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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Wednesday 5 November

Materials Science

Efficient GPU Parallelization of Electronic Transport and Nonequilibrium Dynamics from Electron-Phonon Interactions in the Perturbo Code

Shiyu Peng, Donnie Pinkston, Jia Yao et al. (+3 more)

The Boltzmann transport equation (BTE) with electron-phonon (e-ph) interactions computed from first principles is widely used to study electronic transport and nonequilibrium dynamics in materials. Calculating the e-ph collision integral is the most important step in the BTE, but it remains computationally costly, even with current MPI+OpenMP parallelization. This challenge makes it difficult to study materials with large unit cells and to achieve high resolution in momentum space. Here, we show acceleration of BTE calculations of electronic transport and ultrafast dynamics using graphical processing units (GPUs). We implement a novel data structure and algorithm, optimized for GPU hardware and developed using OpenACC, to process scattering channels and efficiently compute the collision integral. This approach significantly reduces the overhead for data referencing, movement, and synchronization. Relative to the efficient CPU implementation in the open-source package Perturbo (v2.2.0), used as a baseline, this approach achieves a speed-up of 40 times for both transport and nonequilibrium dynamics on GPU hardware, and achieves nearly linear scaling up to 100 GPUs. The novel data structure can be generalized to other electron interactions and scattering processes. We released this GPU implementation in the latest public version (v3.0.0) of Perturbo. The new MPI+OpenMP+GPU parallelization enables sweeping studies of e-ph physics and electron dynamics in conventional and quantum materials, and prepares Perturbo for exascale supercomputing platforms.
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All authors Shiyu Peng, Donnie Pinkston, Jia Yao, Sergei Kliavinek, Ivan Maliyov, Marco Bernardi

Materials Science

Single photon emitters in hBN: Limitations of atomic resolution imaging and potential sources of error

David Lamprecht, Shrirang Chokappa, Alissa M. Freilinger et al. (+9 more)

There is a growing interest in identifying the origin of single-photon emission in hexagonal boron nitride (hBN), with proposed candidates including boron and nitrogen vacancies as well as carbon substitutional dopants. Because photon emission intensity often increases with sample thickness, hBN flakes used in these studies commonly exceed 30 atomic layers. To identify potential emitters at the atomic scale, annular dark-field scanning transmission electron microscopy (ADF-STEM) is frequently employed. However, due to the intrinsic AA' stacking of hBN with vertically alternating boron and nitrogen atoms, this approach is complicated even in few-layer systems. Here, we demonstrate using STEM image simulations and experiments that, even under idealized conditions, the intensity differences between boron- and nitrogen-dominated columns and carbon substitutions become indistinguishable at thicknesses beyond 17 atomic layers (ca. 6 nm). While vacancy-type defects can remain detectable at somewhat larger thicknesses, also their detection becomes unreliable at thicknesses typically used in photonic studies. We further show that common residual aberrations, particularly threefold astigmatism, can lead to artificial contrast differences between columns, which may result in misidentification of atomic defects. We systematically study the effects of non-radially symmetric aberrations on multilayer hBN and demonstrate that even small residual threefold astigmatism can significantly distort the STEM contrast, leading to misleading interpretations.
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All authors David Lamprecht, Shrirang Chokappa, Alissa M. Freilinger, Barbara Maria Mayer, Maximilian Melchior, Jana Dzíbelová, Darwin Lorber, Luiz H. G. Tizei, Mathieu Kociak, Clemens Mangler, Lado Filipovic, Jani Kotakoski

Materials Science

pH-Responsive Glyphosate Adsorption on Hydroxylated Carbon Nanotubes: From Electronic Structure to Molecular Dynamics

H.T. Silva, L.C.S. Faria, T.A. Aversi-Ferreira et al. (+1 more)

This computational study investigates glyphosate adsorption mechanisms on hydroxyl-functionalized carbon nanotubes (CNTs) as an alternative approach for environmental remediation. Single-walled CNTs with (10,0) zigzag chirality were functionalized with hydroxyl groups at concentrations of 5-25% and evaluated for interactions with glyphosate in five different ionization states (G1-G5) corresponding to pH-dependent protonation. Using semi-empirical tight-binding methods implemented in xTB software, molecular geometry optimization, electronic property calculations, topological analyses via Quantum Theory of Atoms in Molecules (QTAIM), and molecular dynamics simulations at 300K were performed. Results demonstrate that functionalization significantly enhances adsorption capacity, with binding energies becoming increasingly negative at higher OH concentrations and with more deprotonated glyphosate forms (G4 and G5). Electronic coupling analyses reveal optimized charge reactivity and transport in systems with 20-25% OH functionalization. Topological characterization identified 477 bond critical points, confirming donor-acceptor interactions with strong covalent contributions, particularly in highly functionalized systems. Radial distribution function profiles from molecular dynamics simulations demonstrate that functionalization promotes spatial organization on nanotube surfaces, increasing contact regions and reducing molecular mobility. Systems with moderate interactions (CNT+OHx+G1 and CNT+OHx+G3) present environmentally and economically viable solutions, enabling adsorbent regeneration and reuse. The findings indicate that OH-functionalized carbon nanotubes show significant promise for glyphosate detection and capture applications in environmental monitoring and remediation, regardless of the pesticide's ionization state.
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All authors H.T. Silva, L.C.S. Faria, T.A. Aversi-Ferreira, I. Camps

Materials Science

Real Chern insulators in two-dimensional altermagnetic Fe$_2$S$_2$O and Fe$_2$Se$_2$O

Yong-Kun Wang, Shifeng Qian, An-Dong Fan et al. (+1 more)

Altermagnets, recently identified as a third class of collinear magnetic materials, have attracted significant attention in condensed matter physics. Despite this growing interest, the realization of real Chern insulators in intrinsic altermagnetic systems has rarely been reported. In this work, based on first-principles calculations and theoretical analysis, we identify monolayer Fe$_2$S$_2$O and Fe$_2$Se$_2$O as a novel class of two-dimensional altermagnetic real Chern insulators. We demonstrate that these materials possess altermagnetic ground states and host a nontrivial mirror real Chern number, leading to the emergence of symmetry-protected zero-dimensional corner states. Notably, these corner modes are spin-polarized, giving rise to a unique spin-corner coupling effect. We further show that the real Chern insulating phases and their associated corner states remain robust against spin-orbit coupling, as well as under both uniaxial and biaxial strain. Additionally, these materials exhibit pronounced linear dichroism and strong optical absorption. Our findings uncover the novel topological character of Fe$_2$S$_2$O and Fe$_2$Se$_2$O, establishing them as promising platforms for exploring real Chern insulators in altermagnetic systems.
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All authors Yong-Kun Wang, Shifeng Qian, An-Dong Fan, Si Li

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

Negative Refraction of Terahertz Phonons via Interfacial Momentum Compensation

Hao Chen, Zhong-Ke Ding, Yuan Yao et al. (+5 more)

Negative refraction provides a route to steer and focus wave energy flow, but it remains difficult to realize for coherent terahertz (THz) phonons. The difficulty stems from conventional dispersion-based mechanisms, which require strongly anisotropic or negative-curvature dispersions, while the long-wavelength acoustic phonons most favorable for coherent transport are nearly isotropic. Here we overcome this limitation by introducing a momentum compensation mechanism mediated by discrete translational symmetry. Discrete translational symmetry parallel to the interface supplies a compensating tangential momentum, reopening transmitted channels beyond the conventional critical condition and enabling negative refraction when this compensation reverses the tangential component. Mode-resolved calculations for hBN/graphene heterostructures establish this mechanism in laterally stitched in-plane interfaces and show how twisted van der Waals moire superlattices shift the negative-refraction window to lower frequencies. These results identify periodic crystalline interfaces as symmetry-engineered elements for THz phonon momentum conversion and wavefront control.
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All authors Hao Chen, Zhong-Ke Ding, Yuan Yao, Chang-Hao Ding, Nannan Luo, Jiang Zeng, Li-Ming Tang, Ke-Qiu Chen

Materials Science

Topological transition and emergent elasticity of dislocation in skyrmion lattice: Beyond Kittel's magnetic-polar analogy

Kohta Kasai, Akihiro Uematsu, Tatsuki Kawakane et al. (+5 more)

Magnetic and polar skyrmions exhibit topologically protected quasiparticle behavior, including emergent fields, deformation, and the formation of a densely packed skyrmion lattice, beyond conventional domain configurations described by Kittel's law. Analogous to atomic crystals, lattice defects, especially dislocations and their associated strain fields, are crucial for understanding the lattice behavior of skyrmions; however, their features and roles remain insufficiently understood. Here, we show that magnetic skyrmion dislocations develop a core-split structure due to a significant skyrmion elongation up to 180% of their original length, reaching a topological transition from a single skyrmion to two half-skyrmions. Despite such a distinct structure, the long-range strain fields around the dislocation perfectly obey conventional Volterra's elasticity theory, in contrast to polar skyrmion lattices, where skyrmion deformations cause a breakdown of the elasticity theory. Furthermore, an energetic analysis shows that Dzyaloshinskii-Moriya interaction drives the large skyrmion deformation of the dislocation core. Our findings not only clarify the coexistence of topological core-reconstruction and a robust long-range elastic field of dislocations in magnetic skyrmion lattices, but also reveal that magnetic and electric domains, long regarded as dual and analogous, exhibit fundamental differences when extended into the regime of collective topological quasiparticles.
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All authors Kohta Kasai, Akihiro Uematsu, Tatsuki Kawakane, Yu Wang, Tao Xu, Chang Liu, Susumu Minami, Takahiro Shimada

Materials Science

Structural characterization and bonding energy analysis for plasma-activated bonding of SiCN films: A reactive molecular dynamics study

Juheon Kim, Minki Jang, Junhyeok Park et al. (+2 more)

Plasma-activated bonding of SiCN films offers high bonding strength at the hybrid-bonding interface, thereby enhancing mechanical reliability. Although experimental studies have shown that the interfacial bonding properties of SiCN films vary with SiCN composition and plasma treatment parameters, a clear correlation between these parameters and the resulting bonding properties has not yet been established. This study presents an atomistic investigation of SiCN-SiCN plasma-activated bonding with controlled SiCN composition and plasma fluence, which performs O2 plasma surface activation, surface hydroxylation, direct bonding, post-bonding annealing, and debonding using reactive molecular dynamics. The structural characterization of the plasma-activated SiCN surface, including density of various covalent bonds and surface roughness, exhibits composition- and plasma fluence-dependent chemical and morphological modification. Bonding energy evaluated from atomic traction-separation responses in cohesive zone volume elements (CZVE) during debonding simulations shows a positive correlation with the interfacial Si-O-Si density. Since the interfacial Si-O-Si density reflects the combined effects of these chemical and morphological modifications, the dependence of bonding energy on composition and plasma fluence is successfully elucidated by the structural characterization. These results establish an atomic-level material-process-property relationship and offer practical guidance for optimizing SiCN composition and plasma treatment parameters for SiCN-SiCN plasma-activated bonding.
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All authors Juheon Kim, Minki Jang, Junhyeok Park, Byungjo Kim, Hayoung Chung

Materials Science

Statistical imaging of NV centers reveals clustered defect formation in diamond

Jason Shao, Richard Monge, Tom Delord et al. (+1 more)

The sharp optical resonances of NV- centers in diamond at cryogenic temperatures offer powerful new capabilities for material characterization, but extracting the most detailed information typically requires careful calibration of individual sensors, limiting scalability. In this work, we use resonant photoluminescence excitation imaging to optically resolve and monitor hundreds of individual NVs across large fields of view, enabling statistical analysis of their spatial distribution with sub-diffraction resolution. This multiplexed, non-destructive approach allows quantum sensors to characterize the material platform they inhabit. Focusing on CVD-grown diamond, we uncover significant deviations from random distributions, including an unexpectedly high occurrence of closely spaced clusters comprising two or more NVs. These findings suggest non-Poissonian formation dynamics and point to spatially correlated defect generation mechanisms. Beyond offering insight into diamond growth and NV center formation, our approach enables the scalable identification of naturally occurring NV clusters - configurations that are promising for entanglement-assisted quantum information protocols and correlated sensing - and establishes a path toward structural and electronic defect analysis in various material hosts at the single-emitter level.
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All authors Jason Shao, Richard Monge, Tom Delord, Carlos A. Meriles

Materials Science

Development of a magnetic interatomic potential for cubic anti-ferromagnets: the case of NiO

Ievgeniia Korniienko, Pablo Nieves, Jakub Sebesta et al. (+2 more)

Interatomic potentials are essential for molecular dynamics simulations of magnetic materials, yet incorporating magnetic features into potentials for complex antiferromagnets remains challenging. Nickel oxide (NiO), a prototypical cubic antiferromagnet, exemplifies this difficulty. Here we develop a methodology to integrate magnetic properties into interatomic potentials for cubic antiferromagnets by adding a magnetic Hamiltonian which includes both the Heisenberg exchange and Néel model. We apply this approach to NiO by constructing two potentials: one based on the Born model of ionic solids and another using a reference-free modified embedded atom method. Both potentials include magnetoelastic interactions and are validated against Density Functional Theory calculations, showing excellent agreement in mechanical and magnetic properties at zero temperature. These models enable large-scale simulations of magnetoelastic phenomena in antiferromagnets and open avenues for molecular dynamics studies involving coupled electric and magnetic fields in metal oxides.
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All authors Ievgeniia Korniienko, Pablo Nieves, Jakub Sebesta, Roberto Iglesias, Dominik Legut

Materials Science

Enhancing composition-based materials property prediction by cross-modal knowledge transfer

Ivan Rubtsov, Ivan Dudakov, Yuri Kuratov et al. (+1 more)

Crystal graph neural networks are widely applicable in modeling experimentally synthesized compounds and hypothetical materials with unknown synthesizability. In contrast, structure-agnostic predictive algorithms allow exploring previously inaccessible domains of chemical space. Here we present a universal approach for enhancing composition-based materials property prediction by means of cross-modal knowledge transfer. Two formulations are proposed: implicit transfer involves pretraining chemical language models on multimodal embeddings, whereas explicit transfer suggests generating crystal structures and implementing structure-aware predictors. The proposed approaches were benchmarked on LLM4Mat-Bench and MatBench tasks, achieving state-of-the-art performance in 25 out of 32 cases. In addition, we demonstrated how another modeling aspect of chemical language models - interpretability - benefits from applying a game-theoretic approach, which is able to incorporate high-order feature interactions.
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All authors Ivan Rubtsov, Ivan Dudakov, Yuri Kuratov, Vadim Korolev

Materials Science

Core-Shell Confinement Blocks Hydride Formation: The Impact of Surface Oxides on Hydrogen Sorption in Nanoporous FeTi

Lukas Schweiger, Florian Spieckermann, Michael Burtscher et al. (+10 more)

Metal hydrides remain an intriguing alternative to conventional gaseous and liquid hydrogen storage methods, offering high volumetric storage density and enhanced hydrogen storage safety at ambient conditions. In this regard, the intermetallic compound FeTi is one of the most promising storage materials. However, its widespread industrial application remains challenging due to the need for activation, slow initial kinetics, large hysteresis, and high material costs. In this study, we aim to overcome these limitations by devising an alternative synthesis pathway to prepare nanoporous and ultra-fine porous FeTi with controlled grain and ligament sizes, allowing us to study the obtained well-defined microstructures in detail. In particular, we observe the confinement of the FeTi phase by surface oxides, which can be correlated with the hydrogen sorption properties of the respective material. These experimental results are further supported by an analytical model allowing the calculation of the absorption pressure as a function of microstructure-dependent elastic stresses. Additionally, we show that such stresses also influence the absorption-desorption hysteresis. This study lays the groundwork for the controlled and systematic study of the processing-structure-properties relations in metal hydrides and FeTi in particular, thereby paving the way to cost-effective and efficient hydrogen storage solutions based on metal hydrides.
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All authors Lukas Schweiger, Florian Spieckermann, Michael Burtscher, Stefan Wurster, Sebastian Stock, Nikolaos Kostoglou, Oskar Paris, Alexander Schökel, Fahim Karimi, Gökhan Gizer, Claudio Pistidda, Daniel Kiener, Jürgen Eckert

Materials Science

Axial phono-magnetic effects

Natalia Shabala, Finja Tietjen and R. Matthias Geilhufe

Axial or circularly polarized phonons are collective lattice vibrations with angular momentum. Over the past decade they have emerged as a promising mechanism for the manipulation of magnetism, in parallel to well established optical protocols. In particular, coherent axial phonons were shown to induce magnetization in materials without spin-ordering, making them a viable tool for ultrafast magnetic switching. The experimental evidence suggests that the size of this magnetization is significant, opening a new research area on the phono-magnetic effect. Remarkably, the coupling of axial phonons to magnetism has been observed a broad class of materials, pointing to a universal nature of the underlying mechanisms. In this review article, we present the recent progress in the field. We give an introduction to the phenomenological perspective and an overview of the experimental evidence for the magnetization emerging from axial phonons, which includes discussing the observations of phonon Zeeman effect, the magneto-optical Kerr effect and the proximity-induced magnetization switching. We present recently proposed microscopic theories for the phono-magnetic effects, based on perturbation theory, adiabatic motion and Floquet theory as well as the emergence of the phonon magnetic moment due to artificial gauge fields or inertial effects. This summary allows us to see correspondences between the seemingly different theoretical approaches, facilitating a more complete perspective of the effect.
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Materials Science · Cross-listed from cond-mat.str-el

Moiré modulated quantum spin liquid candidate 1T-TaSe$_2$

Ziying Wang, Adolfo O. Fumega, Ana Vera Montoto et al. (+7 more)

Quantum spin liquids are quantum phases of matter featuring collectively entangled states and emergent fractional many-body excitations. While methods exist to probe three-dimensional quantum spin liquids experimentally, these techniques lack the sensitivity to probe two-dimensional quantum spin liquids. This seriously hampers the study of potential monolayer quantum spin liquid candidates such as $\alpha$-RuCl$_3$ and 1T-TaSe$_2$. Scanning tunneling microscopy (STM) and spectroscopy (STS) have recently been suggested as promising probes of the quantum spin liquid state, as they can access the spinon spectrum through inelastic tunneling spectroscopy (IETS). In this work, we employ this approach on the quantum spin liquid candidate material 1T-TaSe$_2$ and directly measure its low-energy inelastic excitations. We observe the emergence of a $\sqrt{3}\times\sqrt{3}$ reconstruction driven by the substrate, equivalent spectroscopy across all spin sites and coexistence of zero and finite energy excitations. We show that these observations are consistent with a modulated $\sqrt{3}\times\sqrt{3}$ spin liquid ground state. Our results demonstrate that IETS provides a powerful route to obtain atomic-scale insight into the magnetic excitations of two-dimensional materials, allowing to explore the effects of moiré modulations on potential quantum liquid phases.
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All authors Ziying Wang, Adolfo O. Fumega, Ana Vera Montoto, Mohammad Amini, Büşra Gamze Arslan, Aleš Cahlík, Yuxiao Ding, Jose L. Lado, Robert Drost, Peter Liljeroth

Materials Science · Cross-listed from physics.optics

Graphene-enabled coherent (sub-)terahertz wave detection and thickness determination

Ronny de la Bastida, Enzo Rongione, Karuppasamy Pandian Soundarapandian et al. (+9 more)

Phase-sensitive terahertz (THz) detection enables applications ranging from astronomy to non-destructive testing. However, current THz detectors lack phase sensitivity, unless they are combined with external interferometers, or through photomixing. This implies a large footprint and sensitive dependence on alignment. Here, we demonstrate a graphene-enabled, on-chip, integrated (sub-)THz detector-interferometer with optical cavity and antenna, exhibiting high sensitivity to the phase of incident THz light. We exploit this by determining the thickness of thin films placed in front of the detector-interferometer, obtaining a deep sub-wavelength thickness accuracy of a few micrometer, while we predict that an improved accuracy is within reach. This is relevant for a range of industrial application domains, including automotive, construction, and health. We furthermore achieve a record-high external responsivity - considering bias-free graphene-based (sub-)THz detectors - of 172 mA/W and a noise-equivalent power of 26 pW$~\rm{Hz}^{-1/2}$. This performance is due to enhanced absorption at the resonant cavity mode around 89 GHz, in agreement with multi-physics simulations. These results pave the way to exploiting coherent wave detection in the (sub-)THz regime with utility in spectroscopy, next-generation wireless communication, and beyond.
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All authors Ronny de la Bastida, Enzo Rongione, Karuppasamy Pandian Soundarapandian, Ioannis Vangelidis, Anand Nivedan, David Saleta Reig, Kenji Watanabe, Takashi Taniguchi, Elefterios Lidorikis, Frank H. L. Koppens, Sebastián Castilla, Klaas-Jan Tielrooij

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

The nexus between negative charge-transfer and reduced on-site Coulomb energy in a correlated topological metal CoTe$_2$

A. R. Shelke, C.-W. Chuang, S. Hamamoto et al. (+7 more)

The layered $3d$ transition metal dichalcogenide (TMD) CoTe$_2$ is a topological Dirac Type-II metal. However, the Co $3d$-bands in CoTe$_2$ do not exhibit the expected correlation-induced band narrowing seen in CoO. We address this conundrum by studying the electronic structure of CoTe$_2$ using hard x-ray photoemission spectroscopy (HAXPES), x-ray absorption spectroscopy (XAS) and Resonant-PES. We quantify the on-site Coulomb energy $U_{dd}$ via single-particle partial density of states and the two-hole correlation satellite using valence band Resonant-PES), and obtain $U_{dd}$ = 3.0 eV for CoTe$_2$. Charge-transfer (CT) cluster model simulations of the measured core-level Co $2p$ PES and $L$-edge XAS spectra of CoTe\textsubscript{2} and CoO validate their contrasting electronic parameters:$U_{dd}$ and CT energy $\Delta$ are (3.0 eV, -2.0 eV) for CoTe\textsubscript{2}, and (5.0 eV, 4.0 eV) for CoO, respectively. The $d$-$p$ hybridization strength $T_{eg}$ for CoTe$_2$$<$CoO, and indicates that the reduced $U_{dd}$ in CoTe\textsubscript{2} is not due to $T_{eg}$. The increase in $d^n$-count$\sim$1 by CT from ligand to Co site in CoTe$_2$ is due to a negative-$\Delta$ and reduced $U_{dd}$. Yet, only because $U_{dd}$$>$$\big|\Delta\big|$, CoTe$_{2}$ becomes a topological metal with $p$$\rightarrow$$p$ type lowest energy excitations. The study reveals the nexus between negative-$\Delta$ and reduced $U_{dd}$ required for setting up the electronic structure framework for achieving topological behavior via band inversion in the correlated metal CoTe$_2$.
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All authors A. R. Shelke, C.-W. Chuang, S. Hamamoto, M. Oura, M. Yoshimura, N. Hiraoka, C.-N. Kuo, C.-S. Lue, A. Fujimori, A. Chainani

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

Lorentz Skew Scattering Nonreciprocal Magneto-Transport

Xiu Fang Lu, Xue-Jin Zhang, Naizhou Wang et al. (+9 more)

In materials with broken inversion symmetry, nonreciprocal magneto-transport (NRMT) manifests as a bilinear dependence of charge conductivity on applied electric (E) and magnetic (B) fields. This phenomenon is deeply rooted in symmetry and electronic quantum geometry, holding promise for novel rectification and detector technologies. Existing experimental studies generally attribute NRMT to Zeeman-driven mechanisms and exhibit quadratic scaling with conductivity. Here, we report a previously unknown NRMT microscopic mechanism - Lorentz skew scattering (LSK) - revealed through the discovery of an unprecedented quartic scaling law of NRMT as well as quantitative agreement between theory and experiment in BiTeBr. LSK emerges from the interplay of Lorentz force and skew scattering, bridging classical field effect to quantum scattering effect on the Fermi surface. We demonstrate that the LSK dominates NRMT in BiTeBr, and elucidate that this dominance over other possible contributions stems from high mobility and strong Rashba splitting. The finding of LSK mechanism is of unique importance because it unveils the leading NRMT effect in high-mobility systems and suggests a universal principle towards strong NRMT by enhancing electronic relaxation time in topological materials, rendering a new designing idea for low-dissipation rectifiers and high-performance quantum electronics.
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All authors Xiu Fang Lu, Xue-Jin Zhang, Naizhou Wang, Jin Cao, Dan Zhao, Hui Wang, Tao Wu, Xian Hui Chen, Shen Lai, Cong Xiao, Shengyuan A. Yang, Weibo Gao

Materials Science

Tunable Multistage Refrigeration via Geometrically Frustrated Triangular Lattice Antiferromagnet for Space Cooling

Jianqiao Wang, Chushu Fang, Zhibin Qiu et al. (+8 more)

Low-temperature refrigeration technology constitutes a crucial component in space exploration. The small-scale, low-vibration Stirling-type pulse tube refrigerators hold significant application potential for space cooling. However, the efficient operation of current Stirling-type pulse tube cryocoolers in space cooling applications remains challenging due to the rapid decay of the heat capacity of regenerative materials below 10 K. This study adopts a novel material strategy: using a novel high-spin S = 7/2 magnetic regenerative material, Gd2O2Se, we construct a multistage tunable regenerative material structure to achieve an efficient cooling approach to the liquid helium temperature range. Under substantial geometric frustration from a double-layered triangular lattice, it exhibits two-step specific heat transition peaks at 6.22 K and 2.11 K, respectively. Its ultrahigh specific heat and broad two-step transition temperature range effectively bridge the gap between commercially used high-heat-capacity materials. Experimental verification shows that when Gd2O2Se is combined with Er3Ni and HoCu2 in the Stirling-type pulse tube cryocooler, the cooling efficiency of the pulse tube increases by 66.5 % at 7 K, and the minimum achievable temperature reaches 5.85 K. These results indicate that Gd2O2Se is an ideal magnetic regenerative material for space cooling
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All authors Jianqiao Wang, Chushu Fang, Zhibin Qiu, Yang Zhao, Quan Xiao, Xiying Sun, Zhaoyi Li, Laifeng Li, Yuan Zhou, Changzhao Pan, Shu Guo

Materials Science

Mysterious Role of Cap Configuration in Single-Walled Carbon Nanotube Catalytic Growth

Tianliang Feng and Ziwei Xu

Understanding the role of cap structure during the nucleation and growth of single-walled carbon nanotubes (SWCNTs) is essential for achieving chirality-controlled synthesis. In this work, we propose a novel and intuitive algorithm to determine the chirality of nascent carbon caps by tracking the relative shifts of six pentagons within a topological coordinate system. Based on this algorithm, we propose three routes of pentagon shifts for the chirality mutations from armchair (AC) to near-AC caps, namely the transverse shift (n,n) to (n+1,n-1), inward shift (n,n) to (n-1), and outward shift (n,n) to (n+1,n), can occur according to the energy profiles calculated based on the density function theory (DFT), providing a new perspective to explain the experimental abundance of near-AC SWCNTs. After that, we construct 24 representative short caps and long SWCNTs with different chiralities and symmetries, and perform DFT calculations to evaluate their thermodynamic stability and deformation behaviors on flat Ni(111) surfaces and curved Ni55 particle, respectively. The results reveal that cap topology and catalyst curvature together induce dual deformations that significantly influence the formation and interface energies. Notably, AC and near-AC caps exhibit superior flexibility and robust energetic advantages, especially the (6,6) cap with C6v symmetry. A linear correlation between cap-induced deformation and formation energy is established through a defined shape factor, highlighting the interaction between cap structure and catalyst interface as a key driver of chirality selection. This study theoretically reveals the cap evolution mechanism and lays the foundation for the rational design of SWCNT growth strategies.
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Materials Science

Commutative Algebra Modeling in Materials Science – A Case Study on Metal-Organic Frameworks (MOFs)

Caleb Simiyu Khaemba, Hongsong Feng, Dong Chen et al. (+2 more)

Metal-organic frameworks (MOFs) are a class of important crystalline and highly porous materials whose hierarchical geometry and chemistry hinder interpretable predictions in materials properties. Commutative algebra is a branch of abstract algebra that has been rarely applied in data and material sciences. We introduce the first ever commutative algebra modeling and prediction in materials science. Specifically, category-specific commutative algebra (CSCA) is proposed as a new framework for MOF representation and learning. It integrates element-based categorization with multiscale algebraic invariants to encode both local coordination motifs and global network organization of MOFs. These algebraically consistent, chemically aware representations enable compact, interpretable, and data efficient modeling of MOF properties such as Henry's constants and uptake capacities for common gases. Compared to traditional geometric and graph-based approaches, CSCA achieves comparable or superior predictive accuracy while substantially improving interpretability and stability across data sets. By aligning commutative algebra with the chemical hierarchy, the CSCA establishes a rigorous and generalizable paradigm for understanding structure and property relationships in porous materials and provides a nonlinear algebra-based framework for data-driven material discovery.
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All authors Caleb Simiyu Khaemba, Hongsong Feng, Dong Chen, Chun-Long Chen, Guo-Wei Wei

Materials Science

EGMOF: Efficient Generation of Metal-Organic Frameworks Using a Hybrid Diffusion-Transformer Architecture

Seunghee Han, Yeonghun Kang, Taeun Bae et al. (+5 more)

Designing materials with targeted properties remains challenging due to the vastness of chemical space and the scarcity of property-labeled data. While recent advances in generative models offer a promising way for inverse design, most approaches require large datasets and must be retrained for every new target property. Here, we introduce the EGMOF (Efficient Generation of MOFs), a hybrid diffusion-transformer framework that overcomes these limitations through a modular, descriptor-mediated workflow. EGMOF decomposes inverse design into two steps: (1) a one-dimensional diffusion model (Prop2Desc) that maps desired properties to chemically meaningful descriptors followed by (2) a transformer model (Desc2MOF) that generates structures from these descriptors. This modular hybrid design enables minimal retraining and maintains high accuracy even under small-data conditions. On a hydrogen uptake dataset, EGMOF achieved over 94% validity and 91% hit rate, representing significant improvements of up to 39% in validity and 29% in hit rate compared to existing methods, while remaining effective with only 1,000 training samples. Moreover, our model successfully performed conditional generation across 29 diverse property datasets, including CoREMOF, QMOF, and text-mined experimental datasets, whereas previous models have not. This work presents a data-efficient, generalizable approach to the inverse design of diverse MOFs and highlights the potential of modular inverse design workflows for broader materials discovery.
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All authors Seunghee Han, Yeonghun Kang, Taeun Bae, Junho Kim, Younghun Kim, Varinia Bernales, Alan Aspuru-Guzik, Jihan Kim

Tuesday 4 November

Materials Science · Cross-listed from cs.LG

Fine-Tuning Vision-Language Models for Multimodal Polymer Property Prediction

An Vuong, Minh-Hao Van, Prateek Verma et al. (+2 more)

Vision-Language Models (VLMs) have shown strong performance in tasks like visual question answering and multimodal text generation, but their effectiveness in scientific domains such as materials science remains limited. While some machine learning methods have addressed specific challenges in this field, there is still a lack of foundation models designed for broad tasks like polymer property prediction using multimodal data. In this work, we present a multimodal polymer dataset to fine-tune VLMs through instruction-tuning pairs and assess the impact of multimodality on prediction performance. Our fine-tuned models, using LoRA, outperform unimodal and baseline approaches, demonstrating the benefits of multimodal learning. Additionally, this approach reduces the need to train separate models for different properties, lowering deployment and maintenance costs.
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All authors An Vuong, Minh-Hao Van, Prateek Verma, Chen Zhao, Xintao Wu

Materials Science

A Normalized Descriptor for Unbiased Screening of Second-Order Nonlinear Optical Materials

Aubrey G. J. Nyiri, Michael J. Waters and James M. Rondinelli

Second-order nonlinear optical materials enable frequency doubling of light (second-harmonic generation, SHG), which is essential for optoelectronic applications ranging from materials characterization to quantum technologies. However, comparing SHG performance across materials remains challenging as the second-order nonlinear susceptibility $\chi^{(2)}$ spans several orders of magnitude and strongly depends on the band gap $E_g$. To address this, we empirically validate a theoretical upper bound on $\chi^{(2)}$ using new databases of ab initio-computed nonlinear optical (NLO) properties. We then formulate a normalized descriptor, $\hat{d}$, which expresses the NLO response of a material relative to the band gap-dependent physical limit. We show that $\hat{d}$ exhibits a similar distribution across a wide range of band gap energies. This universality supports the use of $\hat{d}$ as a robust, generalizable descriptor for data-driven and chemistry-informed machine learning models of NLO response, enabling accelerated materials discovery and optimization across broad application frequencies.
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Materials Science

Critical Disconnect Between Structural and Electronic Recovery in Amorphous GaAs during Recrystallization

Ellis Rae Kennedy, Adric Jones, Yongqiang Wang et al. (+6 more)

Understanding the evolution of structure and functionality through amorphous to crystalline phase transitions is critical for predicting and designing devices for application in extreme conditions. Here, we consider both aspects of recrystallization of irradiated GaAs. We find that structural evolution occurs in two stages, a low temperature regime characterized by slow, epitaxial front propagation and a high-temperature regime above dominated by rapid growth and formation of dense nanotwin networks. We link aspects of this structural evolution to local ordering, or paracrystallinity, within the amorphous phase. Critically, the electronic recovery of the materials is not commensurate with this structural evolution. The electronic properties of the recrystallized material deviate further from the pristine material than do those of the amorphous phase, highlighting the incongruence between structural and electronic recovery and the contrasting impact of loss of long range order versus localized defects on the functionality of semiconducting materials.
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All authors Ellis Rae Kennedy, Adric Jones, Yongqiang Wang, Miguel Pena, Hyosim Kim, Chengyu Song, Farida Selim, Blas P. Uberuaga, Samuel Greer

Materials Science

Dirac semimetal strontium iridate thin films with strong spin-orbit interaction for magnetic heterostructures

Gennady A. Ovsyannikov, Nikita V. Dubitskiy, Georgi D. Ulev et al. (+6 more)

The structural crystal features, electron transport and magnetotransport of the epitaxial strontium iridate (SrIrO$_3$) and iridate/manganite SrIrO$_3$/La$_{0.7}$Sr$_{0.3}$MnO$_3$ heterostructure have been investigated. The influence of epitaxial strain relaxation caused by the lattice mismatch between SrIrO$_3$ films and five substrates: SrTiO$_3$, NdGaO$_3$, (LaAlO$_3$)$_{0.3}$(Sr$_2$TaAlO$_6$)$_{0.7}$, LaAlO$_3$, and Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_3$-PbTiO$_3$ on electron and magnetic transport has been observed. A pronounced impact of strong spin-orbit interaction on characteristics of SrIrO$_3$ films has been revealed by means of X-ray photoelectron spectroscopy, magnetoresistance and Hall-resistance measurements at temperatures T = 2-300 K. These findings highlight the tunability of spin-orbit-driven transport phenomena in strain-controlled SrIrO$_3$-based epitaxial systems, relevant for future spintronic oxide heterostructures. The contribution of Kondo scattering on temperature dependence of SrIrO$_3$ films resistance was observed.
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All authors Gennady A. Ovsyannikov, Nikita V. Dubitskiy, Georgi D. Ulev, Karen Y. Constantinian, Ivan E. Moskal, Victoria A. Baydikova, Andrei M. Petrzhik, Anton V. Shadrin, Alexei V. Mashirov

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

Randium: A minimal model of universal viscous liquid dynamics

Ulf R. Pedersen

When liquids are cooled and crystallization is avoided, their dynamics slow dramatically and the material eventually solidifies into an amorphous glass. Experiments show that chemically distinct glass forming liquids share universal features in both the spectral shape and the temperature dependence of the primary structural relaxation. We introduce Randium, a generic, energetically coarse-grained minimal model of viscous liquids. The model, inspired by results from atomistic molecular-dynamics simulations, is implemented on a two-dimensional lattice with Gaussian-distributed nearest-neighbor interactions. Temperature is the only control parameter, and at low temperatures, dynamic facilitation and dynamical heterogeneity emerge from simple nearest-neighbor rearrangements. The relaxation spectra obey time-temperature superposition, and they reproduce shapes observed experimentally for chemically distinct systems. The temperature dependence of the structural-relaxation time follows parabolic scaling, and the relaxation time grows exponentially with the heterogeneity length scale. The mean-squared displacement collapses onto the universal master curve of the random barrier model. The absence of elasticity-induced facilitation in Randium shows that this is not required for universal viscous-liquid dynamics. Other explanations for universal relaxation are discussed in light of Randium.
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Materials Science

An Atomistically Informed Device Engineering (AIDE) Method Realized: A case study in GaAs

Leopoldo Diaz, Harold P. Hjalmarson, Jesse J. Lutz et al. (+1 more)

Radiation-induced defects can have a significant impact on the longevity and performance of semiconductor devices. We present an Atomistically Informed Device Engineering (AIDE) method that integrates first-principles defect properties and experimentally measured parameters into a device model to dynamically simulate the defect chemistry in semiconductors. For a silicon-doped gallium arsenide (GaAs) material, we showcase three capabilities: (i) Fermi level $E_F$ movement including its component electron and hole Fermi levels, (ii) dynamical charge equilibration with the arsenic vacancy serving as an example, and a (iii) diffusion-driven reaction between Coulomb attracted gallium interstitial ($Ga_i$) and arsenic vacancy ($v_{As}$). Governed by charge carrier reactions, the electron and hole Fermi levels remained dissimilar until equilibrium was achieved at $E_F\approx1.32$ eV. The equilibrium Fermi level was verified by successfully identifying $v_{As}^{3-}$ as the most populated charge state within the arsenic vacancy defect. Lastly, a Coulomb attraction, created by the shifted Fermi level and the charge equilibration process, between $Ga_i^{1+}$ and $v_{As}^{3-}$ resulted in the formation of a doubly negative gallium antisite ($Ga_{As}^{2-}$). The AIDE method can access experimentally inaccessible short-time and low-concentration regimes, is generalizable to other more complex systems (e.g., indium gallium arsenide), and, after solving open problems in GaAs, will serve as a virtual experiment to bound estimates for difficult-to-measure physical quantities.
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All authors Leopoldo Diaz, Harold P. Hjalmarson, Jesse J. Lutz, Peter A. Schultz

Materials Science

Electron and hole $g$ factors in semiconductors and nanostructures (Review)

A.V. Rodina, M.A. Semina and E.L. Ivchenko

We present a review of experimental and theoretical studies of the spin response of charge carriers to an external magnetic field in bulk semiconductors and semiconductor nanostructures. The linear response is quantitatively characterized by the magnitude of the electron or hole g factor. Various experimental methods for measuring the electron g factor are considered, beginning with historical works and including modern research. A detailed analysis of theoretical methods for calculating the electron and hole g factors in bulk semiconductors and nanostructures of various shapes also includes fundamental work from previous years and the present time.
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Materials Science · Cross-listed from cond-mat.supr-con

Niobium's intrinsic coherence length and penetration depth revisited using low-energy muon spin spectroscopy and secondary-ion mass spectrometry

Ryan M. L. McFadden, Jonathan W. Angle, Eric M. Lechner et al. (+7 more)

We report direct, simultaneous measurements of the London penetration depth ($\lambda_L$) and Bardeen-Cooper-Schrieffer (BCS) coherence length ($\xi_0$) in oxygen-doped niobium, with impurity concentrations spanning the "clean" to "dirty" limits. Two depth-resolved techniques - low-energy muon spin spectroscopy (LE-$\mu$SR) and secondary-ion mass spectrometry (SIMS) - were used to quantify the element's Meissner screening profiles, analyzed within a framework that accounts for nonlocal electrodynamics. The analysis indicates intrinsic length scales of $\lambda_L = 29.1(10)$ nm and $\xi_0 = 39.9(25)$ nm, corresponding to a Ginzburg-Landau (GL) parameter of $\kappa = 0.70(5)$. The obtained $\lambda_L$ and $\kappa$ values, accurately quantified at the nanoscale, are smaller than values commonly used in applications and modeling, and indicate that clean niobium lies at the boundary between type-I and type-II superconductivity, supporting the contemporary view that its intrinsic state may be type-I.
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All authors Ryan M. L. McFadden, Jonathan W. Angle, Eric M. Lechner, Michael J. Kelley, Charles E. Reece, Matthew A. Coble, Thomas Prokscha, Zaher Salman, Andreas Suter, Tobias Junginger

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

Low-temperature entropies and possible states in geometrically frustrated magnets

Siyu Zhu, Arthur P. Ramirez and Sergey Syzranov

The entropy that an insulating magnetic material releases upon cooling can reveal important information about the properties of spin states in that material. In many geometrically frustrated (GF) magnetic compounds, the heat capacity exhibits a low-temperature peak that comes from the spin states continuously connected to the ground states of classical models, such as the Ising model, on the same GF lattice, which manifests in the amount of entropy associated with this heat-capacity peak. In this work, we simulate numerically the values of entropy released by higher-spin triangular-lattice layered systems and materials on SCGO lattices. We also compare the experimentally measured values of entropy in several strongly GF compounds, $NiGa_2S_4$, $FeAl_2Se_4$ and SCGO/BSZCGO, with possible theoretical values inferred from the classical models to which the quantum states of those materials may be connected. This comparison suggests that the lowest-energy states of higher-spin layered triangular-lattice compounds can be described in terms of doublet states on individual magnetic sites. Our analyses demonstrate how the values of entropy can reveal the structure of low-energy magnetic states in GF compounds and call for more accurate thermodynamic measurement in GF magnetic materials.
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Materials Science

A model for positron annihilation in multi-layer systems by solving the diffusion equation using different positron affinities

Lucian Mathes, Michael Göldl, Michael Leitner et al. (+5 more)

We present a method for solving the positron diffusion equation in multi-layer systems. Our approach incorporates material-specific implantation profiles, diffusion parameters, and positron affinities. It utilizes a Markov chain approach to model annihilation probabilities and provides fitting capabilities for experimental S (lineshape) parameter data. We have implemented this algorithm in Python and made it available for free under the name LIMPID. To demonstrate its performance, we analyze depth-resolved Doppler-Broadening Spectroscopy measurements of a Cu layer on a Si substrate, achieving excellent agreement with the experimental profiles. The LIMPID tool enhances the reproducibility and comparability of positron defect characterization measurements across different research groups.
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All authors Lucian Mathes, Michael Göldl, Michael Leitner, Bettina Kohlhaas, Maximilian Suhr, Vassily Vadimovitch Burwitz, Armin Manhard, Christoph Hugenschmidt