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Physics Condensed Matter Materials Science

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Monday 13 October

Materials Science

Optimizing Cross-Domain Transfer for Universal Machine Learning Interatomic Potentials

Jaesun Kim, Jinmu You, Yutack Park et al. (+11 more)

Accurate yet transferable machine-learning interatomic potentials (MLIPs) are essential for accelerating materials and chemical discovery. However, most universal MLIPs overfit to narrow datasets or computational protocols, limiting their reliability across chemical and functional domains. We introduce a transferable multi-domain training strategy that jointly optimizes universal and task-specific parameters through selective regularization, coupled with a domain-bridging set (DBS) that aligns potential-energy surfaces across datasets. Systematic ablation experiments show that small DBS fractions (0.1%) and targeted regularization synergistically enhance out-of-distribution generalization while preserving in-domain fidelity. Trained on fifteen open databases spanning molecules, crystals, and surfaces, our model, SevenNet-Omni, achieves state-of-the-art cross-domain accuracy, including adsorption-energy errors below 0.06 eV on metallic surfaces and 0.1 eV on metal-organic frameworks. Despite containing only 0.5% r$^2$SCAN data, SevenNet-Omni reproduces high-fidelity r$^2$SCAN energetics, demonstrating effective cross-functional transfer from large PBE datasets. This framework offers a scalable route toward universal, transferable MLIPs that bridge quantum-mechanical fidelities and chemical domains.
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All authors Jaesun Kim, Jinmu You, Yutack Park, Yunsung Lim, Yujin Kang, Jisu Kim, Haekwan Jeon, Suyeon Ju, Deokgi Hong, Seung Yul Lee, Saerom Choi, Yongdeok Kim, Jae W. Lee, Seungwu Han

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

Spinon band flattening by its emergent gauge field in quantum kagome ice

Masafumi Udagawa and Roderich Moessner

Fractional excitations provide a key to identifying sought-after topological quantum spin liquid states in realistic materials. Their single-particle dynamics already presents a challenging many-body problem on account of the coupling to their emergent gauge field. Here, we study the spinon excitations of kagome ice, realized at the $2/3$ magnetization plateau of spin ice, by combining up-to-$63$-site exact diagonalization with an analytical state graph mapping. We find a macroscopically degenerate mode in the spinon spectrum. It originates from the destructive interference due to the interaction with surrounding gauge fields, a form of many-body caging. We explicitly construct, and count, the concomitant many-body wave functions. Finally, we discuss the possible role of these flat modes in the magnetization process of kagome antiferromagnets, in particular with regard to the asymmetric termination of the kagome ice magnetisation plateau.
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Materials Science

In-plane polar domains enhanced energy storage

Yu Lei, Xiaoming Shi, Sihan Yan et al. (+16 more)

Relaxor ferroelectric thin films are recognized for their ultrahigh power density, rendering them highly promising for energy storage applications in electrical and electronic systems. However, achieving high energy storage performance with chemically homogeneous, environmentally friendly and compositionally stable materials remains challenging. In this work, we present a design of dielectrics with high energy storage performance via an in-plane polar domains incorporating polar nanoregions mechanism. Guided by phase-field simulations, we synthesized La/Si co-doping BaTiO3 solid-solution thin films with high chemical homogeneity to realize high energy storage performance. Given that, we achieve a high energy density of 203.7J/cm3 and an energy efficiency of approximately 80% at an electric field of 6.15MV/cm. This mechanism holds significant promise for the design of next-generation high-performance dielectric materials for energy storage and other advanced functional materials.
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All authors Yu Lei, Xiaoming Shi, Sihan Yan, Qinghua Zhang, Jiecheng Liu, Sixu Wang, Yu Chen, Jiaou Wang, He Qi, Qian Li, Ting Lin, Jingfen Li, Qing Zhu, Haoyu Wang, Jing Chen, Lincong Shu, Linkun Wang, Han Wu, Xianran Xing

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

Local-Antisymmetric Flat Band and Coexisting Correlated stripe charge orders in WSe2-Modulated Twisted Bilayer Graphene

Chi Zhang, Shihao Zhang, Mengmeng Zhang et al. (+2 more)

Insulating, atomically flat transition metal dichalcogenides (TMDs) like WSe2 are ideal substrates for probing intrinsic graphene properties. Conventionally, their influence on graphene's band structure is assumed negligible, particularly when small moire patterns form. Combining scanning tunneling microscopy/spectroscopy and theoretical analysis, we reveal that the atomic registry in graphene/WSe2 heterostructures profoundly modulates the electronic structure of magic-angle twisted bilayer graphene (MATBG). At special graphene/WSe2 twist angles, an incommensurate moire superlattice hosts three distinct atomic stacking configurations (A, B, X types). These induce position-dependent potentials that asymmetrically shift MATBG's flat bands, transforming them from hole-side to electron-side asymmetric within a single AA-stacked region. This symmetry breaking enables the unprecedented coexistence of orthogonal stripe charge orders in the correlated regime-a phenomenon previously considered mutually exclusive due to Coulomb repulsion. This band modulation arises from the synergistic effects of the graphene/WSe2 interfacial atomic registry and heterostrain within the MATBG, exhibiting multi-field tunability. Our work establishes interfacial atomic registry as a critical, previously overlooked tuning parameter for flat-band physics, opening avenues to engineer correlated quantum states in van der Waals heterostructures.
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All authors Chi Zhang, Shihao Zhang, Mengmeng Zhang, Lin He, Qi Zheng

Materials Science

Entropy Engineering-Regulated Electron-Phonon Coupling for Highly Efficient Photoluminescence in Se-doped WS2

Chi Zhang, Quan Shen, Mengmeng Zhang et al. (+8 more)

The limited quantum yield of strained monolayer transition metal dichalcogenides grown by vapor-phase methods and during transfer-based stacking poses a fundamental challenge for their optoelectronic applications. Here, we introduce the concept of "entropy engineering" as a transformative strategy to selectively enhance light-matter interactions through controlled electron-phonon coupling. We unveil how tailored entropy introduced via precise selenium doping or interfacial van der Waals proximity can significantly amplify radiative recombination from momentum-dark excitons in WS2 monolayers. Notably, we discover that slight selenium doping drastically enhances the photoluminescence (PL) of WS2 under strain. While both undoped and heavily doped WS2 suffer from strong PL quenching owing to the direct-to-indirect bandgap transition, lightly Se-doped samples exhibit an order-of-magnitude increase in emission intensity. This counterintuitive boost is traced to doping-induced structural disorder, which intensifies electron-phonon interactions and unlocks efficient phonon-assisted emission from otherwise non-radiative indirect excitons. Moreover, we demonstrate that van der Waals coupling to adjacent Se-doped layers can impart interfacial entropy and further augment PL via proximity effects. Our work highlights entropy engineering via controlled doping as a powerful strategy for activating high-efficiency light emission in atomically thin semiconductors.
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All authors Chi Zhang, Quan Shen, Mengmeng Zhang, Zhiming Deng, Taishen Wu, Xuying Zhong, Gang Ouyang, Dongsheng Tang, Qi Zheng, Jiansheng Dong, Weichang Zhou

Materials Science

Frenkel anomaly on co-ordination numbers in liquid CO2 at 100 and 1000 bar studied by Monte Carlo simulation using Kihara potential model

Koji Kobashi

An issue concerning the Frenkel line of liquid CO2 is that its location has not been unequivocally determined. So far, reliable Frenkel lines were identified from velocity autocorrelation functions (VAFs) computed by Molecular Dynamic simulations; however VAFs cannot be directly verified experimentally. By contrast, the co-ordination numbers (CNs) can be measured experimentally by X-ray and neutron scattering or computed by Monte Carlo (MC) simulation, and thus provide an alternative means of determining the location of the Frenkel line. In the present study, the CNs were computed by MC simulation using the Kihara potential, and the Frenkel anomalies were identified at {P = 100 bar, T = 260 K}, in good agreement with previous results based on VAFs, and at {P = 1000 bar, T = 370 K}, which deviates significantly from them.
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Materials Science

Generalized quantum limits of electrical contact resistance and thermal boundary resistance

Alice Ho, Jashan Singhal, Deji Akinwande et al. (+2 more)

The importance of electrical contact resistance and thermal boundary resistance has increased dramatically as devices are scaled to atomic limits. The use of a rich range of materials with various bandstructures (e.g. parabolic, conical), and in geometries exploiting various dimensionalities (e.g. 1D wires, 2D sheets, and 3D bulk) will increase in the future. Here we derive a single general expression for the quantum limit of electrical contact resistivity for various bandstructures and all dimensions. A corresponding result for the quantum limit of thermal boundary resistance is also derived. These results will be useful to quantitatively co-design, benchmark, and guide the lowering of electrical and thermal boundary resistances for energy efficient devices.
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All authors Alice Ho, Jashan Singhal, Deji Akinwande, Huili Grace Xing, Debdeep Jena

Materials Science

Delayed 1T to 2H Phase Transition Upon Electrochemical Delithiation of LiMoS2

Yerin Hong, Juhwan Lim, Jinhong Min et al. (+4 more)

Molybdenum disulfide (MoS2) is a widely studied layered material for electronic, optical, and catalytic applications. It can host lithium ions between the van der Waals layers, which triggers a phase transition between the semiconducting 2H phase and metallic 1T phase. While lithium insertion triggers a phase transition to the 1T phase, the phase behavior upon electrochemical lithium removal is not resolved. In this work, we conduct single-flake electrochemical (de)lithiation of MoS2 using microelectrode arrays. Through both electrochemical voltage analysis and correlative Raman spectroscopy, we show that an electrochemically cycled and delithiated MoS2 flake initially remains in the 1T phase. However, over the course of several days, it transitions back into the thermodynamically stable 2H phase. This result resolves the phase transformation pathway upon delithiation and showcases the ability to electrochemically synthesize the metastable 1T-MoS2 phase.
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All authors Yerin Hong, Juhwan Lim, Jinhong Min, Nishkarsh Agarwal, Robert Hovden, Ageeth A. Bol, Yiyang Li

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

Two-dimensional flat-bands in Moire-diamonds

Yalan Wei, Shifang Li, Yuke Song et al. (+1 more)

The discovery of flat-bands in magic-angle twisted bilayer graphene has underscored the potential of moire engineering for correlated states, but such phases are notoriously difficult to realize and highly fragile against perturbations. Here, we propose an alternative route to flat-bands by introducing sp3 hybridization in twisted graphite. Instead of relying on fine-tuned magic angles, our approach identifies flat-band states at relatively large twist angles with short moire periods. In this regime, sp3-induced reconstructions generate electronic states that, once formed, are locked by substantial energy barriers, rendering them robust against external perturbations. Using twisted graphite as a prototype, we uncover a series moire-diamond that host two-dimensional flat conduction of valence bands, where carriers are localized within specific momentum planes but remain dispersive along orthogonal directions. The emergence of dimensional flat-bands opens a new platform for flat-band-driven correlated physics and suggests opportunities for designing quantum materials with highly directional electronic functionalities.
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All authors Yalan Wei, Shifang Li, Yuke Song, Chaoyu He

Sunday 12 October

Materials Science

Emerging Ferroelectric Domains: Stacking and Rotational Landscape of MoS2 Moire Bilayers

Anikeya Aditya, Ayu Irie, Nabankur Dasgupta et al. (+3 more)

The structures and properties of moire patterns in twisted bilayers of two-dimensional (2D) materials are known to depend sensitively on twist angle, yet their dependence on stacking order remains comparatively underexplored. In this study, we use molecular dynamics simulations to systematically investigate the combined effects of stacking order and rotation in MoS2 bilayers. Beginning from five well-established high-symmetry bilayer stackings, we apply twist angles between 1 and 120 to the top layer, revealing a variety of relaxed moire structures. Our results show that the initial stacking significantly influences the moire domain configurations that emerge at a given twist angle. While all five stacking orders are metastable without twist, they form two moire-equivalent classes- AA/AB and AA',A'B,AB', i.e., for a given twist angle, structures within each class relax to the same moire configuration. Specifically, initial AA and AB stackings give rise to triangular ferroelectric domains near 0+/-3, while AA', A'B, and AB' stackings produce triangular ferroelectric domains near 60+/-3. At precisely 60 and 120 twists, the bilayers relax to into pure high-symmetry stackings, highlighting the rotational relationships between these configurations and explaining the shift of 60 in the ferroelectric rotational range. These findings demonstrate the critical role of stacking order in governing the rich moire landscapes accessible in twistronic systems.
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All authors Anikeya Aditya, Ayu Irie, Nabankur Dasgupta, Rajiv K. Kalia, Aiichiro Nakano, Priya Vashishta

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

On the discovery of meteoritic mineral Zolenskyite; The artificial origin should not be overlooked

Boutros Pierre Embaid

Recently a new meteoritic mineral, Zolenskyite (Fe0.99Mn0.04Ca0.01Cr1.99S3.98), was discovered from the Indarch meteorite. Zolenskyite was structurally indexed as the monoclinic C2/m CrNb2Se4 - Cr3S4 type structure of synthetic FeCr2S4, with unit cell parameters a = 12.84(1) Å, b = 3.44(1) Å, c = 5.94(1) Å and e̱ta} = 117(1){\deg}. Zolenskyite was reported as high-pressure phase formed from Daubréelite at high pressures and temperatures in highly shocked regions of the EH parent asteroid. Although this discovery provides valuable information about the origin of meteoritic mineral assemblages, the results and conclusions raise controversies with those reported in previous articles where the synthetic FeCr2S4 was described. In this review, an alternative analysis of the supplementary X-ray data from Zolenskyite was made and yields to the monoclinic I2/m Cr3S4 type structure of synthetic FeCr2S4, with unit cell parameters a = 5.940 Å, b = 3.440 Å, c = 11.441 Å and e̱ta} = 90.55{\deg}, in agreement with previous results in the literature and differ from those reported above. Regarding the genesis of Zolenskyite and according to solid-state laboratory synthesis, the transformation of cubic FeCr2S4 phase (ideal composition of Daubréelite) to monoclinic FeCr2S4 (ideal composition of Zolenskyite) requires a process whose replication in Shock metamorphism stages is not well established and remains an open issue to address, together with another open issue related to the real composition of meteoritic minerals, with minor and trace metals, which is often overlooked when compared with synthetic ideal compositions. Whatever the results to be obtained by addressing the above open issues, they will shed more light on the genesis of Zolenskyite. In this context, it is worth to promote an open debate about the hypothesis of artificial origin.
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Materials Science

Electron-hole liquid in biological tissues under ultra high dose rate ionizing radiation

Diana Shvydka and Victor Karpov

We develop a quantitative model of ionization processes in biological tissues under Ultra High Dose Rate (UHDR) radiation. The underlying conjecture is that of electron-hole liquid (EHL) forming in water based substances of biological tissues. Unlike the earlier known EHL in semiconductor crystals, the charge carriers here are low mobile due to strong interactions with the background (solvated electrons, etc.); hence, EHL resembling ionic melts. Similar to all ionic systems, the Coulomb coupling makes that EHL energetically favorable that leads to recombination barriers suppressing subsequent structural transformations. In particular, generation of secondary reactive species in such EHL becomes limited translating into reduction of biological damages and tissue sparing effect. We show how these processes are sensitive to the tissue quality and frequency dispersion of the dielectric permittivity. Equations for dose and dose rate defining the sparing thresholds are derived.
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Materials Science

Unveiling the growth mode diagram of GaSe on sapphire

M. Bissolo, M. Dembecki, J. Belz et al. (+10 more)

The growth of two-dimensional epitaxial materials on industrially relevant substrates is critical for enabling their scalable synthesis and integration into next-generation technologies. Here we present a comprehensive study of the molecular beam epitaxial growth of gallium selenide on 2-inch c-plane sapphire substrates. Using in-situ reflection high-energy electron diffraction (RHEED), in-situ Raman spectroscopy, optical and scanning electron microscopies, we construct a diagram of the gallium selenide growth modes as a function of substrate temperature (530-650 {\deg}C) and Se/Ga flux ratio (5-110). The growth mode diagram reveals distinct regimes, including the growth of layered post-transition metal monochalcogenide GaSe with an unstrained in-plane lattice constant of 0.371$\pm$0.001 nm and a partial epitaxial alignment on sapphire. This work demonstrates a RHEED-based pathway for synthesizing gallium selenide of specific phase and morphology, and the construction of a phase diagram for high vapor pressure III-VI compounds that can be applied to a wide range of other metal chalcogenide materials.
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All authors M. Bissolo, M. Dembecki, J. Belz, J. Schabesberger, M. Bergmann, P. Avdienko, F. Rauscher, A. S. Ulhe, H. Riedl, K. Volz, J. J. Finley, E. Zallo, G. Koblmüller

Materials Science

Ultra-transient grating spectroscopy for visualization of surface acoustics

Tomáš Grabec, Pavla Stoklasová, Kristýna Repček et al. (+5 more)

Ultrasonic wave propagation across material surfaces reveals essential information about the materials' elastic behavior. The elastodynamic response of the surface is characterized by the Green's function that fully captures all its direction-dependent and frequency-dependent features. Here we present the first direct experimental visualization of the frequency-domain angular-resolved Green's function, including all its complex details resulting from elastic anisotropy. We achieve this visualization using transient grating spectroscopy (TGS), which is a method otherwise well established for measuring Rayleigh-type surface acoustic waves (SAWs). But here we focus on early-time thermoacoustic phenomena in the TGS experiment, revealing that, along with the transient standing-wave patterns of SAWs, there also emerge oscillations with at least an order of magnitude shorter lifetimes. These oscillations superpose into dynamic displacement patterns that are transient with respect to the classical transient timescales in TGS; the optical diffraction signal from these 'ultra-transient' gratings enables capturing the surface acoustic response with exceptional detail, and the resulting experimental angular dispersion maps strikingly replicate the theoretical frequency-domain Green's functions. By utilizing this feature, ultra-transient grating spectroscopy (UTGS) becomes a powerful tool for detailed contactless characterization of anisotropic solids, opening new pathways for studying single-crystalline or nanostructured materials.
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All authors Tomáš Grabec, Pavla Stoklasová, Kristýna Repček, Jakub Kušnír, David Mareš, Martin Ševčík, Petr Sedlák, Hanuš Seiner

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

Integrable Model of a Superconductor with non-Fermi liquid and Mott Phases

Santhosh M, Jorge Dukelsky and Gerardo Ortiz

We present and analyze an exactly solvable interacting fermionic pairing model, which features interactions that entangle states at momenta $\mathbf{k}$ and $-\mathbf{k}$. These interactions give rise to novel correlated ground states, leading to a rich phase diagram that includes superconducting, multiple metallic, and Mott-insulating phases. At finite interaction strengths, we observe the emergence of multiple many-body Fermi surfaces, which violate Luttinger's theorem and challenge the conventional Landau-Fermi liquid paradigm. A distinguishing feature of our model is that it remains quantum integrable, even with the addition of pairing interactions of various symmetries, setting it apart from the Hatsugai-Kohmoto model. Our results provide an analytically tractable framework for studying strong correlation effects that give rise to fractionalized excitations and unconventional superconductivity, offering valuable insights into a broad class of integrable many-body systems.
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Materials Science

Near-room-temperature antiferromagnetism in Janus Fe$X$F ($X$ = O, S) monolayers

Xixiang Zhang, Busheng Wang, Yanfeng Ge et al. (+2 more)

Inspired by the recently synthesized hexagonal layered phase of FeF$_2$, we studied the magnetic properties of the 1T-FeF$_2$ monolayer and its Janus Fe$X$F ($X$ = O, S) derivatives by first-principles calculations. Our results confirm that these materials are antiferromagnetic semiconductors, and that anion substitution effectively tunes their material properties: the band gap shifts from 3.37 eV (direct, FeF$_2$) to 2.35 eV (direct, FeOF) and 1.13 eV (indirect, FeSF); the magnetic moment of Fe ions increases; and the Néel temperature ($T_N$) rises dramatically to 248 K (FeSF) and 207 K (FeOF). Janus structures exhibit enhanced magnetic moment and direct AFM coupling. Under compression, $T_N$ is further optimized to 274 K ($-2$% strain, FeSF) and 244 K ($-5$% strain, FeOF). Both Janus materials retain their semiconducting nature and direction of easy magnetization axis under $\pm5$% strain. This study validates the Janus structure as a viable approach to enhance 2D antiferromagnetism and highlights Fe-based oxyhalides as promising spintronic materials.
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All authors Xixiang Zhang, Busheng Wang, Yanfeng Ge, Yong Liu, Wenhui Wan

Materials Science

Topology and Martensitic Phase Transformations

M. Yin and D. D. Vvedensky

Triply periodic minimal surfaces (TPMS) are discovered to conform to surfaces of given charge density distributions embedded in crystals [Z. Kristallogr. 170, 138 (1985)]. Based on our previous work [Phys. Rev. Mater. 9, 073802 (2025)], we discovered that crystals can have surfaces of a given charge density converging to TPMS. We also discovered that end states connected by a martensitic phase transformation should have their corresponding TPMS being topologically equivalent. In this work, we gave an explanation for the topological continuity of a martensitic phase transformation and studied how TPMS indicate whether a non-magnetic crystal can undergo a martensitic phase transformation or not.
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Materials Science

Weak-anti-localization-to-spin-dependent scattering at a proximity-magnetized heavy metal interface

Hisakazu Matsuki, Guang Yang, Jiahui Xu et al. (+9 more)

A change in a materials electrical resistance with magnetic field (magnetoresistance) results from quantum interference effects and, or spin-dependent transport, depending on materials properties and dimensionality. In disordered conductors, electron interference leads to weak localization or anti-localization; in contrast, ferromagnetic conductors support spin-dependent scattering, leading to giant magnetoresistance (GMR). By varying the thickness of Au between 4 and 28 nm in a EuS/Au/EuS spin-switches, we observe a crossover from weak anti-localization to interfacial GMR. The crossover is related to a magnetic proximity effect in Au due to electron scattering at the insulating EuS interface. The proximity-induced exchange field in Au suppresses weak anti-localization, consistent with Maekawa-Fukuyama theory. With increasing Au thickness, GMR emerges along with spin Hall magnetoresistance. These findings demonstrate spin transport governed by interfacial exchange fields, building a framework for spintronic functionality without metallic magnetism.
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All authors Hisakazu Matsuki, Guang Yang, Jiahui Xu, Vitaly N. Golovach, Yu He, Jiaxu Li, Alberto Hijano, Niladri Banerjee, Iuliia Alekhina, Nadia Stelmashenko, F. Sebastian Bergeret, Jason W. A. Robinson

Materials Science

Breaking the Sabatier Principle by Dynamic Adsorption-Desorption Decoupling in Electrocatalytic Hydrogen Evolution

Zi-Xuan Yang, Lei Li, Tao Huang et al. (+5 more)

The Sabatier principle establishes a fundamental trade-off in heterogeneous electrocatalysis.In the hydrogen evolution reaction (HER), this trade-off is manifested by the coupling of Volmer step, which requires strong hydrogen adsorption, with the Heyrovsky/Tafel step, which favors facile desorption, thus giving rise to the classical volcano relationship and limiting activity even at $\Delta G=0$. Here, we demonstrate a ferroelectric platform with dynamic tunability – monolayer GeS$_2$ decorated with transition metal atoms as a proof-of-concept – where polarization-driven surface electronic reconstruction enables real-time modulation of intermediate binding strength, thereby breaking the Sabatier constraint. Reversible control of hydrogen adsorption allows strong H binding to accelerate the Volmer step, followed by weakened adsorption to promote the Heyrovsky/Tafel step.This dynamic adsorption-desorption decoupling not only surpasses the volcano limit to achieve unprecedented HER activity, but also establishes a general paradigm for designing adaptive electrocatalysts capable of reconfiguring under operating conditions.
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All authors Zi-Xuan Yang, Lei Li, Tao Huang, Hui Wan, X.S. Wang, Gui-Fang Huang, Wangyu Hu, Wei-Qing Huang

Materials Science

Near room temperature magnetoelectric response and tunable magnetic anisotropy in the two-dimensional magnet 1T-CrTe2

Fengping Li, Bheema Lingam Chittari, Chao Lei et al. (+1 more)

Magnets with controllable magnetization and high critical temperature are essential for practical spintronics devices, among which the two-dimensional 1T-CrTe2 stands out because of its high experimental critical temperature up to about 300K down to the single layer limit. By using ab initio density functional theory, we investigate the magnetic properties of monolayer and bilayer 1T-CrTe2 and demonstrate that the magnetic properties, such as the magnetocrystalline anisotropy, critical Curie temperature and magnetizations, can be influenced by strain or electric fields.
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All authors Fengping Li, Bheema Lingam Chittari, Chao Lei, Jeil Jung

Materials Science

A ferroelectric junction transistor memory made from switchable van der Waals p-n heterojunctions

Baoyu Wang, Lingrui Zou, Tao Wang et al. (+18 more)

Van der Waals (vdW) p-n heterojunctions are important building blocks for advanced electronics and optoelectronics, in which high-quality heterojunctions essentially determine device performances or functionalities. Creating tunable depletion regions with substantially suppressed leakage currents presents huge challenges, but is crucial for heterojunction applications. Here, by using band-aligned p-type SnSe and n-type ferroelectric {\alpha}-In2Se3 as a model, we report near-ideal multifunctional vdW p-n heterojunctions with small reverse leakage currents (0.1 pA) and a desired diode ideality factor (1.95). We realize ferroelectric-tuned band alignment with a giant barrier modulation of 900 meV. Based on such tunable heterojunctions, we propose and demonstrate a fundamental different memory device termed ferroelectric junction field-effect transistor memory, which shows large memory windows (1.8 V), ultrafast speed (100 ns), high operation temperature (393 K), and low cycle-to-cycle variation (2%). Additionally, the reliable synaptic characteristics of these memory devices promise low-power neuromorphic computing. Our work provides a new device platform with switchable memory heterojunctions, applicable to high performance brain-inspired electronics and optoelectronics.
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All authors Baoyu Wang, Lingrui Zou, Tao Wang, Lijun Xu, Zexin Dong, Chuan Qin, Xin He, Shangui Lan, Yinchang Ma, Meng Tang, Maolin Chen, Chen Liu, Zheng-Dong Luo, Lijie Zhang, Zhenhua Wu, Yan Liu, Genquan Han, Bin Yu, Xixiang Zhang, Kai Chang, Fei Xue

Materials Science

Resolving the Structural Duality of Graphene Grain Boundaries

Haojie Guo, Emiliano Ventura-Macías, Mariano D. Jiménez-Sánchez et al. (+9 more)

Grain boundaries (GBs) are ubiquitous in large-scale graphene samples, playing a crucial role in their overall performance. Due to their complexity, they are usually investigated as model structures, under the assumption of a fully relaxed interface. Here, we present cantilever-based non-contact atomic force microscopy (ncAFM) as a suitable technique to resolve, atom by atom, the complete structure of these linear defects. Our experimental findings reveal a richer scenario than expected, with the coexistence of energetically stable and metastable graphene GBs. Although both GBs are structurally composed of pentagonal and heptagonal like rings, they can be differentiated by the irregular geometric shapes present in the metastable boundaries. Theoretical modeling and simulated ncAFM images, accounting for the experimental data, show that metastable GBs form under compressive uniaxial strain and exhibit vertical corrugation, whereas stable GBs remain in a fully relaxed, flat configuration. By locally introducing energy with the AFM tip, we show the possibility to manipulate the metastable GBs, driving them toward their minimum energy configuration. Notably, our high-resolution ncAFM images reveal a clear dichotomy: while the structural distortions of metastable grain boundaries are confined to just a few atoms, their impact on graphene's properties extends over significantly larger length scales.
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All authors Haojie Guo, Emiliano Ventura-Macías, Mariano D. Jiménez-Sánchez, Nicoleta Nicoara, Pierre Mallet, Jean-Yves Veuillen, Vincent T. Renard, Antonio J. Martínez-Galera, Pablo Pou, Julio Gómez-Herrero, Rubén Pérez, Iván Brihuega

Materials Science

Anisotropic Strain Engineering in La0.7Sr0.3MnO3/LaFeO3 Superlattice: Structural Relaxation and Domain Formation

Yu Liu, Thea Marie Dale, Emma van der Minne et al. (+7 more)

Anisotropic strain engineering in epitaxial oxide films provides new opportunities to control the antiferromagnetic and structural properties crucial for advancements of antiferromagnetic spintronics. Here we report on a (La0.7Sr0.3MnO3/LaFeO3)4 superlattice grown on (101)o DyScO3 substrate which imposes significant anisotropic in-plane strain. Reciprocal space mapping reveals selective strain relaxation along the tensile in-plane [010]o axis, while compression along the perpendicular in-plane [-101]o axis remains strained. Scanning precession electron diffraction and higher-order Laue zone analysis show that the relaxation is accommodated by structural domain formation in the LaFeO3 layers, initiating from the second bilayer and propagating out-of-plane. These domains minimise structural defects and correlate with the substrate step edges. X-ray magnetic dichroism measurements reveal bulk-like in-plane antiferromagnetic order with polydomain signature as previously reported. Our findings reveal the presence of structural domains coexisting with antiferromagnetic polydomain states, showing a strain-domain-magnetism relationship that provides insights for applications of strain engineering in spintronics applications.
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All authors Yu Liu, Thea Marie Dale, Emma van der Minne, Susanne Boucher, Romar Avila, Christoph Klewe, Gertjan Koster, Magnus Nord, Mari-Ann Einarsrud, Ingrid Hallsteinsen

Materials Science

Growth control of highly textured Bi2Te3 thin films by pulsed laser deposition

Damian Brzozowski, Yu Liu, Karola Neeleman et al. (+2 more)

Two-dimensional materials have attracted growing interest due to their unique electronic properties and potential applications in spintronics. Interfacing strongly spin-orbit-coupled chalcogenides with functional oxides such as perovskites has a particularly high potential. In this work, highly textured Bi2Te3 thin films were deposited on (111) oriented SrTiO3 by pulsed laser deposition. We show that, by careful selection of the temperature and pressure of growth, the film's stoichiometry can be manipulated between direct stoichiometry transfer from the target and tellurium-deficient phases. Optimized pulsed laser deposition enables the growth of films with coalesced, faceted grains with grain sizes reaching up to 430 nm, while preserving crystalline quality comparable to that of molecular-beam-epitaxy-grown films. We show striking differences arising from tuning the laser's pulsing frequency and fluence, which lead to changes in surface roughness, the film's porosity, and grain boundaries, as well as grain shape. Analysis of cross-sectional transmission electron microscopy images reveals a sharp substrate-film interface without atomic intermixing and without the formation of amorphous intermediate layers. The results demonstrate that pulsed laser deposition is a viable method for producing high-quality Bi2Te3 thin films and opens the door to the integration of chalcogenides with perovskites with this growth technique.
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All authors Damian Brzozowski, Yu Liu, Karola Neeleman, Magnus Nord, Ingrid G. Hallsteinsen

Materials Science

Electric Polarization-Driven Modulation of Fe Adatoms on Ferroelectric $\alpha$-In$_2$Se$_3$

Monirul Shaikh and Aleksander L. Wysocki

The interplay among structural, electronic, and magnetic properties of Fe adatoms on the surface of two-dimensional ferroelectric {\alpha}-In$_2$Se$_3$ is investigated using first-principles electronic structure calculations, with a focus on how these properties are modulated by the direction of the electric polarization of the substrate. We identify two competing adsorption sites for Fe adatoms, whose relative stability depends on the adatom concentration and can be reversed by switching the electric polarization of {\alpha}-In$_2$Se$_3$. The calculated energy barrier for thermally activated hopping between these sites is approximately 0.4 eV, corresponding to a blocking temperature of around 100 K. The hybridization between Fe and In$_2$Se$_3$ orbitals strongly depends on the adsorption site and polarization direction, driven by variations in the local adatom geometry. As a result, the electronic configuration of adatom, magnetic moment, and magnetic anisotropy exhibit a pronounced site dependence and can be effectively modulated by switching the electric polarization of the In$_2$Se$_3$ layer. In particular, at higher adatom concentrations, an exceptionally large perpendicular magnetic anisotropy, exceeding 200 meV per Fe atom, emerges for one polarization direction, but is largely diminished when the polarization is reversed. These findings indicate that ferroelectric substrates offer a promising route for voltage-controlled tuning of magnetic adatom properties via reversible polarization switching.
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Saturday 11 October

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

Utilizing SciPy and other open source packages to provide a powerful API for materials manipulation in the Schrödinger Materials Suite

Alexandr Fonari, Farshad Fallah and Michael Rauch

The use of several open source scientific packages in the Schrödinger Materials Science Suite will be discussed. A typical workflow for materials discovery will be described, discussing how open source packages have been incorporated at every stage. Some recent implementations of machine learning for materials discovery will be discussed, as well as how open source packages were leveraged to achieve results faster and more efficiently.
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Materials Science · Cross-listed from cs.LG

Hydrogen production from blended waste biomass: pyrolysis, thermodynamic-kinetic analysis and AI-based modelling

Sana Kordoghli, Abdelhakim Settar, Oumayma Belaati et al. (+3 more)

This work contributes to advancing sustainable energy and waste management strategies by investigating the thermochemical conversion of food-based biomass through pyrolysis, highlighting the role of artificial intelligence (AI) in enhancing process modelling accuracy and optimization efficiency. The main objective is to explore the potential of underutilized biomass resources, such as spent coffee grounds (SCG) and date seeds (DS), for sustainable hydrogen production. Specifically, it aims to optimize the pyrolysis process while evaluating the performance of these resources both individually and as blends. Proximate, ultimate, fibre, TGA/DTG, kinetic, thermodynamic, and Py-Micro GC analyses were conducted for pure DS, SCG, and blends (75% DS - 25% SCG, 50% DS - 50% SCG, 25% DS - 75% SCG). Blend 3 offered superior hydrogen yield potential but had the highest activation energy (Ea: 313.24 kJ/mol), while Blend 1 exhibited the best activation energy value (Ea: 161.75 kJ/mol). The kinetic modelling based on isoconversional methods (KAS, FWO, Friedman) identified KAS as the most accurate. These approaches provide a detailed understanding of the pyrolysis process, with particular emphasis on the integration of artificial intelligence. An LSTM model trained with lignocellulosic data predicted TGA curves with exceptional accuracy (R^2: 0.9996-0.9998).
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All authors Sana Kordoghli, Abdelhakim Settar, Oumayma Belaati, Mohammad Alkhatib, Khaled Chetehouna, Zakaria Mansouri

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

Ferromagnetic Resonance Spectroscopy on the Kagome Magnet MgMn$_6$Sn$_6$

Riju Pal, Kakan Deb, Nitesh Kumar et al. (+3 more)

MgMn$_6$Sn$_6$ is the itinerant ferromagnet on the kagome lattice with high ordering temperature featuring complex electronic properties due to the nontrivial topological electronic band structure, where the spin-orbit coupling (SOC) plays a crucial role. Here, we report a detailed ferromagnetic resonance (FMR) spectroscopic study of MgMn$_6$Sn$_6$ aimed to elucidate and quantify the intrinsic magnetocrystalline anisotropy that is responsible for the alignment of the Mn magnetic moments in the kagome plane. By analyzing the frequency, magnetic field, and temperature dependences of the FMR modes, we have quantified the magnetocrystalline anisotropy energy density that reaches the value of approximately $ 3.5\cdot 10^6$ erg/cm$^3$ at $T = 3$ K and reduces to about $1\cdot 10^6$ erg/cm$^3$ at $T = 300$ K. The revealed significantly strong magnetic anisotropy suggests a sizable contribution of the orbital magnetic moment to the spin magnetic moment of Mn, supporting the scenario of the essential role of SOC for the nontrivial electronic properties of MgMn$_6$Sn$_6$.
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All authors Riju Pal, Kakan Deb, Nitesh Kumar, Bernd Büchner, Alexey Alfonsov, Vladislav Kataev

Materials Science

Atomic-Scale Origins of Oxidation Resistance in Amorphous Boron Nitride

Onurcan Kaya, Qiushi Deng, Thomas Souvignet et al. (+4 more)

Amorphous boron nitride (\textrm{$\alpha$}-BN) is a promising ultrathin barrier for nanoelectronics, yet the atomistic mechanisms governing its chemical stability remain poorly understood. Here, we investigate the structure-property relationship that dictates the oxidation of \textrm{$\alpha$}-BN using a combination of machine-learning molecular dynamics simulations and angle-resolved X-ray photoelectron spectroscopy. The simulations reveal that the film structure, controlled by synthesis conditions, is the critical factor determining oxidation resistance. Dense, chemically ordered networks with a high fraction of B-N bonds effectively resist oxidation by confining it to the surface, whereas porous, defect-rich structures with abundant homonuclear B-B and N-N bonds permit oxygen penetration and undergo extensive bulk degradation. These computational findings are consistent with experimental trends observed in \textrm{$\alpha$}-BN films grown by chemical vapour deposition. XPS analysis shows that a film grown at a higher temperature develops a more ordered structure with a B/N ratio nearer to stoichiometric and exhibits superior resistance to surface oxidation compared to its more defective, lower-temperature counterpart. Together, these results demonstrate that the oxidation resistance of \textrm{$\alpha$}-BN is a tunable property directly linked to its atomic-scale morphology, providing a clear framework for engineering chemically robust dielectric barriers for future nanoelectronic applications.
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All authors Onurcan Kaya, Qiushi Deng, Thomas Souvignet, Catherine Marichy, Catherine Journet, Ivan Cole, Stephan Roche

Materials Science

A continued fraction approximation for the effective elasticity tensor of two-dimensional polycrystals as a function of the crystal elasticity tensor

Graeme W. Milton

For two-dimensional polycrystals the effective elasticity tensor $C_*$ as a function $C_*(C_0)$ of the elasticity tensor $C_0$ of the constituent crystal is considered. It is shown that this function can be approximated by one with a continued fraction expansion resembling that associated with a class of microstructure known as sequential laminates. These are hierarchical microstructures defined inductively. Rank 0 sequential laminates are simply rotations of the pure crystal. Rank $j$ sequential laminates are obtained by laminating together, on a length scale much larger that the existing microstructure and with interfaces perpendicular to some direction $n_j$, rank $j-1$ sequential laminates with a rotation of the pure crystal. The continued fraction approximation for arbitrary polycrystal microstructures typically takes a more general form than that of sequential laminates, but has some free parameters. It is an open question as to whether these free parameters can always be adjusted so the continued fraction approximation matches exactly that of a sequential laminate. If so, one would have established that the elastic response of two-dimensional polycrystals can always be mimicked by that of sequential laminates. Our analysis carries over to the more general case where the strain is replaced by a field $E(x)$ that is the gradient of a vector potential $u(x)$, i.e. $E=\nabla u$ and the stress is replaced by a matrix valued field $J(x)$ that need not be symmetric but has zero divergence $\nabla\cdot J=0$. The tensor $L(x)$ entering the constitutive relation $J=L E$ is locally a rotation of the tensor $L_0$ of the pure crystal that need not have any special symmetries and has 16 independent tensor elements.
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