Materials Science
Topological passivation makes high strength alloys insensitive to hydrogen embrittlement
Huijie Cheng, Binhan Sun, Aochen Zhang et al. (+6 more)
Infrastructure parts for a hydrogen (H) economy need
alloys that are mechanically strong and at the same time resistant to the most dangerous and abrupt type of failure mode, namely, H embrittlement. These two properties are in fundamental conflict, as increasing strength typically amplifies susceptibility to H-related failure. Here, we introduce a new approach to make
alloys resistant to H embrittlement, by creating a topological passivation layer (up to a few hundred micrometers thick) near the material surface, the region that is most vulnerable to H ingress and attack. It features instead a layer of ultrafine laminated grains with tens of times higher dislocation density than conventional materials, altering H
diffusion, trapping and crack
evolution. We tested the concept on a face-centered cubic (FCC) CoCrNi medium
entropy model
alloy which undergoes severe H-induced intergranular cracking. Two key mechanisms create the topological passivation: First, the high density (up to ~1.3e15 m-2) of H-trapping dislocations within the passivating grain layer decelerates H migration by up to about an order of magnitude, delaying H-induced crack initiation at grain boundaries. More importantly, once unavoidable micro-sized H-induced intergranular cracks emerge in the topmost surface region, they become completely arrested by the laminated grains, due to a transition in the embrittlement mechanism from H-enhanced grain boundary decohesion to highly energy-dissipative dislocation-associated cracking. These effects almost completely eliminate H embrittlement, at even doubled yield strength, when exposing the so architected material to harsh H attack. Our approach leverages surface mechanical treatments to tailor metallic microstructures in surface regions most susceptible to H attack, providing a scalable solution to protect
alloys from H-induced damage.
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All authors Huijie Cheng, Binhan Sun, Aochen Zhang, Dirk Ponge, Fengkai Yan, Tiwen Lu, Xian-Cheng Zhang, Dierk Raabe, Shan-Tung Tu
Materials Science · Cross-listed from cond-mat.soft
Helix alignment, chevrons, and edge dislocations in twist-bend ferroelectric nematics
Bijaya Basnet, Priyanka Kumari, Sathyanarayana Paladugu et al. (+6 more)
We explore surface
alignment and edge dislocations in the recently discovered twist-bend ferroelectric nematic, NTBF, in which the vector of spontaneous polarization follows an oblique helicoidal trajectory around a polar twist-bend axis. In a planar
cell, the polar axis aligns at some angle to the rubbing direction to mitigate surface electric charge. We demonstrate that the pseudolayers in planar
cells form chevron defects, a hallmark defect of one-dimensionally positionally ordered phases, such as smectic A and smectic C. The polar character of the twist-bend axis prevents the cores of NTBF edge dislocations from splitting into semi-integer disclinations, in stark contrast to dislocations in paraelectric and ferroelectric
chiral nematics. The tilt of pseudolayers around the defect core allows us to estimate the elastic penetration length as being close to the pitch of NTBF. Compression/dilation stresses around the core modify the heliconical tilt angle of molecules as evidenced by a substantial variation in local birefringence. The climb of dislocations exhibits high mobility, allowing the system to equilibrate the temperature-dependent pitch. The uncovered properties facilitate the development of NTBF materials for electro-optical applications, such as electrically controlled diffraction
lattices and structural colors.
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All authors Bijaya Basnet, Priyanka Kumari, Sathyanarayana Paladugu, Damian Pociecha, Jakub Karcz, Przemysław Kula, Nataša Vaupotič, Ewa Górecka, Oleg D. Lavrentovich
Materials Science
Non-local Chemistry Driven by Cation-Anion Size Disparity in Helium Inserted Compounds under High Pressure
Zhen Liu, Stefano Raciopp, Katerina P. Hilleke et al. (+6 more)
Opposing the theory that Helium (He) cannot be inserted into AB-type ionic compounds due to the Madelung energy increase, our
crystal structure search and first-principles calculations found that He can form stable compounds with sodium halides (NaX, X=Cl, Br, I) under high-pressure. These reactions are driven by the non-local chemistry arising from the cation-anion size disparity, distinctly different from the He insertion reaction with A2B-type compounds. The large size differences between Na+ and X- enable structures that can effectively host He insertions through volume and inter-atomic distance disproportionation. Furthermore, the insertion of He atoms can significantly relieve the elevated Madelung energy that builds up in NaX under high pressure. This energy increase arises from structural transitions driven by cation-anion size disparity, which are necessary for reducing volume under pressure. The insertion of He allows the reduction of the total volume under high pressure without increasing the Madelung energy. Our predicted compounds and stability analysis reveal a new example of He reactivity governed not by local chemical bond formation, but by long-range electrostatic interactions.
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All authors Zhen Liu, Stefano Raciopp, Katerina P. Hilleke, Abhiyan Pandit, Shuran Ma, Andreas Hermann, Dadong Yan, Eva Zurek, Mao-sheng Miao
Materials Science
Dislocation-induced magnetization reversal in a ferromagnetic film
Jorge F. Soriano and Eugene M. Chudnovsky
We demonstrate that moving edge dislocations can induce the reversal of magnetization in a
ferromagnetic film due to the Barnett effect. The dynamics of magnetization is studied numerically within a discretized Landau-Lifshitz equation on a hexagonal
lattice containing over $10^5$ sites. Local coordinate frames coupled to the crystallographic axes for each
spin are used together with the laboratory coordinate frame. The parameters of a hexagonal close-packed cobalt
lattice have been chosen for illustration. The magnetization reversal from a metastable initial state created by the external
magnetic field occurs on a time scale of a few picoseconds. Our results imply that fast local elastic twists generated by moving dislocations serve as an important mechanism of magnetization dynamics in solids subjected to a mechanical stress.
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Materials Science · Cross-listed from cond-mat.mes-hall
Dual topology and edge-reconstruction in $\alpha$-Sn
Jan Skolimowski, Nguyen Minh Nguyen, Giuseppe Cuono et al. (+2 more)
We formulate the tight-binding model for cubic $\alpha$-Sn based on the DFT calculations. In the model, we incorporate a variable bond angle, which allows us to simulate the effect of the in-plane strain. In the bulk, we demonstrate the presence of the $\mathbb{Z}_2$ topological invariant and a non-zero mirror Chern number, making $\alpha$-Sn one of the rare cases where dual
topology can be observed. We calculate the topological phase diagram of multi-layer $\alpha$-Sn as a function of strain and number of layers. We find that a non-trivial
quantum spin Hall state appears only for compressive strain above five layers of thickness. Quite surprisingly, both in the trivial and non-trivial phases, we find a plethora of edge-states with energies inside the bulk gap of the system. Some of these states are localized at the side surfaces of the slab, some of them prefer top/bottom surfaces and some are localized in the hinges. We trace the microscopic origin of these states back to a minimal model that supports
chiral symmetry and multiple one-dimensional winding numbers that take different values in different directions in the Brillouin zone.
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All authors Jan Skolimowski, Nguyen Minh Nguyen, Giuseppe Cuono, Carmine Autieri, Wojciech Brzezicki
Materials Science
Surface oxidation of Pt and PtPd alloys during NO conversion investigated by Atom Probe Tomography
Yoonhee Lee, Daniel Dobesch, Patrick Stender et al. (+3 more)
In this study, the dynamic oxidation state changes of pure Pt and 50at% PtPd
alloy catalysts were investigated during a temperature ramp from 80 to 450 C under a reactive gas mixture of 500 ppm NO and 3 % Oxygen in Nitrogen atmosphere. These changes are closely correlated with variations in NO conversion efficiency. Sharp tip specimens were prepared from Pt and PtPd
alloy wires by electrochemical polishing and Focused Ion Beam annular milling, with the hemispherical apex serving as a model for nanoscale catalyst surfaces. The samples were exposed to the reactive atmosphere in a dedicated reaction chamber and subsequently analyzed using atom probe
tomography. Effective
oxide thicknesses and three-dimensional surface morphology were quantitatively evaluated. A pronounced decrease in
oxide thickness was observed during the first cooling and second heating cycles, particularly below 200 C, indicating reversible redox behavior on both Pt and PtPd
alloy surfaces. This behavior correlates with the inverse hysteresis of NO conversion measured for both systems, suggesting that the redox reversibility is driven primarily by reaction kinetics rather than thermodynamic stability.
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All authors Yoonhee Lee, Daniel Dobesch, Patrick Stender, Ute Tuttlies, Ulrich Nieken, Guido Schmitz
Materials Science · Cross-listed from cond-mat.supr-con
Nonequilibrium Quasiparticle Dynamics in a MoRe-Based Superconducting Resonator under IR Excitation
O. A. Kalenyuk, S. I. Futimsky, I. A. Martynenko et al. (+5 more)
The response of a MoRe-based superconducting resonator operating near 5 K to pulsed infrared irradiation is investigated, and the underlying physical mechanisms are analyzed. The device exhibits a pronounced nonlinear response dominated by nonequilibrium quasiparticle dynamics rather than uniform thermal heating. Infrared pulses produce strong distortions of the resonance curve and a transient decrease in the resonance frequency, consistent with increased kinetic inductance caused by quasiparticle generation. The frequency shift scales approximately linearly with absorbed power, whereas the dissipation response saturates at higher powers, indicating the formation of a nonequilibrium steady-state quasiparticle population. These observations demonstrate a transition from a linear pair-breaking regime to a saturated dissipation regime, likely associated with a quasiparticle relaxation bottleneck or partial suppression of the smaller superconducting gap in MoRe. The results highlight the relevance of nonequilibrium processes in MoRe and confirm its potential for microwave kinetic-inductance detector applications.
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All authors O. A. Kalenyuk, S. I. Futimsky, I. A. Martynenko, A. P. Shapovalov, O. O. Boliasova, V. I. Shnyrkov, A. L. Kasatkin, A. A. Kordyuk
Materials Science · Cross-listed from cond-mat.str-el
Trion gas on the surface of a failed excitonic insulator
Yuval Nitzav, Abigail Dishi, Himanshu Lohani et al. (+15 more)
Trions, three-body bound states composed of an
exciton and an additional charge, are typically fragile and require external excitation to form. Here, we report the spontaneous emergence of a stable trion gas at the surface of the layered
semiconductor Ta2NiS5, revealed through angle-resolved photoemission spectroscopy. We observe a sharp, highly localized in-gap feature that cannot be explained by conventional band-theory. Instead, we argue that it arises from the formation of negative trions, stabilized by surface-induced band bending and the material's quasi-one-dimensional geometry. Unlike
excitons, these trions form without optical pumping and persist at
equilibrium, marking a rare example of an interaction-driven surface state in a nominally conventional
semiconductor. Our findings establish Ta2NiS5 as a unique platform for exploring many-body physics at surfaces and open new avenues for studying and controlling collective excitations in low-dimensional systems.
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All authors Yuval Nitzav, Abigail Dishi, Himanshu Lohani, Ittai Sidilkover, Noam Ophir, Roni Anna Gofman, Avior Almoalem, Ilay Mangel, Nitzan Ragoler, Francois Bertran, Jaime Sánchez-Barriga, Dmitry Marchenko, Andrei Varykhalov, Nicholas Clark Plumb, Irena Feldman, Hadas Soifer, Anna Keselman, Amit Kanigel
Materials Science
A cascade model for the defect-driven etching of porous GaN distributed Bragg reflectors
Ben Thornley, Maruf Sarkar, Saptarsi Ghosh et al. (+4 more)
Fabrication of porous GaN distributed Bragg reflectors (DBRs) via the selective electrochemical etching (ECE) of conductive Si-doped layers, separated by non-intentionally doped (NID) layers, provides a straightforward methodology for producing highly reflective DBRs suitable for device overgrowth and integration, which has otherwise proven difficult in the III-nitride epitaxial system via conventional alloying. Such photonic materials can be fabricated by a lithography-free defect-driven etching process, where threading dislocations intrinsic to heteroepitaxy form nanoscale channels that facilitate etchant transport through NID layers. Here, we report the first three-dimensional characterisation of porous GaN-on-Si DBRs fabricated in this methodology with different ECE voltages, using serial-section
tomography in a focused ion beam scanning electron microscope (FIB-SEM). These
datasets reconstruct the pore morphology as etching proliferates through the alternating Si-doped/NID layer stack. Volumetric reconstruction enabled us to enhance the established `kebab' model for defect-driven etching by proposing a `cascade' model where etchant cascades through the material via vertical etching down nanopipes and horizontal etching across pores, forming complex networks directly related to the pathways taken. This accounts for premature nanopipe termination and discontinuities in nanopipe formation, where dislocations are observed to activate and deactivate individually. Statistical analysis of individual etching behaviour, across all dislocations for each tomograph, revealed a greater tendency to form continuous structures that follow conventional kebab behaviour at higher ECE voltages. We propose that higher ECE voltages alter the probability of dislocation etching relative to doped layer etching, thereby empowering morphological optimization through improved mechanistic understanding of ECE.
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All authors Ben Thornley, Maruf Sarkar, Saptarsi Ghosh, Martin Frentrup, Menno J. Kappers, Thom R. Harris-Lee, Rachel A. Oliver
Materials Science
Magnetoelectric topology: the rope weaving in parameter space
Ying Zhou, Ziwen Wang, Fan Wang et al. (+2 more)
Topology, as a mathematical concept, has been introduced into condensed matter physics since the discovery of
quantum Hall effect, which characterizes new physical scenario beyond the Landau theory. The topologically protected physical quantities, such as the dissipationless
quantum transport of edge/surface states as well as
magnetic/dipole quasi-particles like skyrmions/bimerons, have attracted great research enthusiasms in the past decades. In recent years, another kind of
topology in condensed matter was revealed in the magnetoelectric parameter space of multiferroics, which deepens our understanding of magnetoelectric physics. This topical review summarizes recent advances in this area, involving three type-II multiferroics. With magnetism-induced ferroelectricity, topological behaviors can be manifested during the magnetoelectric switching processes driven by
magnetic/electric fields, such as Roman-surface/Riemann-surface magnetoelectricity and
magnetic crankshaft. These exotic topological magnetoelectric behaviors may be helpful to pursuit energy-efficient and precise-control devices for spintronics and
quantum computing.
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All authors Ying Zhou, Ziwen Wang, Fan Wang, Haoshen Ye, Shuai Dong
Materials Science
Ferroelectric Control of Spin Textures in Layered Hybrid Perovskites
Divyanshi Tyagi and Saswata Bhattacharya
Hybrid organic–inorganic perovskites with broken inversion
symmetry provide a fertile ground for uncovering coupled
spin-orbit and ferroelectric phenomena. Here, we investigate the layered family (PA)$_2$CsY$_2$X$_7$ (Y = Pb, Sn; X = I, Br) using density functional theory, Berry-phase polarization analysis, and effective $\boldsymbol{k \cdot p}$ modeling. Across all four members, we find indirect bandgaps with extrema near $\Gamma$, sizable
spin splittings at both band edges, and robust in-plane ferroelectric polarization that stabilizes out-of-plane persistent
spin textures (PSTs). Crucially, polarization reversal switches the
spin orientation, enabling electrical control of PSTs and thereby non-volatile manipulation of
spin states. These results establish (PA)$_2$CsY$_2$X$_7$ as a versatile materials platform where compositional design and ferroelectric switching jointly enable spintronic functionality.
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Materials Science · Cross-listed from physics.chem-ph
Toward Unified Interphase Engineering: The Solid-Electrolyte Interphase in Batteries and Supercapacitors
Mehedi Hasan, Ishtiaq Murshed, Khayrul Islam et al. (+1 more)
The development of next-generation electrochemical energy storage requires devices that combine the high energy density of batteries with the power capability and long cycle life of supercapacitors. However, the interfacial phenomena governing performance in these systems remain poorly unified. The solid-electrolyte interphase (SEI), a nanoscale film formed by electrolyte decomposition, is well studied in batteries but its counterpart in supercapacitors has received limited systematic investigation despite growing experimental evidence. This review argues that SEI formation is a universal electrochemical process that occurs whenever electrode potentials drive electron transfer into electrolyte orbitals beyond their stability limits, independent of whether charge storage is Faradaic or non-Faradaic. Differences between battery SEIs and supercapacitor interphases arise mainly from operating conditions, not fundamental chemistry. Engineered interphases created through electrolyte additives, protective coatings, or surface functionalization suppress leakage currents, improve capacitance retention, and enable stable high-voltage operation. By identifying shared mechanisms and establishing transferable design rules, this unified framework provides a foundation for predictive interphase engineering that supports long-lived, high-performance energy-storage technologies.
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All authors Mehedi Hasan, Ishtiaq Murshed, Khayrul Islam, A.K.M. Masud
Materials Science
CsCl seed layer homogenizes co-evaporated perovskite growth for high-efficiency fully textured perovskite-silicon tandem solar cells
Viktor Škorjanc, Stefanie Severin, Alexander Veber et al. (+24 more)
Monolithic perovskite-silicon tandem
solar cells experienced a significant increase in efficiency, making them viable for industrial applications. Among the various scalable and industry-compatible metal halide perovskite deposition techniques, co-evaporation stands out as particularly well-suited for perovskite-silicon tandem
solar cells due to its ability to conformally cover textured silicon bottom
cells. Solution-processed [2-(3,6-Dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz) is commonly used as a hole-transporting material for co-evaporated metal halide perovskites. However, we show that it covers the textured surface of silicon bottom
cells unevenly, impacting the film growth and leading to the formation of residual PbI2 at the buried interface. The present study reveals via X-ray photoemission electron microscopy (XPEEM) and infrared scattering-type scanning near-field optical microscope (IR s-SNOM) that a CsCl seed layer fosters organic precursor incorporation across the MeO-2PACz/perovskite interface, even in the areas with a thin MeO-2PACz layer, thereby preventing the formation of interfacial PbI2 and leading to larger apparent grains. The improvement of the metal halide perovskite film quality on the MeO-2PACz/perovskite interface and the bulk perovskite film led to 30.3% (29.7% certified) efficient perovskite-silicon tandem
solar cell. The present work highlights the importance of a seed layer for a robust growth of co-evaporated metal halide perovskite and represents an important milestone for the transfer of perovskite-silicon tandem
solar cells from laboratory to industry.
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All authors Viktor Škorjanc, Stefanie Severin, Alexander Veber, Mauricio J. Prieto, Liviu C. Tănase, Aleksandra Miaskiewicz, Sebastian Weitz, Jing-Wen Hsueh, Mohamad-Assaad Mawass, Lucas de Souza Caldas, Suresh Manyarasu, Philippe Holzhey, Erik Wutke, Stepan Demchyshyn, Matthew R. Leyden, Angelika Harter, Roberto Felix Duarte, Jona Kurpiers, Philipp Wagner, Bernd Stannovski, Ljiljana Puskar, Roland Mainz, Daniel Abou-Ras, Thomas Schmidt, Lars Korte, Marcel Roß, Steve Albrecht
Materials Science
Observing the spatial and temporal evolution of exciton wave functions
Marcel Theilen, Siegfried Kaidisch, Monja Stettner et al. (+12 more)
Excitons, the correlated electron-hole pairs governing optical and transport properties in organic
semiconductors, have long resisted direct experimental access to their full
quantum-mechanical wave functions. Here, we use femtosecond time-resolved photoemission orbital
tomography (trPOT), combining high-harmonic probe pulses with time- and momentum-resolved photoelectron spectroscopy, to directly image the momentum-space distribution and ultrafast dynamics of
excitons in $\alpha$-sexithiophene thin films. We introduce a quantitative model that enables reconstruction of the
exciton wave function in real space, including both its spatial extent and its internal phase structure. The reconstructed wave function reveals coherent delocalization across approximately three molecular units and exhibits a characteristic phase modulation, consistent with ab initio calculations within the framework of many-body perturbation theory. Time-resolved measurements further show a $\sim 20$% contraction of the
exciton radius within 400 fs, providing direct evidence of self-trapping driven by
exciton-
phonon coupling. These results establish trPOT as a general and experimentally accessible approach for resolving
exciton wave functions – with spatial, phase, and temporal sensitivity – in a broad class of molecular and low-dimensional materials.
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All authors Marcel Theilen, Siegfried Kaidisch, Monja Stettner, Sarah Zajusch, Eric Fackelman, Alexa Adamkiewicz, Robert Wallauer, Andreas Windischbacher, Christian S. Kern, Michael G. Ramsey, François C. Bocquet, Serguei Soubatch, F. Stefan Tautz, Ulrich Höfer, Peter Puschnig
Materials Science · Cross-listed from cond-mat.supr-con
Coexistence of near-EF van Hove singularity and in-gap topological Dirac surface states in superconducting electrides
Yin Yang, Peihan Sun, Ye Shen et al. (+9 more)
Superconducting electrides have attracted growing
attention for their potential to achieve high superconducting transition temperatures (TC) under pressure. However, many known electrides are chemically reactive and unstable, making high-quality single-
crystal growth, characterization, and measurements difficult, and most do not exhibit superconductivity at ambient pressure. In contrast, La3In stands out for its ambient-pressure superconductivity (TC ~ 9.4 K) and the availability of high-quality single
crystals. Here, we investigate its low-energy electronic structure using angle-resolved photoemission spectroscopy and first-principles calculations. The bands near the
Fermi energy are mainly derived from La 5d and In 5p orbitals. A saddle point is directly observed at the Brillouin zone (BZ) boundary, while a three-dimensional van Hove singularity crosses EF at the BZ corner. First-principles calculations further reveal topological Dirac surface states within the bulk energy gap above EF. The coexistence of a high density of states and in-gap topological surface states near EF suggests that La3In offers a promising platform for tuning superconductivity and exploring possible topological superconducting phases through doping or external pressure.
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All authors Yin Yang, Peihan Sun, Ye Shen, Zhijun Tu, Pengcheng Ma, Hongrun Zhen, Tianqi Wang, Longli Tian, Tian Cui, Hechang Lei, Kai Liu, Zhonghao Liu
Materials Science · Cross-listed from cond-mat.mes-hall
Imaging propagating terahertz collective modes in two-dimensional semiconductor double layers
Andrew T. Pierce, Chirag Vaswani, Dimitri Pimenov et al. (+7 more)
Two-dimensional transition metal dichalcogenide (TMD)
semiconductors exhibit a wide range of novel phenomena at millielectronvolt (terahertz-frequency) energy scales, including superconducting and correlation-induced insulating gaps that are frequently accompanied by
symmetry breaking. However, due to the subwavelength dimensions and the often low conductivities of these systems, their intrinsic THz plasmons and meV-scale excitation gaps are difficult to access experimentally. Here we report an optical readout method that can image propagating THz-frequency collective modes in real time. The method relies on a strong coupling between the optical polarons of monolayer TMD
semiconductors and the local THz fields in a waveguide, which enables us to image THz plasmons with micron scale spatial resolution and determine their propagation group velocities. Moreover, at finite
magnetic fields, we observe coherent cyclotron oscillations resulting from Landau level repopulation induced by the THz field. Our findings provide a new near-field platform for probing collective excitations in strongly correlated two-dimensional
semiconductors and enable "all-photonic" TMD-based architectures for time-domain THz plasmonics and optoelectronics.
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All authors Andrew T. Pierce, Chirag Vaswani, Dimitri Pimenov, Sihong Xu, Kenji Watanabe, Takashi Taniguchi, Erich Mueller, Debanjan Chowdhury, Kin Fai Mak, Jie Shan
Materials Science · Cross-listed from cond-mat.str-el
Two-Electron Correlations in the Metallic Electron Gas
Zhiyi Li, Pengcheng Hou, Bao-Zong Wang et al. (+2 more)
We present high-precision ab initio calculations of the four-point vertex function for the three-dimensional uniform electron gas using variational diagrammatic Monte Carlo. From these results, we extract Landau parameters that reveal a density-driven crossover from underscreening to overscreening, and obtain the full two-electron scattering amplitude on the
Fermi surface with controlled accuracy. A residual analysis of the scattering amplitude against the charge-channel Kukkonen–Overhauser (KO$^+$) interaction shows that only a minimal s-wave correction in the antiparallel-
spin channel is needed, defining the sKO$^+$ ansatz: KO$^+$ within the local-density approximation plus this short-range correction. Using both our direct VDMC amplitudes and the sKO$^+$ ansatz, we compute the electron-electron contribution to the thermal resistivity, obtaining quantitative agreement with experiments on simple metals (Al, Na, K, Rb). sKO$^+$ thus provides a controlled UEG-based effective interaction for simple-metal transport and future first-principles extensions.
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All authors Zhiyi Li, Pengcheng Hou, Bao-Zong Wang, Youjin Deng, Kun Chen
Materials Science · Cross-listed from cond-mat.str-el
Development of ultra-high efficiency soft X-ray angle-resolved photoemission spectroscopy equipped with deep prior-based denoising method
Kohei Yamagami, Yuichi Yokoyama, Yuta Sumiya et al. (+3 more)
Soft X-ray angle resolved photoemission spectroscopy (SX-ARPES) is one of the most powerful spectroscopic techniques to visualize the three-dimensional bulk electronic structure in reciprocal
lattice space. Compared with ARPES employing low-energy
photon sources, the time burden imposed by a lower photoelectron yield, stemming from the photoionization cross-section, has been a persistent technical challenge. To address this challenge, we have developed a noise removal system by using the deep prior-based method and integrated it into the micro focused SX-ARPES ({\mu}SX-ARPES) system at BL25SU in SPring-8. Our implemented system effectively eliminates the grid and spike noise typically present in ARPES data acquired using the voltage Fixed-mode, within about 30 seconds. We demonstrate, through the {\mu}SX-ARPES measurements on a single
crystal of CeRu2Si2, that data with sufficient statistical accuracy can be obtained in approximately 40 seconds. In addition, we present the potential of high signal-to-noise ratio ARPES measurement, achieving an energy resolution of 51.6 meV at an excitation energy of 708 eV in {\mu}SX-ARPES measurements on polycrystalline gold. Our developed system successfully reduces the time burden in SX-ARPES and paves the way for advancements in lower photoelectron yield measurements, such as those requiring higher energy resolution and three-dimensional nonequilibrium measurements.
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All authors Kohei Yamagami, Yuichi Yokoyama, Yuta Sumiya, Hayaru Shouno, Tetsuro Nakamura, Masaichiro Mizumaki
Materials Science
Order-Disorder in Fe-Si Alloys: Implications for Seismic and Transport Properties of Earth's Inner Core
Cong Liu, Xin Deng and R. E. Cohen
Understanding the structure and dynamics of Earth's inner core is essential for constraining its composition, thermal
evolution, and seismic behavior. Silicon is widely considered a major light element in the core. Here, we use first-principles molecular dynamics and thermodynamic modeling to investigate the structural, elastic, and transport properties of iron-silicon (Fe-Si)
alloys under inner-core conditions. By computing the Gibbs free energies of multiple solid phases, including ordered B2, hexagonal close-packed (hcp), face-centered cubic (fcc), and body-centered cubic (bcc) Fe-Si, we construct a phase diagram relevant to inner-core pressures and temperatures. We identify a pronounced miscibility gap between hcp and cubic Fe–Si phases, with phase coexistence over approximately 6–11 wt% Si at 6000 K. The cubic phase exhibits a strong order-dependent elastic response, with disordered bcc showing a large intrinsic shear anisotropy (22.9% at 6000 K), in contrast to the nearly isotropic hcp phase (0.6%). Meanwhile, disordered bcc Fe–Si produces shear wave velocities ($V_S=3.73$ km$\cdot$s$^{-1}$) and Poisson's ratios comparable with seismological constraints. In addition, disordered bcc Fe–Si exhibits a lower thermal conductivity than hcp Fe–Si, providing a quantitative constraint on phase-dependent electronic heat transport. These results demonstrate that chemical ordering strongly controls the stability and physical properties of cubic Fe–Si
alloys, and suggest that metastable or localized cubic Fe–Si phases may contribute to the structural and transport complexity of Earth's inner core.
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Materials Science
Evaluating Mechanical Property Prediction across Material Classes using Molecular Dynamics Simulations with Universal Machine-Learned Interatomic Potentials
Konstantin Stracke, Connor W. Edwards and Jack D. Evans
We assess the accuracy of six universal machine-learned interatomic potentials (MLIPs) for predicting the temperature and pressure response of materials by molecular dynamics simulations. Accuracy is evaluated across 13 diverse materials (nine metal-organic frameworks and four inorganic compounds), computing bulk modulus, thermal expansion, and thermal decomposition. These MLIPs employ three different architectures (graph neural networks, graph network simulators, and graph
transformers) with varying training
datasets. We observe qualitative accuracy across these predictions but systematic underestimation of bulk modulus and overestimation of thermal expansion across all models, consistent with potential energy surface softening. From all tested models, three top performers arise; `MACE-MP-0a', `fairchem_OMAT', and `Orb-v3', with average error across metrics and materials of 41%, 44%, and 47%, respectively. Despite strong overall performance, questions arise about the limits of model transferability:
dataset homogeneity and structural representation dominate model accuracy. Our results show that certain architectures can compensate for biases, a step closer to truly universal MLIPs.
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Materials Science
Ready-to-Use Polymerization Simulations Combining Universal Machine Learning Interatomic Potential with Time-Dependent Bond Boosting for Polymer and Interface Design
Hodaka Mori, Shunsuke Tonogai, Yu Miyazaki et al. (+2 more)
Although polymerization and curing reactions govern the performance of advanced materials, their simulation remains challenging owing to the need for accurate, transferable potentials and rarity of chemical events. Conventional reactive force fields such as ReaxFF require system-specific parametrization, while universal machine learning interatomic potentials (uMLIPs) exhibit limited sampling efficiency. This paper introduces a novel simulation framework integrating a uMLIP with a time-dependent bond-boost scheme. The bias potential increases monotonically with time, and the use of a unified parameter set across reaction classes enables consistent acceleration without system-specific tuning. For radical polymerization of vinyl monomers, the proposed framework reproduces characteristic trends, such as linear molecular-weight growth with conversion, initiator-concentration scaling, and relative monomer reactivity trends. For step-growth polycondensation of nylon-6,6, it captures the characteristic sharp increase in molecular weight at high conversion rates, consistent with experimental behavior. For epoxy curing at a copper substrate, it reveals interfacial ring-opening and cross-linking events, consistent with spectroscopic evidence of Cu-O-C bond formation. Overall, coupling uMLIPs with time-dependent bond boost enables practical and transferable simulations of polymerization and curing processes. The proposed framework reliably resolves mechanistic pathways and relative reactivity, offering molecular-level insights into
polymer growth and interfacial adhesion.
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All authors Hodaka Mori, Shunsuke Tonogai, Yu Miyazaki, Akihide Hayashi, Masayoshi Takayanagi
Materials Science · Cross-listed from cond-mat.mes-hall
Confinement-Induced Metastability and Structural Diversity of Hopfions in Chiral Magnetic Films
Andrey O. Leonov and Takayuki Shigenaga
Topological particle-like excitations such as skyrmions and hopfions offer rich opportunities for spintronic and photonic applications. While skyrmions have been extensively studied, the stabilization mechanisms and phase behavior of three-dimensional hopfions remain largely unexplored. Here, we investigate the formation, stability, and interactions of hopfions in thin
chiral magnetic films with surface anchoring, using three-dimensional micromagnetic simulations within a material-independent framework applicable to both
magnetic and
liquid crystalline systems. We identify four distinct types of isolated hopfions, generated by rotating bimeron and finger-like
solitons around a central axis. The metastability regions of these precursor textures closely follow the boundaries of modulated finger phases, enabling their size to be continuously tuned through anisotropydriven inflation and collapse. Remarkably, we demonstrate that hopfions near their inflation threshold possess energies comparable with the homogeneous state, allowing them to enclose regions of modulated phases or other
solitons, forming higher-order, bag-like domains. In contrast, periodic hopfion
lattices remain intrinsically unstable under confinement, spontaneously relaxing into finger phases. These findings establish general principles for stabilizing, tuning, and assembling three-dimensional topological
solitons in confined
chiral systems, suggesting experimentally accessible routes for texture engineering in
liquid crystals via electric-field control.
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Materials Science
Characteristic ferroelectric domains and their dynamic behavior in ordered Pb(Sc$_{1/2}$Nb$_{1/2}$)O$_{3}$
Hiroshi Nakajima, Satoshi Hiroi, Hirofumi Tsukasaki et al. (+5 more)
Pb-based perovskites with multiple cations are fascinating materials showing various phenomena such as high piezoelectric, electromechanical, and relaxor properties. While chemical disordering accompanied by polar nanoregions and nanosized domains is commonly believed to cause the relaxor nature, little is known about ferroelectric microstructures of chemically ordered Pb-based perovskites. In this study, we discovered intriguing meandering ferroelectric domains in chemically ordered ferroelectric Pb(Sc$_{1/2}$Nb$_{1/2}$)O$_{3}$ using in-situ transmission electron microscopy with dark-field imaging. Observation results demonstrate that electric polarization can fluctuate around the [111] direction despite the formation of long-range ordered rhombohedral domains, which results in unique weak relaxor properties. In-situ imaging upon heating successfully reveals the dynamic behavior of domain-wall movements with
lattice distortion and paraelectric-ferroelectric phase coexistence in the vicinity of the Curie temperature, indicating a discontinuous phase transition. Our research provides new insights into the effect of chemical ordering on ferroelectric nanodomains.
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All authors Hiroshi Nakajima, Satoshi Hiroi, Hirofumi Tsukasaki, Yonghong Bing, Stéphane Grenier, Zuo-Guang Ye, Pierre-Eymeric Janolin, Shigeo Mori