Plasma Physics
Plasma Mixing Driven by the Collisionless Kelvin-Helmholtz Instability: Insights from fully kinetic simulation and density-based diagnostics
Silvia Ferro, Fabio Bacchini, Giuseppe Arrò et al. (+2 more)
Simulations and observations of the low-latitude magnetosphere-magnetosheath boundary layer indicate that the Kelvin-Helmholtz instability (KHI) drives
vortex structures that enhance
plasma mixing and
magnetic reconnection, influencing transport and particle acceleration. We investigate the spatial localization, species dependence, and physical mechanisms of
plasma mixing driven by the nonlinear
evolution of the KHI. We perform high-resolution two-dimensional Particle-In-
Cell simulations using a finite-Larmor-radius shear-flow initial configuration.
Plasma mixing is quantified using particle labeling, a complementary density-based mixing tracer, and diagnostics of
magnetic reconnection. Mixing across the shear layer is present but localized, occurring mainly in narrow interface regions and
plasma structures. Ions mix more effectively than electrons, which remain largely frozen to field lines. Enhanced mixing spatially and temporally correlates with localized
magnetic reconnection within and between KH
vortices. Cross-boundary transport driven by the kinetic KHI remains intrinsically localized and is mediated by
vortex advection and
magnetic reconnection. Electron mixing is strongly constrained, indicating that kinetic-scale transport across collisionless shear layers remains limited.
Read the full abstract ▾
All authors Silvia Ferro, Fabio Bacchini, Giuseppe Arrò, Francesco Pucci, Pierre Henri
Plasma Physics
Resistive instabilities of current sheets in stratified plasmas with a gravitational field
Faisal Sayed, Anna Tenerani and Richard Fitzpatrick
Magnetic reconnection can develop spontaneously via the tearing instability, often invoked to explain disruptive instabilities in fusion devices,
solar flares, the generation of periodic density disturbances at the tip of helmet streamers, and flux transfer events at the Earth's dayside magnetopause. However, in many such environments the presence of
gravity,
magnetic field
curvature or other forms of acceleration often result in situations of a heavy-over-light
plasma in an effective gravitational field with an embedded current sheet. This paper studies the linear stability of a slab current sheet with respect to reconnecting modes in the presence of a density gradient under the effect of a constant gravitational acceleration. We show that the presence of stratification and
gravity modify the properties of the tearing mode instability both in the case of favorable and unfavorable stratification. Favorable stratification suppresses reconnection while unfavorable stratification strongly destabilizes the tearing mode. Furthermore, we show that the classical constant-{\psi} regime effectively does not exist, even for weak unfavorable stratification, for S>>1. Instead, the
gravity-modified tearing progressively transitions into the G-mode, which is a
gravity-driven reconnecting mode with a growth rate scaling as S^-1/3. As a consequence, unfavorable stratification only permits rapidly reconnecting modes.
Read the full abstract ▾
Instrumentation and Detectors
Prospects for Direct Electron Detectors in Ultrafast Electron Diffraction and Scattering Experiments
Laurenz Kremeyer, David Cai, Malik Lahlou et al. (+3 more)
Ultrafast electron diffraction and
phonon-diffuse scattering [UED(S)] experiments make use of photo-induced changes to electron scattering intensity across 2D detectors to report on a very wide range of dynamic structural phenomena in molecules and materials. Hybrid pixel counting detectors (HPCDs) are a promising technology for improved sensitivity and signal-to-noise in UED(S) experiments, as they offer near-zero readout noise and dark counts with the possibility of new acquisition modalities (e.g., shot-to-shot normalization) due to their high frame rates. However, it is well known that HPCDs suffer from count losses at high electron fluxes even in CW beam applications. How this translates to ultrashort electron pulse exposures has yet to be determined and is critical to understanding the application of this technology to ultrafast electron scattering experiments. Here we show that count losses are significantly exacerbated in ultrafast (pulsed) experiments and that HPCDs require unconventional data handling and saturate above $\approx\!2$ electrons per pixel per pulse. This count-rate limitation presents a severe constraint on electron bunch charge when interrogating single
crystal samples. Normalization strategies to optimize signal-to-noise in UED(S) and a complete model for measurement uncertainties using HPCDs are developed and tested using a large
dataset. Finally, we suggest ways HPCDs could be better adapted to ultrashort pulsed beam experiments.
Read the full abstract ▾
All authors Laurenz Kremeyer, David Cai, Malik Lahlou, Sebastian Hammer, Raphael Schwenzer, Bradley J. Siwick
Fluid Dynamics
Controlled dripping from a grooved condensing plate
Matteo Leonard and Nicolas Vandewalle
Condensed water on vertical surfaces ultimately leaves the substrate at the lower edge, where accumulated
liquid detaches as drops. While droplet growth and surface transport have been extensively studied, this final release step remains poorly understood and largely uncontrolled. Yet this boundary event determines how and when condensed water is removed. We ask whether geometry can replace randomness as the governing mechanism of edge dripping. By engraving vertical grooves upstream, we redirect water from surface flow into groove-guided drainage toward the boundary. This switch in transport mode changes how
liquid accumulates and detaches at the edge. Using rapid forced condensation and high-resolution imaging, we systematically vary groove spacing s, aspect ratio d/w, and orientation. We then analyse how these
geometric parameters influence the formation, stability, and spatial organization of droplets hanging below the edge. Smooth substrates exhibit irregular, impact-driven detachment. Grooved substrates produce localized and steady dripping points. When grooves converge, dripping occurs at fixed, geometry-defined locations. For convergent designs, a simple condensation-capillarity model captures the dependence of the dripping period on the area of the drainage basin. Together, these results demonstrate that geometry alone can transform
stochastic edge dripping into spatially organized and temporally regular release, with implications for dew harvesting, passive cooling, and millifluidic transport.
Read the full abstract ▾
Medical Physics
Geometric and topological constraints on oral seal formation during infant breastfeeding
Arturo Tozzi
Breastfeeding efficiency relies on coordinated tongue motion, sustained tissue contact and maintenance of an effective intraoral seal. Current assessments of seal formation mainly use local kinematic descriptors or pressure recordings, which do not capture the global structural continuity of the sealing region. We introduce a systolic geometry based approach in which each sagittal ultrasound frame is modeled as a two dimensional deformable domain bounded by tongue, palate and nipple contours. Global seal continuity is formalized through the shortest closed curve that cannot be contracted to a point because of the overall geometry of the domain. The nipple defines a central region that must be circumferentially enclosed by a contact band to maintain suction. Within this band, closed curves encircling the nipple exactly once can be identified; the shortest of these curves defines a normalized systolic index representing the tightest admissible sealing loop. Simulations of symmetric thinning, localized discontinuities and cyclic perturbations reveal feasibility boundaries separating seal preserving from seal breaking configurations. Notably, admissible encircling curves may transiently disappear even when overall
geometric motion remains smooth. By capturing global circumferential continuity that cannot be inferred from local metrics alone, our approach generates testable hypotheses linking the existence and temporal stability of admissible encircling curves to milk transfer efficiency and
vacuum stability. Applied to segmented ultrasound data and integrated with pressure measurements, our systolic approach could provide a quantitative framework for objective assessment of seal integrity and longitudinal monitoring of latch stability.
Read the full abstract ▾
Applied Physics · Cross-listed from cond-mat.mtrl-sci
Atomic-Scale Surface Imaging of bulk Epitaxial CsPbBr3 Perovskite Single Crystals on Mica using Light Assisted Scanning Tunneling Microscopy at Low-Temperature (80 K)
Eric Duverger, Vladimir Bruevich, Vitaly Podzorov et al. (+1 more)
Epitaxial single-crystalline CsPbBr3 perovskite films on mica, prepared ex-situ, are explored using a low-temperature scanning tunneling microscope (STM) by probing the unoccupied electronic states of their surface in ultra-high
vacuum (UHV) at 80 K. Light-assisted STM measurements under a broadband illumination with visible light were employed to enhance and stabilize surface conductivity. STM imaging across the surface of macroscopic bulk CsPbBr3 films reveals large flat terraces characterized by a specific type of surface reconstruction, consisting of parallel rows of U-shaped atomic nanostructures. These structures are spaced by 12 angstroms and exhibit an internal periodicity of 5.1 angstroms. Density functional theory (DFT) calculations reproduce the experimental observations and reveal a competition between different orthorhombic CsPbBr3(110) surface reconstructions: a Cs-rich structure, identified as the most energetically stable, and three alternative PbBr rich reconstructions, which are slightly higher in energy yet remain consistent with the STM data. Additional analyses that explicitly account for the mica substrate exclude the cubic CsPbBr3 phase and other orthorhombic surface orientations, while showing that variations in the mica surface termination do not alter the preferred CsPbBr3(110) reconstruction. This combined approach thereby confirms our assignment and resolves previous STM interpretations of CsPbBr3.
Read the full abstract ▾
All authors Eric Duverger, Vladimir Bruevich, Vitaly Podzorov, Damien Riedel
Optics
All-optical programming of polarization singularities in a photonic-crystal laser
Abhishek Padhy, Zhiyi Yuan, Mohammed Hamdad et al. (+11 more)
Singular optics has emerged as an important research area with diverse applications, yet controlling optical singularities in nanophotonic emitters remains largely constrained by the fixed subwavelength geometry of optical resonators. Here, we circumvent this limitation and demonstrate all-optical programming of real-space polarization singularities in a photonic-
crystal laser, while preserving a momentum-space
vortex inherited from a
symmetry-protected bound state in the continuum. The principle is to use a shaped optical pump to create a smooth mesoscopic potential, whose spatial variations are slow compared with the
lattice period. This potential localizes a negative-mass Bloch band into trapped lasing states whose envelope functions, and therefore far-field singularity textures, are defined by the pump geometry. Using a honeycomb photonic
crystal supporting a
symmetry-protected bound state in the continuum, we achieve room-temperature telecom-band lasing with real-space polarization singularities pinned to the critical points of the envelope function, where its gradient vanishes, and reconfigurable in number and position by pump shaping, while the intrinsic momentum-space singularity at the $\Gamma$ point remains fixed. The experimental observations agree quantitatively with an analytical framework combining the Bloch mode of the photonic
crystal with envelope-function theory, establishing optical envelope engineering as a route to programmable structured emission from active photonic
lattices.
Read the full abstract ▾
All authors Abhishek Padhy, Zhiyi Yuan, Mohammed Hamdad, Panagiotis Nianios, Romane Houvenaghel, Aziz Benamrouche, Nicolas Roy, Thanh Phong Vo, Christian Seassal, Xavier Letartre, Lotfi Berguiga, Michaël Lobet, Ségolène Callard, Hai Son Nguyen
Physics and Society
Non-Pharmaceutical Interventions Reshape Network Immunization Outcomes
Sámuel G. Balogh, Gergely Ódor and Márton Karsai
Herd immunity is shaped not only by the infection capacity of a spreading epidemic or the contact structure of the hosting population, but also by how and under what circumstances individuals acquire immunity. Immunization strategies may interact with ongoing non-pharmaceutical interventions, which commonly aim to reduce social contact numbers. We demonstrate that these interactions can induce unexpectedly strong and counterintuitive effects on herd immunity. We explore these phenomena on spatially embedded contact networks and uncover a reversal in the relative effectiveness of disease- versus vaccine-induced immunization schemes, highlighting the average number of contacts as a critical determinant of emerging herd immunity. In sparse
geometric networks with limited degree heterogeneity, uniform vaccination proves most effective; however, as average contact numbers increase, naturally acquired immunity ultimately becomes the better strategy. We show that this phenomenon may emerge not only in synthetic networks but also in real-world mixing networks, observed during non-pharmaceutical intervention periods across multiple states of the United States.
Read the full abstract ▾
Fluid Dynamics
Wavy-wall-based flow control for the suction side geometry of NACA4412 at Retau = 3000
Artur Dróżdż, Mathias Romańczyk and Witold Elsner
The paper presents a high Reynolds number experimental study of turbulent boundary layer separation control on a convex plate using the wavy-wall method, which was initially proposed for a flat plate by Dróżdż et al. 2021 (Exp Therm Fluid Sci 2021;121:110291). The application of this method increases the friction coefficient by up to 42.3%, resulting in a substantial delay in turbulent separation from the convex wall, while maintaining total momentum, quantified by changes in momentum-loss thickness. Other parameters indicating the high efficiency of the method are the invariant value of the friction Reynolds number along the flow and the thinner boundary layer. The above indicators demonstrate promising aerodynamic improvements in airfoils, similar to those achieved when active suction is applied to the suction side. The new insight into the physical mechanism of the wavy wall suggests that small-scale turbulent activity is the primary determinant of the effectiveness of the wavy wall in enhancing small-scale streamwise convection and the sweeping motion, resulting in superior momentum transport. However, when the wavy wall, due to poorly selected geometry, induces large-scale motions, such as separation in the trough, it counteracts the mechanism. Then this geometry has a detrimental effect on the efficiency of the method.
Read the full abstract ▾
Data Analysis and Statistics · Cross-listed from quant-ph
Detecting nonequilibrium phase transitions via continuous monitoring of space-time trajectories and autoencoder-based clustering
Erik Fitzner, Francesco Carnazza, Federico Carollo et al. (+1 more)
The characterization of collective behavior and nonequilibrium phase transitions in
quantum systems is typically rooted in the analysis of suitable system observables, so-called order parameters. These observables might not be known a priori, but they may in principle be identified through analyzing the
quantum state of the system. Experimentally, this can be particularly demanding as estimating
quantum states and expectation values of
quantum observables requires a large number of projective measurements. However, open
quantum systems can be probed in situ by monitoring their output, e.g. via heterodyne-detection or
photon-counting experiments, which provide space-time resolved information about their dynamics. Building on this, we present a machine-learning approach to detect nonequilibrium phase transitions from the measurement time-records of continuously-monitored
quantum systems. We
benchmark our method using the
quantum contact process, a model featuring an absorbing-state phase transition, which constitutes a particularly challenging test case for the
quantum simulation of nonequilibrium processes.
Read the full abstract ▾
All authors Erik Fitzner, Francesco Carnazza, Federico Carollo, Igor Lesanovsky
Chemical Physics
Semi-Local Exchange-Correlation Approximations in Density Functional Theory
Fabien Tran, Susi Lehtola, Stefano Pittalis et al. (+1 more)
Density functional theory has become the workhorse of modern electronic structure calculations, with wide-ranging applications in chemistry, physics, materials science, biochemistry, etc. At its heart lies the exchange-correlation functional, a quantity which exactly encapsulates the many-body effects stemming from the
quantum mechanical interactions between the electrons. Yet, the exact functional is unknown, and computationally tractable approximations are therefore necessary for practical applications. Over the past six decades, hundreds of density functional approximations have been proposed with varying accuracy and computational efficiency. This review surveys the theoretical foundations of semi-local functionals, including local density approximations, generalized gradient approximations, and meta-generalized gradient approximations. We provide a comprehensive, consistently organized discussion that consolidates both historical developments and recent advances in this field. Beginning with the essentials of Kohn-Sham density functional theory, we present the construction principles of semi-local exchange-correlation functionals. Special
attention is given to the physical motivations underlying functional development, the mathematical properties that guide their construction, and the practical considerations that determine their applicability across different chemical and physical systems. This work is intended to serve as both an introduction for newcomers to the field and a comprehensive reference for practitioners. By consolidating the extensive literature on semi-local functionals and providing a unified framework for their construction and application, we aim to facilitate further developments in density functional approximations and their use in tackling the diverse challenges of modern computational chemistry and condensed matter physics.
Read the full abstract ▾
All authors Fabien Tran, Susi Lehtola, Stefano Pittalis, Miguel A. L. Marques
Applied Physics
g4chargeit: Geant4-based kinetic Monte Carlo simulations of charging in dielectric materials
Kush P. Gandhi, Advik D. Vira, William M. Farrell et al. (+5 more)
We present g4chargeit, a kinetic Monte Carlo framework built on Geant4 for self-consistent simulation of time-dependent electrostatic charging in dielectric materials. The model explicitly incorporates
stochastic particle transport and scattering processes using validated Geant4 cross-sections, while self-consistently evolving the electric potential and field. As a representative application, we simulate the charging of regolith grains under average dayside conditions on the Moon. The surface of the Moon, in addition to other airless planetary bodies, are regularly exposed to
solar ultraviolet
photons and
solar-wind
plasma, creating a radiation environment in which electrostatic interactions among regolith grains become significant. Until now, simulations of regolith charging have often relied on analytical approximations that oversimplify grain geometry and interaction mechanisms. Our Geant4-based simulations reveal charge accumulation within intergrain micro-cavities, leading to repulsive electrostatic forces consistent with experimental observations. The framework establishes a multiscale approach that links microscopic scattering events to the continuity equation of surface charge density and to the formation of macroscopic surface charge patches in complex grain geometries. Although demonstrated here for planetary regolith, the method is general and applicable to a broad range of dielectric charging problems. The code is openly available at https://github.com/kgandhi63/g4chargeit.git.
Read the full abstract ▾
All authors Kush P. Gandhi, Advik D. Vira, William M. Farrell, Nikolai Simonov, Alvaro Romero-Calvo, Thomas M. Orlando, Phillip N. First, Zhigang Jiang
Atomic Physics
Formation of Hydroxyl Anion via a 2-Particle 1-Hole Feshbach Resonance in DEA to 2-Propanol: A Joint Experimental and Theoretical Study
Siddique Ali, Meeneskhi Rana, Soumya Ghosh et al. (+3 more)
Absolute cross sections for the formation of OH- from 2-propanol (CH3CH(OH)CH3) via dissociative electron attachment (DEA) are reported in the incident electron energy range of 3.5-13 eV. Four fragment anions are observed: OH-, C2H2O-, C2H4O-, and C3H7O-. The OH- yield exhibits a pronounced resonance centered at 8.2 eV together with a broader structure extending over the 8-10 eV region. Equation-of-Motion Coupled-Cluster (electron attached) calculations with Singles and Doubles combined with a Complex Absorbing Potential (CAP/EOM-EA-CCSD) assign this feature to a two-particle-one-hole (2p-1h) core-excited Feshbach resonance. Potential energy curves along the C-OH dissociation coordinate reveal that core-excited anion states in this energy range promote efficient cleavage of the hydroxyl group. Analysis of Dyson orbitals and resonance widths demonstrates that only states with repulsive antibonding sigma(C-OH) character and sufficiently long lifetimes contribute significantly to the observed OH- production. These results provide fundamental insight into the DEA dynamics of secondary alcohols and highlight the role of multi-electron-attached resonances in site-specific bond rupture induced by low-energy electrons.
Read the full abstract ▾
All authors Siddique Ali, Meeneskhi Rana, Soumya Ghosh, Narayan Kundu, Aryya Ghosh, Dhananjay Nandi
Optics
Far-field heat transfer and monochromatic thermal currents in a cylindrical nonreciprocal cavity
Guillem Masdemont, Julien Legendre and Georgia T. Papadakis
Breaking Kirchhoff's law of thermal radiation yields new opportunities in one-way radiative thermal transport and circuitry. We investigate its consequences in the far-field regime in cylindrical cavities, by employing a specular ray-tracing
algorithm. At thermal
equilibrium, we show that violation of Kirchhoff's law yields non-vanishing heat rectification coefficients within different sections of the cavity, which can be tuned for perfect rectification and circulation, while internal monochromatic currents vanish due to the intrinsic coupling between emission and absorption at specular surfaces. This constraint is lifted under nonequilibrium conditions, where rotational heat fluxes within the cavity can be precisely controlled by appropriately combining reciprocal and nonreciprocal materials. These findings open new avenues for thermal management and provide design principles for nonreciprocal photonic devices.
Read the full abstract ▾
Data Analysis and Statistics · Cross-listed from hep-ex
Lepton and photon energy scale and resolution corrections based on the minimization of an analytical likelihood: IJazZ2.0
F. Couderc, P.Gaigne and M. Ö. Sahin
We present a novel method to determine
lepton energy scale and resolution corrections by means of an analytical likelihood maximization applied to Drell–Yan \(Z \to \ell\ell\) events. The approach relies on an exact analytical treatment of the Gaussian energy smearing model, avoiding random-number-based convolution techniques. This formulation results in a fully differentiable likelihood enabling the use of automatic differentiation
algorithms, and thus a substantial reduction in computational cost. The method, implemented in the \ijazz software, allows the simultaneous extraction of scale and resolution parameters across multiple
lepton categories defined by detector or kinematic variables. We validate the technique using toy Monte Carlo studies and realistic Pythia-based simulations, demonstrating unbiased parameter recovery and accurate uncertainty estimates. Particular
attention is given to categorizations involving
lepton transverse momentum, for which a relative-\(p_T\) strategy is introduced to mitigate biases induced by category migration and kinematic correlations. The method is further adapted to
photon-energy scale measurement in \(Z \to \mu^+\mu^-\gamma\) decays. Compared to conventional approaches, the analytical method improves numerical stability, robustness of the minimization, and computational performance, making it well suited for large-scale precision calibration tasks at the LHC.
Read the full abstract ▾
Biological Physics · Cross-listed from q-bio.TO
Spatio-temporal air flow properties in a 3D personalised model of the human lung
Jonathan Stéphano, Michaël Brunengo, Riccardo Di Dio et al. (+2 more)
We propose a multi-scale lung model to investigate spatio-temporal distributions of ventilation variables. Lung envelope and large airway geometries are derived from CT scans; smaller airways are generated using a physiologically consistent
algorithm. Tissue mechanics is modeled using nonlinear elasticity under small deformations, coupled with local air pressure from fluid dynamics within the bronchial tree. Airflow accounts for inertia and static airway compliance. Simulations employ finite elements. Using this model, we explore spatio-temporal airflows and shear stresses distributions.
Read the full abstract ▾
All authors Jonathan Stéphano, Michaël Brunengo, Riccardo Di Dio, Thomas Laporte, Benjamin Mauroy
Physics and Society
On the Concept of Violence: A Comparative Study of Human and AI Judgments
Mariachiara Stellato, Francesco Lancia, Chiara Galeazzi et al. (+1 more)
Background: What counts as violence is neither self-evident nor universally agreed upon. While physical aggression is prototypical, contemporary societies increasingly debate whether exclusion, humiliation, online harassment or symbolic acts should be classified within the same moral category. At the same time, Large
Language Models (LLMs) are being consulted in everyday contexts to interpret and label complex social behaviors. Whether these systems reproduce, reshape or simplify human conceptions of violence remains an open question. Methods: Here we present a systematic comparison between human judgements and LLM classifications across 22 scenarios carefully designed to be morally dividing, spanning from physical and verbally aggressive behavior, relational dynamics, marginalization, symbolic actions and verbal expressions. Human responses were compared with outputs from multiple instruction-tuned models of varying sizes and architectures. We conducted global, sentence-level and thematic-domain analyses, and examined variability across models to assess patterns of convergence and divergence. Findings: This study treats violence as a strategically chosen proxy through which broader belief formation dynamics can be observed. Violence is not the focus of the study, but it serves as a tool to investigate broader analysis. It enables a structured investigation of how LLMs operationalize ambiguous moral constructs, negotiate conceptual boundaries, and transform plural human interpretations into singular outputs. More broadly, the findings contribute to ongoing debates about the epistemic role of conversational AI in shaping everyday interpretations of harm, responsibility and social norms, highlighting the importance of transparency and critical engagement as these systems increasingly mediate public
reasoning.
Read the full abstract ▾
All authors Mariachiara Stellato, Francesco Lancia, Chiara Galeazzi, Nico Curti
Atmospheric and Oceanic Physics
Weak 21st-century AMOC response to Greenland meltwater in a strongly eddying ocean model
Oliver Mehling and Henk A. Dijkstra
Climate models project that the Atlantic Meridional Overturning Circulation (AMOC) will weaken in the 21st century, but the magnitude is highly uncertain. Some of this uncertainty is structural, as most
climate models neglect increasing meltwater from the Greenland ice sheet and do not explicitly capture mesoscale ocean eddies. Here, we quantify the impact of Greenland meltwater on the AMOC until 2100 under SSP5-8.5 forcing for the first time in a strongly eddying (1/10{\deg} horizontal resolution) ocean model. The meltwater-induced additional AMOC weakening is small (0.6 $\pm$ 0.2 Sv) compared to the weakening due to warming alone, and similar at high and low resolution. The same meltwater would cause a stronger AMOC weakening under present-day
climate conditions. We link both resolution-independence and state-dependence to large-scale controls of the AMOC. Our results demonstrate that the background ocean state is more important than resolution in determining how Greenland meltwater affects the AMOC.
Read the full abstract ▾
Data Analysis and Statistics · Cross-listed from cond-mat.mtrl-sci
Wide-Surface Furnace for In Situ X-Ray Diffraction of Combinatorial Samples using a High-Throughput Approach
Giulio Cordaro, Juande Sirvent, Cristian Mocuta et al. (+7 more)
The combinatorial approach applied to functional
oxides has enabled the production of material libraries that formally contain infinite compositions. A complete ternary diagram can be obtained by pulsed
laser deposition (PLD) on 100 mm silicon wafers. However, interest in such materials libraries is only meaningful if high-throughput characterization enables the information extraction from the as-deposited library in a reasonable time. While much commercial equipment allows for XY-resolved characterization at room temperature, very few sample holders have been made available to investigate structural, chemical, and functional properties at high temperatures in controlled atmospheres. In the present work, we present a furnace that enables the study of 100 mm wafers as a function of temperature. This furnace has a dome to control the atmosphere, typically varying from nitrogen gas to pure oxygen atmosphere with external control. We present the design of such a furnace and an example of X-ray diffraction (XRD) and fluorescence (XRF) measurements performed at the DiffAbs beamline of the SOLEIL synchrotron. We apply this high-throughput approach to a combinatorial library up to 735 {\textdegree}C in nitrogen and calculate the thermal expansion coefficients (TEC) of the ternary system using custom-made MATLAB codes. The TEC analysis revealed the potential limitations of Vegard's law in predicting
lattice variations for high-
entropy materials.
Read the full abstract ▾
All authors Giulio Cordaro, Juande Sirvent, Cristian Mocuta, Fjorelo Buzi, Thierry Martin, Federico Baiutti, Alex Morata, Albert Tarancòn, Dominique Thiaudière, Guilhem Dezanneau
Chemical Physics
Vibrational infrared and Raman spectra of the methanol molecule with equivariant neural-network property surfaces
Ayaki Sunaga, Albert P. Bartók and Edit Mátyus
Electric dipole and polarizability surfaces are developed for the methanol (CH$_3$OH) molecule using ab initio electronic structure data, computed at the CCSD/aug-cc-pVTZ level of theory, and equivariant neural networks. These property surfaces are used to compute vibrational infrared and Raman intensities with variational vibrational energies and wave functions. The energies and wave functions, fully accounting for the large-amplitude motion and tunneling splitting states, are from continued variational vibrational computations, based on earlier work [Sunaga et al., J. Chem. Phys., 2025, 163, 064101], up to 3700 cm$^{-1}$ beyond the zero-point vibration, now reaching the O-H stretching fundamental. All vibrational fundamentals, combination and overtone bands are in excellent agreement with available (gas-phase) experimental data, with a 2.2 cm$^{-1}$ root-mean-squared deviation of the fundamentals from experiment. These developments constitute an important step towards a quantitative and comprehensive exact
quantum dynamics model of the methanol molecule, and a linelist for astrophysical applications.
Read the full abstract ▾
Optics · Cross-listed from quant-ph
Phonon-enhanced strain sensitivity of quantum dots in two-dimensional semiconductors
Sumitra Shit, Yunus Waheed, Jithin Thoppil Surendran et al. (+4 more)
Two-dimensional
semiconductors have attracted considerable interest for integration into emerging
quantum photonic networks. Strain engineering of monolayer transition-metal dichalcogenides (ML-TMDs) enables the tuning of light-matter interactions and associated optoelectronic properties, and generates new functionalities, including the formation of
quantum dots (QDs). Here, we combine spatially resolved micro-photoluminescence ($\mu$-PL) spectroscopy from cryogenic (4$\text{-}$94 K) to room temperature with micro-Raman spectroscopy at room temperature to investigate the strain-dependent emission energies of thousands of individual QDs in ML-WS$_2$ and ML-WSe$_2$, integrated across multiple
heterostructures and a piezoelectric device. Compared with delocalized
excitons, QDs in both materials exhibit enhanced strain sensitivities of their emission energies $-$ approximately fourfold in WS$_2$ and twofold in WSe$_2$ $-$ leading to pronounced broadening of the ensemble emission linewidth. Temperature-dependent $\mu$-PL spectroscopy combined with dynamic strain tuning experiments further reveal that the enhanced strain sensitivity of individual QDs originates from strengthened interactions with low-energy
phonons induced by
quantum confinement. Our results demonstrate a versatile strain-engineering approach with potential for spectral matching across solid-state, atomic, and hybrid
quantum photonic networks, and provide new insights into
phonon-QD interactions in two-dimensional
semiconductors.
Read the full abstract ▾
All authors Sumitra Shit, Yunus Waheed, Jithin Thoppil Surendran, Indrajeet Dhananjay Prasad, Kenji Watanabe, Takashi Taniguchi, Santosh Kumar
Optics
Engineering correlated disorder for tailored light scattering
Denis Langevin, Emma Bosbaty-Galliot, Emmanuel Centeno et al. (+5 more)
Correlated disorder is known to shape light scattering in ways uncorrelated disorder cannot, from hyperuniform transparency to the structural colors of naturally occurring structures. What has been missing in photonics is a direct link between the disorder and the scattering pattern it produces. Here we show that adding correlated noise to a periodic array splits the scattering pattern into three distinct components: diffraction peaks, a diffuse background, and correlation
halos. Often mistaken for broadened diffraction peaks, these
halos are in fact independent features: their positions are set by the correlation range, meaning that they can appear between Bragg peaks, and - crucially - they persist far beyond the regime where the diffraction peaks vanish. Shaping the disorder itself offers further control: tuning the noise distribution suppresses selected diffraction peaks, while tuning the correlation statistics moves the
halos away from the Bragg positions. This approach reproduces the scattering signatures of natural photonic structures, such as Morpho butterfly wings, and reveals multiple pathways from order to disorder, each with distinct optical properties. It also offers a practical route to inverse design - finding the disorder that produces a desired scattering pattern. This establishes scattering as a designable quantity, expanding the toolkit for metasurfaces and structural colors.
Read the full abstract ▾
All authors Denis Langevin, Emma Bosbaty-Galliot, Emmanuel Centeno, Pauline Bennet, Rémi Carminati, Bodo D. Wilts, Patrick Bouchon, Antoine Moreau
Computational Physics · Cross-listed from cond-mat.mtrl-sci
NextCrystal: a Symmetry-Driven Generative Framework for Crystal Structure Prediction
Jinming Mu, Lixin He, Xudong Zhu et al. (+1 more)
Crystal structure prediction (CSP), which aims to predict the 3D atomic arrangement of a
crystal from its composition, is central to materials discovery and mechanistic understanding.
Crystal symmetry plays a crucial role in CSP, but given the composition in a unit
cell, existing methods either struggle with the NP-hard combinatorial challenge of enforcing
symmetry rigorously or rely on retrieving known templates, inherently limiting both physical fidelity and the discovery of genuinely new materials. To address this challenge, we introduce NextCrystal, a
symmetry-driven generative framework that employs large
language models to encode chemical semantics and directly generate fine-grained Wyckoff site patterns from atomic stoichiometry, eliminating reliance on database lookups. To overcome the combinatorial complexity of site assignments, we incorporate domain knowledge via an efficient, linear-complexity heuristic beam search, rigorously enforcing algebraic consistency between site multiplicities and atomic stoichiometry. By integrating this
symmetry-consistent template into a
diffusion backbone, the framework constrains the
stochastic generative trajectory to a physically plausible
geometric manifold. NextCrystal achieves state-of-the-art performance on stability, uniqueness, and novelty (SUN)
benchmarks, as well as superior structural matching, establishing a rigorous paradigm for exploring previously unexplored crystallographic space without relying on prior structural templates. As a representative application, first-principles screening of HfO2 candidates generated by NextCrystal identifies a previously unreported dynamically stable Pnma phase, 0.056~eV/atom lower in energy than the conventional high-pressure Pnma phase.
Read the full abstract ▾
All authors Jinming Mu, Lixin He, Xudong Zhu, Shi Yin
Accelerator Physics
Standards and Safety: an Overview
Luca Dassa
This note is intended to provide an overview of the implications of regulations and standards on the safety of mechanical equipment, with a focus on accelerator components. Each research facility has different internal rules and standards which are applicable to specific cases; however, the main reference legal frame in Europe is everywhere based on the applicable European Directives. After a brief introduction to the 'safety' for mechanical systems, the process of 'risk analysis' will be introduced. The majority of this note will then deal with regulations and standards for pressure and cryogenic equipment. The European Pressure Equipment Directive (PED) will be briefly described, together with the concept of 'harmonized standards' and their implications on the entire lifecycle of a pressure equipment, with some hints at the peculiarities of accelerator components. In the second part of this note, regulations and standards for machinery, load-lifting accessories and buildings will be briefly mentioned to complete the picture of the most common cases in an accelerator facility.
Read the full abstract ▾
Chemical Physics · Cross-listed from cond-mat.str-el
Ghost Embedding Bridging Chemistry and One-Body Theories
Carlos Mejuto-Zaera and Michele Fabrizio
Phenomenological rules play a central role in the design of chemical reactions and materials with targeted properties. Typically, these are formulated heuristically in terms of non-interacting orbitals and bands, yet show remarkable accuracy in predicting the complex behavior of intrinsically interacting many-body systems. While their non-interacting formulation makes them easy to interpret, it potentially hinders the development of new rules for systems governed by strong correlation, such as transition metal-based materials. In this work, we present a rigorous framework that allows bridging between fully interacting, even strongly correlated, systems and an effective one-body picture in terms of quasiparticles. Further, we present a computational strategy to efficiently and accurately access the main components of such a description: the
embedding approximation of the ghost Gutzwiller Ansatz. We illustrate the capabilities of this quasiparticle formulation on the Woodward-Hoffmann rules, and apply their reformulated version to toy “reactions” which exemplify the main scenarios covered by them.
Read the full abstract ▾
Biological Physics · Cross-listed from cond-mat.soft
How Molecular Motors' Interaction Shapes Flagellar Beat and Its Fluctuations
F. Fanelli and A. Puglisi
The
stochastic dynamics of flagellar beating for micro-swimmers, such as flagellated
cells, sperms and microalgae, is widely thought to include a feedback mechanism between flagellar shape and the rate of activation/de-activation of the $N \gg 1$ driving molecular motors. In the context of the so-called rigid filament models, where the axoneme is described by a single degree of freedom $X(t)$, we investigate the effect of direct coupling between the activity dynamics of adjacent motors, parametrized by $K \ge 0$. A functional Fokker-Planck equation for $X$ and the state of the $N$ motors is obtained. In the limit of small coupling $K \ll 1$, we derive a system of equations governing the dynamics of the
Fourier modes of the active motor density, obtaining estimates for several observables and the fluctuations' quality factor $Q$. For larger $K$ we resort to numerical simulations. The effect of introducing the coupling $K>0$ is to increase characteristic times and the beating period. Moreover for large $K$s the limit cycle becomes bi-stable, with abrupt avalanches of the motor dynamics. Increasing $K$ is similar to what observed in the case $K=0$ when the confining elastic force is strongly reduced. The quality factor of fluctuations has a non-monotonic behavior: it first increases with $K$, then decreases. This is accompanied by the reduction and eventual disappearance of regions where the fraction of activated motor is nor $0$ neither $1$.
Read the full abstract ▾
Chemical Physics
Jiace Sun and Garnet Kin-Lic Chan
Many computational methods in ab initio
quantum chemistry are formulated in terms of high-order tensor contractions, whose cost determines the size of system that can be studied. We introduce
stochastic tensor contraction to perform such operations with greatly reduced cost, and present its application to the gold-standard
quantum chemistry method, coupled cluster theory with up to perturbative triples. For total energy errors more stringent than chemical accuracy, we reduce the computational scaling to that of mean-field theory, while starting to approach the mean-field absolute cost, thereby challenging the existing cost-to-accuracy landscape.
Benchmarks against state-of-the-art local correlation approximations further show that we achieve an order-of-magnitude improvement in both total computation time and error, with significantly reduced sensitivity to system dimensionality and electron delocalization. We conclude that
stochastic tensor contraction is a powerful computational primitive to accelerate a wide range of
quantum chemistry.
Read the full abstract ▾
Fluid Dynamics
Penetration of impact-induced jets into skin-simulating materials
Kohei Yamagata, Yuto Yokoyama, Shoto Sekiguchi et al. (+3 more)
This study compares the penetration characteristics of impact-induced jets with those of
laser-induced jets, focusing on the underlying penetration mechanism rather than device performance for needle-free injection. Using an impact-induced jet system capable of ejecting a highly focused
liquid jet at high speed without the use of
lasers, we examine jet penetration into skin-simulating materials. Unlike conventional needle-free injectors that produce diffused
liquid jets, the impact-induced method generates a highly focused jet that limits the injected area, thereby reducing invasiveness. Comparative experiments with
laser-induced jets show that, even at similar jet tip velocities, impact-induced jets achieve greater penetration depth. The penetration depth remains constant regardless of the offset distance D from the target, owing to the high and nearly uniform velocity of the cylindrical jet root region, indicating that penetration is governed by the cylindrical jet structure. Furthermore, we systematically vary the
liquid viscosity, jet inertia, and elastic modulus of the skin-simulating material. To account for cylindrical
liquid jet penetration, a shear deformation model is proposed, in which the jet kinetic energy is dissipated through deformation of the gelatin. The model shows good agreement with experimental results and provides a unified physical basis for
liquid jet penetration.
Read the full abstract ▾
All authors Kohei Yamagata, Yuto Yokoyama, Shoto Sekiguchi, Hiroya Watanabe, Prasad Sonar, Yoshiyuki Tagawa
Optics
Cryogenic piezoelectric effects in thin film strontium titanate devices
Ahmed Khalil, Anja Ulrich, Kamal Brahim et al. (+12 more)
Next generation
quantum technologies will need to rely on efficient transduction between electrical, optical, and mechanical
quantum degrees of freedom to generate large-scale
entanglement over large distances. The performance of such transducers is fundamentally limited by the cryogenic properties of the underlying materials. Here, we demonstrate that engineering strain in ferroelectric thin-film strontium titanate ($\mathrm{SrTiO_3}$) not only results in an exceptionally large Pockels coefficient, but also in a robust linear piezoelectric response at cryogenic temperatures, surpassing previous thin-film
benchmarks. We measure piezoelectric tensor elements of $d_{15} = 151.8 \pm 1.5$ pm/V and $d_{33} = 54.8 \pm 4$ pm/V, and an effective photoelastic coefficient of $p_{\mathrm{eff}}$ = 0.56 at 5~K. Utilizing these enhanced properties, we demonstrate the first $\mathrm{SrTiO_3}$-on-
oxide acousto-optic modulator with a voltage-length product ($V_{\pi}L$) of $0.874 \pm 0.084$ V cm, outperforming state-of-the-art unreleased modulators that typically feature a $V_{\pi}L$ of a few V cm. Our results establish thin-film $\mathrm{SrTiO_3}$ as a promising material system for integrated
quantum photonics operating at cryogenic temperatures.
Read the full abstract ▾
All authors Ahmed Khalil, Anja Ulrich, Kamal Brahim, Andries Boelen, Danut-Valentin Dinu, Halil Cuma, Ioannis Petrides, Sandeep Seema Saseendran, Xavier Rottenberg, Pol Van Dorpe, Kristiaan De Greve, Oskar Painter, Clement Merckling, Frédéric Peyskens, Christian Haffner
History and Philosophy of Physics
The Causal Second Law
Balazs Gyenis
I argue that if a special science satisfies certain key assumptions that are familiar from physicalist accounts of the special sciences and from physics, then its causal regularities have an associated notion of
entropy, and that this causal
entropy cannot decrease from a robust cause to its effect. Due to its analogy with the second laws of thermodynamics and statistical physics, I call the latter conclusion the causal second law. In this paper, I clarify the key assumptions, prove the causal second law, give sufficient conditions for causal
entropy increase, relate the causal second law to statistical mechanics and thermodynamics, and argue that the reversibility objection does not threaten it. In addition, I claim that the causal second law is compatible with a non-metaphysical understanding of supervenience and the open systems view, argue that it does not imply a causal time arrow, reflect on relaxing the robustness condition, question whether it is necessary to invoke thermodynamics to show that special sciences' time arrows exist, and discuss a transition-relative-frequency-based, special-science-internal characterization of causal regularities.
Read the full abstract ▾