface, resulting in an enhanced lifetime (64.70 ns) of charged species, an efficient CO yield (65.75 mmole g-1.h-1), and high selectivity (95.93%). DFT calculations and experimental findings confirmed the Fermi level shift toward the conduction band and the existence of spin-hybridization. Operando-DRIFTS and the free-energy diagram unveil a H+ mediated mechanism at the interface, alongside a reduction in energy barrier for CO2 photoreduction from *COOH to *CO. Thus, this study presents an excellent approach that integrates defect-engineering, strain-compression, and interfacial design in advancing solar fuels production.
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Materials Science

Effect of Misfit and Threading Dislocations on Surface Energies of PbTe-PbSe Interfaces

Emir Bilgili, Nicholas Taormina, Yang Li et al. (+3 more)

This work quantifies the effect of misfit and threading dislocations on the surface energies of PbTe-PbSe interfaces, with the defect structures of the interfaces being obtained from atomistic and multiscale simulations of their manufacturing processes. Simulation results show that direct bonding produces semi-coherent interfaces with two-dimensional misfit dislocation networks, while heteroepitaxial processes produce complex three-dimensional dislocation structures with both misfit and threading dislocations. Surface energies at these interfaces were determined by computing the interaction energies across these interfaces. Compared with coherent interfaces, directly bonded interfaces exhibit up to ~23% lower surface energy, while the surface energies of epitaxially grown interfaces can be nearly 50% lower. The results demonstrate the significant effects of dislocations on interfacial energy.
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All authors Emir Bilgili, Nicholas Taormina, Yang Li, Adrian Diaz, Simon R. Phillpot, Youping Chen

Materials Science

Defect-Mediated Phase Engineering of 2D Ag at the Graphene/SiC Interface

Arpit Jain, Boyang Zheng, Sawani Datta et al. (+23 more)

Atomically thin silver (Ag) films offer unique opportunities in plasmonic, quantum optics, and energy harvesting, yet conventional growth methods struggle to achieve structural control at the monolayer limit. Here, we demonstrate phase-selective synthesis of large-area, crystalline 2D Ag films via defect-engineered confinement heteroepitaxy (CHet) at the epitaxial graphene/silicon carbide (EG/SiC) interface. By tuning graphene growth and post-growth defect introduction, two distinct Ag phases are achieved with disparate properties: a nearly commensurate Ag(1) lattice stabilized by vacancy and line defects in epitaxial graphene, and a denser Ag(2) phase preferentially grown with sp3-rich zero-layer graphene. Structural and spectroscopic characterization confirm lattice registry with the SiC substrate, while theoretical calculations reveal a thermodynamic preference for Ag(2) but an easier nucleation for Ag(1). Both phases are found to be semiconducting, with the Ag(2) phase exhibiting slightly enhanced n-doping of graphene. Notably, nonlinear optical measurements reveal a three-order magnitude difference in second-order susceptibility between the two phases, demonstrating promise for phase-tunable 2D metals in reconfigurable optoelectronic and metamaterial platforms.
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All authors Arpit Jain, Boyang Zheng, Sawani Datta, Kanchan Ulman, Jakob Henz, Matthew Wei-Jun Liu, Van Dong Pham, Wen He, Chengye Dong, Li-Syuan Lu, Alexander Vera, Nader Sawtarie, Wesley Auker, Ke Wang, Bob Hengstebeck, Zachary W. Henshaw, Shreya Mathela, Maxwell Wetherington, William H. Blades, Kenneth Knappenberger, Ursula Wurstbauer, Su Ying Quek, Ulrich Starke, Shengxi Huang, Vincent H. Crespi, Joshua A. Robinson

Materials Science

Cathodoluminescence, light injection and EELS in STEM: From comparative to coincidence experiments

Luiz H. G. Tizei, Yves Auad, Florian Castioni et al. (+1 more)

Electron spectroscopy implemented in electron microscopes provides high spatial resolution, down to the atomic scale, of the chemical, electronic, vibrational and optical properties of materials. In this review, we will describe how temporal coincidence experiments in the nanosecond to femtosecond range between different electron spectroscopies involving photons, inelastic electrons and secondary electrons can provide information bits not accessible to independent spectroscopies. In particular, we will focus on nano-optics applications. The instrumental modifications necessary for these experiments are discussed, as well as the perspectives for these coincidence techniques.
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All authors Luiz H. G. Tizei, Yves Auad, Florian Castioni, Mathieu Kociak

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

Effect of uniaxial stress on helimagnetic phases in the square-lattice itinerant magnet EuAl$_{4}$

Masaki Gen, Takuya Nomoto, Hiraku Saito et al. (+5 more)

We investigate uniaxial-stress effects on the magnetic phase diagram of the square-lattice itinerant magnet EuAl$_{4}$, where strong coupling among spin, lattice, and charge produces a variety of helimagnetic phases, including rhombic and square skyrmion lattices. Combining resistivity and magnetization measurements with neutron scattering, we find that compressive stresses of only several tens of megapascal along [010] enhance antiferromagnetic character and shorten the magnetic modulation period in the lowest-temperature single-Q spiral state, thereby driving the critical temperatures and fields of multiple phases to higher values. First-principles calculations show that increasing orthorhombic lattice distortion deforms the Fermi surface relevant to the magnetism, providing compelling evidence that Fermi-surface nesting plays a crucial role in stabilizing the helical magnetic modulations in EuAl$_{4}$.
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All authors Masaki Gen, Takuya Nomoto, Hiraku Saito, Taro Nakajima, Yusuke Tokunaga, Rina Takagi, Shinichiro Seki, Taka-hisa Arima