Materials Science
New insights into hydrogen-assisted intergranular cracking in nickel
S. Quan, A. Zafra, E. Martínez-Pañeda et al. (+3 more)
We characterize the grain boundary (GB) susceptibility to hydrogen-assisted intergranular cracking in pure nickel as a function of coincident site
lattice value ($\Sigma$-n), over a wide range of hydrogen concentrations (4 to 14 wppm). Cracks on the surface and within the bulk material were identified across the entire gauge region of the specimens. The susceptibility of GBs to crack initiation and propagation was evaluated by separating cracks containing single GB or multiple GBs. A larger loss in fracture strain, a smaller reduction in area, and an increase in the percentage of intergranular fracture indicated a higher degree of embrittlement at elevated hydrogen concentrations. The number of cracks was significantly higher on the surface than in the bulk for the most severe hydrogen charging conditions ($\geq$ 8 wppm), while a similar number was observed for lower concentrations. The propensity for hydrogen-assisted intergranular cracking at different types of GBs on the surface and in the bulk material was consistent, indicating that while cathodic charging can promote surface cracks, it does not significantly impact the GBs relative susceptibility. The $\Sigma$-3 boundaries were the most resistant to cracking, as evidenced by the considerably lower fraction of these GBs exhibiting intergranular cracking at all hydrogen concentrations considered. This contrasts literature findings for Ni
alloys and can be explained by the segregation energies and reductions in the cohesive strength with hydrogen, with less favorable trapping at the $\Sigma$-3 boundaries. No evidence of plasticity-mediated cracking initiation was observed.
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All authors S. Quan, A. Zafra, E. Martínez-Pañeda, C. Wu, Z.D. Harris, L. Cupertino-Malheiros
Materials Science
Altermagnetoelectric Spin Field Effect Transistor
Ziye Zhu, Xianzhang Chen, Xunkai Duan et al. (+4 more)
Spin field-effect transistors (SFETs) are promising candidates for low-power
spin-based electronics, yet existing realizations that rely on
spin-orbit coupling are constrained by limited material choices and short
spin-coherence lengths. Here we propose a different operating principle based on multiferroic altermagnets, in which
spin splitting is tuned by an electric field through
symmetry control rather than conventional
spin-orbit physics. Using an effective model combined with
quantum transport simulations, we show that the conductance is determined by the degree of matching between the electrically controlled
spin texture of the channel and the fixed
spin polarization of
ferromagnetic contacts, enabling clear ON and OFF states. Remarkably, we also address a long-standing challenge in multiferroic device design: spintronic channels require metallic carriers, whereas ferroelectricity is usually suppressed in metals. We resolve this conflict by imprinting multiferroic altermagnetism into highly conductive materials via the proximity effect. First-principles calculations for
graphene on multiferroic vanadium sulfide halides confirm that
graphene acquires a ferroelectrically switchable
spin splitting while retaining its metallic character. These results establish a practical route to SFET implementation and identify multiferroic altermagnets as a versatile platform for next-generation spintronic devices.
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All authors Ziye Zhu, Xianzhang Chen, Xunkai Duan, Zhou Cui, Jiayong Zhang, Igor Zutic, Tong Zhou
Materials Science
Representation of Inorganic Synthesis Reactions and Prediction: Graphical Framework and Datasets
Samuel Andrello, Daniel Alabi and Simon J. L. Billinge
While machine learning has enabled the rapid prediction of inorganic materials with novel properties, the challenge of determining how to synthesize these materials remains largely unsolved. Previous work has largely focused on predicting precursors or reaction conditions, but only rarely on full synthesis pathways. We introduce the ActionGraph, a directed acyclic graph framework that encodes both the chemical and procedural structure, in terms of synthesis operations, of inorganic synthesis reactions. Using 13,017 text-mined solid-state synthesis reactions from the Materials Project, we show that incorporating PCA-reduced ActionGraph adjacency
matrices into a $k$-nearest neighbors
retrieval model significantly improves synthesis pathway prediction. While the ActionGraph framework only results in a 1.34% and 2.76% increase in precursor and operation F1 scores (average over varying numbers of PCA components) respectively, the operation length matching accuracy rises 3.4 times (from 15.8% to 53.3%). We observe an interesting trade-off where precursor prediction performance peaks at 10-11 PCA components while operation prediction continues improving up to 30 components. This suggests composition information dominates precursor selection while structural information is critical for operation sequencing. Overall, the ActionGraph framework demonstrates strong potential, and with further adoption, its full range of benefits can be effectively realized.
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Materials Science
Magnetic field induced polarization enhancement in the photoluminescence of MBE-grown WSe$_2$ layers
Maksymilian Kuna, Mateusz Raczyński, Julia Kucharek et al. (+5 more)
We report an experimental study of the
magnetic-field dependence of the optically pumped valley polarization in an epitaxial tungsten diselenide (WSe$_2$) monolayer grown by molecular-beam epitaxy (MBE) on a hexagonal boron nitride (hBN) substrate. Circularly polarized photoluminescence (PL) measurements reveal that applying a weak out-of-plane
magnetic field, on the order of 0.1 T, dramatically increases the effectiveness of the optical orientation of the emission associated with defect-bound localized
excitons. We compare the obtained results with the earlier studies on the reference exfoliated monolayers, discussing both qualitative similarity as well as quantitative differences. Our observations are further supplemented by the results of time-resolved PL measurements, which confirm the pseudospin relaxation time of approximately 25 ps, a value significantly shorter than the $\approx$100 ps previously reported for mechanically exfoliated samples.
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All authors Maksymilian Kuna, Mateusz Raczyński, Julia Kucharek, Takashi Taniguchi, Kenji Watanabe, Tomasz Kazimierczuk, Wojciech Pacuski, Piotr Kossacki
Materials Science
Intervention Strategies for Polarization Switching in Hybrid Improper Ferroelectrics
Ayana Ghosh, Palanichamy Gayathri, Sathiyamoorthy Buvaneswaran et al. (+1 more)
The potential of hybrid improper ferroelectrics (HIFs) in electronic and spintronic devices hinges on their ability to switch polarization. Although the coupling between octahedral rotation and tilt is well established, the factors that govern switching barriers remain elusive. In this study, we explore this area to demonstrate the critical role of causal
reasoning in uncovering the mechanisms to control the ferroelectric switching barrier in HIFs. By combining causal discovery, causal interventions, and first-principles simulations, we identify tolerance factor, A-site cation radii mismatch, epitaxial strain, and octahedral rotation/tilt as key parameters and quantify how their interplay directly influences switching barrier. Three key insights emerge from our work: (a) the analysis identifies the structural descriptors controlling polarization reversal across a broad family of A-site-layered double perovskites and superlattices, (b) it uncovers non-trivial, material-specific rotation-tilt mechanisms, including a counterintuitive cooperative pathway where both rotation and tilt change while lowering the barrier, an effect mostly inaccessible to conventional Landau or first-principles-based approaches and (c) it maps these material-specific mechanisms to experimentally realizable parameters, showing that epitaxial strain from orthorhombic substrates (e.g., NdScO$_3$, NdGaO$_3$) selectively tunes octahedral distortions to achieve barrier reduction across varied compositions. These results establish actionable, materials-by-design principles linking composition, structure, and strain to polarization switching, while highlighting the potential of causal
reasoning to guide intelligent, mechanism-driven strategies for engineering complex functional
oxides.
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All authors Ayana Ghosh, Palanichamy Gayathri, Sathiyamoorthy Buvaneswaran, Saurabh Ghosh
Materials Science · Cross-listed from cond-mat.mes-hall
Electrically driven plasmon-polaritonic bistability in Dirac electron tunneling transistors
Shuai Zhang, Yang Xu, Junhe Zhang et al. (+12 more)
Bistability-two distinct stable states under identical parameter-is not only a fundamental physical concept but also of importance in practical applications. While plasmon-polaritonic bistability representing history-dependent stable states within plasmonic systems has been theoretically predicted, it has yet to be demonstrated experimentally due to challenges in realizing suitable nonlinearity at feasible electric-field strengths. Here, we report the experimental observation of electrically driven plasmon-polaritonic bistability in
graphene/hexagonal-boron-nitride/
graphene tunneling transistors, achieved through momentum-conserving resonant tunneling of Dirac electrons. Using a small twist angle between
graphene layers, we engineered devices exhibiting both electronic and plasmon-polaritonic bistability. This bistable plasmonic behavior can be precisely tuned through load resistance and electrostatic gating. Our findings open new pathways for exploring nonlinear optical and electronic phenomena in van der Waals
heterostructures and mark a significant advance in nanoplasmonics, with potential applications in optical
memory, sensing, and optoelectronic switching.
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All authors Shuai Zhang, Yang Xu, Junhe Zhang, Dihao Sun, Yinan Dong, Matthew Fu, Takashi Taniguchi, Kenji Watanabe, Cory R. Dean, Monica Allen, Jeffery Allen, F. Javier Garcia de Abajo, Antti J. Moilanen, Lukas Novotny, D. N. Basov
Materials Science
Exploring the Electronic Nature of Spinel Oxides: A Review of Their Electron Interactions and Prospects
Jagadis Prasad Nayak, Raju Saini, Sourav Dash et al. (+1 more)
This review discusses the multifaceted electronic properties of spinel
oxides with a particular focus on Lithium Vanadate (LiV2O4), Lithium Titanate (LiTi2O4), and Magnesium Titanate (MgTi2O4). We selected LiTi2O4, LiV2O4, and MgTi2O4 because they serve as quintessential examples of spinel
oxides' diverse and intriguing electronic phenomena. LiV2O4 heavy
fermion behaviour challenges traditional theories in d-electron systems, LiTi2O4 being the first
oxide superconductor provides critical insights into unconventional superconductivity driven by strong electron-
phonon interactions, and MgTi2O4 pronounced orbital ordering and metalinsulator transition offers a clear model for exploring electron-
lattice coupling. This shows how the inherent structural versatility of the spinel
lattice, characterised by its cubic close-packed oxygen network and variable cation distributions, enables a rich interplay of electron-electron correlations, electron-
lattice coupling, and orbital degrees of freedom. In LiV2O4, the combination of mixed-valence vanadium ions and a geometrically frustrated pyrochlore
lattice gives rise to heavy
fermion behaviour, whereas LiTi2O4 exhibits unconventional superconductivity driven by a high density of states at the
Fermi level and strong electronphonon interactions. MgTi2O4 undergoes a pronounced metal-
insulator transition, where orbital ordering triggers a Peierls-like distortion that stabilises a low-temperature insulating state through Ti-Ti dimerization. How the composition of these compounds affects their properties, based on both theoretical research and experimental findings, is illustrated by this review. It illustrates the promise of Spinels in practical technologies such as energy storage, electrocatalysis, and high-temperature lubrication.
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All authors Jagadis Prasad Nayak, Raju Saini, Sourav Dash, Gopi Nath Daptary
Materials Science
Realization of polytype heterostructures via delicate structural transitions from a doped-Mott insulator
Yanyan Geng, Manyu Wang, Shumin Meng et al. (+9 more)
Transition metal dichalcogenides (TMDs) host multiple competing structural and electronic phases, making them an ideal platform for constructing polytype
heterostructures with emergent
quantum properties. However, controlling phase transitions to form diverse
heterostructures inside a single
crystal remains challenging. Here, we realize vertical/lateral polytype
heterostructures in a hole-doped Mott
insulator via thermal-annealing-induced structural transitions. Raman spectroscopy, atomic force microscopy (AFM) and scanning Kelvin probe force microscopy (SKPM) confirm the coexistence of T-H polytype
heterostructures. Atomic-scale scanning tunneling microscopy/spectroscopy (STM/STS) measurements reveal the transparent effect in 1H/1T vertical
heterostructures, where the charge density wave (CDW) of the underlying 1T-layer superposes on the top 1H-layer under positive bias. By systematically comparing 1T/1H and 1T/1T interfaces, we demonstrate that the metallic 1H-layer imposes a Coulomb screening effect on the 1T-layer, suppressing the formation of CDW domain walls and forming more ordered electronic states. These results clarify the interfacial coupling between distinct
quantum many-body phases and establish a controllable pathway for constructing two-dimensional polytype
heterostructures with tunable electronic properties.
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All authors Yanyan Geng, Manyu Wang, Shumin Meng, Shuo Mi, Chang Li, Huiji Hu, Jianfeng Guo, Rui Xu, Fei Pang, Wei Ji, Weichang Zhou, Zhihai Cheng
Materials Science · Cross-listed from cond-mat.supr-con
Intrinsic Second-Order Topological Superconductors with Tunable Majorana Zero Modes
Xiao-Jiao Wang, Yijie Mo, Zhi Wang et al. (+2 more)
Dirac semimetals, with their protected Dirac points, present an ideal platform for realizing intrinsic topological superconductivity. In this work, we investigate superconductivity in a two-dimensional, square-
lattice nonsymmorphic Dirac semimetal. In the normal state near half-filling, the
Fermi surface consists of two distinct pockets, each enclosing a Dirac point at a time-reversal invariant momentum ($\textbf{X}=(\pi,0)$ and $\textbf{Y}=(0,\pi)$). Considering an on-site repulsive and nearest-neighbor attractive interaction, we use self-consistent mean-field theory to determine the ground-state pairing
symmetry. We find that an even-parity,
spin-singlet $d_{x^{2}-y^{2}}$-wave pairing is favored as it gives rise to a fully gapped superconducting state. Since the pairing amplitude has opposite signs on the two Dirac
Fermi pockets, the superconducting state is identified as a second-order topological
superconductor. The hallmark of this topological phase is the emergence of Majorana zero modes at the system's boundaries. Notably, the positions of these Majorana modes are highly controllable and can be manipulated simply by tailoring the boundary sublattice terminations. Our results highlight the promise of nonsymmorphic Dirac semimetals for realizing and manipulating Majorana modes.
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All authors Xiao-Jiao Wang, Yijie Mo, Zhi Wang, Zhigang Wu, Zhongbo Yan
Materials Science
Ultrasensitive Anti-Stokes Luminescence Thermometry in Transition Metal Dichalcogenide Monolayers
Sharada Nagarkar, Fahrettin Sarcan, Elanur Hut et al. (+4 more)
Accurate temperature mapping at the nanoscale is a critical challenge in modern science and technology, as conventional methods fail at these dimensions. To address this challenge, we demonstrate a highly sensitive nanothermometer using anti-Stokes photoluminescence, also known as photoluminescence upconversion (UPL), in monolayer tungsten disulfide ($\mathrm{WS_2}$). Leveraging the direct band gap and strong
exciton-
phonon coupling in the two-dimensional monolayers, we achieve an exceptional relative sensitivity above $4\%\,\mathrm{K}^{-1}$ across the 300 K to 425 K range, ranking it among the best-performing materials reported. A strong resonantly enhanced UPL is observed, confirming the central role of optical
phonons in the upconversion mechanism. Furthermore, we introduce a new analytical model to quantitatively describe the UPL process, taking into account the interplay of
phonon populations, bandgap narrowing, and substrate effects, which predicts resonant temperatures and provides a framework with broad applicability to any material exhibiting an anti-Stokes photoluminescence response. To demonstrate its use as a high-resolution optical thermometer, we map a $20\,^{\circ}\mathrm{C}$ thermal gradient across a $20\,\mu\mathrm{m}$ long monolayer with a spatial resolution of $1\,\mu\mathrm{m}$. With its high sensitivity, strong signal, and excellent reproducibility, our work establishes monolayer transition metal dichalcogenide as a leading platform for non-invasive thermal sensing in advanced microelectronic and biological systems.
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All authors Sharada Nagarkar, Fahrettin Sarcan, Elanur Hut, Emiliano R. Martins, Stuart A Cavill, Thomas F. Krauss, Yue Wang
Materials Science · Cross-listed from quant-ph
Dynamic Modulation of Long Range Photon Magnon Coupling
Alban Joseph, Mawgan A. Smith, Martin P. Weides et al. (+1 more)
Evidence of non-hermitian behavior has been recently demonstrated in cavity magnonics, including the emergence of mode level attraction and exceptional points in spectroscopic measurements. This work demonstrates experimental evidence of time-domain dynamics of
magnon-
photon systems that are coupled through a long-range interaction (i.e. remote coupling) exhibiting level attraction mediated by an auxiliary mode. We directly observe the temporal
evolution of dissipatively coupled cavity-
magnon modes, where heavily damped transmission line modes mediate the interaction. Our frequency-domain measurements confirm the predicted level attraction, while time-domain ring-down measurements reveal the characteristic signatures of dissipative coupling dynamics. Our approach offers in situ tunability over the dissipative coupling strength, including complete suppression, without requiring physical modifications to the experimental setup, providing a versatile platform for exploring tunable, non-Hermitian physics.
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All authors Alban Joseph, Mawgan A. Smith, Martin P. Weides, Rair Macêdo
Materials Science · Cross-listed from cond-mat.soft
Adaptive hydrogels with spatiotemporal stiffening using pH-modulating enzymes
Natascha Gray, Zoe Grämiger, André R. Studart et al. (+1 more)
Biological systems achieve adaptive mechanical responses through reaction-
diffusion processes that couple chemical wave propagation to structural transitions. Although synthetic hydrogels with enzymatic reactions offer a platform for replicating such autonomous behavior, the mechanistic principles governing chemomechanical transduction remain poorly understood. Here, we present a glucose oxidase-embedded polyacrylamide-alginate hydrogel with slower transduction kinetics that enable independent resolution of chemical waves and mechanical adaptation. Enzymatic pH waves propagate at 15-44 um/min, triggering calcium-mediated alginate crosslinking through pH-responsive calcium-EDTA dissociation. Independent tracking of chemical and mechanical waves reveals that mechanical wavefronts (12 um/min) lag behind chemical propagation, establishing transduction as the rate-limiting step in this chemomechanical coupling. Remarkably, the enzymatic system must continuously supply chemical energy to both propagate the chemical wave and drive ongoing mechanical transitions, imposing energetic costs on reaction-
diffusion beyond kinetic constraints alone. Our adaptive system achieves up to 2.1-fold increase in stiffness and enables autonomous conversion of localized stimuli into system-wide mechanical responses. These mechanistic insights establish design principles for engineering adaptive materials with predictable spatiotemporal control in soft robotics and biomedical applications.
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All authors Natascha Gray, Zoe Grämiger, André R. Studart, Rafael Libanori
Materials Science
Rational regulation strategies of interstitial localized electrons in electride: A density functional theory study
L. Zhang, D. Wang, H. Wang et al. (+4 more)
As a class of electron-rich materials, electrides demonstrate promising applications in many fields. However, the required high pressure restricts the practical applications to some extent. This study reveals that the unique feature of electride, i.e., the localization of interstitial electrons, can be greatly enhanced and tuned by self-defective doping, applying tensile/compressive stress, or shear stress. Moreover, the requirement of orbital orthogonality between the valence and core electron wave functions, as well as the Pauli exclusion principle, should be the driven force for the electron interstitial localization; and the exertion of external pressure modifies the available space to accommodate the electronic wave functions, thus enhances the interstitial localization. These discoveries lay down the ground for searching for promising electrides that are practicable at ambient conditions.
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All authors L. Zhang, D. Wang, H. Wang, J. Li, Y. F. Wang, Q. Wu, Hua Y. Geng
Materials Science
Competing excitonic couplings as origin of mimicked phase transitions in zinc-phthalocyanine single crystals
Lisa Schraut-May, Sebastian Hammer, Luca Nils Philipp et al. (+9 more)
The optical properties of molecular
crystals are largely determined by the excitonic coupling of neighboring molecules. This coupling is extremely sensitive to the arrangement of adjacent molecular units, as their electronic interaction is defined by the relative orientation of the individual transition dipole moments and their wave function overlap. Hence, the optical properties, such as fluorescence, are usually highly anisotropic and good indicators of structural changes during the variation of intensive thermodynamic parameters like temperature or pressure. Here, we discuss the peculiar though archetypical case of $\beta$-phase zinc-phthalocyanine: In single
crystals, we report a sudden change of spectral emission with temperature from a broad, unpolarized Frenkel-
exciton type luminescence to a narrow, highly polarized superradiance-like fluorescence below 80 K. Surprisingly, we find that there is no sign of a discrete structural phase transition in this temperature regime. To understand this apparent contradiction, we perform polarization-, temperature- and time-dependent photoluminescence measurements along different crystallographic directions to fully map the emission characteristics of the
crystal-
exciton. By means of ab-initio calculations on a density functional theory level we conclude that our observations are consistent with a dimer
exciton model when considering thermalized electronic states. As such, our study presents a representative case study on a well-established molecular material class demonstrating that caution is advised when attributing discrete changes in electronic observables to a structural phase transition. As we show for zinc-phthalocyanine in its $\beta$-phase modification, slowly varying excitonic couplings and thermal redistribution of excitations can mimic the same signatures attributed to a structural phase transition.
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All authors Lisa Schraut-May, Sebastian Hammer, Luca Nils Philipp, Krzysztof Radacki, Gabriele Tauscher, Helena Hollstein, Kilian Strauß, Martin Kamp, Heinrich Schwoerer, Holger Braunschweig, Roland Mitric, Jens Pflaum
Materials Science
Electric-Field and Doping-Induced Non collinear Magnetic Interactions in Monolayer Ti$_2$Si
Dimple Rani, Gayatri Panda, Subrata Jana et al. (+1 more)
Two-dimensional (2D) silicides are an emerging class of materials whose
magnetic and relativistic properties remain largely unexplored. Using first-principles calculations, we investigate how electric-field modulation and transition-metal doping influence the
magnetic exchange, magnetocrystalline anisotropy, and antisymmetric Dzyaloshinskii-Moriya interaction (DMI) in monolayer Ti2Si. Pristine Ti2Si is a dynamically stable
ferromagnetic metal with in-plane anisotropy and centrosymmetric bonding, which suppresses DMI even under strong perpendicular electric fields. To overcome this
symmetry constraint, we introduce Pt and Co substitution at Ti sites. Co enhances the
magnetic exchange, whereas Pt provides strong
spin orbit coupling (SOC), and the combined chemical asymmetry breaks inversion
symmetry sufficiently to induce a sizable DMI. A Wannier-based tight-binding model captures the orbital-resolved superexchange pathways and reveals a clear hierarchy between a weak Si-mediated channel and a dominant Pt-mediated interlayer channel. First-principles calculations confirm that the Pt-assisted pathway governs the magnitude and sign of the total DMI. Among all configurations, Pt0.5CoTi0.5Si exhibits the strongest
chiral interaction, with its intralayer and interlayer contributions favoring opposite rotation senses, namely counterclockwise (CCW) and clockwise (CW). Our results establish chemically engineered Ti2Si monolayers as a promising platform for realizing and tuning
chiral magnetic textures in 2D silicides.
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All authors Dimple Rani, Gayatri Panda, Subrata Jana, Prasanjit Samal
Materials Science · Cross-listed from cs.LG
Modeling and Inverse Identification of Interfacial Heat Conduction in Finite Layer and Semi-Infinite Substrate Systems via a Physics-Guided Neural Framework
Wenhao Sha and Tienchong Chang
Heat transfer in
semiconductor devices is dominated by chip and substrate assemblies, where heat generated within a finite chip layer dissipates into a semi-infinite substrate with much higher thermophysical properties. This mismatch produces steep interfacial temperature gradients, making the transient thermal response highly sensitive to the interface. Conventional numerical solvers require excessive discretization to resolve these dynamics, while physics-informed neural networks (PINNs) often exhibit unstable convergence and loss of physical consistency near the material interface. To address these challenges, we introduce HeatTransFormer, a physics-guided
Transformer architecture for interface-dominated
diffusion problems. The framework integrates physically informed spatiotemporal sampling, a Laplace-based activation emulating analytical
diffusion solutions, and a mask-free
attention mechanism supporting bidirectional spatiotemporal coupling. These components enable the model to resolve steep gradients, maintain physical consistency, and remain stable where PINNs typically fail. HeatTransFormer produces coherent temperature fields across the interface when applied to a finite layer and semi-infinite substrate configuration. Coupled with a physics-constrained inverse strategy, it further enables reliable identification of three unknown thermal properties simultaneously using only external measurements. Overall, this work demonstrates that physics-guided
Transformer architectures provide a unified framework for forward and inverse modeling in interface-dominated thermal systems.
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Materials Science
Precise Twist Angle Determination in twisted WSe2 via Optical Moiré Phonons
Nicolai-Leonid Bathen, Thorsten Deilmann, Ana Senkić et al. (+7 more)
Twisted
bilayers of transition metal dichalcogenides (TMDC) form moiré superlattices resulting in moiré minibands in momentum space and hosting localized
excitons in real space. While moiré superlattices provide access to Mott-Hubbard physics, their energy potential landscape and electronic correlations are highly sensitive to fluctuations of the twist angle, disorder and
lattice reconstructions. However, fast and non-invasive experimental access to local twist angle and its spatial variations is challenging. Here, we systematically correlate twist angle variations of twisted WSe2
bilayers across micrometer length scales using a combined lateral force microscopy (LFM) and a micro- Raman spectroscopy approach. These measurements uncover lateral variations in the twist angle by more than 1{\deg} across length scales relevant to optical and transport measurements. We demonstrate that twist angles in the range of 3{\deg} < $\alpha$ < 12{\deg} show distinct Raman response from scattering on optical moiré
phonons allowing twist angle determination with high precision and sub-micrometer spatial resolution under ambient conditions. These modes are particularly sensitive in the low-angle twist regime, predicted to host emergent
quantum phases. Our results establish micro-Raman spectroscopy of optical moiré
phonons as a rapid, non-invasive probe to determine twist angle and to screen local twist angle variations with a precision better than $\pm$ 0.3{\deg} and a lateral resolution below one micrometer. This methodology is also applicable to fully hBN-encapsulated
heterostructures.
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All authors Nicolai-Leonid Bathen, Thorsten Deilmann, Ana Senkić, Hendrik Lambers, Rami Dana, Kenji Watanabe, Takashi Taniguchi, Frances M. Ross, Julian Klein, Ursula Wurstbauer
Materials Science
Accurate Modeling of Gate Leakage Currents in SiC Power MOSFETs
Ang Feng, Alexander Karl, Dominic Waldhör et al. (+3 more)
Silicon carbide (SiC) metal-
oxide-
semiconductor field-effect-transistors (MOSFETs) enable high-voltage and high-temperature power conversion. Compared to Si devices, they suffer from pronounced gate leakage due to the reduced electron tunneling barrier at the interface between SiC and amorphous silicon dioxide (a-SiO$_2$). We develop a self-consistent, physics-based simulation framework that couples electrostatics,
quantum tunneling, carrier transport, impact ionization, and charge trapping for both electrons and holes. The model quantitatively reproduces measured gate-current-voltage characteristics of SiC MOS capacitors over a wide temperature (80-573 K) range and a wide bias range without empirical fitting. Simulations reveal that conduction electrons in a-SiO$_2$ can trigger impact ionization, which generates electron-hole pairs, and leads to capture of holes in the
oxide bulk, thereby enhancing gate leakage current. The framework captures these coupled processes across multiple orders of magnitude in time and field, providing predictive capability for
oxide reliability. Although demonstrated for SiC devices, the methodology also applies to Si technologies that uses the same gate dielectric.
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All authors Ang Feng, Alexander Karl, Dominic Waldhör, Marina Avramenko, Peter Moens, Tibor Grasser
Materials Science
Strengthening and toughening mechanisms in heterostructured laminates revealed by a phase field-enhanced crystal plasticity simulation
Yukai Xiong, Jianfeng Zhao, Jinling Liu et al. (+3 more)
Heterostructured (HS) materials exhibit excellent mechanical properties, combining high strength and significant ductility. Hetero-deformation-induced (HDI) hardening and strain de-localization are key to their strength-ductility synergy. However, existing models often fall short in addressing these aspects. In this work, a coupled framework integrating strain gradient
crystal plasticity and phase field damage models is developed. The interface dominated HDI hardening in HS laminates is handled by introducing a heterogeneity coefficient into the back stress. The phase field model accounts for defect energy-driven damage and accurately represents the materials ductile damage behavior by accounting for effects of microstructure on crack initiation and propagation. Simulation results on HS laminates align well with experimental results and reflect the distribution of geometrically necessary dislocations and back stresses at interfaces between regions with dissimilar microstructure. Crack initiation and propagation are accurately described, providing valuable insights into fracture behavior. The model can predict how strength and ductility change upon variations of the HS laminate microstructure, thus providing an essential tool for microstructure optimization. This work enhances the understanding of deformation mechanisms in HS laminates and provides valuable insights for design and optimization of this class of materials.
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All authors Yukai Xiong, Jianfeng Zhao, Jinling Liu, Jie Wang, Michael Zaiser, Xu Zhang
Materials Science
Let Cyclic Electrochemical Data Speak for Your Energy Storage Material and Processing
Vinod Sarky, P. Laxman Mani Kanta, Shivangi Keshri et al. (+3 more)
Efforts to improve performance, like energy and power density of electrochemical energy storage devices (batteries, capacitors, and super-capacitors), are being made using a range of experimental and computational tools. The most common strategy involves exploring new material chemistries, developing advanced synthesis routes, and advanced ways to integrate these materials into device architectures. Although it is desirable to evaluate the performance of such efforts at a fixed
cell format, not all studies conduct testing across the same
cell formats. Specific performance normalized per mass of active material has been adopted as a universal indicator of performance, but it is not a reliable way to compare across
cell formats. We propose a new mass normalization, i.e., the mass of electrochemical participants, to calculate specific performance. This new specific performance makes it possible to efficiently compare the efficacy of materials, synthesis, and
cell assembly across different
cell formats. We developed a framework to comprehensively report materials, synthesis, and
cell assembly, and performance data, which facilitates succinctly reporting all performance indicators, including charge discharge curves over all cyclic stability assessments. The new specific performance and mass of the electrochemical participants per unit area of the electrode allows us to create a calculator to estimate performance at any commercial device-level
cell format from measured data at the laboratory-level
cell. The new specific performance also helps in optimizing the coating thickness and the loading of the active material. The framework can be adapted by journals to facilitate the reporting of data in a comprehensive way. Leveraging this framework, we have also compiled a database (hosted at https://power.tattvasar.com/) by extracting pertinent data from existing literature.
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All authors Vinod Sarky, P. Laxman Mani Kanta, Shivangi Keshri, Mannanvali Shaik, B. R. K. Nanda, Satyesh K. Yadav
Materials Science
Low-temperature thermal conductivity of the substrate material YAlO3 and its unconventional sister compound YbAlO3
Parisa Mokhtari, Ulrike Stockert, Stanislav E. Nikitin et al. (+3 more)
We present thermal conductivity data on single
crystals of YAlO3 and YbAlO3 for temperatures between 2 K and 300 K and the heat current along b and c. Both materials are very good thermal conductors in the investigated temperature range. The thermal conductivity in these electrical
insulators is due to
phonons. The effect of Y-Yb exchange is found to be rather small despite the considerable difference in density and average atomic mass. For YAlO3 we find a moderate thermal conductivity anisotropy with weak temperature dependence and a ratio of c to b direction between at most 1 and 2.2. It is discussed with regard to the velocities of sound and relevant scattering processes. For YbAlO3 the small
crystal size limits the precision of absolute thermal conductivity values and does not allow drawing conclusions on the anisotropy. Our results on YAlO3 confirm that the material is suitable for applications requiring a good thermal conductivity at temperatures down to
liquid helium, such as
lasers, substrates, and detectors.
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All authors Parisa Mokhtari, Ulrike Stockert, Stanislav E. Nikitin, Leonid Vasylechko, Manuel Brando, Elena Hassinger
Materials Science · Cross-listed from cond-mat.str-el
Emergent Chiral Spin Crystal Phase in (111) SrRuO3 Thin Films
Zhaoqing Ding, Yongjie Xie, Xuejiao Chen et al. (+13 more)
Perovskite ruthenates are fascinating playgrounds for exploring topological
spin textures, but generally rely on extrinsic mechanisms to trigger the noncoplanar states. Here we report the discovery of an emergent
chiral spin crystal phase in (111) SrRuO3 epitaxial films, characterized by a significant topological
Hall effect and noncoplanar
spin arrangements with different propagation vectors along two orthogonal directions. Instead of driven by the enhanced Dzyaloshinskii-Moriya interaction due to broken inversion
symmetry at heterointerfaces, this emergent state arises intrinsically from the interplay of dipolar interactions and
magnetic frustration, leading to the stabilization of topological phases in much thicker films. These findings open a new pathway for creating and controlling the topological
spin states in perovskites, with broad implications for spintronic device design.
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All authors Zhaoqing Ding, Yongjie Xie, Xuejiao Chen, Sheng Wang, Zhen Wang, Zeguo Lin, Enling Wang, Xiaofeng Wu, Mingyu Yang, Yuelong Xiong, Meng Meng, Fang Yang, Jiandi Zhang, Xianggang Qiu, XIaoran Liu, Jiandong Guo
Materials Science · Cross-listed from cond-mat.str-el
Quasi-steady electron-excitonic complexes coupling in a two-dimensional semiconductor
Shangkun Mo, Hao Zhong, Keming Zhao et al. (+10 more)
Excitons and their complexes govern optical-related behaviors in
semiconductors. Here, using angle-resolved photoemission spectroscopy (ARPES), we have elucidated the light-matter interaction mediated by quasi-steady excitonic complexes within a monolayer of the prototypical two-dimensional (2D)
semiconductor WSe2. Under continuous incident light, we have observed the generation of quasi-steady
excitons and their complexes, encompassing ground and excited state
excitons, trions, as well as their intricate interplay. We further show spectral evidence of electronic excitation states within the background of quasi-steady excitonic complexes, characterized by valence band (VB) effective mass renormalization, the enhanced
spin-orbit coupling (SOC), the formation of an excitonic gap near the
Fermi level (EF ) of the conduction band (CB), and intervalley excitonic band folding. Our findings not only unveil a quasi-steady excitonic complex background for the creation of diverse electronic excitations in 2D
semiconductors but also offer new insights into the role of
excitons in the charge density wave (CDW) formation mechanism and facilitate the advancement of correlated electronic state engineering based on the coupling between electrons and excitonic complexes in a quasi-
equilibrium state.
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All authors Shangkun Mo, Hao Zhong, Keming Zhao, Yunfei Bai, Dingkun Qin, Chunlong Wu, Qiang Wan, Renzhe Li, Cao Peng, Xingzhe Wang, Enting Li, Sheng Meng, Nan Xu
Materials Science
Harnessing Multifractality to Enhance Thermal Stability in Mixed-Phase Vanadium Oxide Thin Films
Abhijeet Das, Ram Pratap Yadav, Rashmi Roy Karmakar et al. (+2 more)
Vanadium
oxide thin films exhibit temperature-driven electronic transitions desirable for sensing and microelectronic applications, yet their performance is often limited by thermal hysteresis. This study demonstrates that electronic stability is governed not simply by roughness or crystallinity but by a unique combination of surface morphological complexity and thermal hysteresis, revealed across films deposited with varying working pressure using Direct Current/
Radio Frequency magnetron sputtering. Specifically, the film grown at 15 mTorr shows a distinct convergence of highest morphological vertical complexity and lowest thermal hysteresis, exhibiting nearly reversible transport with activation energies ranging from 0.26 to 0.28 eV and negative temperature coefficients of resistance between -0.0337 and -0.035 K-1. While conventional roughness metrics and mono-fractal parameters do not capture this behavior, multifractal detrended fluctuation analysis uncovers a pronounced peak in multifractality strength, which correlates inversely with thermal hysteresis. This highlights multifractality strength as a predictive descriptor of electronic stability, identifying a multiscale structural signature that enhances stress accommodation during thermal cycling. These results define an optimal deposition window and provide a morphology-guided pathway for developing thermally robust mixed-phase vanadium
oxide films.
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All authors Abhijeet Das, Ram Pratap Yadav, Rashmi Roy Karmakar, Jyoti Jaiswal, Sanjeev Kumar
Materials Science
Coupled plastic strain- and stress-induced phase transformations and microstructure evolution in Fe-7%Mn alloy in a dynamic rotational diamond anvil cell
Sorb Yesudhas, Mrinmay Sahu, Valery I. Levitas et al. (+3 more)
Studies of severe plastic deformation (SPD), microstructure
evolution, and plastic strain-induced phase transformations (PTs) are crucial for various fundamental and applied disciplines and phenomena. However, they are performed either quasi-statically or at low strain rates and pressures. Here, in situ experiments in a dynamic rotational diamond anvil
cell (dRDAC) on SPD and BCC<->HCP PTs at pressures up to 27.6 GPa, rotation rates up to 1,500 RPM, and strain rates up to 2,299/s are performed, considering Fe-7%Mn
alloy as an example. Strong plastic straining leads to a unique mechanism and kinetics with simultaneous direct and reverse PTs, which has not been studied for any material. For quasi-static loading, we determine the kinetic parameters for strain-induced direct-reverse PTs and the stationary volume fraction $c$ versus pressure. During torsion at 1,000 and 1,500 RPM, $c$ does not change. After torsion stops, 51 minutes later, it increases by 31% at 1,000 RPM and $c$->0, 7 minutes later at 1,500 RPM. These findings contradict the general wisdom that strain-induced PTs occur only during straining and are governed by strain, independent of time; they reveal an alternative mechanism. It is revealed that the crystallite size of ~28(6) nm, microstrain ~0.0035(8), and dislocation density ~1.3(6)x$10^{15}$/$m^2$ in the HCP phase are steady during static compression and dynamic torsion, during and after the PT, and after torsion. These parameters are independent of pressure, plastic strain tensor, its path, strain rates, and $c$. The results obtained open fundamental research on combined strain- and stress-induced PTs and microstructure
evolution under dynamic SPD and high pressure, with various important applications.
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All authors Sorb Yesudhas, Mrinmay Sahu, Valery I. Levitas, Dean Smith, Aniket Singh, Jeffrey T. Lloyd
Materials Science
Effective Mass of a Migrating Interface
Xinyuan Song and Chuang Deng
Interfaces are ubiquitous in materials and play a central role in microstructural
evolution and material properties. Although interface migration has been studied for more than a century and remains an active field, several foundational assumptions of interface kinetics remain largely untested. In particular, interfaces are commonly treated as massless objects governed by overdamped dynamics. In this study, we show that grain boundaries exhibit measurable inertial behavior under high-frequency oscillatory driving. We introduce a quantitative method to extract an effective interface mass from the phase lag between the applied force and the interface velocity, and find that this mass scales with the atoms participating in boundary migration. Using this framework, we identify regimes in which inertial effects significantly modify interfacial kinetics, especially at frequencies relevant to thermal fluctuations. These results challenge the conventional overdamped description and establish effective interface mass as a key ingredient in a physically complete theory of interface migration.
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Materials Science
An experimentally validated end-to-end framework for operando modeling of intrinsically complex metallosilicates
Jong Hyun Jung, Tom Schächtel, Yongliang Ou et al. (+5 more)
Structurally and chemically complex materials such as amorphous metallosilicates underpin major catalytic and separation technologies, yet their intrinsic complexity challenges reliable atomistic modeling under realistic conditions. Consequently, simulations that connect composition to material properties remain largely inaccessible for these materials. Here, we enable quantitative operando atomistic modeling of intrinsically complex materials through an experimentally validated end-to-end computational framework. The approach combines separation of simulation domains, lightweight machine-learning potentials trained on high-fidelity data, and large-scale de novo in silico synthesis that mimics experimental procedures. We apply the framework to realistic mesoporous SiO$_2$(Al$_2$O$_3$)$_{x/2}$ (0 $\leq x \leq$ 0.4) and validate the results experimentally. Simulations quantitatively reproduce multiple experimental observables, including bulk densities, pair distribution functions, infrared spectra, and hydroxyl densities. Beyond prediction, the framework enables analysis of acid sites and vibrations for catalytic and adsorption processes. By integrating simulation and experiment within a unified workflow, we advance the realism and reliability of atomistic modeling for intrinsically complex materials.
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All authors Jong Hyun Jung, Tom Schächtel, Yongliang Ou, Selina Itzigehl, Marc Högler, Niels Hansen, Johanna R. Bruckner, Blazej Grabowski