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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Friday 15 May

Materials Science

Rapid Atmospheric Vapor Deposition of H:In2O3 Transparent Conducting Oxide Thin Films

Xiaoyu Guo, Hae-Jun Seok, Eilidh L. Quinn et al. (+14 more)

Transparent conducting oxides (TCOs) are essential for the optoelectronics industry, but there is a critical gap in cost-effective methods to rapidly deposit low sheet resistance, high transmittance films without damaging delicate materials, including emerging soft semiconductors like metal-halide perovskites. In this work, atmospheric pressure chemical vapor deposition (AP-CVD) is used to synthesise H:In2O3 films with 7.20+/-0.01 Ohm/sq sheet resistance (0.50+/-0.06 mOhm.cm resistivity) and transmittance up to 89% in the near-infrared (NIR), surpassing commercial sputter-deposited indium tin oxide. The growth rate is 40x higher than atomic layer deposition (ALD), and the AP-CVD films are fully processed under atmospheric conditions at only 140 C. Comparison of secondary ion mass spectrometry and time-of-flight elastic recoil detection analysis with changes in carrier concentration indicate that H dopants are introduced from the water oxidant. There is an increase in mobility form 40+/-10 cm2/Vs to 160+/-30 cm2/Vs when changing from O2 to H2O as the oxidant, which is attributed to H dopants passivating oxygen vacancies that act as carrier scattering centers. This work establishes AP-CVD as a promising method for manufacturing high figure-of-merit TCOs in a rapid, scalable and cost-effective manner, using mild growth conditions compatible with thermally-sensitive materials.
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All authors Xiaoyu Guo, Hae-Jun Seok, Eilidh L. Quinn, Matthew K Sharpe, Callum. D. McAleese, Yi-Teng Huang, Xinjuan Li, Kexue Li, Chia-Yu Chang, Yongjie Wang, John O'Sullivan, Katie L. Moore, Caterina Ducati, Ruy Sebastian Bonilla, Han-Ki Kim, Abderrahime Sekkat, Robert L. Z. Hoye

Materials Science

Thermal conductivity of seifertite and pyrite-type SiO$_2$: A comparative study

Doyoon Park, Yihang Peng and Jie Deng

Thermal conductivity is a fundamental material property that plays a crucial role in understanding the dynamics and evolution of planetary interiors. Despite its importance, the thermal conductivity of seifertite and pyrite-type SiO$_2$ remains unknown. Here, we calculate the lattice thermal conductivities of seifertite and pyrite-type SiO$_2$ using the Green-Kubo method based on molecular dynamics (MD) simulations driven by two machine learning potentials (MLPs) constructed from the SCAN and PBEsol exchange-correlation functionals, with $\textit{ab initio}$-level accuracy. To demonstrate our methodology, we also compute thermal conductivities using the phonon quasiparticle approach for comparison. Overall, the Green-Kubo method predicts up to 119 % higher thermal conductivity with a temperature dependence close to $T^{-1}$, as it fully captures diffusion-like phonons at high temperatures that are missed by the phonon quasiparticle approach. The 19 % reduction in thermal conductivity across the phase transition from seifertite to the pyrite-type phase suggests the potential formation of a thermally insulating layer in the mantle of super-Earths.
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Materials Science

Causation-guided mechanism identification and interpretable reduced-order modeling of damage-driving grain-boundary stress in creep

Weichen Kong, Yanwei Dai, Yinling Zhang et al. (+1 more)

GB local stress is central to the initiation and evolution of long-term creep damage in polycrystalline superalloys. Owing to the high-dimensional nonlinear relationships between the GB stress response and multiple crystallographic, microstructural, and micromechanical characteristics, it remains challenging to identify the key characteristics governing GB stress and to elucidate their mechanisms of influence. Dislocation-climb-affected crystal-plasticity finite-element simulations of minimal grain clusters are combined with an integrated causation-guided machine-learning framework, in which mechanics-informed descriptors are analyzed by causation entropy (CE) to identify governing mechanisms and then distilled into a reduced-order regression form for interpretable prediction of GB normal stress. Unlike conventional black-box surrogate models, the proposed framework combines physically meaningful descriptors, CE-based mechanism identification, and an explicit compact regression form, enabling the dominant physical variables and their effects on GB normal stress to be directly interpreted. Among 18 physically motivated characteristics, the GB inclination angle, the slip transmission, the climb-related Schmid-type indicator, and the elastic-modulus mismatch are found to be dominant, revealing the coupled roles of interfacial geometry, crystallographic compatibility, creep stress relaxation, and micromechanical contrast. The identified characteristics hierarchy and functional representation remain effective under multiaxial loading and can be extended to tricrystal systems through physically interpretable nonlocal augmentation when a purely local description becomes insufficient, demonstrating strong physical consistency and robust generalizability across physical conditions.
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All authors Weichen Kong, Yanwei Dai, Yinling Zhang, Yinghua Liu

Materials Science

Long-range magnetic ordering and structural phase transition in disordered high-entropy spinel chromites

Sushanta Mandal, Koushik Chakraborty, Isha et al. (+4 more)

High-entropy spinel oxides provide an excellent platform for investigating entropy-stabilized correlated systems with strong configurational disorder. In this work, we systematically study the temperature evolution of the structural and magnetic properties of Cr-based high-entropy spinels with compositions $(Mn_{0.2}Co_{0.2}Ni_{0.2}Cu_{0.2}Zn_{0.2})Cr_2O_4$ and $(Mg_{0.2}Co_{0.2}Ni_{0.2}Cu_{0.2}Zn_{0.2})Cr_2O_4$. Our results reveal that both systems crystallize in cubic structure with space group \textit{$Fd\overline{3}m$} at room temperature. Each system undergoes antiferromagnetic ordering below the Néel temperatures $ T_N$ = 49 K and 35 K, respectively. Neutron diffraction measurements confirm the emergence of long-range magnetic order with spiral spin arrangement. Both systems exhibit a structural phase transition from cubic \textit{$Fd\overline{3}m$} to orthorhombic Fddd symmetry at approximately 55 K and 85 K, respectively. Notably, despite the significant chemical disorder at the A site, both systems undergo transitions analogous to those observed in low entropy spinel systems. This behavior suggests that high configurational entropy may promote global structural stabilization despite local chemical disorder, thereby preserving long-range orderings and the characteristic symmetry-breaking transitions of the pristine spinel systems.
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All authors Sushanta Mandal, Koushik Chakraborty, Isha, Arvind Kumar Yogi, S. D. Kaushik, Sourav Marik, Tirthankar Chakraborty

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

Machine learning potential as a guide for eutectic in ultra-refractory multicomponent ceramics

V.E. Valiulin, A.V. Mikheyenkov, N.M. Chtchelkatchev et al. (+1 more)

The experimental determination of eutectic points is a long-established and widely used technique, but it is generally only practical for systems with relatively low melting points. Many modern, promising materials, however, are ultra-refractory, with melting points exceeding 3000 K. For these systems, conventional melting experiments become prohibitively expensive and technically challenging. Advanced AI modeling can serve as a powerful precursor to guide successful experimentation in such cases. This work proposes a novel criterion for determining the eutectic point concentration in ultra-refractory alloys. The approach is verified using the Ti-B-C system - the most thoroughly studied three-component refractory system to date. The core of the algorithm is a machine-learning interatomic potential, based on a neural network, which achieves accuracy comparable to ab initio methods. Crucially, the algorithm operates effectively in the liquid phase, eliminating the need for information about the solid alloy's crystalline structure to estimate eutectic points.
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All authors V.E. Valiulin, A.V. Mikheyenkov, N.M. Chtchelkatchev, E.A. Levashov

Materials Science

Charge Transfer from Perovskite Quantum Dots to Multifunctional Ligands with Tethered Molecular Species

Mariam Kurashvili, Lena S. Stickel, Jordi Llusar et al. (+6 more)

Perovskite quantum dots (pQDs) are promising materials for optoelectronic and photocatalytic applications due to their unique optical properties. To enhance charge carrier extraction or injection donor/acceptor molecules can be tethered to the pQD. These molecules must strongly bind to the ionic surfaces of pQDs without compromising colloidal stability. These we achieve by using multifunctional ligands containing a quaternary ammonium binding group for strong pQDs surface attachment, a long tail group for colloidal stability, and a functional group near the pQD surface. Such pQDs with ferrocene-functionalized ligands show fast photoexcited hole transfer with near-unity efficiency. Density functional theory calculations reveal how ferrocene's molecular structure reorganizes following hole transfer, affecting its charge separation efficiency. This approach can also be extended to in photoexcited electron and energy transfer processes with pQDs. Therefore, this strategy offers a blueprint for creating efficient QD-molecular hybrids for applications like photocatalysis.
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All authors Mariam Kurashvili, Lena S. Stickel, Jordi Llusar, Christian Wilhelm, Fabian Felixberger, Ivana Ivanović-Burmazović, Ivan Infante, Jochen Feldmann, Quinten A. Akkerman

Materials Science

Fuzzy band structure of quantum dots by Bloch Orbital Expansion, unconventional insights into geometry-electronic structure relations

Zeger Hens, Jordi Llusar and Ivan Infante

The extension of ab-initio methods like density functional theory (DFT) to quantum dot (QD) geometries has enabled researchers to explore relationships between QD surface termination and electronic structure. However, fully utilizing the data from DFT requires novel classification methods for QD orbitals. Here, we identify relationships between QD geometry and electronic structure by transforming real-space QD orbitals into momentum-space using Bloch orbital expansion (BOE), yielding a fuzzy QD band structure. Comparing with bulk band structures, we show that truncated, unpassivated facets in III-V and II-VI QDs produce mid-gap orbitals derived from bulk surface orbitals; an identification challenging in real space. QDs with reconstructed facets, however, feature delocalized orbitals formed by superposition of bulk Bloch orbitals. Moreover, we prepare for the first time atomistic core/shell QD models and by the BOE expansion we can clearly identify the core/shell band alignment not possible in real space. These findings emphasize BOE as a vital tool for connecting computational and experimental insights in nanocrystal research.
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Materials Science

A practical Laser-Heated Diamond Anvil Cell synthesis technique and recovery workflow for metastable MnSb2 and YbZn2 phases

S. Huyan, R. F. S. Penacchio, D. Zhang et al. (+5 more)

The creation and exploration of new materials under extreme pressure-temperature conditions has become increasingly reliant on laser-heated diamond anvil cell (LHDAC) techniques, which provide direct access to previously unexplored regions of multinary phase diagrams. Whereas numerous high-pressure phases have been identified in situ, systematic recovery and post-synthesis physical property characterization of these materials remain significant challenges. In this work, we present the development of an integrated LHDAC synthesis and demonstrate a practical LHDAC-based synthesis workflow that enables stabilization and recovery of metastable intermetallic phases for subsequent structural and transport studies. Using this approach, we successfully achieved LHDAC synthesis of high-pressure MnSb2 and YbZn2 phases under moderate pressures. Synchrotron X-ray diffraction and spatial mapping confirm dominant formation of the targeted phases, whereas laboratory-based refinement quantifies phase fractions despite intrinsic microstrain and minor secondary phases. High-pressure transport measurements on recovered samples reveal tunable by pressure electronic instabilities in both systems. In MnSb2, pressure suppresses two high-temperature magnetic ordering anomalies, observed in transport, by 5 GPa and for higher pressures induces a new low-temperature feature that increases with further pressure increase. In hexagonal high-pressure YbZn2, an electronic reconstruction emerges at ~11 GPa, characterized by semiconducting-like behavior from ~ 30 K to 300 K and a broad low-temperature coherence crossover near 30 K. Our results establish LHDAC synthesis not only as a structural discovery tool, but also as an experimental platform for investigating correlated quantum states stabilized far from equilibrium thermodynamic conditions.
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All authors S. Huyan, R. F. S. Penacchio, D. Zhang, Z. Li, S. L. Morelhão, Raquel Ribeiro, P. C. Canfield, S. L. Bud'ko

Materials Science

Interfacial Reconstructions and Engineering in III-V@II-VI Core-Shell Quantum Dots

Jordi Llusar, Abdessamad El Adel, Luca De Trizio et al. (+3 more)

In core/shell quantum dots (QDs), the interface between semiconductors of different chemical character largely determines their optoelectronic properties. In III-V/II-VI systems, this boundary involves pronounced chemical and electronic discontinuities that can generate trap states even under complete surface passivation. Using density functional theory on atomistic models of InAs/CdSe QDs, we systematically reconstruct atomic arrangements at the surface and interface to evaluate how local coordination and interfacial dipoles influence the electronic structure. Abrupt interfaces induce charge imbalance and band-gap collapse, whereas introducing an alloyed interlayer that mixes core and shell atoms and vacancies restores energetic alignment and yields delocalized band-edge states, consistent with experimental findings. We also introduce a charge-flow analysis that quantifies charge redistribution across the QD, providing a framework for realistic modeling of interlayer formation and predictive design of defect-free interfaces in core@shell architectures.
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All authors Jordi Llusar, Abdessamad El Adel, Luca De Trizio, Liberato Manna, Zeger Hens, Ivan Infante

Materials Science

Benchmarking empirical and machine-learned interatomic potentials using phase diagram predictions for Lead

Tom Hellyar, Pascal T. Salzbrenner, Peter I. C. Cooke et al. (+3 more)

We compare the predicted phase behaviour of lead (Pb) using three different interatomic potential models, including an embedded atom method (EAM), a modified embedded atom method (MEAM), and a neural network-based machine-learned model in the form of an ephemeral data-derived potential (EDDP). Using nested sampling and replica-exchange nested sampling simulations, we computed thermodynamic and structural properties at pressures up to 60 GPa, mapping both melting behaviour and solid-phase stability. Both the EAM and MEAM models predict the face-centred cubic (FCC) phase to remain stable up to approximately 60 GPa. In contrast, the EDDP model captures the experimentally-observed FCC-to-hexagonal close-packed (HCP) transition at around 15 GPa. These results highlight the importance of training data and model flexibility in accurately describing high-pressure phase behaviour, and demonstrate the effectiveness of nested sampling as a robust framework for exploring phase stability in materials. Particularly, the combination of nested sampling with modern machine-learned interatomic potentials - delivering near ab initio accuracy at tractable cost - opens the door to truly predictive and exhaustive exploration. EDDPs trained on diverse, out-of-equilibrium configurations appear particularly well suited to this task, offering a robust and transferable framework for unbiased phase discovery.
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All authors Tom Hellyar, Pascal T. Salzbrenner, Peter I. C. Cooke, Chris J. Pickard, Scott Habershon, Livia B. Pártay

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

Tunable Crossed Andreev Reflection in Bipolar Magnetic Semiconductors

Polireddi Naveen and Abhiram Soori

Crossed Andreev reflection (CAR) is a nonlocal quantum transport phenomenon that arises at the interface between a superconductor and two spatially separated metals. In this process, an electron incident from one metal combines with another electron originating from the other metal to form a Cooper pair in the superconductor. As a consequence, a hole is emitted into the second metal, establishing a nonlocal electron-hole conversion process. In contrast to local Andreev reflection – where electron-to-hole conversion occurs within the same region – CAR intrinsically links two spatially separated carriers, giving rise to nonlocal correlations and quantum entanglement. In bipolar magnetic semiconductors (BMSs), the conduction and valence bands possess opposite spin polarizations. We propose to achieve tunable control of CAR by independently adjusting the chemical potentials of the two regions. By engineering the alignment of spin-polarized bands in the two BMS leads, CAR can be selectively enhanced or suppressed. This tunability enables precise manipulation of nonlocal transport, and correlated electron dynamics, offering promising prospects for spintronic and superconducting device applications.
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Materials Science · Cross-listed from cond-mat.mes-hall

Stable magnetic nanodomains engineered via Ga+-ion irradiation for deterministic sequential switching

Gijs W.A. Simons, Rik F.J. van Haren and Bert Koopmans

Precise control of magnetic domain formation at the nanoscale remains constrained by stochastic defect-mediated and unstable pinning, limiting scalability and reproducibility in spintronic architectures. Here we demonstrate that spatially engineered anisotropy gradients provide a deterministic alternative. Using focused Ga+-ion irradiation, we pattern magnetic energy landscapes containing nanoscale "anisotropy wells" that confine magnetic domain walls and enable bidirectional sequential switching without reliance on difficult-to-control material disorder. An analytical framework describing domain-wall energetics in graded anisotropy profiles yields predictive design rules for depinning and stability, which are supported by micromagnetic simulations and experiments. We realize programmable multi-domain configurations in continuous ferromagnetic films and demonstrate robust, reproducible switching of 750 nm regions, while first results for 100 nm are shown, approaching the theoretical limit set by the domain-wall width. By replacing unstable pinning with engineered energy landscapes, this anisotropy landscape establishes a scalable materials strategy for deterministic magnetic-state programming and opens a pathway toward dense, energy-efficient spintronic and reconfigurable magnetic nanodevices.
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Materials Science · Cross-listed from cond-mat.supr-con

Observation of flat-bottom U-shaped energy gap in high-Tc nickelate (La,Pr)3Ni2O7 thin films

Zhen Liang, Tianheng Wei, Wei Ren et al. (+5 more)

The discovery of high transition temperature (high-Tc) superconductivity in Ruddlesden-Popper (R-P) bilayer nickelates under high pressure has stimulated extensive work to understand the underlying mechanism and search for superconductors with higher Tc. The recent realization of superconductivity in R-P bilayer nickelate thin films with onset Tc above 40 K at ambient-pressure enables the use of a wide array of powerful experimental tools to investigate the unconventional high-Tc superconductivity in bilayer nickelates. Here, using ultra-low temperature scanning tunneling microscopy/spectroscopy (STM/S) and electrical transport study, we report the first successful observation of an energy-symmetric, flat-bottom U-shaped gap with zero residual density of states around the Fermi level in the high-Tc nickelate (La,Pr)3Ni2O7 thin film grown on SrLaAlO4 substrate. Before and after STM/S studies, transport measurements on the same sample reveal consistent superconducting behaviors showing zero resistance, with an onset Tc above 40 K and zero resistance Tc above 20 K. The tunneling spectra exhibit highly unconventional temperature evolution, characterized by a rapid filling of the U-shaped energy gap to a V-shaped gap as the temperature increases. Furthermore, the U-shaped energy gap is reduced under a c-axis magnetic field of 14 T. The energy-symmetric U-shaped gap, taken together with its dependence on magnetic field and temperature, is consistent with the behavior of a superconducting gap, suggesting a nodeless gap function at ultra-low temperatures. Our findings shed new lights on the nature of high-Tc superconductivity and provide an encouraging and thought-provoking hint for a local superconductivity with Tc above liquid nitrogen boiling temperature in nickelate superconductors at ambient or zero pressure.
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All authors Zhen Liang, Tianheng Wei, Wei Ren, Haoran Ji, Zheyuan Xie, Yanzhao Liu, Ziqiang Wang, Jian Wang

Materials Science · Cross-listed from math-ph

Thermodynamic Invariants of Coupled Channels: A Many-Channel Tolman-Ehrenfest Effect

Benjamin Hamblin, Victor Calo and Klaus Regenauer-Lieb

When multiple thermodynamic channels are coupled, single-channel equilibrium conditions fail. Extending the Tolman–Ehrenfest effect to the entropy manifold, we derive the unique $n$-channel invariant $\zeta_i T_i = C$, where $\zeta_i$ is the holonomy of the Ruppeiner connection. For the granular volume–stress ensemble, Rowe's dilatancy ratio and energy restriction emerge as geometric consequences of the off-diagonal curvature $g_{V\sigma}$, and the 60-year puzzle of state-dependent $K_\mu$ is resolved: the correction $\zeta_V$ reaches $O(1)$ near jamming. The prediction $\zeta_V\chi=\mathrm{const}$ across a shear band is experimentally testable.
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Materials Science

Local distortions as a source of piezoelectric/stiffness decoupling in B-doped AlScN

Laszlo Wolf, Geoff L. Brennecka and Vladan Stevanović

We present a first-principles analysis of the wurtzite pseudo-ternary (Al,Sc,B)N to elucidate the structural origin of a decoupling between stiffness $C_{33}$ and piezoelectric response $e_{33}$ upon boron incorporation, using DFT-relaxed 100-atom special quasirandom structures across a broad composition range. Pair distribution function analysis reveals interstitial threefold-coordinated boron atoms that have displaced from the tetrahedral cation site. Direct structural analysis establishes their preferential orientation along the $c$-axis and identifies a scandium-activated creation mechanism. The vertical coordination asymmetry of each cation is quantified through a site-specific axial asymmetry ratio (AAR), showing that boron incorporation progressively symmetrizes the Sc environment. Correlation with Born effective charges demonstrates that this symmetrization is the mechanism behind the piezoelectric enhancement.
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Materials Science

p-Wave Orbital Angular Momentum Texture in a Chiral Crystal

Dongjin Oh, Chiara Pacella, Xiangyu Luo et al. (+8 more)

The spin and orbital angular momentum (SAM and OAM) are conceptually analogous, yet their roles in condensed matter systems have not been often treated on equal footing. While SAM has been extensively explored, OAM has long been regarded as quenched in crystalline environments and thus largely overlooked. Recent experimental and theoretical advances, however, have demonstrated that OAM can drive a variety of novel electronic phenomena, highlighting the importance of probing OAM textures in the electronic band structure. Here, we investigate the momentum-space OAM texture of (TaSe4)2I, a one-dimensional chiral crystal. Using circular-dichroism angle-resolved photoemission spectroscopy (CD-ARPES), we uncover a p-wave OAM texture accompanied by OAM dipole structures. This orbital p-wave texture is intimately connected to, and thus controllable by the chirality of the host lattice. Complementary spin-resolved ARPES measurements and first-principles calculations reveal that the OAM polarization overwhelmingly dominates the low-energy electronic properties of (TaSe4)2I, far exceeding the SAM polarization. These observations represent the experimental verification of a new type of OAM texture in crystalline materials. Most importantly, these findings underscore a promising material platform for spinless orbitronics applications and lay the foundation for realizing multipolar OAM textures-orbital counterparts of the spin texture in unconventional magnets.
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All authors Dongjin Oh, Chiara Pacella, Xiangyu Luo, Chris Jozwiak, Aaron Bostwick, Eli Rotenberg, Mats Leandersson, Craig Polley, Angel Rubio, Domenico Di Sante, Riccardo Comin

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

Quantum Geometry-Driven Nonlinear Spin Currents in Floquet Non-Hermitian Altermagnets

Kai Chen and Jie Zhu

Altermagnets are rapidly emerging as a highly promising platform for spintronics, yet dynamically controlling their spin responses remains a fundamental challenge. In this work, we demonstrate that introducing periodic optical driving and non-Hermiticity provides a powerful route to achieve tunable control over these systems. We derive a general analytical expression for nonlinear spin currents in non-Hermitian phases with a spectral line gap, revealing that the intrinsic response cleanly separates into quantum metric, Berry curvature, and Berry connection dipole contributions. Applying this formalism to a Floquet non-Hermitian $d$-wave altermagnet, we uncover that the nonlinear spin conductivity is overwhelmingly dominated by the bare quantum metric. Furthermore, we show that the optical field's polarization can actively tune – and even strictly reverse – the direction of both longitudinal and transverse spin currents. Our work establishes a quantum geometric framework for the optical manipulation of nonlinear spin transport in advanced magnetic materials.
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Thursday 14 May

Materials Science

Reversible nanoscale patterning of WTe$_2$ with a scanning tunneling microscope

Kevin Hauser, Danyang Liu, Berk Zengin et al. (+6 more)

Manipulating the lattice structure of ferroelectric quantum materials enables their use in low-power electronic devices, including field-effect transistors. WTe$_2$ is a Weyl-semimetal candidate and ferroelectric, both properties arising from the reduced crystal symmetry of its T$_\mathrm{d}$ ground state. The T$_\mathrm{d}$ crystal phase results from a Peierls distortion of the 1T parent structure and an interlayer shift. While experiments in WTe$_2$ have established ferroelectric switching and transient control of the predicted topological phase via ultrafast excitations, persistent electronic changes on the nanometer scale remain elusive. Here, we demonstrate that current pulses applied via scanning tunneling microscopy can both write and erase persistent nanometer-scale patterns on the surface of WTe$_2$. These patterns consist of apparent picometer in-plane and out-of-plane atomic displacements, accompanied by changes to the local density of states. The out-of-plane displacements further modulate the Peierls-like distortion present in WTe$_2$, while the in-plane displacements are indicative of ferroelectric switching. The induced patterns can be repositioned and erased, suggesting a nanoscale handle on the ferroelectric properties of WTe$_2$.
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All authors Kevin Hauser, Danyang Liu, Berk Zengin, Jens Oppliger, Samuel Mañas-Valero, Catherine Witteveen, Fabian O. von Rohr, Jennifer E. Hoffman, Fabian D. Natterer

Materials Science

Chemical Origins of Non-Bonded Interactions Within and Between Solids

Paul J. Robinson, Adam Rettig, Hieu Q. Dinh et al. (+2 more)

Non-bonded interactions govern structure, stability, and function across a wide range of solid-state materials, yet their chemical origins are often difficult to resolve from total energies alone. Here we generalize absolutely localized molecular orbital energy decomposition analysis to quantify and interpret non-bonded interactions within and between solids at the density functional theory level. Across molecular crystals, moiré heterobilayers, and layered perovskite heterostructures, this framework separates lattice-formation energies, interlayer binding energies, and band-structure changes into chemically intuitive contributions from frozen interactions, polarization, and charge transfer. The analysis reveals how dispersion controls polymorph stability in pharmaceutical crystals, how local stacking modulates interlayer coupling in MoS2/WSe2, and how alkali-cation substitution switches the quantum-well character of layered perovskite heterostructures. By connecting emergent solid-state properties to microscopic interaction mechanisms, this framework provides a chemically transparent basis for understanding and designing complex materials.
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All authors Paul J. Robinson, Adam Rettig, Hieu Q. Dinh, Anton Z. Ni, Joonho Lee

Materials Science

Disorder-driven symmetry suppression by van der Waals planar defects in a magnetic topological insulator

Rikkie Joris, Heyi Xia, Ana Beatriz Pedro Fontes et al. (+17 more)

Magnetic topological insulators offer a platform to control electronic topology through magnetic order, yet reliable routes to tune their properties remain limited. Here, we show that ion irradiation allows to modify the magnetic properties and the anomalous Hall response of the van der Waals magnetic topological insulator MnBi$_2$Te$_4$. Using noble gas ion beams, intrinsic defects are introduced via collision cascades without chemical doping. We identify two distinct regimes. At low fluence, cation antisite disorder leads to a near-complete redistribution of Bi over cation sites while preserving long-range crystallographic order, accompanied by a transition from $p$-type to $n$-type transport. At high fluence, cation-anion intermixing drives the formation of a previously unreported layer-disordered phase characterized by a high density of van der Waals-specific planar defects, including swapped bilayers. Despite significant structural disorder, the system retains partial periodic order up to high displacement levels. Magnetometry and X-ray spectroscopy show that the Mn high-spin state and intralayer antiferromagnetic interactions likely persist, while macroscopic magnetic anisotropy is strongly reduced. At the same time, the magnitude of the anomalous Hall conductivity is reduced by an order of magnitude, far exceeding the change in magnetization, and its sign is modified. The observations are consistent with a suppression of the Berry curvature of the occupied states. These results establish ion irradiation as a means to tune anomalous Hall conductivity in topological insulators through defect engineering and reveal a disorder-driven approach to control symmetry and electronic structure in van der Waals magnetic materials.
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All authors Rikkie Joris, Heyi Xia, Ana Beatriz Pedro Fontes, Sara Bey, Seul-Ki Bac, Jiaqi Zhou, Zviadi Zarkua, Ahmed Samir Lotfy, Muhammad Saad, Philippe Ohresser, Bence G. Márkus, László Forró, Margriet van Bael, Clement Merckling, Xinyu Liu, Francisco Molina-Lopez, Jean-Christophe Charlier, Jin Won Seo, Badih A. Assaf, Lino M. C. Pereira

Materials Science

Limitations of Debye-Waller lattice temperature extraction under electronic excitation

N. Medvedev, M. Kopecky, J. Chalupsky et al. (+1 more)

Ultrafast diffraction is the cutting-edge technique to extract the atomic temperature at femtosecond timescales, and further related quantities - in particular, electron-phonon coupling strength at elevated electronic temperatures. The present work demonstrates limitations of such an analysis, emphasizing the importance of careful evaluation of the evolution of the Debye temperature. It is shown that, due to the sensitivity of the Debye-Waller analysis to this parameter, neglecting its changes under electronic excitation may lead to significant deviations of the atomic temperature extracted from its true values.
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All authors N. Medvedev, M. Kopecky, J. Chalupsky, L. Juha

Materials Science

The Emergence of Photonic Crystalline Order and Time-Series Dynamics in NaCl Droplet Deposition

Grzegorz S. Żmija, Grzegorz Cios and Benedykt R. Jany

Crystallization during droplet evaporation gives rise to complex, self-organized structures, yet the mechanisms underlying the emergence of ordered functional phases remain poorly understood. In this study, we present a comprehensive, multi-scale investigation into the crystallization dynamics of NaCl during droplet evaporation on a germanium (001) substrate, relevant for its IR applications. Through systematic microscopic characterization, we identify the formation of diverse microstructures, including 1D photonic crystal nanostructures formed within hybrid crystal-glass photonic system. To enable quantitative comparison across experimental conditions, we introduce the NaCl equivalent height as a unified metric to describe and classify the evolution of crystalline morphology. Our results reveal that diffusion anisotropy, rather than growth kinetics, primarily governs the maximal attainable structure size. Quantitative thin film interference analysis demonstrates the presence of discrete thickness layers in the film. Controlled evaporation experiments yield homogeneous crystallization patterns across the entire droplet area, facilitating the emergence of ordered photonic structures. Time-series dynamics analysis of height profiles uncovered the spatiotemporal evolution of the crystallization front, providing insights into the details of underlying physical mechanisms. Together, these results establish a robust experimental framework for understanding and predicting crystallization behavior in evaporating droplets, with potential applications in materials synthesis, photonics, and microscale pattern formation.
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Materials Science · Cross-listed from physics.comp-ph

Fast contracted Clebsch–Gordan tensor products for equivariant graph neural networks

Anton Bochkarev, Yury Lysogorskiy and Ralf Drautz

We present an $\mathcal{O}(L^3)$ algorithm for evaluating contracted Clebsch–Gordan tensor products in $\mathrm{O}(3)$-equivariant machine learning potentials at fixed Canonical Polyadic (CP) rank. Mapping the angular integral to a structured Gauss–Legendre and Fourier tensor-product grid decouples the radial channel contractions from the angular transforms. The antisymmetric parity-odd Clebsch–Gordan channels, unreachable by the symmetric pointwise product on a scalar $S^2$ grid, are recovered through the surface-curl pairing $\hat r \cdot [\nabla_{S^2} A \times \nabla_{S^2} B]$, the spherical Poisson bracket, which supplies the $L=1$ angular momentum on the grid while preserving rotational equivariance. The construction extends to parity-aware equivariant message passing in atomic-cluster-expansion-style architectures and is verified by direct numerical quadrature. The full uncontracted Clebsch–Gordan tensor product remains subject to the $\mathcal{O}(L^4)$ output-size lower bound. A benchmark shows wall-clock scaling empirically as $L^2$ across the practical $l_{\max}$ range. For the on-site contraction this is pre-asymptotic, giving way to $L^3$ at large $l_{\max}$. For message passing it is structural and the runtime is memory-bandwidth bound on $L^2$-sized grid tensors.
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Materials Science · Cross-listed from physics.optics

Multifunctional Barophotonic Control of Resonators and Metasurfaces

Ping-Chun Chen, Mashnoon Alam Sakib, Mariia Stepanova et al. (+2 more)

Actively tunable nanophotonic platforms that control light-matter interactions enable reconfigurable optical systems and programmable photonic integrated circuits. Hydrostatic pressure provides a noninvasive and material-agnostic mechanism for modulating the refractive index and resonance conditions without introducing free carriers or structural damage. Here, we demonstrate multiple pressure-dependent functionalities in silicon nitride nanostructures, including resonance tuning, refractive index modulation, and polarization state conversion. Applying a pressure of up to 5 GPa, we observe a Fabry-Pérot resonance shift of up to 30 nm and a relative refractive index decrease of up to 4%. Based on the results, we design and examine, to the best of our knowledge, the first extreme-pressure-tunable, polarization-converting metasurface, which tunes the ellipticity and orientation angle of the output light. These findings establish pressure-controllable silicon nitride as a viable platform for reconfigurable photonics and extreme-environment nanophotonic systems, including deep-ocean exploration, planetary interiors, and space applications.
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All authors Ping-Chun Chen, Mashnoon Alam Sakib, Mariia Stepanova, Melika Momenzadeh, Maxim R. Shcherbakov

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

Current induced magneto-optical Kerr effect as a probe of Dirac carriers in Bi$_{1-x}$Sb$_x$ alloy

Ryota Miyazaki, Shunzhen Wang, Guanxiong Qu et al. (+4 more)

We study the current-induced magneto-optical Kerr effect (MOKE) in Bi$_{1-x}$Sb$_x$ semi-metalic alloys. The MOKE signal is found to be the largest in pure Bi ($x=0$), exceeding that of transition metals by nearly four orders of magnitude, and decreases monotonically with increasing Sb concentration. We find the MOKE signal scales with the resistivity ($\rho$) as $\rho^{1.7 \pm 0.6}$ and with the mobility ($\mu_\mathrm{c}$) as $\mu_\mathrm{c}^{2.0 \pm 0.2}$. Model calculations show that such exponent can be accounted for if the Dirac electrons are responsible for the generation of spin current. This is in contrast to the $\rho^{2}$ and $\mu_\mathrm{c}^{-2}$ scaling of the MOKE signal induced by the free electrons in parabolic band. The scaling of the MOKE amplitude with the resistivity also partly accounts for the order of magnitude differences of the signal observed between metals, semimetals, and semiconductors. These results demonstrate that current induced MOKE serves as an effective means to characterize the nature of spin current in materials with diverse electronic structures.
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All authors Ryota Miyazaki, Shunzhen Wang, Guanxiong Qu, Yukihiro Marui, Yuta Kobayashi, Masashi Kawaguchi, Masamitsu Hayashi

Materials Science

Generative reconstruction of 2D and 3D polycrystalline microstructures using symmetrized hyperspherical harmonics

Ali R. Safi, Paul Seibert, Santiago Benito et al. (+3 more)

Establishing structure-property linkages in polycrystalline materials requires representative two- (2D) and three- (3D) dimensional microstructural inputs for full-field simulations. A core objective of microstructure characterization and reconstruction is the generative synthesis of 2D and 3D microstructures that reflect a target statistical ensemble using limited 2D data as a reference. This work introduces an orientation-based differentiable microstructure characterization and reconstruction framework, implemented in MCRpy, to perform reconstructions of voxelized images. Unit quaternions in combination with symmetrized hyperspherical harmonics are utilized to derive a continuous, symmetry-invariant representation of crystallographic orientations to overcome the numerical singularities and discontinuities associated with traditional Euler-based methods. The descriptor-based reconstructions are driven by a set combining two-point spatial correlations, a novel hybrid three-point variogram, and a mean variation regularizer to capture both global texture and local interfacial topology. The framework's efficiency is demonstrated by reconstructing 3D realizations from 2D orientation data of an aluminum alloy after thermo-mechanical processing, successfully recovering both morphological features and crystallographic distribution. Systematic benchmarking indicates that second-order gradient-based optimization, utilizing the L-BFGS-B algorithm, effectively navigates the complex loss landscape to generate high-fidelity realizations with minimal residuals. This methodology provides a versatile, open-source framework for the digital synthesis of polycrystalline representative volume elements to facilitate the rapid development of microstructure-informed materials design workflows.
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All authors Ali R. Safi, Paul Seibert, Santiago Benito, Alexander Raßloff, Markus Kästner, Benjamin Klusemann

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

Atomically resolved intrinsic superconducting gap in (La,Pr)3Ni2O7 films

Xinxin Wang, Yaqi Chen, Cui Ding et al. (+7 more)

Ruddlesden-Popper bilayer nickelates provide an emerging platform for studying high-temperature superconductivity, yet the superconducting pairing symmetry remains under debate. Here, we use atomic-resolution scanning tunnelling microscopy and spectroscopy to investigate superconducting 1.5-unit-cell (La,Pr)3Ni2O7 films grown on SrLaAlO4. A cryogenic ultrahigh-vacuum (UHV) sample transfer preserves an ordered sqrt(2) * sqrt(2) surface and yields reproducible U-shaped spectra with two gap scales of ~14 and ~20 meV and extended flat zero-conductance bottoms. By contrast, samples exposed for a longer time in UHV without cooling during transfer show V-shaped spectra despite retaining the surface reconstruction and a transport superconducting transition onset above 40 K. Wide-energy-range spectra indicate that oxygen loss can mix density-wave-related spectral weight. Our measurements provide an atomic-scale observation of the intrinsic nodeless superconducting gap in bilayer nickelate ultrathin films.
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All authors Xinxin Wang, Yaqi Chen, Cui Ding, Lizhi Xu, Jian-Jian Miao, Guangdi Zhou, Zhuoyu Chen, Yu-Jie Sun, Jin-Feng Jia, Qi-Kun Xue

Materials Science

Melting Behavior and Phase Stability of CaO from Neural Network Potentials: a Molecular Dynamics Study

Francesca Menescardi and Stefano de Gironcoli

We investigate the melting behavior of calcium oxide (CaO) under extreme conditions, a problem that remains poorly constrained due to experimental limitations despite its relevance for geophysical and technological applications. We develop a Machine Learning Interatomic Potential (MLIP) for CaO with PANNA 2.0 and the LATTE descriptor, training it on a dataset of $\sim$12,000 configurations including solid, liquid, interfacial, and void-containing structures, extracted from ab-initio molecular dynamics data employing PBEsol exchange-correlation functional. We perform large-scale molecular dynamics simulations to compute the melting temperature at ambient pressure using both the void-nucleated melting (VNM) and two-phase coexistence (TPC) methods, obtaining $T_m=3055\pm11$ K and $T_m=2847\pm15$ K, respectively.\\ We calculate an enthalpy of fusion of $\Delta H_f\sim73$ kJ/mol, in agreement with thermodynamic assessments and ab initio calculations. We also reproduce the thermal expansion and obtain a volume increase of $\sim$29% at Tm, consistent with the corresponding decrease in density extracted from spatially resolved number density profiles. Finally, we calculate the high-pressure melting curve of CaO up to 20 GPa, providing one of the very few computational determinations of this quantity to date. The results confirm that the overheating ratio $\eta$ is not constant under pressure, increasing from 17% at ambient pressure to 24% at 20 GPa, confirming previous findings and ruling out the assumption of a fixed overheating ratio. Our results establish MLIP-based simulations as a robust and efficient framework for investigating phase stability in ionic oxides and provide new insight into the melting behavior of CaO under extreme conditions.
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Materials Science

Thermal expansion of FeWO$_4$ (Ferberite) and FeWO$_4$:Fe$_2$WO$_6$ (7:1): a comparative X-ray and neutron diffraction study

O. Fabelo, L. Cañadillas-Delgado, D. Vie et al. (+3 more)

The thermal expansion of natural FeWO$_4$ (ferberite) and synthetic FeWO$_4$:Fe$_2$WO$_6$ (7:1) was investigated over the 2-1123 K temperature range combining single-crystal and powder X-ray diffraction together with neutron powder diffraction. High-precision lattice parameters were obtained for both samples. The temperature dependence of the unit-cell volume was analysed using physically based thermodynamic models, including the Kroll and Berman approaches as implemented in EoSFit7. All datasets are well reproduced within their respective temperature intervals. However, significant differences are observed between the behavior of ferberite and FeWO$_4$:Fe$_2$WO$_6$, which has a \~40% smaller thermal expansion coefficient and a reduced reference volume. Possible origins, including microstructural and phase-coexistence effects, are discussed. The results provide a comprehensive description of the thermal expansion behavior of FeWO$_4$ across a wide temperature range.
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All authors O. Fabelo, L. Cañadillas-Delgado, D. Vie, E. Matesanz, J. Gonzalez-Platas, D. Errandonea

Materials Science

Functional and Density-Driven Errors in Density Functional Theory: Quantum Monte Carlo Benchmarks for Solids

Ayoub Aouina, Nicolas Tancogne-Dejean and Silvana Botti

We introduce a systematic analysis of density functional approximation errors in solids by separating functional-driven from density-driven contributions using quantum Monte Carlo densities of silicon, sodium chloride, and copper as reference. Typically, functional errors dominate, but we identify important exceptions where density-driven errors exceed functional errors by factors of 2-3, notably for SOGGA11 and {\tau}-HCTH in the semiconductor and the insulator. Material dependence is striking: 63% of functionals show error cancellation in silicon versus 18% in copper, and only five functionals surpass LDA accuracy for metallic copper even with exact densities. For silicon and sodium chloride, GILL or BECKE exchange combined with PBE, PW91, or P86 correlation achieves near-exact xc energies on QMC densities, while copper requires specialized functionals like PBEsol or PBELYP. High-quality densities consistently reduce density-driven errors across all systems. Historical analysis reveals that 1990s GGA functionals outperform many modern meta-GGAs, contradicting expectations of systematic improvement along Jacob's ladder. These results provide practical guidance for functional selection and highlight implications for machine learning potential development, where material-dependent error cancellation may compromise transferability.
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