Materials Science · Cross-listed from cond-mat.supr-con
Mechanism for Nodal Topological Superconductivity on PtBi$_2$ Surface
Kristian Mæland, Giorgio Sangiovanni and Björn Trauzettel
Experiments show that the Weyl semimetal PtBi$_2$ hosts unconventional superconductivity in its topological surface states. Hence, the material is a candidate for intrinsic topological superconductivity. Measurements indicate nodal gaps in the center of the
Fermi arcs. We derive that anisotropic electron-
phonon coupling on Weyl semimetal surfaces, combined with statically screened Coulomb repulsion, is a microscopic mechanism for this nodal pairing. The dominant solution of the linearized gap equation shows nodal gaps when the surface state bandwidth is comparable to the maximum
phonon energy, as is the case in PtBi$_2$. We further predict that if the screening of Coulomb interaction on the surface is enhanced by Coulomb engineering, the superconducting gap becomes nodeless, and the critical temperature increases.
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Materials Science · Cross-listed from cond-mat.supr-con
Superconductivity and geometric superfluid weight of a tunable flat band system
M. A. Mojarro and Sergio E. Ulloa
We study superconductivity and superfluid weight of the two-dimensional $\alpha$-$\mathcal{T}_3$
lattice with on-site asymmetries, hosting an isolated quasi-flat band with tunable bandwidth via a parameter $\alpha$. Within a mean-field approximation of the attractive Hubbard model, we obtain the superconducting order parameters on the three inequivalent sublattices and show their strong dependence on $\alpha$, interaction strength, and electron filling. At quasi-flat band filling, a superconducting gap opens and grows power-law fast with interaction strength, instead of the usual slow exponential growth, due to diverging density of states. We calculate the superfluid weight from linear response theory and study its band dispersion and
geometric contributions. While the conventional part proportional to band derivatives is suppressed in the quasi-flat band regime, the contribution dominated by the
quantum metric grows linearly for small interaction strength. We further demonstrate how tuning $\alpha$ enhances the
quantum metric and thus the
geometric superfluid weight especially near half-filling, while increasing on-site asymmetries increases the conventional contribution by broadening the quasi-flat band. We obtain the Berezinskii-Kosterlitz-Thouless transition temperature and demonstrate its strong dependence and enhancement with the parameter $\alpha$. Our results establish a tunable flat band system, the $\alpha$-$\mathcal{T}_3$
lattice model, as a candidate for tunable
quantum geometry and superfluid weight and as a prototype of related behavior in tunable
quantum materials.
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Materials Science
The Impact of Magnons, Defects, and Rapid Energy Migration on the Optical Properties of the 2D Magnet CrPS4
Jacob T. Baillie, Eden Tzanetopoulos, Rachel T. Smith et al. (+2 more)
Strong coupling between optical and
magnetic excitations could enable contactless, spatially resolved, or ultrafast interrogation and control of magnetism in two-dimensional (2D) materials and devices. The layered 2D A-type antiferromagnet CrPS4 stands out among van der Waals (vdW) magnets for its rich optical fine structure, but its spectroscopy is not yet understood and has so far been interpreted without consideration of
magnetic exchange. Here, we show that this fine structure comes primarily from exchange-mediated coupling between on-site optical "
spin-flip" transitions of Cr3+ and low-energy
spin transitions involving the surrounding
lattice. Well-resolved
magnon sidebands to optical 4A2 <–> 2E transitions are observed in photoluminescence (PL) and PL excitation spectra, as well as a pronounced PL sideband due to short-range exchange splitting. Energy migration is probed using Yb3+ dopants as traps, revealing sub-picosecond inter-site excitation hopping. Formation of dispersive Frenkel
excitons of coupled on-site d-d transitions due to inter-site exchange is discussed. In addition to impacting how optical fine structure is interpreted in this and potentially other vdW magnets, these findings may have ramifications for future applications of layered 2D magnets by revealing new opportunities to drive mode-specific
spin-wave excitations using light.
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All authors Jacob T. Baillie, Eden Tzanetopoulos, Rachel T. Smith, Remi Beaulac, Daniel R. Gamelin
Materials Science
Linear and Nonlinear Optical Properties of SiO$_2$/TiO$_2$ Heterostructures Grown by Plasma Enhanced Atomic Layer Deposition
Jinsong Liu, Martin Mičulka, Raihan Rafi et al. (+7 more)
Second harmonic (SH) radiation can only be generated in non-centrosymmetric bulk
crystals under the electric-dipole approximation. Nonlinear thin films made from bulk
crystals are technologically challenging because of complex and high temperature fabrication processes. In this work,
heterostructures made of amorphous materials SiO$_2$ and TiO$_2$ were prepared by a CMOS-compatible technique named
plasma enhanced atomic layer deposition (PEALD) with deposition temperature at 100 {\deg}C. By using the uniaxial dispersion model, we characterized the form-birefringence properties, which can enable the phase matching condition in waveguides or other nonlinear optical applications. By applying a fringe-based technique, we determined the largest diagonal component of the effective second-order bulk susceptibility $\chi_{zzz}^{(2)}$ = 1.30$\pm$0.13 pm/V at a wavelength of 1032 nm. Noteworthy, we observed strong SH signals from two-component nanolaminates, which are several orders of magnitude larger than from single layers. The SH signals from our samples only require the broken inversion
symmetry at the interface. Here optical properties of nanocomposites can be precisely tuned by the promising PEALD technology.
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All authors Jinsong Liu, Martin Mičulka, Raihan Rafi, Sebastian Beer, Denys Sevriukov, Stefan Nolte, Sven Schröder, Andreas Tünnermann, Isabelle Staude, Adriana Szeghalmi
Materials Science
A Rapid-prototyping CMOS-RRAM Integration Strategy
Andreas Tsiamis, Spyros Stathopoulos and Themis Prodromakis
Moore's law has long served the
semiconductor industry as the driving force for producing ever-advancing electronics technologies. However, given the economic implications and technological challenges associated with the present
semiconductor scaling constraints, a shift from a traditional more Moore approach to a beyond Moore paradigm is desirable for sustaining the current pace of innovation beyond the established development route. Resistive random-access
memories (RRAM) are one such beyond Moore technology that offers many avenues for innovation, and when integrated with mature complementary metal
oxide semiconductors (CMOS), can extend CMOS capabilities in a scalable and power-efficient manner, both in terms of
memory and computation. Nevertheless, as emerging and established technologies fuse, existing
semiconductor-optimised manufacturing faces significant challenges, while the methodologies and complexities of integration are often not highlighted in depth, or overlooked at the expense of demonstrating the application-specific integrated-technologies. In this article, we focus on the integration, and detail a cost-effective, rapid-prototyping, and technology agnostic CMOS-RRAM integration strategy that employs hybridised wafer-level and multi-reticle processing techniques, supported by a systematic increased complexity approach. Leveraging the fact that CMOS technologies can be readily realised by taking advantage of mature front-end-of-line fabrication processes offered by
semiconductor foundries, we establish an in-house RRAM development program that allows to combine fundamental material and device-level knowledge with custom-designed CMOS electronics. This approach utilises fully CMOS-compatible and transferable processes, ultimately enabling a seamless transition from research and development to volume production.
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Materials Science
Mechanical Detuning of Exciton-Phonon Resonance in WS2
Álvaro Rodríguez, Carmen Munuera and Andres Castellanos-Gomez
Controlling resonant Raman scattering in two-dimensional
semiconductors typically requires tuning the excitation energy to match excitonic transitions. Here we show that mechanical deformation can achieve the same effect without changing the
laser energy, enabling a controlled transition between resonant and non-resonant Raman scattering at fixed excitation. By applying biaxial strain up to 1.3% to WS2, the B
exciton is red-shifted by 180 meV. This large excitonic shift leads to a pronounced collapse of the double-resonant 2LA(M) mode under 532 nm excitation, quantitatively described by a resonance model formulated in terms of the B
exciton energy. Meanwhile, first-order
phonons remain narrow and reversible, confirming elastic deformation and efficient strain transfer. These results establish mechanical strain as an effective knob to control
exciton-
phonon mediated light-matter interactions. They enable deterministic and reversible tuning of resonance-enhanced Raman scattering and excitonic optical responses in layered
semiconductors.
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Materials Science
Gate tuning of coupled electronic and structural phase transition in atomically thin Ta$_2$NiSe$_5$
Keyu Wei, Yixuan Luo, Kenji Watanabe et al. (+3 more)
Realizing an excitonic
insulator phase from narrow-gap
semiconductors remains challenging, as unambiguous experimental signatures are difficult to establish. Ta$_2$NiSe$_5$ has been widely regarded as a leading candidate, yet the nature of its phase transition and insulating state remains controversial. Here, we report a systematic Raman spectroscopy study of Ta$_2$NiSe$_5$ as a function of thickness and field-effect doping, complemented by electrical transport measurements. The phase transition persists down to the monolayer limit, with the critical temperature increasing as thickness decreases. In
bilayer samples, both electron and hole doping suppress the insulating state, with electron doping lowering and hole doping raising the transition temperature. Importantly, the quasi-elastic scattering, previously attributed to excitonic fluctuations, evolves monotonically across the entire doping range, inconsistent with the expected suppression of excitonic correlations by Coulomb screening. These findings rule out a dominant excitonic mechanism and instead point to a coupled electronic and structural phase transition, whose stability is tunable by carrier doping. Our doping-based approach offers a general strategy for evaluating the role of excitonic effects in candidate excitonic
insulators.
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All authors Keyu Wei, Yixuan Luo, Kenji Watanabe, Takashi Taniguchi, Yanfeng Guo, Xiaoxiang Xi
Materials Science
Structural Optimization in Tensor LEED Using a Parameter Tree and $R$-Factor Gradients
Alexander M. Imre, Paul Haidegger, Florian Kraushofer et al. (+10 more)
Quantitative low-energy electron diffraction [LEED $I(V)$] is a powerful method for surface-structure determination, based on a direct comparison of experimentally observed $I(V)$ data with computations for a structure model. As the diffraction intensities $I$ are highly sensitive to subtle structural changes, local structure optimization is essential for assessing the validity of a structure model and finding the best-fit structure. The calculation of diffraction intensities is well established, but the large number of evaluations required for reliable structural optimization renders it computationally demanding. The computational effort is mitigated by the tensor-LEED approximation, which accelerates optimization by applying a perturbative treatment of small deviations from a reference structure. Nevertheless, optimization of complex structures is a tedious process. Here, the problem of surface-structure optimization is reformulated using a tree-based data structure, which helps to avoid redundant function evaluations. In the new tensor-LEED implementation presented in this work, intensities are computed on the fly, eliminating limitations of previous
algorithms that are limited to precomputed values at a grid of search parameters. It also enables the use of state-of-the-art optimization
algorithms. Implemented in Python with the JAX library, the method provides access to gradients of the $R$ factor and supports execution on graphics processing units (GPUs). Based on these developments, the computing time can be reduced by more than an order of magnitude.
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All authors Alexander M. Imre, Paul Haidegger, Florian Kraushofer, Ralf Wanzenböck, Tobias Hable, Sarah Tobisch, Marie Kienzer, Florian Buchner, Jesús Carrete, Georg K. H. Madsen, Michael Schmid, Ulrike Diebold, Michele Riva
Materials Science
Molecular Dynamics Simulations of $\gamma$-Belite(010)-Water Interfaces with High-Dimensional Neural Network Potentials
Bernadeta Prus and Jörg Behler
Belite – dicalcium silicate Ca$_2$SiO$_4$ – is a main constituent of low-carbon cement. In this work, we study several terminations of the (010) surface of $\gamma$-belite, its most stable polymorph, by molecular dynamics simulations. The energies and forces are provided by a high-dimensional neural network potential trained to density functional theory data. Water can interact in molecular form as well as dissociatively with the investigated interfaces, and the degree of dissociation is determined primarily by the protonation of SiO$_4$ groups accessible at the surface. A major part of the simultaneously formed hydroxide ions is adsorbed at surface calcium atoms, whose octahedral coordination spheres are completed by additional water molecules. The T3 termination, which is most stable in
vacuum, shows only little reactivity in water. For the only slightly less stable T2 termination, however, two distinct types of surface defects are observed. The type I defect is even stable in
vacuum and leads to a reconstruction of the entire surface, while the type II defect is only found in the presence of water. Overall, our results suggest that a variety of structures may be formed at the Ca$_2$SiO$_4$(010) surface, which are stabilized in the presence of water.
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Materials Science
Resistance Switching Properties of Stoichiometric and Nitrogen Implanted Silicon Nitride Nanolayers on N and P-Type Si Substrates
A. E. Mavropoulis, P. Karakolis, N. Vasileiadis et al. (+6 more)
This paper examines the resistive switching characteristics of LPCVD SiNx MNOS ReRAM
cells on both heavily doped n- and p-type silicon substrates, focusing on the effects of nitrogen doping. Detailed comparisons of electrical properties through nitrogen implantation reveal variations in trap density and SET-RESET voltages between n and p conductivity Si substrates. Impedance spectroscopy further elucidates the conductive path formation and its resistance.
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All authors A. E. Mavropoulis, P. Karakolis, N. Vasileiadis, L. Sygellou, E. Stavroulakis, V. Ioannou-Sougleridis, P. Normand, G. Ch. Sirakoulis, P. Dimitrakis
Materials Science
Breakdown characteristics of SiNx with different stoichiometries for resistive memories
A.E. Mavropoulis, I. Kanellopoulos, G. Pissanos et al. (+6 more)
The breakdown characteristics of SiNx layers with different stoichiometries are explored. The stoichiometry of SiNx is modified by changing the gas flow rates during the LPCVD deposition. These layers are suitable for RRAM
cells.
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All authors A.E. Mavropoulis, I. Kanellopoulos, G. Pissanos, G. Samara, N. Vasileiadis, E. Stavroulakis, P. Normand, G. Ch. Sirakoulis, P. Dimitrakis
Materials Science
SiNx RRAMs performance with different stoichiometries
A.E. Mavropoulis, G. Pissanos, N. Vasileiadis et al. (+3 more)
The microstructure of SiNx is strongly affected by its stoichiometry, x. The stoichiometry of SiNx thin films can be modified by adjusting the gas flow rates during LPCVD deposition. The deficiency or excess of Si atoms enhance the formation of defects such as nitrogen vacancies, silicon dangling bonds etc., and thus can enable performance tuning of the resulting MIS RRAM devices. DC electrical characterization, impedance spectroscopy and constant voltage stress measurements were carried out to investigate the properties of non-stoichiometric silicon nitride films as resistive switching material. The average SET time for each device was measured by applying voltage ramps. Improvement in the SET/RESET voltages and SET time is observed. Finally, the stoichiometric film exhibits the lowest breakdown acceleration factor, while the Si-rich film the highest.
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All authors A.E. Mavropoulis, G. Pissanos, N. Vasileiadis, P. Normand, G.Ch. Sirakoulis, P. Dimitrakis
Materials Science
Theoretical Characterization of the Magnetic Properties of Vanadium-doped Ti2C MXenes
Carlos Patiño, Pablo Díaz, Nicolás Vidal-Silva et al. (+3 more)
MXenes are two-dimensional materials composed of transition metals and light elements, known for their high conductivity and versatile surface chemistry. The introduction of
spin centers via doping can lead to promising materials for spintronics,
magnetic sensing, and data storage. We study the effect of V doping in Ti2C using first principle and Monte-Carlo simulations. Our results show that pristine Ti2C exhibits
ferromagnetic intralayer and
antiferromagnetic interlayer exchange interactions, yielding an
antiferromagnetic ground state. Vanadium incorporation alters these couplings, yet all doped configurations - Ti7VC4 and three Ti6V2C4 variants - retain predominantly
antiferromagnetic order. Despite the preserved ground state, V doping enhances the
magnetic response, most notably in the p-Ti6V2C4 configuration, which displays increased low-field susceptibility and partial
spin alignment across layers. As experimentally isolating individual doped phases is unlikely, samples will consist of mixed configurations whose collective behavior nonetheless exhibits clear signatures of V-induced
magnetic modification. These results reveal how transition-metal substitution tunes exchange interactions in MXenes and offer guidance for engineering their
magnetic functionalities.
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All authors Carlos Patiño, Pablo Díaz, Nicolás Vidal-Silva, Eduardo Cisternas, Eugenio Vogel, Fabian Dietrich
Materials Science · Cross-listed from cond-mat.mes-hall
Unconventional bright ground-state excitons in monolayer TiI$_2$ from first-principles calculations
Franz Fischer, Carl Emil Mørch Nielsen, Marta Prada et al. (+1 more)
Based on ab initio screened configuration interaction calculations we find that TiI$_2$ has a bright
exciton ground state and identify two key mechanisms that lead to this unprecedented feature among transition metal dichalcogenides. First, the
spin-orbit induced conduction band splitting results in optically allowed
spin-
alignment for electrons and holes across a significant portion of the Brillouin zone around the $\mathbf{K}$-valley, avoiding band crossings seen in materials like monolayer MoSe$_2$. Second, a sufficiently weak exchange interaction ensures that the bright
exciton remains energetically below the dark
exciton state. We further show that the bright
exciton ground state is stable under various mechanical strains and that trion states (charged
excitons) inherit this bright ground state. Our findings are expected to spark further investigation into related materials that bring along the two key features mentioned, as bright ground-state
excitons are crucial for applications requiring fast radiative recombination.
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All authors Franz Fischer, Carl Emil Mørch Nielsen, Marta Prada, Gabriel Bester
Materials Science · Cross-listed from cond-mat.str-el
Single-crystal growth, structural characterization, and physical properties of a decorated square-kagome antiferromagnet KCu$_7$TeO$_4$(SO$_4$)$_5$Cl
Jingjing Jing, Andreas Eich, Yiqiu Liu et al. (+9 more)
The square-kagome
lattice, composed of two-dimensional corner-sharing triangles, provides a novel platform for studying frustrated magnetism. However, material realizations of the square-kagome
lattice remain scarce. Here, we report the single-
crystal growth, structural characterization,
magnetic and electric properties of KCu$_7$TeO$_4$(SO$_4$)$_5$Cl, a nabokoite compound featuring a distorted and decorated square-kagome
lattice. Weak anomalies near 4 K are observed in both magnetization and specific heat, indicating the onset of a
magnetic transition.The formation of a long-range
antiferromagnetic state below 4.5 K is further confirmed by $^{35}$Cl
nuclear magnetic resonance (NMR) measurements.
Magnetic susceptibility data reveal nearly isotropic Curie-Weiss temperatures ($\sim-145$ K) and $g$-factors ($\sim2.4$) for both in-plane and out-of-plane
magnetic fields. Moreover, we observe two successive ferroelectric transitions at $T_\mathrm{FE1}\sim30$ K and $T_\mathrm{FE2}\sim27$ K, driven by inversion-
symmetry breaking, most likely associated with distortions in the Cu2O$_4$Cl$_1$ pyramids and the adjacent SO$_4$ tetrahedra. These results suggest that a three-dimensional model incorporating interlayer couplings via decorating Cu2 sites is essential for capturing the
magnetic and electric behaviors in KCu$_7$TeO$_4$(SO$_4$)$_5$Cl.
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All authors Jingjing Jing, Andreas Eich, Yiqiu Liu, Lunhua He, Aifeng Wang, Yisheng Chai, Young Sun, Yi Cui, Weiqiang Yu, Xinrun Mi, Michael Merz, Mingquan He
Materials Science
Structural Phase Transition and Cooperative Luminescence in K3Yb(PO4)2:Eu3+ for Multimodal Down-shifting and Up-converting Luminescence Thermometry
Anam Javaid, Maja Szymczak, Damian Szymanski et al. (+1 more)
To develop a more universal luminescent thermometer that provides both high relative sensitivity and the ability to measure temperature across different spectral ranges and excitation wavelengths, the K3Yb(PO4)2:Eu3+ system was proposed in this work. It was demonstrated that this material undergoes a structural phase transition from the monoclinic to the hexagonal phase above 450 K. This transition enabled the construction of a ratiometric, phase-transition-based thermometer utilizing the luminescence intensity ratio of Stark lines of Eu3+ and Yb3+ ions, which exhibit SRmax values of 4.2% K^-1 and 1.15% K^-1, respectively. Moreover, increasing the Eu3+ ion concentration was shown to raise the phase transition temperature, thereby shifting the thermal operating range of both luminescent thermometers. Under 980 nm excitation, K3Yb(PO4)2:Eu3+ exhibits both cooperative luminescence from Yb3+ pairs and up-conversion emission from Eu3+ ions. Increasing the Eu3+ concentration enhances the Eu3+ luminescence intensity relative to the cooperative luminescence of Yb3+ pairs, resulting in a change in the emitted light color. The difference in the thermal quenching behavior of these two signals further enabled the development of a ratiometric thermometer with SRmax = 0.58% K^-1. These findings identify K3Yb(PO4)3:Eu3+ as a promising candidate for
multimodal temperature sensing.
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All authors Anam Javaid, Maja Szymczak, Damian Szymanski, Lukasz Marciniak
Materials Science
Magnetic properties of molecular beam epitaxy-grown ultrathin Cr2Ge2Te6 films down to monolayer limit on Si substrates
Pengfei Ji, Ruixuan Liu, Tianchen Zhu et al. (+13 more)
Cr2Ge2Te6, a prototypical van der Waals
ferromagnetic semiconductor, have attracted significant interest for its potential applications in high-performance spintronics. However, the
magnetic ground state of monolayer Cr2Ge2Te6 remains elusive due to fragile and irregular-shaped thin flake samples with weak
magnetic signals. Here, we successfully grow uniform
ferromagnetic Cr2Ge2Te6 films down to monolayer by molecular beam epitaxy. By exploiting a self-limiting growth mode, we achieve synthesis of uniform monolayer Cr2Ge2Te6 films across entire millimeter-scale Si substrates. Through a combination of superconducting
quantum interference device magnetometry and anomalous
Hall effect measurements, we establish that monolayer Cr2Ge2Te6 exhibits intrinsic ferromagnetism with perpendicular
magnetic anisotropy below ~10 K, albeit with strong
magnetic fluctuations characteristic of its two-dimensional nature. Furthermore, a systematic thickness-dependent study reveals a crossover from this fluctuation-dominated two-dimensional magnetism turns into conventional long-range
ferromagnetic order as the film thickness increases. Our work not only definitively establishes the intrinsic
ferromagnetic ground state of monolayer Cr2Ge2Te6, but also provides a scalable, silicon-compatible route for preparing the two-dimensional magnet for future spintronic or
quantum devices.
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All authors Pengfei Ji, Ruixuan Liu, Tianchen Zhu, Jinxuan Liang, Yang Chen, Yitian Tong, Yunhe Bai, Zuhan Geng, Fangting Chen, Yunyi Zang, Xiyu Hong, Jiatong Zhang, Luyi Yang, Qi-Kun Xue, Ke He, Xiao Feng
Materials Science · Cross-listed from cond-mat.supr-con
Checkerboard-type Zhang-Rice States in Overdoped Cuprate Superconductors
Xiongfang Liu, Kun Han, Yan Peng et al. (+13 more)
Cuprate
superconductors remain central to condensed matter physics due to their technological relevance and unconventional, incompletely understood electronic behavior. While the canonical phase diagram and low-energy models have been shaped largely by studies of underdoped and moderately doped cuprates, the overdoped regime has received comparatively limited
attention.Here, we track the
evolution of the electronic structure from optimal to heavy overdoping in La2-xSrxCuO4(LSCO) using broadband optical spectroscopy across x=0.15-0.60. The measured spectral changes–including the redistribution of Zhang-Rice-related spectral weigh–are in qualitative agreement with determinant
quantum Monte Carlo simulations of the three-orbital Emery model, which together indicate a pronounced reconstruction of the electronic structure beyond hole concentrations x>0.2. Guided by these observations, we propose a spontaneous checkerboard-type Zhang-Rice electronic configuration that captures the coexistence of itinerant and localized carriers characteristic of the heavily overdoped state. Our results refine the doping-dependent Zhang-Rice-based framework for cuprates, illuminate how correlations persist deep into the overdoped regime, and provide new constraints on microscopic mechanisms of high-temperature superconductivity, with broader implications for correlated transition-metal
oxides.
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All authors Xiongfang Liu, Kun Han, Yan Peng, Yuanjie Ning, Jing Wu, Zhaoyang Luo, Difan Zhou, Zhigang Zeng, Qian He, Chuanbing Cai, Mark. B. H. Breese, Ariando Ariando, Chi Sin Tang, George A. Sawatzky, Mi Jiang, Xinmao Yin
Materials Science
Effect of cold rolling strain on the microstructural evolution in equimolar MoNbTaTiZr refractory complex concentrated alloy: Comprehensive characterization
Andrea Skolakova, Haruka Katayama, Pavel Lejcek et al. (+8 more)
This work presents a pilot study on a strained complex concentrated
alloy based on refractory elements: MoNbTaTiZr. Initially, the as-cast and homogenization-annealed conditions were characterized. After casting, the
alloy consists of two solid solutions with BCC 1 and BCC 2
crystal structures. Homogenization annealing promotes the growth, ordering, and refinement of the BCC 2 phase. TEM and AES analyses indicate possible Zr segregation at grain boundaries in the as-cast state. In contrast, annealing followed by cooling results in the formation of Ti-Zr-based particles without segregation. Subsequently, the annealed
alloy was cold-rolled, and its microstructure was investigated. During rolling, grain fragmentation occurs within the structure. In addition to the two BCC solid solutions, a phase with an FCC
crystal structure is identified after rolling. Its composition corresponds to the Zr2Ta phase, which is a Laves phase of the A2B type. Rotational relationships, relatively rare in rolled materials with BCC structures, are identified. The texture components found after 10% rolling deformation are related to that present after 20% deformation by a 45 degrees <110> rotation, and this component is related to that appearing after 30% deformation by a 20 degrees <100> rotation. However, no distinct rolling texture or clear texture development was observed, although some mutual relationships among preferred orientations can be identified. Schmid and Taylor factor maps demonstrate that, despite deformation, the
alloy remains capable of further strain accumulation and plastic deformation. Twinning is also observed after rolling, which may be beneficial, as deformation twinning contributes to improved ductility in the
alloy.
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All authors Andrea Skolakova, Haruka Katayama, Pavel Lejcek, Orsolya Molnarova, Sadahiro Tsurekawa, Petr Vertat, Jan Duchon, Jaroslav Cech, Petr Svora, Ondrej Ekrt, Jan Pinc
Materials Science
Transport Novelty Distance: A Distributional Metric for Evaluating Material Generative Models
Paul Hagemann, Simon Müller, Janine George et al. (+1 more)
Recent advances in generative machine learning have opened new possibilities for the discovery and design of novel materials. However, as these models become more sophisticated, the need for rigorous and meaningful evaluation metrics has grown. Existing evaluation approaches often fail to capture both the quality and novelty of generated structures, limiting our ability to assess true generative performance. In this paper, we introduce the Transport Novelty Distance (TNovD) to judge generative models used for materials discovery jointly by the quality and novelty of the generated materials. Based on ideas from Optimal Transport theory, TNovD uses a coupling between the features of the training and generated sets, which is refined into a quality and memorization regime by a threshold. The features are generated from
crystal structures using a graph neural network that is trained to distinguish between materials, their augmented counterparts, and differently sized supercells using contrastive learning. We evaluate our proposed metric on typical toy experiments relevant for
crystal structure prediction, including memorization, noise injection and
lattice deformations. Additionally, we validate the TNovD on the MP20 validation set and the WBM substitution
dataset, demonstrating that it is capable of detecting both memorized and low-quality material data. We also
benchmark the performance of several popular material generative models. While introduced for materials, our TNovD framework is domain-agnostic and can be adapted for other areas, such as images and molecules.
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All authors Paul Hagemann, Simon Müller, Janine George, Philipp Benner
Materials Science · Cross-listed from cond-mat.soft
Breaking the Logarithmic Barrier: Activity-Induced Recovery of Phase Separation Dynamics in Confined Geometry
Preethi M, Parameshwaran A and Bhaskar Sen Gupta
Phase separation in confined environments is a fundamental process underlying geological flows, porous filtration, emulsions, and intracellular organization. Yet, how confinement and activity jointly govern coarsening kinetics and interfacial morphology remains poorly understood. Here, we use large-scale molecular dynamics simulations to investigate vapor-
liquid phase separation of passive and active fluids embedded in complex porous media. By generating porous host structures via a freeze-quench protocol, we systematically control the average pore size and demonstrate that confinement induces a crossover from the Lifshitz-Slyozov power-law growth to logarithmically slowed coarsening, ultimately arresting domain
evolution. Analysis of correlation functions and structure factors reveals that confined passive systems exhibit fractal interfaces, violating Porod's law and indicating rough morphological arrest. In contrast, introducing self-propulsion dramatically changes the coarsening pathway: activity restores smooth interfaces, breaks the confinement-induced scaling laws, and drives a transition from logarithmic to ballistic domain growth at high activity levels. Our findings reveal an activity-controlled mechanism to overcome
geometric restrictions and unlock coarsening in structurally heterogeneous environments. These insights establish a unifying framework for nonequilibrium phase transitions in porous settings, with broad relevance to active colloids, catalytic media, and biologically crowded systems, where living matter routinely reorganizes within
geometric constraints to sustain function.
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Materials Science
Twin Domains in 111 oriented {CdO/MgO} superlattices: homoepitaxy versus heteroepitaxy
Ewa Przeździecka, Aleksandra Wierzbicka, Abinash Adhikari et al. (+1 more)
The structural properties of (111)-oriented {CdO/MgO} superlattice structures grown on c-sapphire and cubic MgO substrates have been studied by high resolution X-ray diffraction. The growth was performed in a
plasma-assisted molecular beam epitaxy system. Although both superlattices are (111)-oriented and the {CdO/MgO} structure has 3m
symmetry. It was shown that the superlattice on c-sapphire consists of misoriented domains, whereas no such domains were observed on (111) MgO. The twin domains are rotated by 180{\deg} with respect to each other and by 30{\deg} with respect to the sapphire substrate. We show that the crucial phenomena based on the formation of rotation domains and their number in heteroepitaxy depend fundamentally on the relationship between substrate and epilayer
symmetries.
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All authors Ewa Przeździecka, Aleksandra Wierzbicka, Abinash Adhikari, Marta A. Chabowska
Materials Science
Symmetry-driven giant magneto-optical Kerr effects in altermagnet hematite
Jiaxin Luo, Xiaodong Zhou, Jinxuan Liang et al. (+7 more)
Altermagnets have attracted tremendous interest for revealing intriguing physics and promising spintronics applications. In contrast to conventional antiferromagnets, altermagnets break both PT and Tt
symmetries, and simultaneously exhibit
spin-split band structures with a vanishing net magnetization. To quantify insulating altermagnets without conduction electron, we propose to use magneto-optical Kerr effect (MOKE) to identify the altermagnetic fingerprints. In particular, we demonstrate not only the
giant MOKE responses, but also their connection with the orientations of Neel vectors at room temperature in altermagnet hematite alpha-Fe_2O_3. Specifically, under the Neel vector along the [1-100] axis, we find a
giant polar Kerr rotation angle 93.4 mdeg in the (11-20) plane, which is allowed by the
magnetic space group C2'/c'. Under the Neel vector along the [11-20] axis, we find a longitudinal Kerr angle 9.6 mdeg in the (0001) plane, which is allowed by the
magnetic space group C2/c. Further, we show that such pronounced MOKE effects directly enable an optical imaging of altermagnetic domains, together with their reversible domain wall (DW) motion. Our studies not only suggest MOKE can be used to identify altermagnet candidates, but also signify the feasibility of exploring altermagnetic optical and DW spintronics, which could largely expand the current research paradigm of altermagnetism.
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All authors Jiaxin Luo, Xiaodong Zhou, Jinxuan Liang, Ledong Wang, Qiuyun Zhou, Yong Jiang, Wenhong Wang, Yugui Yao, Luyi Yang, Wanjun Jiang
Materials Science
Electrical Characterization of High-k (k>115) Crystalline SrTiO3 (STO) thin film integration with GaN with Nanomembrane Transfer Process
Md Tahmidul Alam, Kyoungjun Lee, Guangying Wang et al. (+2 more)
High-k (115), crystalline SrTiO3 (STO) thin film was transferred on GaN for potential applications in power devices (transistor and diodes) by nanomembrane transfer method and the detailed electrical properties such as leakage current, CV profiles, dielectric constant, frequency dispersion was reported from fabricated MOSCAP structures. The leakage current was negligible (under noise-level of tool) up to 6 V and 11 V for 50 nm and 200 nm STO membrane respectively A high-quality dielectric was indicated by the CV profile, which showed almost negligible frequency dispersion in the frequency range of 10 kHz to 500 kHz. The dielectric constant was 50 to 82 with the 50 nm thick STO membrane and 115 to 186 in the 200 nm thick STO membrane. Thermal annealing of the membrane in ambient conditions at 250 degrees for 2 hours led to a slight improvement in the dielectric constant (8 to 20 percent), albeit at the expense of degraded leakage current performance, as indicated by a reduction of 1 V to 3 V in the "no leakage region" of the IV curves after annealing. The possible physical mechanisms responsible for these changes were also analyzed and discussed.
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All authors Md Tahmidul Alam, Kyoungjun Lee, Guangying Wang, Chang-beom Eom, Chirag Gupta
Materials Science · Cross-listed from cs.DL
Optimizing Data Extraction from Materials Science Literature: A Study of Tools Using Large Language Models
Wenkai Ning, Musen Li, Jeffrey R. Reimers et al. (+1 more)
Large
Language Models (LLMs) are increasingly utilized for large-scale extraction and organization of unstructured data owing to their exceptional Natural
Language Processing (NLP) capabilities. Empowering materials design, vast amounts of data from experiments and simulations are scattered across numerous scientific publications, but high-quality experimental databases are scarce. This study considers the effectiveness and practicality of five representative AI tools (ChemDataExtractor, BERT-PSIE, ChatExtract, LangChain, and Kimi) to extract bandgaps from 200 randomly selected Materials Science publications in two presentations (arXiv and publisher versions), comparing the results to those obtained by human processing. Although the integrity of data extraction has not met expectations, encouraging results have been achieved in terms of precision and the ability to eliminate irrelevant papers from human consideration. Our analysis highlights both the strengths and limitations of these tools, offering insights into improving future data extraction techniques for enhanced scientific discovery and innovation. In conjunction with recent research, we provide guidance on feasible improvements for future data extraction methodologies, helping to bridge the gap between unstructured scientific data and structured, actionable databases.
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All authors Wenkai Ning, Musen Li, Jeffrey R. Reimers, Rika Kobayashi
Materials Science
Translating Chirality into Multidirectional Motion through Broadband Chiroptical MXenes
Wookjin Jung, Dongkyu Lee, Yonghee Lee et al. (+2 more)
The integration of chirality into functional materials enables control of light-matter interactions beyond binary illumination (on/off). Conventional photoactuators rely on binary modulation, limiting them to unidirectional motion. In contrast, we introduce a ternary optical logic paradigm where actuation direction is encoded by the handedness of circularly polarized light (CPL). Here, we establish a
chiral Ti$_{3}$C$_{2}$T$_{x}$ MXene platform bridging molecular chirality and mechanical actuation. Phenylalanine enantiomers are covalently anchored onto MXene nanoflakes via
chiral nanopainting. The 2D confinement forces ligands into vertically aligned supramolecular networks. Interlayer-spacing analysis and simulations corroborate that such supramolecular networks unlock exceptionally broadband circular dichroism from the ultraviolet to the near-infrared. This supramolecular chirality synergizes with MXene's plasmonic properties to drive handedness-dependent photothermal conversion, with a 30% differential temperature rise between matched and mismatched CPL.
Embedding this
chiral MXene into thermoresponsive hydrogels realizes, to the best of our knowledge, the first CPL-driven soft actuator that implements LCP/RCP/off as a ternary input to program multidirectional deformation based on a photothermal mechanism. This molecular-to-macroscopic translation demonstrates a new paradigm for chirality-encoded soft robotics and adaptive photonics.
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All authors Wookjin Jung, Dongkyu Lee, Yonghee Lee, Ki Hyun Park, Jihyeon Yeom
Materials Science · Cross-listed from cond-mat.str-el
Low-dimensionality-induced tunable ferromagnetism in SrRuO$_3$ ultrathin films
Jinyoung Kim, Minjae Kim, Donghan Kim et al. (+5 more)
Quantum materials near electronic or
magnetic phase boundaries exhibit enhanced tunability, as their emergent properties become highly sensitive to external perturbations. Here, we demonstrate precise control of ferromagnetism in a SrRuO$_3$ ultrathin film, where a high density of states (DOS), arising from low-dimensional
quantum states, places the system at the crossover between a non-
magnetic and bulk
ferromagnetic state. Using
spin- and angle-resolved photoemission spectroscopy (SRPES/ARPES), transport measurements, and theoretical calculations, we systematically tune the
Fermi level via electron doping across the high-DOS point. We directly visualize the
spin-split band structure and reveal its influence on both
magnetic and transport properties. Our findings provide compelling evidence that magnetism can be engineered through DOS control at a phase crossover, establishing a pathway for the rational design of tunable
quantum materials.
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All authors Jinyoung Kim, Minjae Kim, Donghan Kim, Sungsoo Hahn, Younsik Kim, Minsoo Kim, Byungmin Sohn, Changyoung Kim
Materials Science
Single-crystalline high-quality beta-Ga2O3 pseudo-substrate on sapphire through sputtering for epitaxial deposition
Guangying Wang, Shuwen Xie, William Brand et al. (+10 more)
Solid-phase epitaxy (SPE) of beta-Ga2O3 thin films by
radio-frequency (RF) sputtering and then crystallized through high-temperature post-deposition annealing is employed on sapphire substrates, yielding a high-quality pseudo-substrate for subsequent buffer growth via MOCVD and LPCVD. Low roughness (<0.5 nm) and sharp single-crystalline diffraction peaks corresponding to the (-201), (-402), and (-603) reflections of beta-Ga2O3 were observed in the SPE beta-Ga2O3 film and the subsequent epitaxial buffer layer. N-doped Ga2O3 film on SPE Ga2O3 film grown by LPCVD showed step-assisted growth mode with reasonable electronic behavior with 45 cm^2/V-s mobility at a bulk carrier concentration of 1.3e17 cm^-3. These results suggest that SPE Ga2O3 is a promising pathway to advance the development of beta-Ga2O3 on foreign substrates.
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All authors Guangying Wang, Shuwen Xie, William Brand, Saleh Ahmed Khan, Ahmed Ibreljic, Darryl Shima, Yueying Ma, Brahmani Challa, Fikadu Alema, Andrei Osinsky, Anhar Bhuiyan, Ganesh Balakrishnan, Shubhra S. Pasayat
Materials Science
A physics-augmented neural network framework for modeling and detecting thermo-visco-plastic behavior
Reese E. Jones, Asghar Jadoon, D. Thomas Seidl et al. (+1 more)
Although considerable
attention has been devoted to the development of models for isothermal, rate-independent plasticity, many high-consequence performance assessments involve viscoplastic processes that generate substantial heat. In addition, materials may transit from a nearly isothermal, rate-independent regime to a viscous, temperature-dependent regime during these processes, which makes modeling more challenging. In this work, we develop a physics-augmented neural network (PANN) framework for modeling general temperature-dependent, rate-dependent inelastic processes firmly based on physical principles, including the second law of thermodynamics and coordinate equivariance. These embedded properties are enabled by a number of architectural innovations in the structure and training of an input convex and potential-based neural ordinary differential equation framework. The resulting neural network models are capable of representing a wide spectrum of rate- and temperature-dependence ranging from isothermal, rate-independent elastic-plastic phenomenology to rate-dependent fully viscous inelastic behavior, as we demonstrate. We also show that the framework is capable of modeling complex microstructural inelasticity and predicting the conversion of plastic work to heating when calibrated to stress-temperature observations.
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All authors Reese E. Jones, Asghar Jadoon, D. Thomas Seidl, Jan N. Fuhg
Materials Science · Cross-listed from physics.optics
Scalable van der Waals Photonics: High-Refractive-Index Gallium Sulfide Films with Single-Crystal Optical Properties
Aleksandr Slavich, Georgy Ermolaev, Dmitriy Grudinin et al. (+15 more)
The integration of high-refractive-index dielectrics into scalable photonic architectures is foundational to advancing integrated
circuits and augmented reality (AR) displays. Van der Waals (vdW) materials offer exceptional optical properties, including high refractive indices and
giant anisotropy, but their implementation is constrained by the small area and uncontrolled thickness of mechanically exfoliated flakes. Here, we demonstrate that atomic layer deposition (ALD) grown gallium sulfide (GaS) overcomes the trade-off between high optical performance and manufacturability, emerging as a large-scale vdW dielectric platform. Through rigorous optical and structural benchmarking against pristine single
crystals, we establish that the optical constants (n, k) of ALD-GaS are virtually indistinguishable from single-
crystal counterparts. By leveraging the retained out-of-plane anisotropy, we demonstrate that ALD-GaS enables superior suppression of crosstalk in densely integrated waveguides compared to conventional scalable high-index platforms. Our findings establish ALD-GaS as a technologically viable pathway for implementing anisotropic vdW materials in visible-spectrum photonics.
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All authors Aleksandr Slavich, Georgy Ermolaev, Dmitriy Grudinin, Mikhail Tatmyshevskiy, Alexander Syuy, Nikolay Pak, Dmitry Yakubovsky, Mikhail Mironov, Adilet Toksumakov, Alexander Melentev, Elena Zhukova, Anton Minnekhanov, Gleb Tselikov, Ivan Kruglov, Sergey M. Novikov, Andrey Vyshnevyy, Aleksey Arsenin, Valentyn Volkov