Materials Science
Compositional gradient engineering for enhanced ferroelectricity in ultrathin AlScN
Zekun Hu, Haiwen Zhang, Rajeev Kumar Rai et al. (+12 more)
Ferroelectric AlScN is promising for CMOS-compatible non-volatile
memory, but thickness scaling is limited by leakage, premature breakdown, and defect-mediated failure. Here we show that compositional grading within a continuous wurtzite AlN-AlScN
lattice mitigates these limitations by distributing structural and polarization discontinuities across the film thickness, reducing defect formation and local field concentration. In a 20 nm graded
heterostructure, monotonic Sc incorporation and AlN-rich boundaries produce reversible ferroelectric switching, an as-grown metal-polar state, a 21% higher breakdown field, 10% enhanced remanent polarization, and 40x higher resistivity relative to homogeneous AlScN. Time-domain PUND measurements reveal strongly suppressed post-switching leakage, consistent with reduced defect-assisted and polarization-coupled conduction. This improved dielectric robustness enables ferroelectric functionality in 5 nm graded stacks containing only a 2 nm $\mathrm{Al}_{0.64}\mathrm{Sc}_{0.36}\mathrm{N}$ region, with measurable switching near 1 V. These results establish compositional grading as a defect- and field-management strategy for scalable ultrathin wurtzite ferroelectrics.
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All authors Zekun Hu, Haiwen Zhang, Rajeev Kumar Rai, Yuhong Cao, Xiaolei Tong, Pedram Yousefian, Hyunmin Cho, Bongjun Choi, Chao-Chuan Chen, Yunfei He, Kefei Bao, Chloe Leblanc, Eric A. Stach, Roy Olsson, Deep Jariwala
Materials Science
Hierarchical Interdiffusion Kinetics in Nanoscale Ni/Al Multilayers
S.S. Riegler, I. Gallino, N.J. Peter et al. (+11 more)
Reactive metallic multilayers store chemical energy that can be released rapidly through interdiffusion and intermetallic formation. Predictive control of this heat release requires distinguishing transport and phase-formation processes that occur in rapid succession. Here we combine free-standing nanoscale Ni/Al multilayers with chip-based flash calorimetry and isoconversional kinetic analysis over five orders of magnitude in heating rate. Selected reaction states are quenched and examined by scanning transmission electron microscopy. This workflow separates pre-ignition interdiffusion into two regimes and quantifies activation energies of (81 $\pm$ 24) and (168 $\pm$ 17) kJ/mol, consistent with grain-boundary and
lattice diffusion of Ni in Al, respectively. Microscopy supports this assignment: no significant compositional changes are observed after the first regime, whereas the second increases the Ni content of the Al layers and produces Ni-enriched features spaced by 5$-$10 nm, matching the Al grain size. These results identify the Al grain-boundary network as the dominant low-barrier pathway, providing rapid transport across the Al layers and priming
lattice-mediated mixing and intermetallic phase formation. More broadly, the workflow links calorimetric signatures to pathway-specific kinetics and transient microstructures, enabling direct assessment of how microstructural design redirects coupled transport and reaction pathways in reactive multilayers and other materials driven far from
equilibrium.
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All authors S.S. Riegler, I. Gallino, N.J. Peter, A. Tarasov, T. Meyer, J. Schmauch, C. Pauly, M. Frey, Y.H. Sauni Camposano, H. Bartsch, R. Schwaiger, P. Schaaf, R. Busch, J. Arlt
Materials Science · Cross-listed from cond-mat.supr-con
Charting the emergent low-dimensional manifold of quantum materials
Jason Z. Kim, Omri Lesser and Debanjan Chowdhury
The periodic table of elements transformed chemistry by revealing simple organizing principles underlying atomic behavior. Despite decades of effort, no analogous framework has emerged for crystalline materials – their microscopic complexity and vast configurational space have defied reduction to fundamental organizing principles. Current databases catalog thousands of synthesized materials, but extracting predictive, interpretable models from this wealth of data remains a formidable challenge. Here we demonstrate that the materials landscape possesses a hidden
geometric organization that can be unveiled through unsupervised nonlinear dimensionality reduction. Applying differential geometry techniques to the Inorganic
Crystal Structure Database (ICSD), we reveal that just a few combinations of microscopic descriptors capture the vast majority of variance in material properties. This low-dimensional
embedding autonomously segregates
superconductors from ordinary materials and further distinguishes superconducting families in ways that transcend chemical similarity alone. Remarkably, the discovered
geometric organization directly governs critical temperatures ($T_c$) across diverse superconducting families, enabling accurate $T_c$ predictions without any knowledge of the pairing mechanism. Our approach uncovers emergent organizing principles that control macroscopic
quantum behavior, offering a new paradigm in how we build models of complex
quantum materials directly from experimental data.
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Materials Science · Cross-listed from cond-mat.str-el
Spin correlations, low-energy scales, and anisotropy scaling in kagome frustrated magnets
Phillip Popp, Stephan Rosenkranz, Arthur P. Ramirez et al. (+1 more)
Neutron scattering is central to identifying
quantum states of
magnetic materials. In the search for
quantum spin liquids, broad spectral features of inelastic spectra have been cited as evidence for spinon excitations, but can also arise from
magnon excitations excitations in the presence of quenched disorder and strong
magnon interactions. We develop a new approach to this problem, based on the adiabatic continuity in the $XXZ$ Heisenberg model on geometrically frustrating (GF)
lattices as a function of the model's anisotropy. Using this approach, we identify universal features and energies of finite-temperature
spin correlators. Focusing on the kagome
lattice, we show that the low-energy
spin spectral function contains robust, momentum-independent peaks with frequencies: $\omega_1 \approx 3.4 T^*$ and $\omega_2 \approx 6.3 T^*$, where the “hidden energy scale” $T^*$ is the characteristic scale of a low-temperature peak in the heat capacity, at which many GF magnets also display
spin-glass freezing. We show that the spectral features at low energies $\omega\lesssim T^*$ arise from single-
magnon scattering and identify the magnetizations of the respective excitations. We explore the
evolution of the spectral features with temperature and discuss extensions to other GF
lattices. Our results provide a sharp spectroscopic criterion for interpreting
neutron scattering in kagome and other GF
quantum magnets.
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All authors Phillip Popp, Stephan Rosenkranz, Arthur P. Ramirez, Sergey Syzranov
Materials Science · Cross-listed from physics.optics
Quantifying the Distribution of Biexciton Emission Efficiencies in Colloidal Quantum Shells
Tjom Arens, Dulanjan Harankahage, Divesh Nazar et al. (+2 more)
The efficiency of multi-
photon emission is an important characteristic of
quantum light sources. Bright multi-
photon emission is desirable for high-power lighting and
lasers, while its complete suppression is required for high-purity single-
photon generation. In colloidal
quantum emitters, multi-
photon emission can vary significantly between individual particles. Resolving this heterogeneity remains challenging with conventional particle-by-particle approaches. Here, we introduce a crosstalk-suppressed SPAD-array
photon-correlation approach for high-throughput quantification of multi-
photon emission from more than 1000 colloidal
quantum shells. By projecting two images of the same sample onto distant regions of the detector array, we avoid short-range crosstalk between detector pixels. Time gating suppresses dark-count coincidences and distinguishes individual emitters from clusters. Applying this method to
quantum shells reveals a near-Gaussian distribution of biexciton emission efficiencies, with a mean of 0.55 and an estimated intrinsic standard deviation of 0.12. Intra-batch correlations between the biexciton efficiency and the particle brightness are consistent with the volume scaling of Auger quenching. These results establish SPAD-array
photon correlation as a scalable route to resolve multi-
photon heterogeneities in nanoparticle ensembles.
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All authors Tjom Arens, Dulanjan Harankahage, Divesh Nazar, Mikhail Zamkov, Freddy T. Rabouw
Materials Science
Effect of polar distortions on the linear and nonlinear anomalous Hall conductivity of altermagnetic $\alpha$-MnTe
Mathews Benny, Sahar Izadi Vishkayi, Amar Fakhredine et al. (+2 more)
Altermagnetic $\alpha$-MnTe with Néel vector along the $y$-axis exhibits a finite anomalous
Hall conductivity (AHC) and weak ferromagnetism along the $z$-axis. As already demonstrated in the bulk, there is the breaking of the C$_6$
symmetry by the in-plane Néel vector, leaving a C$_2$-type
magnetic symmetry. The surface of $\alpha$-MnTe breaks the C$_2$, leaving only a time-reversed mirror
symmetry with respect to the $x=0$ plane. Therefore, we demonstrate that on the surface, the interplay between breaking of the
crystal symmetry and Néel vector orientation produces a reduction of the space group from hexagonal P6$_3$/mmc to orthorhombic Amm2. As a result, the surface exhibits not only a polar distortion along the $z$-axis, but also a polar distortion and a weak ferrimagnetism along the $y$-axis. To describe the surface of MnTe in an accessible way, we simplify the problem and examine the effect of the in-plane electric field in bulk MnTe. Moreover, as a doped ionic
semiconductor, the properties of MnTe can be influenced by
lattice polarization under an applied electric field. We investigate the interplay between the intrinsic anomalous
Hall effect and
lattice polarization, showing that polarization effects can substantially affect the AHC. Since the electric field breaks inversion
symmetry, this contribution from the
lattice polarization coexists with the non-linear anomalous
Hall effect, highlighting the rich transport phenomenology of altermagnets.
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All authors Mathews Benny, Sahar Izadi Vishkayi, Amar Fakhredine, Chanchal K. Barman, Carmine Autieri
Materials Science
Plasmonic properties and correlation energies from a compact multipole representation of the dielectric response in 2D metals
Dario A. Leon, Claudia Cardoso and Kristian Berland
Multipole-Padé approximants provide a compact representation of dynamical response functions in terms of a small number of collective modes. Here, we generalize this framework to incorporate momentum dependence across the full Brillouin zone of 2D metals by constructing a
symmetry-conserving, anisotropic representation of the inverse dielectric function. This analytic form enables efficient and accurate evaluation of quantities involving dynamical screening, including spectral features and correlation energies. We construct such compact representations for a set of seven two dimensional metals spanning distinct electronic regimes, and show that a small number of dispersive plasmonic modes suffices to accurately describe the dielectric response across the full Brillouin zone, while also yielding accurate correlation energies. The proposed representation therefore establishes a direct bridge between ab initio calculations and analytical models of screening, opening new avenues for applications in condensed matter systems.
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Materials Science · Cross-listed from cond-mat.supr-con
Superconductivity in the pressure-amorphized topological insulator CrP$_4$
Chutong Zhang, Xiangzhuo Xing, Na Zuo et al. (+12 more)
The interplay among superconductivity, magnetism, and nontrivial band
topology represents one of the most compelling frontiers in condensed matter physics. The exploration of novel superconductivity in 3d transition-metal compounds, particularly the rare Cr-based systems containing strongly
magnetic Cr ions, has long attracted
attention owing to their unconventional pairing mechanisms that challenge conventional wisdom. Yet, Cr-based
superconductors remain scarce, especially those possessing nontrivial topological character, underscoring the urgent need to uncover new members. Here we report the observation of superconductivity in pressure-amorphized Cr-based topological
insulator CrP$_4$. Upon compression, CrP$_4$ undergoes an anomalous
quantum phase transition from a metallic to a semiconducting-like state at around 15 GPa, driven by significant changes in the electronic structure. At approximately 70 GPa, re-metallization with superconductivity occurs alongside an irreversible amorphization. The superconducting transition temperature Tc increases monotonically with pressure, reaching 4.8 K at 141.3 GPa. Furthermore, theoretical calculations predict multiple topological phase transitions from a strong topological
insulator to a trivial state and finally back to a strong topological state under pressure. Our study not only establishes CrP$_4$ as the first Cr-based amorphous
superconductor but also opens a new paradigm for exploring superconducting and topological properties in amorphous materials.
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All authors Chutong Zhang, Xiangzhuo Xing, Na Zuo, Bowen Zheng, Bin Li, Jiajia Feng, Xiaolei Yi, Yan Meng, Xiaoran Zhang, Bingchao Yang, Chao Wang, Xin Chen, Yongsheng Zhang, Xiaofeng Xu, Xiaobing Liu
Materials Science
Thermodynamically consistent phase field model for hydrogen-assisted cracking
G. F. Bouobda-Moladje, A. Ruffini, Y. Le Bouar et al. (+1 more)
We propose a phase field model able to simulate hydrogen-assisted cracking in polycrystalline materials. Within a variational framework, the model simultaneously describes crack propagation and hydrogen segregation on crack surfaces and grain boundaries together with the associated reduction in interfacial energies. In the context of hydrogen-enhanced decohesion (HEDE) mechanisms, we demonstrate the ability of the model to capture the transition from transgranular cracking to hydrogen-assisted intergranular cracking.
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All authors G. F. Bouobda-Moladje, A. Ruffini, Y. Le Bouar, A. Finel
Materials Science · Cross-listed from cond-mat.str-el
Structural responses incipient to pressure-driven antiferromagnetic quantum critical point of van der Waals heavy-fermion metal CeSiI
Hanming Ma, Tong Shi, Wenhao Li et al. (+12 more)
CeSiI is a van der Waals heavy-
fermion metal recently found to exhibit unconventional superconductivity near a pressure-induced
antiferromagnetic quantum critical point (QCP) at Pc =6 GPa. Here, we report a comprehensive single-
crystal X-ray diffraction study of CeSiI under high pressures up to 8.3 GPa at room temperature, revealing subtle structural responses that precede pressure-driven QCP. We find that the unit-
cell volume decreases smoothly upon compression without showing any structural phase transition in the investigated pressure range. Intriguingly, we observe abrupt and concurrent anisotropic responses of the
lattice parameters around Pc =6 GPa, i.e., the a-axis contracts while the c-axis enlongated suddenly, with the unit-
cell volume smoothily varies with pressure. Structural refinements further show that these
lattice anomalies primarily originate from changes of Ce-Ce and Ce-Si bond lengths, as well as a flattening of the inner honeycomb Si layer within the CeSiI monolayer around Pc. Our findings establish an interesting case linking pressure-driven electronic transition of QCP at low temperatures to incipient structural responses at room temperature, thereby providing fresh insight into the pressure-temperature phase diagram of CeSiI.
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All authors Hanming Ma, Tong Shi, Wenhao Li, Qingxin Dong, Xiaoli Ma, Shaoheng Ruan, Zhongjin Wu, Pengtao Yang, Zhaoming Tian, Jianping Sun, Yoshiya Uwatoko, Xiaohui Yu, Hechang Lei, Bosen Wang, Jinguang Cheng
Materials Science
Quantum dynamic simulation of triplet formation in an effective model of Y6 (BTP-4F)
Isabel Creed, Lucy J. F. Hart, Pranay Venkatesh et al. (+2 more)
We construct a five-state model for photoexcitation in Y6 (BTP-4F) dimers, and then solve the non-adiabtic dynamics using the Hierarchical Equations of Motion (HEOM) method. We find that triplets are populated mainly via a transiently excited intermolecular charge-transfer singlet to triplet Frenkel
exciton route; this route is not available to the monomer. Analysis of one-particle transition density
matrices suggests that the charge-transfer states are spatially distinct to the Frenkel
exciton states, indicating that the large
spin-orbit-coupling for this transition is due to it being permitted by an associated change in orbital character. Aggregation in Y6 therefore directly enables fast and high-yield intersystem crossing. We selenise our model dimers, significantly enhancing
spin-orbit-coupling, which then accelerates this charge-transfer mediated route. Looking forwards to simulations on larger aggregates, we show that, though Marcus theory gives qualitatively correct dynamics, the long-time yields are incorrect due to it missing
quantum recurrences. Instead, we show that the recently developed
memory-kernel projector\cite{Gestsson2025-ez} method can produce semi-classical rates directly from the HEOM equations which lead to quantitatively correct dynamics and yields.
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All authors Isabel Creed, Lucy J. F. Hart, Pranay Venkatesh, Tom Ward, Jarvist Moore Frost
Materials Science · Cross-listed from cond-mat.mes-hall
Experimental straintronics in nanotube quantum dots
L. Huang, I. G. Rebollo and A. R. Champagne
Single-wall carbon nanotubes (SWCNTs) are narrow ribbons of
graphene with atomically precise edges and a single
quantum transport channel, at experimentally-relevant dopings. This makes them ideal systems to harness
quantum transport straintronics (QTS), i.e. using mechanical strain to control accurately
quantum transport. We present QTS data from three single-wall carbon nanotube
quantum dot (SWCNT-QD) transistors over a broad range of in-situ tunable and reversible uniaxial strain ($\Delta\varepsilon_\text{mech}\approx$ 0 to 3 %). We first present the nanofabrication of the suspended SWCNT transistors whose channel lengths are $\approx$ 30 nm. The channels are strained by moving gold clamps holding firmly the nanotubes. We present detailed charge transport data, $dI/dV_{\text{B}} - V_{\text{B}} - V_{\text{G}}$ and $dI/dV_{\text{B}} - V_{\text{B}} - \Delta\varepsilon_\text{mech}$, showing a large mechanical-gating effect of the SWCNT-QDs. The precise reversibility of the data, and their agreement with QTS theory, confirms that the tubes are strained elastically. We demonstrate that the mechanical control of the QD doping is not due to capacitive-gating effects, but to quantitatively predictable bandstructure changes including a strain-tunable bandgap. This precise mechanical control of the doping and bandgap of SWCNT-QDs could find applications in
qubits, condensed matter physics, and homojunction molecular transistors.
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Materials Science
Tracking atomic-scale interdiffusion in immiscible bimetallic nanoparticles via four-dimensional electron tomography
Jisheng Xie, Dijin Jiang, Zhen Sun et al. (+4 more)
The interdiffusion of immiscible elements is generally considered both thermodynamically unfavorable and kinetically hindered. At the nanoscale, however, the mixing behavior of multielements materials often diverges from bulk
equilibrium, yet a quantitative, atomically resolved description of this transformation has remained challenging. Using ex situ four dimensional atomic resolution electron
tomography combined with in situ scanning transmission electron microscopy, here we reveal the atomic scale miscible transition driven by interdiffusion in immiscible PdIr nanoparticles at temperatures far below the melting point. The pathway involves surface reconstruction atom hopping at 200oC and surface flattening at 300oC, followed by a critical transition at 400oC where Ir interfacial
diffusion and discrete Ir intermediates drive miscible intermixing. Upon reaching the nanoscale melting point 900oC, collective inward Ir
diffusion yields the thermodynamically stable IrPd configuration. Our findings provide quantitative atomic scale insights into how metastable nanostructures evolve through distinct intermediates, offering a design framework for advanced multielement materials.
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All authors Jisheng Xie, Dijin Jiang, Zhen Sun, Yiheng Dai, Zezhou Li, Yao Zhang, Jihan Zhou
Materials Science · Cross-listed from cond-mat.supr-con
Structural Changes and Transport Properties of $\mathrm{YBa_2Cu_3O_7}$ Locally Modified by a He$^+$ Focused Ion Beam
Ross Carter, Robin Hutt, Paul Zimmermann et al. (+9 more)
Irradiation of a material with ions can cause various defects that can lead to structural phase transitions and the modification of the material's properties. Here we study the irradiation of the epitaxyally grown thin films of the high-temperature
superconductor $\mathrm{YBa_2Cu_3O_7}$ with $30\,\mathrm{keV}$ He$^{+}$ ions which leads to the expansion of the
crystal lattice, decrease of the critical temperature $T_c$ and eventually transition to an
insulator. Fabrication of such insulating regions with a focused He-Ion beam with a spot size of $\sim 10\,\mathrm{nm}$ is a powerful technique for fabrication of superconducting nano-devices. Using low-temperature resistivity measurements, diffraction with a nanofocused X-ray beam and atomic force microscopy, we investigated how the structure and the electric transport properties of $\mathrm{YBa_2Cu_3O_7}$ depend on the irradiation dose in a range $10$–$100\,\mathrm{ions/nm^2}$ and on the lateral size of the irradiated area in a range $30$–$5000\,\mathrm{nm}$.
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All authors Ross Carter, Robin Hutt, Paul Zimmermann, Ainur Abukaev, Jan Ullmann, Simon Koch, Christoph Schmid, Manfred Burghammer, Reinhold Kleiner, Dieter Koelle, Edward Goldobin, Ivan A. Zaluzhnyy
Materials Science
All-electric picosecond field-free spin-orbit torque switching in magnetic trilayers
Xinhou Chen, Shishun Zhao, Yuchen Pu et al. (+2 more)
Spin-orbit torque (SOT) enables the electrical manipulation of the magnetization with high speed and low energy consumption for
magnetic random-access
memory (MRAM) applications. Previous studies of short-pulse SOT switching have mainly focused on the nanosecond regime, whereas reports employing picosecond pulses remain scarce and have largely relied on field-assisted switching using bulky, high-power
laser systems, limiting prospects for chip-level integration. Here, we introduce an all-electrical on-chip nanoplasma pulse generator capable of producing pulses as short as 6.4 ps, enabling ultrafast picosecond field-free SOT switching in
magnetic trilayers. We show that reducing the pulse width lowers the writing energy by 2-3 orders of magnitude, with ultrafast Joule heating assistance playing an essential role in the enhanced efficiency of the picosecond regime. Our demonstration of ultrafast, all-electrical, and field-free SOT switching establishes the nanoplasma pulse generator as an on-chip platform for ultrafast spintronic studies, with promise for high-speed, energy-efficient, and scalable SOT-MRAM technologies.
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All authors Xinhou Chen, Shishun Zhao, Yuchen Pu, Qu Yang, Hyunsoo Yang
Materials Science
Scalable Conformal MoSx Catalyst for Efficient Hydrogen Evolution at Industrial-Level Current Density in Alkaline Electrolyzers
Yong Zuo, Sebastiano Bellani, Meysoun Jabrane et al. (+13 more)
The development of simple and scalable fabrication strategies for cost-effective electrodes is crucial to advance water splitting in alkaline water electrolyzers (AWEs). Here, we present a coating-annealing method to conformally coat a MoSx catalyst layer onto a porous Ni foam (NF) substrate. By controlling the annealing process, the composition of the MoSx layer could be tuned from MoS2 to MoS3 and its catalytic performance for hydrogen
evolution reaction (HER) in alkaline media was optimized. The MoS3@NF synthesized by this method achieved industrially relevant HER current densities of 200 mA/cm2 at a low overpotential of 246 mV, maintaining stable operation for over 240 h. The MoS3@NF cathode, combined with a stainless steel anode, enabled an alkaline water electrolyzer (AWE)
cell to operate steadily at 1.96 V and 1 A/cm2 for 1000 h. This performance surpasses that of most of the previously reported water electrolyzers employing MoSx-based cathodes. Our work demonstrates the potential of MoS3 (with its abundant edge-sulfur atoms serving as active sites) as a high-performance cathode material for industrial AWEs.
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All authors Yong Zuo, Sebastiano Bellani, Meysoun Jabrane, Gabriele Saleh, Thi-Hong-Hanh Le, Michele Ferri, Davide Salusso, Zhanzhao Li, Valentina Mastronardi, Marilena I. Zappia, Manjunath Chatti, Mirko Prato, Silvia Dante, Francesco Bonaccorso, Yongsheng Han, Liberato Manna
Materials Science
Direct nanoscale observation of melting and solute redistribution in a hypoeutectic Al-Cu alloy with $\it{in\ situ}$ STEM
Martin Hasenburger, Rostislav Daniel, Phillip Dumitraschkewitz et al. (+3 more)
Melting and solidification of eutectic systems are classical topics in physical metallurgy, yet the mechanisms at nanoscale are less investigated, due to experimental limitations in spatiotemporal resolution. The advent of $\it{in\ situ}$ STEM heating with MEMS technology has recently enabled investigation of eutectic behavior as a function of temperature, time and electrical resistivity. Using this methodology, we investigate the
evolution of a nanocrystalline hypoeutectic Al-Cu
alloy. Melting initiated in the hotter central region and propagated outward, with grain boundaries acting as preferred sites for eutectic
liquid formation via Cu enrichment. The Al$_2$Cu phase melted prior to complete
matrix melting.
Liquid-state Cu redistribution over a distance of 258 $\mu$m - several orders of magnitude beyond solid-state
diffusion limits - resulted in Al-rich rim accumulations and Cu enrichment at the outermost edge of the observed chip region. These observations are discussed in the context of classical predictions for melting of eutectic systems.
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All authors Martin Hasenburger, Rostislav Daniel, Phillip Dumitraschkewitz, Thomas M. Kremmer, Matheus A. Tunes, Stefan Pogatscher
Materials Science · Cross-listed from physics.geo-ph
Effects of microstructural heterogeneity on the macroscopic spectrum of elastically accommodated grain-boundary sliding
Zhengxuan Li and John F. Rudge
Elastically accommodated grain-boundary sliding (EAGBS) is a plausible source of upper-mantle seismic attenuation and dispersion, yet classical theory predicts a localized Debye-like peak that is absent or only weakly expressed in dry olivine experiments. Here we test whether microstructural heterogeneity can explain this discrepancy using 2-D finite-element simulations on periodic Voronoi tessellations. We find that irregular grain geometry changes the baseline EAGBS response relative to the regular hexagonal
benchmark, but increasing grain-size variance alone produces only modest changes in modulus and peak height, with little spectral broadening. In contrast, a broad distribution of grain-boundary viscosities progressively suppresses and broadens the Debye-like loss peak into a weak background spanning a wide frequency interval. This broadening arises from the superposition of many localized relaxation processes with distinct characteristic timescales and motivates a reduced-order 0-D description of the aggregate response. These results suggest that the absence of a pronounced EAGBS peak in dry olivine does not necessarily imply the absence of EAGBS mechanism itself. If grain boundaries sample a sufficiently broad viscosity distribution, the macroscopic EAGBS contribution may appear experimentally only as part of a broad attenuation background, while still remaining relevant for upper-mantle seismic attenuation and velocity dispersion.
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Materials Science
Multilayer Screening of Double and Conventional Perovskite Solar Cells Using SCAPS-1D and Machine Learning: Optimization of ETL, HTL, and Absorber for High-Efficiency Architectures
Neda Nasiri, Seyed Mahdi Mastoor and Amirhosein Ahmadkhan Kordbacheh
The combinatorial design space of multilayer perovskite
solar cells is vast, yet exhaustive experimental or computational screening of all possible material combinations remains impractical. Here, we integrate SCAPS-1D device simulations with machine learning to systematically explore 125 device architectures constructed from five electron transport layers (ETL), five absorbers (including lead-free double perovskites), and five hole transport layers (HTL). A representative subset of configurations is used to train a machine learning (ML) model, which predicts the power conversion efficiency (PCE) of the remaining unexplored structures. Leave-One-Group-Out cross-validation yields a Spearman rank correlation, demonstrating reliable ranking capability. SHAP (SHapley Additive exPlanations) analysis reveals that the HTL band gap, absorber band gap, and ETL electron affinity are the most influential descriptors, providing physical insights into interfacial recombination and charge extraction. The machine learning model identifies several high-performance configurations that are subsequently verified by full SCAPS-1D simulations. Among them, the device FTO/TiO$_2$/Cs$_2$AgBiBr$_6$/NiO/Ag achieves a PCE of 28.85%, and the ML-suggested structure FTO/SnO$_2$/Cs$_2$AgInBr$_6$/NiO/Ag exhibits 28.62%, outperforming a closely related literature architecture by approximately 4% absolute. Notably, eight of the top-11 structures employ the lead-free double perovskite Cs$_2$AgInBr$_6$. This work demonstrates that a physics-based, data-driven workflow combining SCAPS-1D, ML, and SHAP can accelerate the discovery of high-efficiency, environmentally friendly perovskite
solar cells while providing transparent design rules. The approach is generalizable to other multilayer optoelectronic systems.
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Materials Science · Cross-listed from cond-mat.soft
When and how particles are removed by drops
Abhinav Naga, Franziska Sabath, Doris Vollmer et al. (+1 more)
Particulate contaminants decrease the power output of
solar panels, the transparency of windows, and are detrimental to microelectronics, where even a single particle can induce a short
circuit. Despite significant research on particle adhesion and self-cleaning, it remains unclear when and how a drop can remove a particle from a surface, thus efficiently cleaning the surface. Here, by combining
lattice Boltzmann simulations and confocal microscopy experiments, we show that at least six different scenarios arise from the complex interplay between capillary and friction forces when a drop collides with a particle on a surface. Notably, the capillary force plays a dual role in particle removal: while its tangential component always drives removal, its normal component can also hinder it. We introduce a dimensionless capillary capture parameter that successfully predicts particle removal across a wide range of particle and surface properties. Our results reveal that the design of easy-to-clean surfaces should not focus only on maximizing hydrophobicity, but also on minimizing the particle-surface friction.
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All authors Abhinav Naga, Franziska Sabath, Doris Vollmer, Halim Kusumaatmaja
Materials Science
In Situ Dynamics of the Microscopic Crystallographic Dehydration Pathway in a Model Channel Hydrate, Theophylline
Natalia Koniuch, Sang T. Pham, Mohsen Danaie et al. (+9 more)
Solid-state phase transformations in molecular
crystal hydrates govern stability and functional performance across a range of applications, including pharmaceutical, agrochemical and coordination framework materials. During dehydration, these hydrates can undergo substantial structural reorganisation involving changes in molecular orientation, intermolecular interactions, and
lattice symmetry. Despite extensive study, the microscopic crystallographic pathways by which such transformations proceed remain poorly understood. Here, we investigate the dynamics of solid-state dehydration of theophylline monohydrate as a model molecular hydrate using in situ low-dose scanning electron diffraction (SED). Simultaneous observations of changes in morphology and crystallographic phase and orientation mapped across single particles reveal how complete dehydration proceeds via a two-step, reconstructive topotactic solid-state transformation: anisotropic, surface-specific mass loss of material near water channel sides (suggesting the monohydrate adopts a non-centrosymmetric
crystal structure) is followed by surface-localised nucleation and growth of anhydrous form II on the parent monohydrate while preserving similar molecular orientations at a common plane. By providing direct, local crystallographic insight into hydrate dehydration, this work demonstrates how surface-controlled mass loss, morphological changes, and
lattice orientation jointly govern solid-state transformations in molecular hydrates. More broadly, it establishes low-dose SED as an effective approach for probing dynamic phase transformations in beam-sensitive molecular
crystals.
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All authors Natalia Koniuch, Sang T. Pham, Mohsen Danaie, Fanny Costa, Zabeada Aslam, Stephanie Foster, Helen Blade, Les Hughes, Nicole Hondow, Rik Drummond-Brydson, Sean M. Collins, Andy P. Brown
Materials Science
Residual stress gradient in a thin film within the dislocation pile-up theory
A. V. Druzhinin and C. Cancellieri
A model for predicting the residual stress gradient in a thin film segment is developed on the basis of the theory of dislocation pile-ups. The initial shear stress within the film is relaxed via the formation of a pile-up of screw dislocations against the impenetrable film-substrate interface. Plastic strain is related to the dislocation density, leading to a fundamental equation, which links the residual stress to this density. The distribution of dislocations within the pile-up for an arbitrary, non-uniform residual stress profile is derived analytically by applying the force balance condition. This results in a singular integro-differential equation for the residual stress profile. The equation is solved numerically by a collocation method for various initial stress distributions: constant, linear,
parabolic, and exponential functions. The solutions demonstrate that the established residual stress profile strongly depends on the film segment's thickness-to-width ratio and the initial stress distribution. As this ratio increases, stress relaxation becomes more effective away from the film-substrate interface. In all cases,
equilibrium requires a pile-up containing dislocations with both positive and negative Burgers vectors. The total number of dislocations and their density distribution vary significantly with the initial stress profile. This model provides a critical step towards more complex models of residual stress formation in constrained material systems, specifically, thin films.
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Materials Science
Coupling Chirality, Polar Order, and Altermagnetic Spin Splitting in a Hybrid Manganese Chloride
Li Liang, Ding Ning, Mingqiang Gu et al. (+2 more)
Hybrid manganese halides enable the coexistence of molecular chirality, polar order, and
magnetic exchange within a single
lattice. Here, we combine first-principles calculations with
spin-space-group analysis to investigate the synthesized enantiomeric pair [(R)/(S)-MPA]2[MnCl4(H2O)] (MPA = beta-methylphenethylammonium). We predict that its compensated
magnetic state hosts altermagnetic
spin splitting in the nonrelativistic limit, and that the coupled
chiral, polar, and
magnetic degrees of freedom define a
symmetry-related
manifold. From this
manifold, we derive simple sign rules for the electronic and magneto-optical response: reversing both chirality and polarity, or reversing the
magnetic domain alone, inverts the
spin splitting throughout the Brillouin zone, whereas reversing chirality alone or polarity alone changes the
spin-splitting sign only in
symmetry-selected regions. With
spin-orbit coupling, reversing chirality or
magnetic order flips the Kerr rotation angle, while changing the polar variant leaves it unchanged. These results reveal a chemically accessible route to translate molecular handedness into
symmetry-controlled
spin splitting and magneto-optical readout in hybrid manganese halides. Critically, we show that the sign and momentum pattern of the splitting are governed by the interplay of the
chiral, polar, and
magnetic degrees of freedom. This interplay opens the possibility to control the
spin splitting through a judicious design of the organic cations, by modulating their chirality and polarity.
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All authors Li Liang, Ding Ning, Mingqiang Gu, Shanshan Wang, Alessandro Stroppa
Materials Science
Interfacial Coupling and Sparse Intercalation of 7-Atom-Wide Armchair Graphene Nanoribbons by N-Heterocyclic Carbene Monolayers
Dominik Lüthi, Lin Yang, Xiuling Yu et al. (+5 more)
Graphene nanoribbons (GNRs) synthesized on metal substrates experience electronic coupling and screening from the underlying surface, which, although often weak, can modify their observed properties and complicate their transfer to device-compatible substrates. Intercalation of GNRs by self-assembled monolayers (SAMs) offers a possible route to reduce this interaction. Here, we investigate the intercalation of 7-atom-wide armchair
graphene nanoribbons (7-AGNRs) on Au(111) using N-heterocyclic carbenes (NHCs). Low-temperature scanning tunneling microscopy and spectroscopy, Raman spectroscopy, and density functional theory calculations reveal that the adsorption geometry of the NHCs strongly influences the intercalation yield for GNRs. Methyl-substituted NHCs form flat-lying dimers that partially intercalate the GNRs, producing locally decoupled segments. In contrast, bulkier isopropyl-substituted NHCs form upright monomers that embed the GNRs within the monolayer, preventing intercalation. The low intercalation yield indicates that lifting the nanoribbon from the Au surface is energetically costly. These results establish molecular adsorption geometry and packing as key parameters controlling intercalation at GNR-metal interfaces, with implications for the rational design of decoupling layers for GNR-based device integration pathways.
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All authors Dominik Lüthi, Lin Yang, Xiuling Yu, Ji Ma, Xinliang Feng, Carlo A. Pignedoli, Roman Fasel, Gabriela Borin Barin
Materials Science
Boron Co-Alloying in AlScN Wurtzite Ferroelectrics: Insights from an 850-Sample Combinatorial Study
Federica Messi, Nathan Rodkey, Manuel Kober-Czerny et al. (+1 more)
AlScN wurtzite ferroelectrics are promising candidates for energy-efficient non-volatile
memory. However, AlScN suffers from a high coercive field and reduced cycling endurance, and the limited tunability of its properties constrains further optimization. Co-doping AlScN with boron offers the promise of independently tailoring the chemical and structural properties, making AlScBN an attractive quaternary system. This material has already been explored for a few selected compositions, however, no systematic study of the full AlScBN compositional space exists. A combinatorial approach consisting of gradient deposition with HiPIMS at low temperatures of 250{\deg}C and automatic analysis of film properties allowed us to analyze a total of 850 unique samples within the AlScBN phase space. In addition to a full screening of the materials' chemical and structural properties, we fabricate and characterize combinatorial device libraries. XPS charge transfer analysis experimentally confirms that bond ionicity correlates with a reduction in the coercive field for AlScN and AlScBN systems, opposite trends are instead observed for AlBN. While the films maintain a high remanent polarization of 130-150 {\mu}C/cm2, Sc and B co-doping reduces the coercive field from 7 MV/cm to 3 MV/cm. Notably, B co-alloying lowers the amount of Sc needed to lower the coercive field, reducing reliance on this scarce element. In addition, we find that co-alloying with B, notably improves cycling endurance, which is related to a reduction in defect density. These results establish AlScBN as a scalable, CMOS-compatible ferroelectric, positioning it as an interesting alternative to AlScN.
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All authors Federica Messi, Nathan Rodkey, Manuel Kober-Czerny, Sebastian Siol
Materials Science
Spin-Polarized Electronic Structure and Chemical Bonding Data for 2,500+ Halide Double Perovskites
Luc Walterbos, Alex McEwan, Ravindra Shinde et al. (+2 more)
Halide double perovskites (A$_2$BB'X$_6$) are a long-known class of materials that has recently been rediscovered for diverse applications, including photovoltaics, photocatalysis, and radiation detection. Their doubled unit
cell provides immense chemical tunability, allowing the incorporation of
magnetic ions and enabling access to a wide range of electronic-structure features, including different band-edge characters,
alignments, and
symmetries.
Magnetic elements may further introduce
spin degrees of freedom and
magnetic behaviour, thereby broadening the functional landscape of these compounds. Here, we present the first comprehensive database of
spin-polarised electronic-structure data for all halide double perovskites predicted to be stable by the recently introduced $\tau$ tolerance factor by Bartel et al. The
dataset focuses on the Cs$_2$BB'X$_6$ family, with X = I, Br, Cl, and F, and includes density of states (DOS) for $>$2,500 compounds, calculated using hybrid-functional density functional theory. Among these, 719 compounds exhibit band gaps in the visible range and 118 display half-metallic character. In addition, we provide chemical-bonding analysis using lobster, which provides insights into orbital interactions across the
dataset. To facilitate exploration, we further offer UMAP-based visualisations and an interactive app for systematic investigation of chemical composition, electronic structure, and
magnetic properties.
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All authors Luc Walterbos, Alex McEwan, Ravindra Shinde, Janine George, Linn Leppert
Materials Science
Sonochemically Boosted Hydrogen Evolution Activity of Janus TMD Monolayers
Rayantan Sadhukhan, Md Tarik Hossain, Julian Picker et al. (+5 more)
2D electrocatalysts that enable hydrogen
evolution at low overpotentials offer an attractive alternative to expensive platinum-based systems. Here, we report the growth of Janus transition metal dichalcogenide (TMD) monolayers (MLs), SeMoS and SeWS, on Au foils using chemical vapor deposition, and systematically compare their catalytic properties in the context of hydrogen
evolution reaction (HER) with those of their parent TMDs. The Janus MLs exhibited significantly enhanced catalytic performance relative to the parent TMDs. Furthermore, these MLs on Au foils were subjected to sonochemical treatment in polar and non-polar solvents, in which the treatment with polar solvents led to a substantial improvement in the HER activity of Janus MLs. In particular, SeMoS MLs treated with water showed a low overpotential of ~63 mV, a Tafel slope of ~42 mV/dec, and an exchange current density of ~10$^{-3}$ mA cm$^{- 2}$, approaching that of platinum. Analyses indicate that enhanced electrocatalytic activity is associated with tensile strain induced by Au surface restructuring and the formation of defects in Janus MLs, as shown by experimental observations and by density functional theory calculations. The enhancement in catalytic performance due to sonochemical treatment emphasizes the importance of our results for developing novel catalytic systems for HER based on Janus 2D materials.
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All authors Rayantan Sadhukhan, Md Tarik Hossain, Julian Picker, Mahdi Ghorbani-Asl, Christof Neumann, Arkady V. Krasheninnikov, Tharangattu N. Narayanan, Andrey Turchanin
Materials Science
Modelling magnetic material properties with uncertainty-aware neural networks
Clemens Wager, Heisam Moustafa, Alexander Kovacs et al. (+10 more)
Machine learning is increasingly used to accelerate materials discovery across large compositional and structural design spaces, but limited and heterogeneous data make reliable uncertainty estimation essential. In this work, we investigate uncertainty quantification for permanent magnet modeling across three complementary studies. First, on a public Curie temperature surrogate
dataset, we
benchmark Gaussian process regression, random forest bagging, and dropout-based
Bayesian neural networks and show that calibration, sharpness, and confidence curve diagnostics reveal differences in uncertainty quality that are not visible from point-prediction metrics alone. Second, we transfer this framework to the prediction of intrinsic
magnetic properties in Nd2 Fe14 B-based magnets. Third, we extend the same uncertainty-aware perspective to coercivity prediction from microstructural information using a graph neural network. Together, these studies show that uncertainty quantification improves the trustworthiness of
magnetic material property predictions and can be transferred from composition-based surrogate models to more complex structure-sensitive learning tasks.
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All authors Clemens Wager, Heisam Moustafa, Alexander Kovacs, Qais Ali, Harald Oezelt, Hayate Yamano, Masao Yano, Noritsugu Sakuma, Hyuga Hosoi, Akihito Kinoshita, Tetsuya Shoji, Akira Kato, Thomas Schrefl
Materials Science · Cross-listed from cond-mat.mes-hall
Ferroelectric Altermagnetic Chern Insulator in magnetic field: electrical control of the Chern number
Meysam Bagheri Tagani and Carmine Autieri
We investigate electrically controllable Chern
topology in a two-dimensional compensated (d)-wave altermagnet described by a
lattice-regularized Bernevig–Hughes–Zhang model. In the altermagnetic reference state, the two Kramers sectors acquire momentum-dependent
spin splitting and opposite sector Chern numbers, while the combined $C_{4z}\mathcal T$
symmetry enforces a vanishing total charge Chern number. We show that this hidden topological structure can be activated by orbital-selective
magnetic coupling and independently tuned by ferroelectric orbital hybridization. The
magnetic coupling removes the sector cancellation and generates $C=\pm1$ and $\pm2$ phases, whereas the polar distortion shifts the Dirac gap closing away from high-
symmetry momenta and enables electrical transitions such as $C=0\rightarrow-1$ and $C=1\rightarrow2$. The resulting phases exhibit the expected
chiral edge-state multiplicity and quantized anomalous
Hall conductivity. Their
topology is further reflected in the orbital magnetization through the in-gap relation $\partial_\mu \widetilde M_z=-C$. Finally, we show that the Chern phases remain robust against transverse Kramers-sector mixing and
symmetry-allowed inversion-asymmetric
spin–orbit coupling. These results establish a
symmetry-based route to electrically tunable Chern insulating phases in compensated altermagnets.
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Materials Science · Cross-listed from physics.geo-ph
Breakdown of the classical rupture theory and earthquake propagation in the "forbidden" super-Rayleigh range
Anna Pomyalov, Fabian Barras and Eran Bouchbinder
Earthquakes propagating faster than the shear wave-speed are commonly thought to undergo a super-shear transition upon which they discontinuously jump from the sub-Rayleigh regime to the super-shear one. The super-Rayleigh regime, i.e., the range of propagation speeds between the Rayleigh and shear wave-speeds, is regarded as "forbidden" by the two-dimensional classical rupture theory. Here, we revisit the assumptions underlying the classical theory and develop a rupture theory that takes into account the dependence of the fault strength (frictional resistance) on the slip rate. The theory quantitatively agrees with numerical simulations nearly up to the Rayleigh wave-speed. Yet, very close to the latter, two-dimensional rupture solutions change their character due to frictional rate nonlinearity and rupture continuously propagates through the "forbidden" super-Rayleigh range into the super-shear regime, without a sharp super-shear transition. These results demonstrate that frictional rate dependence, generically observed in experiments, can have profound implications for fast earthquake propagation.
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