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
Superconductivity
Proximity-induced unconventional superconductivity and chiral topological phases in twisted graphene/NbSe$_2$ van der Waals heterostructure
Adam Hložný and Marko Milivojević
We study proximity-induced unconventional superconductivity in a twisted
graphene/NbSe$_2$ van der Waals
heterostructure using the Bogoliubov-de Gennes formalism. The normal-state parameters of proximitized
graphene are extracted from ab initio calculations at a twist angle of $23.4^\circ$, which reduces the common
symmetry of the
heterostructure to $\mathbf{C}_3$. We construct
symmetry-allowed superconducting gap functions of the
graphene layer according to the irreducible representations of the $\mathbf{C}_3$ group, containing singlet and triplet pairing channels and their mixtures. Computing the topological invariants as a function of the mixing parameters, we find a rich phase diagram of
chiral topological superconducting phases, characterized by nonzero Chern numbers $C\in\{-4,-2,2,4\}$. While the nature of the superconducting order parameter of NbSe$_2$ remains debated, the formation of the van der Waals
heterostructure and the related
symmetry reduction can alter the relative stability of competing pairing channels, potentially stabilizing a
chiral component that is proximity-induced into
graphene and triggers the topological phases identified here, making the twisted
graphene/NbSe$_2$
heterostructure a promising platform for
chiral topological superconductivity detectable via quasiparticle interference imaging and transport measurements.
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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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Disordered Systems and Neural Networks
Non-Hermitian Delocalization Realizes Random Dirac Criticality in One Dimension
Bo Li, Shen Zhang and Ren Zhang
Non-Hermitian systems can evade Anderson localization and exhibit delocalized states even in one dimension. Here, we show that such non-Hermitian delocalized states under periodic boundary conditions (PBC) are intrinsically critical, realizing the universality class of one-dimensional random Dirac
fermions. By linking spectral winding to topological Anderson transitions via Hermitization, we demonstrate that the delocalized PBC states exhibit a Dirac-type criticality with universal algebraic correlations. In contrast to Hermitian systems, where this criticality occurs only at fine-tuned transition points, it emerges generically in non-Hermitian systems as a consequence of spectral
topology. These results identify a universal mechanism by which non-Hermiticity promotes criticality, providing a unified description of non-Hermitian delocalization in one dimension.
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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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Soft Condensed Matter
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
Disordered Systems and Neural Networks · Cross-listed from stat.ML
Phase Transitions in Attention: A Bayesian Theory of Copy Head Emergence
Itay Lavie, Kirsten Fischer, Andrey Lekov et al. (+3 more)
Attention is the key mechanism underlying in-context learning in
transformers, and
attention patterns have been observed empirically to emerge abruptly during training. We present a
Bayesian theory of feature learning in
attention; we then focus on how the copy subcircuit in the first layer of an induction head is learned by analyzing a single-layer softmax
attention network trained on a copy task. We derive a closed-form posterior over the
attention matrix and reduce it to a low-dimensional order parameter space. This reduction reveals a phase transition in the amount of training data, which we verify using both
Bayesian sampling and standard training with Adam. We contrast our results with linear
attention and find that softmax
attention exhibits a first-order phase transition while in linear
attention an initial second-order phase transition is followed by a smooth, continuous
evolution toward the structured
attention pattern (crossover). Our work provides a first-principles theoretical account of the abrupt emergence of the copy subcircuit, reminiscent of the one observed in training large
language models.
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All authors Itay Lavie, Kirsten Fischer, Andrey Lekov, Frederic Van Maele, Zohar Ringel, Moritz Helias
Mesoscale and Nanoscale Physics
Heisenberg-Langevin theory of an exciton mirror
Sergueï V. Andreev
We develop a Heisenberg-Langevin theory of an
exciton mirror accounting for the retardation and the long-range electron-hole exchange. A particular case of a strong transverse
magnetic field is analyzed in detail. The optical bistability due to repulsion between the
excitons inside the light cone appears to be prone to a modulational instability towards the non-radiative surface polariton modes. Above the corresponding threshold, the pumped 2D
exciton gas acts as an optical parametric generator of twin polariton beams. Conversely, below the threshold, the mirror acquires the phase-conjugating properties.
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Quantum Gases · Cross-listed from astro-ph.HE
Marek Nikołajuk, Tomasz Karpiuk and Mirosław Brewczyk
Our study focuses on the strong
tidal disruption of a cold helium white
dwarf passing a black hole. We model the white
dwarf as a Bose-
Fermi droplet and use
quantum hydrodynamic equations to simulate the binary system's
evolution. As the white
dwarf passes through periastron, it loses a significant amount of mass. This mass falls onto the black hole and forms an
accretion disc. Quantized
vortices appear in the
accretion disc, manifesting as strong electromagnetic radiation signals that exhibit characteristic flickering patterns changing on a timescale of a few seconds. Meanwhile, the white
dwarf moves away from the black hole. As the white
dwarf moves through space,
vortices run along its surface. This elongates its geometry, causing it to rotate and emit gravitational waves.
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Mesoscale and Nanoscale Physics
Reflective Metastructure Q-plate for Ultrashort Laser Pulses
Christopher G. O. Weiß, Bert Lägel, Benjamin Stadtmüller et al. (+2 more)
The orbital angular momentum of light is an intriguing property for developing light driven applications. It emerged as an independent degree of freedom by which to manipulate light and, consequently, the interaction of light with matter. Several methods exist for the generation of light carrying orbital angular momentum, mostly employing transmitting or reflecting optical components, which radially modulate the phase profile of the light. As one of such components, transmissive q-plates established themselves as standard elements due to their usability over a broad wavelength range. Here, we present our approach to build a highly reflective q-plate based on a plasmonic metasurface capable of converting orbital angular momentum from the nanostructure to ultrashort
laser pulses without temporal broadening. We highlight its working principle over a wide range of wavelengths for reflection under normal and gracing incidence.
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All authors Christopher G. O. Weiß, Bert Lägel, Benjamin Stadtmüller, Martin Aeschlimann, Tobias Eul
Strongly Correlated Electrons
Phonons and magnetism of kagome FeGe probed by nuclear resonant scattering
Yu Tang, Saizheng Cao, Sijie Xu et al. (+6 more)
Kagome FeGe hosts a $2\times2\times2$ charge-density wave (CDW) that strongly interplays with
antiferromagnetic order. Here, we report $^{57}$Fe
nuclear resonant scattering measurement to study FeGe across its long-range CDW and incommensurate
magnetic transitions. Upon entering the CDW state, hardening of acoustic
phonons and optical
phonons around 22~meV, 27~meV, and 31~meV are observed in the Fe partial
phonon density of states, which can be qualitatively captured by first-principle calculations. Upon entering the incommensurate
magnetic phase, neither the
phonon density of states nor the hyperfine interaction parameters change significantly, although a subtle feature associated with the incommensurate
magnetic order or slow fluctuations is detected in the time-domain Mössbauer spectra. These findings show that the CDW in kagome FeGe significantly modifies its
lattice dynamics and magnetism, evidencing an intertwined nature of the
spin, charge, and
lattice degrees of freedom.
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All authors Yu Tang, Saizheng Cao, Sijie Xu, Xiaokun Teng, Sven Velten, Ilya Sergeev, Pengcheng Dai, Yilin Wang, Yu Song
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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Statistical Mechanics
Estimation of conserved charges for a one dimensional system with inhomogeneous hopping
Triparna Mondal
Quantum integrability in a system is characterized by a large number of conserved charges. However, finding the conserved charges in a generic
quantum system is highly challenging. The integrable
matrix theory provides a unified framework to obtain the conserved charges in a certain class of systems. We demonstrate this framework in case of a single-particle system on a 1D finite-sized
lattice with inhomogeneous nearest neighbor hopping to study the statistical properties of the system across its chaotic–integrable crossover from the perspective of the conserved charges. The eigenspectrum of our random
matrix model is studied first. We then estimate the conserved charges and find their properties throughout the chaotic to integrable transition of the system. We calculate the number of conserved charges across this crossover and observe that it is nearly equal to the size of the system at its integrable limit. Our result suggests that the number of conserved charges, estimated using the integrable
matrix theory, can be a measure of
quantum integrability.
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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
Strongly Correlated Electrons
The Kondo effect in ferromagnetic quantum critical CeRh$_6$Ge$_4$
Martin Sundermann, Joe D. Thompson, Eric D. Bauer et al. (+6 more)
The mechanism of a pressure-induced
quantum critical point in the heavy
fermion ferromagnet CeRh$_6$Ge$_4$ has attracted interest, as
ferromagnetic quantum criticality in a clean itinerant Ce compound is typically avoided. The localized versus itinerant character of the 4f electrons is a key aspect for understanding this behavior. We investigated the electronic structure of the 4f shell in CeRh$_6$Ge$_4$ using core-level photoelectron and x-ray absorption spectroscopy, demonstrating the hybridization of Ce 4f with the conduction electrons. Linearly polarized x-ray absorption reveals a temperature-dependent linear dichroism consistent with the
crystal-electric-field (CEF) sequence as inferred from the static susceptibility. This dichroism cannot be described by an ionic full-multiplet model alone, but is reproduced by including the Kondo effect within a single-
impurity Anderson model in the non crossing approximation (SIAM/NCA). The Kondo effect mixes higher lying
crystal-field states into a resulting multiorbital ground state with 4f occupancy n$_f$\,$\sim$\,0.9. Deviations at low temperatures between the measured linear dichroism and calculated dichroism suggest an orbital-dependent Kondo effect. A scenario in which there is a multiorbital ground state and orbital-dependent Kondo hybridization should be a starting point for a model of pressure-induced criticality in CeRh$_6$Ge$_4$.
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All authors Martin Sundermann, Joe D. Thompson, Eric D. Bauer, Chun Fu Chang, Sheng-Huai Chen, Chang-Yang Kuo, Liu Hao Tjeng, Getrud Zwicknagl, Andrea Severing
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
Disordered Systems and Neural Networks
Exact distribution of the output of a deep-layered machine
Thomas Fink
Deep learning builds complex global functions through the repeated composition of local functions. But the resulting distribution over global functions is unknown. We derive this distribution exactly for finite width and depth when the local functions are chosen at random. Surprisingly, depth first creates a sharply structured distribution, then erases this structure as probability drains into two absorbing states. This competition produces a crossover at a depth exponential in the number of inputs, beyond which additional layers mainly drive collapse. The transient structure may help explain why highly overparameterized networks can still generalize.
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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
Soft Condensed Matter
Perspective: The Physics of Active Solids – From Hamiltonians to Active Matter Models
Antik Bhattacharya, Jürgen Horbach and Smarajit Karmakar
The physics of active matter, wherein constituent particles consume energy to generate autonomous motion, has revolutionized non-
equilibrium statistical mechanics. While a large body of work has successfully elucidated the behavior of dilute active systems, the dense regime – characterized by “active glasses and active solids” – presents profound challenges that defy conventional theoretical frameworks. Recent observations reveal two striking features in these dense systems: an apparent enhancement of Mermin-Wagner-Hohenberg (MWH) fluctuations leading to anomalous long-wavelength density fluctuations, and a remarkable correspondence between activity-induced annealing and annealing via oscillatory shear. In this perspective article, we propose a novel approach toward a deeper understanding of dense active matter: by developing active
Hamiltonian models as
equilibrium reference frameworks, we map out pathways toward non-
equilibrium active systems. This strategy allows us to elucidate both the correspondence between driven and active systems and the enhanced MWH fluctuations, which likely arise from a strong coupling between spatially random active forces and long-wavelength density (
phonon) modes. We outline a comprehensive roadmap employing complementary approaches, including the active
Hamiltonian formalism, comparative studies of oscillatory shear in active and passive solids, and investigations of
chiral active matter. Establishing this activity-oscillatory shear correspondence across diverse systems is essential to demonstrate its universality, reveal the underlying large-scale emergent physics, and place our hypothesis on a firmer theoretical ground.
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Soft Condensed Matter
Visualizing Transient Ordering Phenomena in Dense Nanoparticle Clouds
Rieke von Seggern, Jasmin Pongratz, Christine Ziegler et al. (+1 more)
The dynamics of nanoparticles within nanoscale
liquid environments exhibit a range of complex phenomena driven by the interplay of processes at varying length scales. While these dynamics have profound technical implications, such as in nanoscale catalytic kinetics, ion-transport pathways in energy storage, and macromolecular crowding in biological systems, real-space imaging of dense, confined nanoparticle assemblies remains a significant challenge. Here, we present a
liquid-phase transmission electron microscopy approach in which dense clouds of gold nanoparticles are formed within microfluidic channels, rendering the particle ensemble visible in bright-field electron imaging. This strategy enables direct imaging of different density-dependent particle ordering phenomena, including a local structuring of the colloidal
liquid in nanoscale spaces, disordered dynamic clouds at high nanoparticle densities and the reversible formation of superlattice structures. Our results provide a unique window into the complex processes of colloidal self-organization at the nanoscale.
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All authors Rieke von Seggern, Jasmin Pongratz, Christine Ziegler, Sascha Schäfer
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
Quantum Gases
Quantum tidal locking in orbiting Bose-Einstein condensates
Yaoyuan Fan, Shuoyu Shi, Lang Cao et al. (+7 more)
Angular momentum coupling manifests widely in diverse physical systems, underpinning the emergent properties and collective dynamics across different scales. The
tidal locking, which originates from the synchronization of rotational and orbital motions, has far-reaching impacts in celestial mechanics, reflecting fundamental processes of angular momentum transfer, energy dissipation, and
evolution toward dynamical
equilibrium. However, its counterpart in mesoscopic
quantum fluids has remained largely unexplored. Here we demonstrate the emergence of
quantum tidal locking in Bose-Einstein condensates undergoing central force motion in an anharmonic potential. The condensate follows a well-defined orbital trajectory in a static trap and experiences an effective rotating potential induced by the trap anharmonicity. The sustained
geometric squeezing continuously deforms the condensate and drives a self-organized synchronization process, in which the intrinsic rotation gradually locks to the orbital motion. Numerical simulations further reveal the formation of a ring-shaped
vortex array over longer timescales, arising from the coherent
evolution of the rotating matter wave during the locking dynamics. Our findings establish
quantum tidal locking in mesoscopic systems as a robust self-organized mechanism for generating and stabilizing circulating states.
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All authors Yaoyuan Fan, Shuoyu Shi, Lang Cao, Ziyue He, Qiuxin Zhang, Dong Hu, Yu Wang, Qing Wang, Tianwei Zhou, Xiaoji Zhou
Mesoscale and Nanoscale Physics
Robust Spin Logic Enabled by Generalized $\mathrm{SU}(2)$ Symmetry in $p$-Wave Magnets
Hao-Kun Ke, Gong Zhao, Siqing Li et al. (+2 more)
Unconventional magnets combine the vanishing stray fields of antiferromagnets with the strong
spin-splitting of ferromagnets, offering a unique material platform for spintronics. However, a critical challenge in realizing functional
spin-logic devices lies in preserving long-range
spin coherence against momentum-degrading scattering and gate-induced dephasing. Here, we demonstrate that the intrinsic momentum-dependent exchange field of a three-dimensional $p$-wave magnet can be precisely tuned against gate-induced Rashba
spin-orbit coupling to establish a generalized $\mathrm{SU}(2)$
spin-rotation
symmetry. This emergent conservation law generates a
symmetry-protected Persistent
Spin Helix (PSH), effectively integrating the high energy scales of 3D bulk
magnetic exchange with the macroscopic coherence of
symmetry protection. By modeling a synergistic $p$-wave
magnetic spin field-effect transistor (
spin-FET), we reveal high-visibility Datta-Das conductance oscillations controlled purely by electrical gating. Crucially, our
quantum transport simulations confirm that this
symmetry-engineered transport regime exhibits exceptional resilience against strong non-
magnetic Anderson disorder and
geometric variations. These results establish a synergistic paradigm for non-magnetized spintronics, demonstrating how the active integration of
spin-orbit coupling and unconventional magnetism can yield disorder-resilient spintronic logic.
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All authors Hao-Kun Ke, Gong Zhao, Siqing Li, Ruixiang Chen, Chui-Zhen Chen
Mesoscale and Nanoscale Physics
Intrinsic Nonreciprocity in Electron-Phonon Interaction Driven Thermoelectric Diodes
Hao-Kun Ke, Lie-Run Tian, Pei-Hao Fu et al. (+3 more)
We study an electron-
phonon interaction driven thermoelectric diode. The nonreciprocity in this diode arises from the asymmetry between the probabilities of
phonon emission and absorption in the electron-
phonon interaction, as well as the structural reflection asymmetry. We reveal the intrinsic nature of this nonreciprocity, as the forward and backward electron transport remains asymmetric even when the applied temperature difference is not reversed. This intrinsic nonreciprocity gives rise to two novel transport phenomena. One is a novel thermoelectric effect which is driven by the temperature difference between the leads and the central device region, rather than the conventional temperature difference between the two leads. The second, and more significant, phenomenon is the suppression of electronic backscattering in the load resistor. This suppression decreases the resistance of the load resistor, which leads to the breakdown of Ohm's addition law. Under suitable conditions, the presence of electron-
phonon interaction can yield a larger thermoelectric current compared to the case without it. This intrinsic nonreciprocity opens up a new pathway for low-power electronics besides
topology and superconductivity, and for nonreciprocal thermoelectric devices.
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All authors Hao-Kun Ke, Lie-Run Tian, Pei-Hao Fu, Jun-Feng Liu, Jun Wang, H. Xu
Statistical Mechanics
Universal Information-Theoretic Structure of the Quasi-Stationary Domany–Kinzel Automaton
Hyun-Yong Lee, Kenji Harada and Naoki Kawashima
We characterize the quasi-stationary distribution (QSD) of the bond directed-percolation line of the Domany–Kinzel automaton using a
matrix-product-state representation of the probability distribution, obtained by projecting out the absorbing state and iterating the transfer
matrix. Unlike moment- or sampling-based methods, this yields the full conditional distribution and direct access to information-theoretic diagnostics. The spatial structure of the QSD changes sharply across the transition: the active phase is bulk-like with finite density, whereas in the inactive phase the surviving activity collapses into a single flock – the smallest interval containing all active sites – occupying a vanishing fraction of the chain. Throughout the inactive phase the bipartite mutual information of the QSD equals the
entropy of a single binary choice – whether the flock lies to the left or right of the cut – so the surviving clusters together encode just one bit of positional information, corresponding to a single effective cluster.
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Statistical Mechanics · Cross-listed from quant-ph
Tensor-Network Algorithm for Many-Body Trace Norms
Seunghun Lee and Eun-Gook Moon
Trace norms are fundamental to
quantum information theory, yet in many-body systems their evaluation remains a major computational bottleneck, as it generally requires diagonalizing exponentially large operators. Here, we overcome this bottleneck by introducing a controlled tensor-network
algorithm for estimating the trace norm of
matrix product operators without full diagonalization. The key idea is to combine Zolotarev's rational approximation to the sign function with a variational formulation solved using a density-
matrix-renormalization-group-like
algorithm. The resulting approximation is systematically improvable, with its accuracy controlled by the rational approximation parameters and the spectral weight near zero. Beyond the reach of exact diagonalization, we demonstrate controlled trace-norm calculations for
entanglement negativity,
quantum fidelity and
quantum Fisher information, achieving substantially improved accuracy over
polynomial-based Lanczos approaches. Our results establish trace-norm-based quantities as practical tensor-network observables, opening a route toward tensor-network studies of
quantum information in mixed states.
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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