Materials Science
Anisotropic Band-Split Magnetism in Magnetostrictive CoFe$_2$O$_4$
Harry Lane, Guratinder Kaur, Masahiro Kawamata et al. (+9 more)
Single
crystal spinel CoFe$_2$O$_4$ exhibits the largest room-temperature saturation magnetostriction among non-rare-earth compounds and a high Curie temperature ($T_c \sim 780$ K), properties that are critical to a wide range of industrial and medical applications.
Neutron spectroscopy reveals a large band splitting ($\sim$ 60 meV) between two ferrimagnetic
magnon branches, which is driven by site mixing between Co$^{2+}$ and Fe$^{3+}$ cations, and a significantly weaker magnetocrystalline anisotropy ($\sim$ 3 meV). Central to this behavior is the competition between extremely large mismatched molecular fields on the tetrahedral $A$-site and octahedral $B$-site sublattices and the single-ion anisotropy on the $B$-site. This creates a strong energetic anisotropy that locks the
magnetic moment within each structural domain in place. As a result of these differing energy scales, switching structural domains is energetically favored over a global
spin reorientation under applied
magnetic fields, and this is what amplifies the magnetostrictive nature of CoFe$_2$O$_4$.
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All authors Harry Lane, Guratinder Kaur, Masahiro Kawamata, Yusuke Nambu, Lukas Keller, Russell A. Ewings, David J. Voneshen, Travis J. Williams, Helen C. Walker, Dwight Viehland, Peter M. Gehring, Chris Stock
Superconductivity
Pressure-Induced Changes in Structure, Magnetic Order and Development of Superconductivity in the Ferromagnetic Topological Insulator MnBi8Te13
S. Huyan, T. Qian, L. Wang et al. (+14 more)
We report a comprehensive study of pressure-induced
evolution of the magnetism and development of superconductivity (SC) in MnBi8Te13, a promising ambient pressure,
ferromagnetic (FM) topological
insulator candidate. By employing high-pressure electrical transport, magnetoresistance, DC
magnetic susceptibility, and X-ray diffraction measurements, we construct a detailed temperature-pressure phase diagram. At ambient pressure, MnBi8Te13 exhibits FM ordering with an easy-axis along the c-axis which is progressively suppressed under pressure and replaced by an
antiferromagnetic (AFM) order. Density functional theory calculations predicted an
evolution from FM to a G-type AFMg2 phase near 5 GPa. Above 16.6 GPa, a bulk SC state emerges with a maximum transition temperature ~6.8 K, as confirmed by resistance and
magnetic susceptibility measurements. This pressure-induced SC may co-exist with another AFM dome that shows a weak anomaly in the transport data. In contrast, our work on MnBi6Te10 shows no SC up to 40 GPa. Indeed, in contrast to MnBi8Te13, the MnBi2Te4(Bi2Te3)n compounds with n < 3, didn't exhibit SC, highlighting the crucial role of Mn concentration in stabilizing SC. The observation of pressure-induced FM-AFM-SC transitions in MnBi8Te13 not only establishes it as a rare Mn-based SC but also provides a platform to study the interplay between magnetism, SC, and potentially nontrivial band
topology in correlated
magnetic materials.
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All authors S. Huyan, T. Qian, L. Wang, W. Bi, F. Xue, D. Zhang, C. Hu, B. Kalkan, Y. Huang, Z. Li, A. Das, J. Schmidt, R. A. Ribeiro, T. J. Slade, N. Ni, P. C. Canfield, S. L. Bud'ko
Soft Condensed Matter
Revisiting the Phase Diagram of Hard Sphere Dumbbells with Nested Sampling: Known Phases and New Packing Variants
Omar-Farouk Adesida, David Quigley and Livia B. Partay
We explore the use of the nested sampling technique to sample the configuration space of non-spherical hard particles. We employ the technique on the hard dumbbell system consisting of two hard spheres connected by a rigid bond, and investigate the phase stability across a wide pressure range and for bond lengths from completely overlapping to tangential hard spheres. Nested sampling recovers all previously identified features of the phase diagram and identifies a family of new packing variants. The fluid phase, plastic
crystal, close packed solid phases and aperiodic
crystal are all sampled, and the transition points between these are mapped. Our results show good agreement with predictions made by existing equations of state, and former Monte Carlo simulations. Nested sampling also identified a close packed structure with Pnma
symmetry which has not previously been considered.
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Materials Science
Understanding the effect of drying time in process-structure-performance relationships for PM6-Y6 organic solar cells
Marc Steinberger, Maxime Siber, Hans-Joachim Egelhaaf et al. (+13 more)
Making solution-cast organic
solar cells industrially available generally comes at the cost of significant performance losses compared to device prototypes manufactured under laboratory conditions. Adjusting solvent evaporation kinetics is postulated to recover efficiency. Yet, a comprehensive characterization of their effect, independently of other property-defining parameters, is lacking. Thus, the present objective is to isolate the influence of the solvent drying rate on solution-deposited organic active layer nanomorphologies and performances. To this end, a specially designed gas quenching technique is employed to fabricate PM6:Y6 donor-acceptor films under systematic variations of evaporation conditions. Using an extensive investigation protocol that combines insights from numerical simulations and experimental measurements, process-structure-performance relationships are unraveled. It is found that higher drying rates imply finer and more dispersed nanomorphologies with increased fractions of amorphous material. This enhances electric charge generation, thereby improving short-
circuit current density and overall
cell performance. The open-
circuit voltage is also boosted under accelerated evaporation due to changes in the aggregation mode of the Y6 small molecule that induce higher effective bandgaps. The results demonstrate that the developed gas-quenching technique is a valuable tool for optimizing the performance of upscaled organic photovoltaics, as it is readily compatible with high-throughput equipment, such as roll-to-roll coating machines.
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All authors Marc Steinberger, Maxime Siber, Hans-Joachim Egelhaaf, Mingjian Wu, Irene Kraus, Johannes Will, Xianqiang Xie, Laju Bu, Jonas Graetz, Tobias Unruh, Larry Lüer, Erdmann Spiecker, Andreas Distler, Jens Harting, Christoph J. Brabec, Olivier J.J. Ronsin
Materials Science
Polaritonic Bloch's Theorem beyond the Long-Wavelength Approximation
Giovanna Bruno, Rosario Roberto Riso, Henrik Koch et al. (+1 more)
Cavity
quantum electrodynamics provides a powerful tool to manipulate material properties, yet it remains a matter of debate whether and how quantized fields affect the periodicity of
crystals. Here, we extend Bloch's
theorem to
crystals under strong light-matter coupling, revealing that polariton quasiparticles preserve
lattice periodicity. We introduce a general framework to incorporate multimode cavity fields in a simple and tractable way, showing that additional modes contribute small energy corrections noticeable only at low frequencies. Within the single-
photon approximation, these contributions reduce to a spatially uniform effective field in the
crystal plane, providing a formal justification for the single-mode and long-wavelength approximations commonly used in molecular polaritonics. Together, these results establish a rigorous framework for describing polaritonic states in crystalline solids.
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All authors Giovanna Bruno, Rosario Roberto Riso, Henrik Koch, Enrico Ronca
Soft Condensed Matter · Cross-listed from physics.flu-dyn
A reduced model for droplet dynamics with interfacial viscosity
Fabio Guglietta, Diego Taglienti and Mauro Sbragaglia
We propose an extension of the phenomenological Maffettone-Minale (MM) model (P.L. Maffettone and M. Minale, J. Non-Newton. Fluid Mech. 78, 227-241 (1998)) to describe the time-dependent deformation of a droplet with interfacial viscosity in a shear flow. The droplet, characterised by surface tension $\sigma$, is spherical at rest with radius $R$ and deforms into an ellipsoidal shape under a shear flow of rate $G$, described by a symmetric second-order morphological tensor $\boldsymbol{S}$. In addition to surface tension, the extended MM (EMM) model incorporates interfacial shear and dilatational viscosities, $\mu_s$ and $\mu_d$, through the corresponding Boussinesq numbers $\mbox{Bq}_s=\mu_s/\mu R$ and $\mbox{Bq}_d=\mu_d/\mu R$, where $\mu$ is the bulk viscosity. A central goal of this work is to quantify the parameter range over which the EMM model provides a realistic description of droplet deformation, as a function of the capillary number Ca$=\mu R G/\sigma$ and the Boussinesq numbers. To this end, model predictions are systematically compared with fully resolved numerical simulations.
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Soft Condensed Matter
Experimental methods to control pinned and coupled actomyosin contraction events
James Clarke, Hyunjae Lee, Kyla Wong et al. (+4 more)
Actin and myosin drive many instances of force generation, deformation, and shape change in
cells, tissues, and organisms. In particular, cytoskeletal actomyosin is remarkable in its adaptive architecture, responding to a host of actin-binding
proteins. Equally important, however, is actomyosin's interaction with its mechanical environment. Actomyosin contractility and environmental properties, such as geometry and stiffness, are inherently coupled. To understand this coupling, novel experimental techniques are needed. Here we describe methods to spatially control the anchoring of reconstituted contractile actomyosin networks to two, opposing surfaces ("transverse anchoring"). The two surfaces can be either rigid ("pinned contraction"), or one of the surfaces may be compliant ("coupled contraction"). We introduce compliance by manufacturing flexure hinges, and describe their calibration. Calibration permits a direct measurement of the contractile force and mechanical work that actomyosin exerts on the environment. The methods described here provide an avenue toward a more complete characterization of actomyosin's role as an actuator, an essential property in its context of driving deformation and shape change in living systems.
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All authors James Clarke, Hyunjae Lee, Kyla Wong, Julia Glenn, Aniket Marne, Yoichi Miyahara, José Alvarado
Materials Science
From Complex Magnetic Ground States to Magnetocaloric Effects: A Review of Rare Earth R$_2$In Intermetallic Compounds
Anis Biswas, Ajay Kumar, Prashant Singh et al. (+1 more)
R2In (R = rare earth) intermetallics exhibit unusual
magnetic and magnetocaloric properties, driven by subtle electronic effects,
lattice distortions, and
spin-
lattice coupling. Most of these binary compounds adopt the hexagonal Ni2In-type structure at room temperature, with Eu2In and Yb2In stabilizing in the orthorhombic Co2Si-type
lattice. Lighter lanthanide compounds Eu2In, Nd2In, and Pr2In undergo first-order
magnetic transitions with negligible hysteresis and minimal
lattice volume change and exhibit
giant cryogenic magnetocaloric effects, while heavy lanthanide R2In compounds including Gd2In show second-order transitions with moderate magnetocaloric effect. No lanthanide-based R2In compound exhibits
symmetry-breaking structural transition, while Y2In transforms from hexagonal to orthorhombic structure near 250 K. Secondary low-temperature transitions, including
spin reorientation or
antiferromagnetic ordering, further enrich the
magnetic phase landscape in these compounds. Integrating theoretical descriptors such as charge-induced strain and electronic structure provides predictive insight into phase stability and magnetocaloric performance, guiding the design of rare-earth intermetallics with tunable
magnetic properties for cryogenic applications
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All authors Anis Biswas, Ajay Kumar, Prashant Singh, Yaroslav Mudryk
Statistical Mechanics
Subsampling of avalanches in the fiber bundle models of fracture
Narendra Kumar Bodaballa and Soumyajyoti Biswas
We study the subsampling of the avalanches in the fiber bundle model of fracture. In cases where only a part of the system is observed for the micro-failure events, the recorded avalanche statistics gets distorted compared to the actual fracture events. We show that, particularly in the cases where the load redistribution is localized, this distortion is significant. Surprisingly, however, near an elastic failure regime, the distortion is minimized, suggesting a much reduced observational capacity could still represent the actual failure dynamics in the case of fracture of elastic solids.
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Superconductivity
Multiple Quasiparticle Bound States in a Trap Created by a Local Superconducting Gap Variation
Romy Morin, Denis M. Basko, Manuel Houzet et al. (+1 more)
At low temperature, the concentration of quasiparticles observed in superconducting
circuits far exceeds the predictions of microscopic BCS theory at
equilibrium. As a source of dissipation, these excess quasiparticles degrade the performance of various devices. Therefore, understanding their dynamics, especially their recombination into Cooper pairs, is an active topic of current research. In disordered
superconductors, spatial fluctuations in the superconducting gap can trap quasiparticles and modify their eigenspectrum. Since this spectrum plays a key role in quasiparticle dynamics, it must be carefully investigated. To this end, we introduce a toy model of a single trap. Specifically, we consider a shallow disk-shaped gap variation in a clean
superconductor. Using a semiclassical approximation, we demonstrate the existence of multiple bound states and give the dependence of their number on the size and depth of the gap suppression. Extending our analysis beyond the semiclassical regime, in dimensions larger than one, we observe an infinite number of bound states very close to the gap edge, even for an arbitrarily small trap. These results deepen our understanding of trapped quasiparticles and may have important implications for their recombination in disordered
superconductors.
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All authors Romy Morin, Denis M. Basko, Manuel Houzet, Julia S. Meyer
Quantum Gases · Cross-listed from physics.optics
Guided vortex bullets
Carlos F. Sánchez, Ángel Paredes, Humberto Michinel et al. (+2 more)
By means of the variational method and numerical simulations, we demonstrate the existence of stable 3D nonlinear modes, viz.
vortex “bullets”, in the form of pulsed beams carrying orbital angular momentum, that can self-trap in a 2D waveguiding structure. Despite the attractive self-interaction, which is necessary for producing the bullets (bright
solitons), and which readily leads to the collapse in the 3D setting as well as to spontaneous splitting of
vortex modes, we find a critical value of the trapping depth securing the stabilization of the
vortex bullets. We identify experimental conditions for the creation of these topological modes in the context of coherent optical and matter waves. Collisions between the bullets moving in the unconfined direction are found to be elastic. These findings contribute to the understanding of self-trapping in nonlinear multidimensional systems and suggest new possibilities for the stabilization and control of 3D topological
solitons.
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All authors Carlos F. Sánchez, Ángel Paredes, Humberto Michinel, Boris A. Malomed, José R. Salgueiro
Materials Science
First-principles simulation of spin diffusion in static solids using dynamic mean-field theory
Timo Gräßer, Götz S. Uhrig and Matthias Ernst
The dynamics of disordered
nuclear spin ensembles are the subject of
nuclear magnetic resonance studies. Due to the through-space long-range dipolar interaction generically many
spins are involved in the time
evolution, so that exact brute force calculations are impossible. The recently established
spin dynamic mean-field theory (spinDMFT) represents an efficient and unbiased alternative to overcome this challenge. The approach only requires the dipolar couplings as input and the only prerequisite for its applicability is that each
spin interacts with a large number of other
spins. In this article, we show that spinDMFT can be used to describe spectral
spin diffusion in static samples and to simulate zero-
quantum line shapes which eluded an efficient quantitative simulation so far to the best of our knowledge. We perform
benchmarks for two test substances that establish an excellent match with published experimental data. As spinDMFT combines low computational effort with high accuracy, we strongly suggest to use it for large-scale simulations of
spin diffusion, which are important in various areas of
magnetic resonance.
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Statistical Mechanics
Macroscopic fluctuation theory of interacting Brownian particles
Aurélien Grabsch, Davide Venturelli and Olivier Bénichou
We apply the macroscopic fluctuation theory (MFT) to study the large-scale dynamical properties of Brownian particles with arbitrary pairwise interaction. By combining it with standard results of
equilibrium statistical mechanics for the collective
diffusion coefficient, the MFT gives access to the exact large-scale dynamical properties of the system, both in- and out-of-
equilibrium. In particular, we obtain exact results for dynamical correlations between the density and the current of particles. For one-dimensional systems, this allows us to obtain a precise description of these correlations for emblematic models, such as the Calogero and Riesz gases, and for systems with nearest-neighbor interactions such as the Rouse chain of hardcore particles or the recently introduced model of tethered particles. Tracer
diffusion with the single-file constraint (but for arbitrary pairwise interaction) is also studied. For higher-dimensional systems, we quantitatively characterize these dynamical correlations by relying on standard methods such as the virial expansion.
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Materials Science · Cross-listed from cs.AI
Evaluating Large Language Models in Scientific Discovery
Zhangde Song, Jieyu Lu, Yuanqi Du et al. (+53 more)
Large
language models (LLMs) are increasingly applied to scientific research, yet prevailing science
benchmarks probe decontextualized knowledge and overlook the iterative
reasoning, hypothesis generation, and observation interpretation that drive scientific discovery. We introduce a scenario-grounded
benchmark that evaluates LLMs across biology, chemistry, materials, and physics, where domain experts define research projects of genuine interest and decompose them into modular research scenarios from which vetted questions are sampled. The framework assesses models at two levels: (i) question-level accuracy on scenario-tied items and (ii) project-level performance, where models must propose testable hypotheses, design simulations or experiments, and interpret results. Applying this two-phase scientific discovery evaluation (SDE) framework to state-of-the-art LLMs reveals a consistent performance gap relative to general science
benchmarks, diminishing return of scaling up model sizes and
reasoning, and systematic weaknesses shared across top-tier models from different providers. Large performance variation in research scenarios leads to changing choices of the best performing model on scientific discovery projects evaluated, suggesting all current LLMs are distant to general scientific "superintelligence". Nevertheless, LLMs already demonstrate promise in a great variety of scientific discovery projects, including cases where constituent scenario scores are low, highlighting the role of guided exploration and serendipity in discovery. This SDE framework offers a reproducible
benchmark for discovery-relevant evaluation of LLMs and charts practical paths to advance their development toward scientific discovery.
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All authors Zhangde Song, Jieyu Lu, Yuanqi Du, Botao Yu, Thomas M. Pruyn, Yue Huang, Kehan Guo, Xiuzhe Luo, Yuanhao Qu, Yi Qu, Yinkai Wang, Haorui Wang, Jeff Guo, Jingru Gan, Parshin Shojaee, Di Luo, Andres M Bran, Gen Li, Qiyuan Zhao, Shao-Xiong Lennon Luo, Yuxuan Zhang, Xiang Zou, Wanru Zhao, Yifan F. Zhang, Wucheng Zhang, Shunan Zheng, Saiyang Zhang, Sartaaj Takrim Khan, Mahyar Rajabi-Kochi, Samantha Paradi-Maropakis, Tony Baltoiu, Fengyu Xie, Tianyang Chen, Kexin Huang, Weiliang Luo, Meijing Fang, Xin Yang, Lixue Cheng, Jiajun He, Soha Hassoun, Xiangliang Zhang, Wei Wang, Chandan K. Reddy, Chao Zhang, Zhiling Zheng, Mengdi Wang, Le Cong, Carla P. Gomes, Chang-Yu Hsieh, Aditya Nandy, Philippe Schwaller, Heather J. Kulik, Haojun Jia, Huan Sun, Seyed Mohamad Moosavi, Chenru Duan
Materials Science
Fabrication of (In,Ga)N pseudo-substrates by a three-step growth protocol without ex-situ processing
Huaide Zhang, Aidan F. Campbell, Jingxuan Kang et al. (+3 more)
We fabricate (In,Ga)N pseudo-substrates with a total thickness of ~1 um grown on GaN templates using
plasma-assisted molecular beam epitaxy. In a three-step process, we change growth conditions from N-rich to metal-rich in order to sequentially form a roughened GaN layer, relaxed (In,Ga)N nanostructures, and a coalesced, smooth (In,Ga)N layer. Samples are analyzed by scanning electron and atomic force microscopy, X-ray diffraction, as well as photo- and cathodoluminescence spectroscopy. Compared to a reference layer grown directly on GaN, the pseudo-substrate exhibits a higher In content (~0.3), strain relaxation degree (~80%), narrower photoluminescence linewidth, and larger area fraction of bright regions in cathodoluminescence maps, showing the benefits of the three-step growth protocol. This straightforward approach does not necessitate any ex-situ processing and could enable the scalable fabrication of (In,Ga)N pseudo-substrates for high-efficiency red-emitting (In,Ga)N devices.
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All authors Huaide Zhang, Aidan F. Campbell, Jingxuan Kang, Jonas Laehnemann, Oliver Brandt, Lutz Geelhaar
Materials Science
Exciton radiative lifetimes in hexagonal diamond Ge and Si$_x$Ge$_{1-x}$ alloys
Michele Re Fiorentin, Michele Amato and Maurizia Palummo
Recent reports of strong room-temperature photoluminescence in hexagonal diamond (2H) germanium stand in marked contrast to theoretical predictions of very weak band-edge optical transitions. Here we address radiative emission in 2H-Ge and related materials through a comprehensive investigation of their excitonic properties and radiative lifetimes, performing Bethe-Salpeter calculations on pristine and uniaxially strained 2H-Ge, 2H-Si$_x$Ge$_{1-x}$
alloys with $x=\frac{1}{6},\,\frac{1}{4},\,\frac{1}{2}$, and wurtzite GaN as a reference. Pristine 2H-Ge features sizable
exciton binding energies ($\sim\!30$ meV) but extremely small dipole moments, yielding radiative lifetimes above $10^{-4}$ s. Alloying with Si reduces the lifetime by nearly two orders of magnitude, whereas a 2% uniaxial strain along the $c$ axis induces a band crossover that strongly enhances the in-plane dipole moment of the lowest-energy
exciton and drives the lifetime down to the nanosecond scale. Although strained 2H-Ge approaches the radiative efficiency of GaN, its much lower
exciton energy prevents a full match. These results provide the missing excitonic description of 2H-Ge and 2H-Si$_x$Ge$_{1-x}$, demonstrating that, even when excitonic effects are fully accounted for, the strong photoluminescence reported experimentally cannot originate from the ideal
crystal.
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Disordered Systems and Neural Networks · Cross-listed from physics.optics
Photonics-Enhanced Graph Convolutional Networks
Yuan Wang and Oleksandr Kyriienko
Photonics can offer a hardware-native route for machine learning (ML). However, efficient deployment of photonics-enhanced ML requires hybrid workflows that integrate optical processing with conventional CPU/GPU based neural network architectures. Here, we propose such a workflow that combines photonic positional
embeddings (PEs) with advanced graph ML models. We introduce a photonics-based method that augments graph convolutional networks (GCNs) with PEs derived from light propagation on synthetic frequency
lattices whose couplings match the input graph. We simulate propagation and readout to obtain internode intensity correlation
matrices, which are used as PEs in GCNs to provide global structural information. Evaluated on Long Range Graph
Benchmark molecular
datasets, the method outperforms baseline GCNs with
Laplacian based PEs, achieving $6.3\%$ lower mean absolute error for regression and $2.3\%$ higher average precision for classification tasks using a two-layer GCN as a baseline. When implemented in high repetition rate photonic hardware, correlation measurements can enable fast feature generation by bypassing digital simulation of PEs. Our results show that photonic PEs improve GCN performance and support optical acceleration of graph ML.
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Other Condensed Matter · Cross-listed from physics.optics
Unveiling nonlinearities of electromagnetically induced transparency in a THz metamaterial
Amit Haldar, Shriganesh Prabhu and Shovon Pal
Electromagnetically induced transparency (EIT) in terahertz (THz) metamaterials relies on the coherent coupling between a radiative (bright) mode and a subradiant (dark) mode. Understanding the dynamic interplay between the bright and dark modes holds the key to manipulate the mutual interference and hence the transparency. Here, we use nonlinear 2D-THz spectroscopy to scrutinize the dynamics through nonlinearities of the EIT-like phenomenon in a metamaterial platform that comprises of two coupled resonators. From the temporal profiles of the nonlinear pump-probe and
photon-echo signals, we found that the bright mode relaxation time is almost twice the time for the coherent exchange of energy between the two coupled resonators. The multi-peak nature of
photon-echo signal and the corresponding temporal signatures further provides a direct visualization of the interference between the dressed states that drives the transparency window in our THz metamaterial. A time-resolved density
matrix model accurately describes the observed features, including the cross-peak behavior and the temporal dynamics, establishing the coherent mode coupling as the origin of the transparency window.
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Strongly Correlated Electrons
Anomalous Dynamical Scaling at Topological Quantum Criticality
Menghua Deng, Sheng Yang, Chen Sun et al. (+2 more)
We study the nonequilibrium driven dynamics at topologically nontrivial
quantum critical points (QCPs), and find that topological edge modes at criticality give rise to anomalous dynamical scaling behavior. By analyzing the driven dynamics of bulk and boundary order parameters at topologically distinct QCPs in
quantum spin chains, we demonstrate that, while the bulk dynamics remain indistinguishable and follow standard Kibble Zurek (KZ) scaling, the anomalous boundary dynamics are unique to topological criticality, obeying modified scaling relation beyond the traditional KZ framework. To elucidate the unified origin of this anomaly, we further study the dynamics of defect production at topologically distinct QCPs in free-
fermion models and demonstrate similar anomalous scaling exclusive to topological criticality. These findings establish the existence of anomalous dynamical scaling arising from the interplay between
topology and driven dynamics, challenging standard paradigms of
quantum critical dynamics.
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All authors Menghua Deng, Sheng Yang, Chen Sun, Fuxiang Li, Xue-Jia Yu
Materials Science
Atomically-precise synthesis and simultaneous integration of 2D transition metal dichalcogenides enabled by nano-confinement
Ce Bian, Yifan Zhao, Roger Guzman et al. (+15 more)
Two-dimensional (2D) materials, such as
graphene, transition metal dichalcogenides (TMDs), and hBN, exhibit intriguing properties that are sensitive to their atomic-scale structures and can be further enriched through van der Waals (vdW) integration. However, the precise synthesis and clean integration of 2D materials remain challenging. Here, using
graphene or hBN as a vdW capping layer, we create a nano-confined environment that directs the growth kinetics of 2D TMDs (e.g., NbSe2 and MoS2), enabling precise formation of TMD monolayers with tailored morphologies, from isolated monolayer domains to large-scale continuous films and intrinsically-patterned rings. Moreover, Janus S-Mo-Se monolayers are synthesized with atomic precision via vdW-protected bottom-plane chalcogen substitution. Importantly, our approach simultaneously produces ultraclean vdW interfaces. This in situ encapsulation reliably preserves air-sensitive materials, as evidenced by the enhanced superconductivity of nano-confined NbSe2 monolayers. Altogether, our study establishes a versatile platform for the controlled synthesis and integration of 2D TMDs for advanced applications.
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All authors Ce Bian, Yifan Zhao, Roger Guzman, Hongtao Liu, Hao Hu, Qi Qi, Ke Zhu, Hao Wang, Kang Wu, Hui Guo, Wanzhen He, Zhaoqing Wang, Peng Peng, Zhiping Xu, Wu Zhou, Feng Ding, Haitao Yang, Hong-Jun Gao
Materials Science
Machine-learned accelerated discovery of oxidation-resistant NiCoCrAl high-entropy alloys
Dennis Boakye and Chuang Deng
The development of oxidation-resistant high-
entropy alloy (HEA) bond coats is restricted by the limited understanding of how multi-principal element interactions govern scale formation across temperatures. This study uncovers new oxidation trends in NiCoCrAl HEAs using a data-driven analysis of high-fidelity experimental oxidation data. The results reveal a clear temperature-dependent transition between alumina- and chromia-dominated protection, identifying the compositional regimes where
alloys rich in Al dominate at $\ge1150$ {\deg}C, mixed Al-Cr chemistries are optimal at intermediate temperatures, and, unexpectedly, Cr-rich low-Al
alloys perform best at 850 {\deg}C-challenging the assumption that high Al is universally required. The effects of Hf and Y are shown to be strongly composition-dependent with Hf producing the largest global reduction in oxidation rate, while Y becomes effective primarily in NiCo-lean
alloys. Y-Hf co-doping offers consistent improvement but exhibits site-saturation behavior. These insights identify new high-performing HEA bond-coat families, including $\mathrm{Ni_{17}Co_{23}Cr_{30}Al_{30}}$ as a substitute for conventional mutlilayer thermal barrier coatings.
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Materials Science
Electromechanical properties of the 180{\deg} domain wall in PbTiO3
I. Rychetsky, A. Klic and W. Schranz
We analyze the electromechanical response of the 180 degree ferroelectric domain wall in tetragonal PbTiO3 by combining first-principles calculations with a Landau-Ginzburg-Devonshire (LGD) description. Using regular multidomain structures with varying domain-wall density, we extract polarization profiles and
lattice distortions and map them onto the continuum model to determine conventional (homogeneous) and gradient (inhomogeneous) electrostriction. Conventional electrostriction yields only a small negative length change of the sample, whereas gradient electrostriction–arising from the coupling between strain and polarization gradients–produces a positive contribution nearly an order of magnitude larger and localized at the wall core. Our results demonstrate that gradient electrostriction dominates the electromechanical response of 180 degree walls in PbTiO3, supporting its inclusion in LGD models that stabilize Bloch-type domain wall structures.
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Statistical Mechanics
Correlations between rare events due to long-term memory
Apurba Biswas and Thomas Guérin
Rare events refer to qualitatively unlikely events whose realization can nevertheless have important consequences. Typically, the prediction of the kinetics of these events relies on Arrhenius laws, with exponentially distributed waiting times, and no correlations between successive occurrences. However, this description breaks down in the presence of long-term
memory, as has been observed in the contexts of geophysical time series or
protein dynamics. So far, existing analytical approaches do not quantify the correlations between rare events due to long-term
memory. Here, for non-Markovian Gaussian processes, we determine analytically the impact of long-term
memory on the distribution of first and second passage times to a rarely reached threshold. This distribution is non-exponential, thus going beyond the Arrhenius paradigm. We obtain an explicit expression for the covariance between the first and second passage times, and we predict how the mean time to the next extreme event depends on the previous passage time, illustrating the phenomenon of clustering of extreme events. These analytical results, validated through extensive
stochastic simulations, shed lights on the strong correlation between successive occurrences of extreme events due to long-term
memory.
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Materials Science
Thermal Stabilization of Defect Charge States and Finite-Temperature Charge Transition Levels
Tobias Hainer, Ethan Berger, Esmée Berger et al. (+3 more)
Point defects introduce localized electronic states that critically affect carrier trapping, recombination, and transport in functional materials. The associated charge transition levels (CTLs) can depend on temperature, requiring accurate treatment of vibrational and electronic free-energy contributions. In this work, we use machine-learned interatomic potentials to efficiently compute temperature-dependent CTLs for vacancies in MgO, LiF, and CsSnBr3. Using thermodynamic integration, we quantify free-energy differences between charge states and calculate the vibrational
entropy contributions at finite temperatures. We find that CTLs shift with temperature in MgO, LiF and CsSnBr3 from both
entropy and electronic contributions. Notably, in CsSnBr3 a neutral charge state becomes thermodynamically stable above 60 K, introducing a temperature-dependent
Fermi-level window absent at 0 K. We show that the widely used static, zero-kelvin defect formalism can miss both quantitative CTL shifts and the qualitative emergence of new stable charge states.
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All authors Tobias Hainer, Ethan Berger, Esmée Berger, Olof Hildeberg, Paul Erhart, Julia Wiktor
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Non-linear X-ray Coherent Diffractive Imaging
Arnab Sarkar and Allan S. Johnson
The advent of nonlinear X-ray processes like sum-frequency generation and four-wave mixing raises the possibility of non-linear X-ray imaging, combining the high-resolution and elemental specificity of X-ray imaging with the state selectivity and sensitivity of non-linear optical imaging. While scanning imaging methods may be feasible, for linear X-ray processes coherent diffractive imaging has emerged as a key approach, enabling lensless reconstruction of nanoscale structure and dynamics with high spatial and temporal resolution. In this work, we propose a coherent diffractive approach to imaging using X-ray nonlinear processes, introducing an analysis method to isolate the nonlinear component from the overall diffraction pattern by leveraging the property of mutual incoherence between different wavelengths. For examples such as sum-frequency generation in ferroelectrics, this method reveals both domain structure and orientation through the retrieved amplitude and phase of the nonlinear signal. We discuss the feasibility of the proposed method in the presence of experimental noise, most relevantly shot noise. This analysis method is applicable in both static and dynamic imaging, offering a pathway beyond traditional spectroscopy toward XUV/X-ray coherent imaging of spatio-temporal dynamics in
quantum materials and biological systems.
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Mesoscale and Nanoscale Physics
The role of the exchange-Coulomb potential in two-dimensional electron transport
J. L. Figueiredo, J. T. Mendonça and H. Terças
We develop a
quantum kinetic theory of two-dimensional electron gases in which exchange is treated self-consistently at the Hartree-Fock level and enters as a nonlocal, momentum-dependent field in phase space. By starting from the Coulomb
Hamiltonian, we derive a Hartree-Fock-Wigner equation for the electronic Wigner function and obtain a closed fluid model with exchange-corrected pressure, force, and current. For a single layer, we show that exchange renormalizes the
Fermi velocity and can drive a long-wavelength plasmonic instability at low densities. In coupled layers, the same framework predicts acoustic-optical mode coupling, and an instability forming long-lived charge-imbalance patterns that are not predicted by classical Vlasov and Boltzmann models. Finally, we apply the kinetic model to the Coulomb drag problem and show how exchange substantially enhances the drag resistivity in dilute GaAs double wells, quantitatively matching experimental observations.
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Materials Science · Cross-listed from physics.optics
Towards coherent polaritonic circuits operating at room temperature
Addhyaya Sharma, Ezra Bader, Ravindra K. Yadav et al. (+6 more)
Polariton condensation is a potential system state for performing analog computations, given that it exhibits
quantum behavior at macroscopic scales readily probed with low-cost optical methods. Current methods of fabricating devices in polariton microcavities largely involve patterning the devices via e-beam lithography before the cavity is completed, which offers less flexibility in device creation and reduces the maximum possible refractive index contrast. Moreover, the momentum and spatial distributions of the condensate are highly dependent on the host platform, and it has been difficult to preserve the desired behavior when modifying a given cavity. Here we introduce a method that addresses both of these challenges with the creation of polaritonic
circuits of arbitrary forms etched via Focused Ion Beam into an organic microcavity based on Rhodamine 3B Perchlorate within a Small Molecule Ionic Isolation
Lattices complex. We demonstrate room temperature condensation and propagation of polaritons in rectangular and trapezoidal waveguides by analyzing spatial and angle-resolved photoluminescence. We also discuss the blue-shifting and non-zero momentum of the condensate and show that it is strongly confined up to several higher energy levels. As an example, we report the spatial profiles of condensation in custom devices, such as a ring waveguide, a Y-splitter, and a Mach-Zehnder interferometer. This work represents a first step towards the realization of more complex, fully integrated, coherent polaritonic
circuits operating at room temperature.
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All authors Addhyaya Sharma, Ezra Bader, Ravindra K. Yadav, Juan Carlos Obeso Jureidini, Michael Reitz, Daegwang Choi, Rishabh Kaurav, Joel Yuen-Zhou, Vinod M. Menon
Disordered Systems and Neural Networks
Interacting Hysterons with Asymptotically Small or Large Spans
Margot Teunisse and Martin van Hecke
Models of interacting hysteretic elements, called hysterons, capture the sequential response and complex
memory effects in a wide range of complex systems and can guide the design of intelligent metamaterials. However, even simple models with few hysterons feature a bewildering number and variety of behaviors. Here we study the hysteron model in two physically relevant limits, where {the} response {of a hysteron system} is easier to understand. First, when the hysteron span - the gap between its two hysteretic transitions - dominates all other scales, the range of pathways encoded in transition graphs (t-graphs) becomes limited because many avalanches {are} absent. Second, when the hysteron span becomes vanishingly small, hysterons behave as interacting binary
spins, {which require avalanches in order to} exhibit nontrivial pathways. Finally we show that hysterons can be mimicked by pairs of strongly interacting
spins, {such} that collections of $n$ interacting hysterons can be mapped to $2n$ interacting
spins, albeit {via} highly specific interactions. {Altogether,} our work provides a deeper understanding of the role of the hysteron parameters on their collective behavior, and points to connections and differences between
spin- and hysteron-based models of complex matter.
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Materials Science
Lithium-ion battery degradation: Introducing the concept of reservoirs to design for lifetime
Mohammed Asheruddin Nazeeruddin, Ruihe Li, Simon E. J. OKane et al. (+2 more)
Designing lithium-ion batteries for long service life remains a challenge, as most
cells are optimized for beginning-of-life metrics such as energy density, often overlooking how design and operating conditions shape degradation. This work introduces a degradation-aware design framework built around finite, interacting reservoirs (lithium, porosity, and electrolyte) that are depleted over time by coupled degradation processes. We extend a physics-based Doyle-Fuller-Newman model to include validated mechanisms such as SEI growth, lithium plating, cracking, and solvent dry-out, and simulate how small design changes impact lifetime. Across more than 1,000 cycles, we find that increasing electrolyte volume by just 1% or porosity by 5% can extend service life by over 30% without significantly affecting
cell energy density. However, lithium excess, while boosting initial capacity, can accelerate failure if not supported by sufficient structural or ionic buffers. Importantly, we show that interaction between reservoirs is crucial to optimal design: multi-reservoir tuning yields either synergistic benefits or compound failures, depending on operating conditions. We also quantify how C-rate and operating temperature influence degradation pathways, emphasizing the need for co-optimized design and usage profiles. By reframing degradation as a problem of managing finite internal reservoirs, this work offers a predictive and mechanistic foundation for designing lithium-ion batteries that balance energy, durability, and application-specific needs.
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All authors Mohammed Asheruddin Nazeeruddin, Ruihe Li, Simon E. J. OKane, Monica Marinescu, Gregory J. Offer
Strongly Correlated Electrons
Functional renormalization group for extremely correlated electrons
Jonas Arnold, Peter Kopietz and Andreas Rückriegel
At strong on-site repulsion $ U $, the fermionic Hubbard model realizes an extremely correlated electron system. In this regime, it is natural to derive the low-energy physics with the help of non-canonical operators acting on a projected
Hilbert space without double occupancies. Using a strong-coupling functional renormalization group technique, we study the physics of such extreme correlations in the strict $ U = \infty $ limit, where only kinematic interactions due to the
Hilbert space projection remain. For nearest-neighbor hopping on a square
lattice, we find that the electronic spectrum is significantly renormalized, with bandwidth and quasi-particle residue strongly decreasing with increasing electron density. On the other hand, damping and particle-hole asymmetry increase, while a polaronic continuum forms in the hole sector, below the single-particle band.
Fermi liquid phenomenology applies only at low densities, where the system remains paramagnetic. At higher densities, we find a bad metal with strong
magnetic correlations, indicating that the ground state is the Nagaoka ferromagnet at high densities and a stripe antiferromagnet at intermediate densities. Both in the paramagnetic and the
ferromagnetic regimes, we observe a violation of Luttinger's
theorem.
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