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Physics Physics

physics Watch Physics

Tuesday 4 November

Chemical Physics

Atomistic QM/Classical Modeling of Surface-Enhanced Infrared Absorption

Sveva Sodomaco, Piero Lafiosca, Tommaso Giovannini et al. (+1 more)

We present a multiscale quantum mechanics/classical (QM/MM) approach for modeling surface-enhanced infrared absorption (SEIRA) spectra of molecules adsorbed on plasmonic nanostructures. The molecular subsystem is described at the density functional theory (DFT) level, while the plasmonic material is represented using fully atomistic, frequency-dependent Fluctuating Charges ($\omega$FQ) and Fluctuating Charges and Dipoles ($\omega$FQF$\mu$) models. These schemes enable an accurate and computationally efficient description of the plasmonic response of both graphene-based materials and noble metal nanostructures, achieving accuracy comparable to ab initio methods. The proposed methodology is applied to the calculation of SEIRA spectra of adenine adsorbed on gold nanoparticles and graphene sheets. The quality and robustness of the approach are assessed through comparison with surface-enhanced Raman scattering (SERS) spectra and available experimental data. The results demonstrate that the proposed framework provides a reliable route to simulate vibrational responses of plasmon-molecule hybrid systems.
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All authors Sveva Sodomaco, Piero Lafiosca, Tommaso Giovannini, Chiara Cappelli

Computational Physics

Making PLUMED fly: a tutorial on optimizing performance

Daniele Rapetti, Massimiliano Bonomi, Carlo Camilloni et al. (+2 more)

PLUMED is an open-source software package that is widely used for analyzing and enhancing molecular dynamics simulations that works in conjunction with most available molecular dynamics softwares. While the computational cost of PLUMED calculations is typically negligible compared to the molecular dynamics code's force evaluation, the software is increasingly being employed for more computationally demanding tasks where performance optimization becomes critical. In this tutorial, we describe a recently implemented tool that can be used to reliably measure code performance. We then use this tool to generate detailed performance benchmarks that show how calculations of large-numbers of distances, angles or torsions can be optimized by using vector-based commands rather than individual scalar operations. We then present benchmarks that illustrate how to optimize calculations of atomic order parameters and secondary structure variables. Throughout the tutorial and in our implementations we endeavor to explain the algorithmic tricks that are being used to optimize the calculations so others can make use of these prescriptions both when they are using PLUMED and when they are writing their own codes.
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All authors Daniele Rapetti, Massimiliano Bonomi, Carlo Camilloni, Giovanni Bussi, Gareth A. Tribello

Instrumentation and Detectors

Time-based Selection of Kaonic Atom X-ray Events with Quasi-Hemispherical CZT Detectors at the DAFNE collider

Francesco Artibani, Leonardo Abbene, Antonino Buttacavoli et al. (+37 more)

This work presents the results of a time-based event selection for searching X-ray signals from kaonic atom X-ray transition using a single quasi-hemispherical Cadmium-Zinc-Telluride (CZT) detector at the DA$\Phi$NE collider. To mitigate the high background level in the measured X-ray spectrum, a dedicated event selection strategy was developed, exploiting the precise timing correlation between e+e- collisions and detector signals. This approach enabled, for the first time, the observation of two characteristic X-ray transitions from kaonic aluminum atoms using a CZT detector: for the 5-4 transition at 50~keV, 362~$\pm$~41~(stat.)~$\pm$~20~(sys.) signal events over 1698~$\pm$~197~(stat.)~$\pm$~25~(sys.) background events in 5$\sigma$ were observed, with a resolution of 9.2%~FWHM; for the 4-3 transition at 106~keV, 295~$\pm$~50~(stat.)~$\pm$~20~(sys.) signal events over 2939~$\pm$~500~(stat.)~$\pm$~16~(sys.) background events in 5$\sigma$ were measured, with a resolution of 6.6 ~FWHM. A strong background suppression of approximately 95% of the triggered data was achieved through this time-based selection. The demonstrated timing capability of the CZT detector proved highly effective in isolating time-correlated events within an 80 ns window, setting an important benchmark for the application of these semiconductors in timing-based X-ray spectroscopy. These results highlight the potential of CZT-based detection systems for future precision measurements in high-radiation environments, paving the way for compact, room-temperature X-ray and $\gamma$-ray spectrometers in fundamental physics and beyond.
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All authors Francesco Artibani, Leonardo Abbene, Antonino Buttacavoli, Manuele Bettelli, Gaetano Gerardi, Fabio Principato, Andrea Zappettini, Massimiliano Bazzi, Giacomo Borghi, Damir Bosnar, Mario Bragadireanu, Marco Carminati, Alberto Clozza, Francesco Clozza, Raffaele Del Grande, Luca De Paolis, Carlo Fiorini, Ivica Friscic, Carlo Guaraldo, Mihail Iliescu, Masahiko Iwasaki, Aleksander Khreptak, Simone Manti, Johann Marton, Pawel Moskal, Fabrizio Napolitano, Hiroaki Ohnishi, Kristian Piscicchia, Francesco Sgaramella, Michal Silarski, Diana Laura Sirghi, Florin Sirghi, Magdalena Skurzok, Antonio Spallone, Kairo Toho, Lorenzo G. Toscano, Oton Vazquez Doce, Johann Zmeskal, Catalina Curceanu, Alessandro Scordo

Atomic Physics · Cross-listed from cond-mat.quant-gas

Angular momentum of rotating fermionic superfluids by Sagnac phonon interferometry

Marcia Frómeta Fernández, Diego Hernández Rajkov, Giulia Del Pace et al. (+5 more)

Fermionic many-body systems provide an unrivaled arena to investigate how interactions drive the emergence of collective quantum behavior, such as macroscopic coherence and superfluidity. Central to these phenomena is the formation of Cooper pairs, correlated states of two fermions that behave as composite bosons and condense below a critical temperature. However, unlike elementary bosons, these pairs retain their internal structure set by underlying fermionic correlations, essential for understanding superfluid properties throughout the so-called Bose-Einstein condensate (BEC) to Bardeen-Cooper-Schrieffer (BCS) crossover – a cornerstone of strongly correlated fermionic matter. Here, we harness a sonic analog of the optical Sagnac effect to disclose the composite nature of fermionic condensates across the BEC-BCS crossover. We realize an in-situ loop interferometer by coherently exciting two counter-propagating long-wavelength phonons of an annular fermionic superfluid with tuneable interparticle interactions. The frequency degeneracy between clock- and anticlock-wise sound modes is lifted upon controllably injecting a quantized supercurrent in the superfluid ring, resulting in a measurable Doppler shift that enables us to probe the elementary quantum of circulation and the angular momentum carried by each particle in the fermionic fluid. Our observations directly reveal that the superflow circulation is quantized in terms of $h/2m$, where $m$ is the mass of the constituents, in striking contrast to bosonic condensates where $h/m$ is the relevant circulation quantum. Further, by operating our interferometer at tunable temperature, we measure the thermal depletion of the superfluid in the unitary Fermi gas, demonstrating phonon interferometry as a powerful technique for probing fundamental properties of strongly-correlated quantum systems.
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All authors Marcia Frómeta Fernández, Diego Hernández Rajkov, Giulia Del Pace, Nicola Grani, Massimo Inguscio, Francesco Scazza, Sandro Stringari, Giacomo Roati

Physics and Society

Stochastic Redistribution of Indistinguishable Items in Shared Habitation: A Multi-Agent Simulation Framework

Syed Haseeb Shah

This paper presents a discrete-event stochastic model for the redistribution of indistinguishable personal items, exemplified by socks, among multiple cohabitants sharing a communal laundry system. Drawing on concepts from ecological population dynamics, diffusion processes, and stochastic exchange theory, the model captures the probabilistic mechanisms underlying item mixing, recovery, and loss. Each cohabitant is represented as an autonomous agent whose belongings interact through iterative cycles of collective washing, sorting, and partial correction. The system's evolution is characterized by random mixing events, selective recollection, and attrition over time. Implemented using the SimPy discrete-event simulation framework, the model demonstrates that even minimal exchange probabilities can generate emergent asymmetries, quasi-equilibrium distributions, and long-term disorder. The findings illustrate how stochastic processes inherent to shared domestic systems can produce persistent imbalances, offering a quantitative perspective on an everyday social phenomenon.
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Chemical Physics

Atom-centered electric multipole moments dynamically generated from QM/MM MD simulations

Andrea Levy, Andrej Antalík, Jógvan Magnus Haugaard Olsen et al. (+1 more)

Atom-centered electric multipole moments can be extremely useful in chemistry as they enable the systematic mapping of a complex electrostatic problem to a simpler model. However, since they do not correspond to physical observables, there is no unique way to define them. In this work, we present an extension of the dynamically generated RESP charges (D-RESP) method, referred to as xDRESP, where atom-centered multipoles are computed from mixed quantum mechanics/molecular mechanics (QM/MM) molecular dynamics simulations. We compare the ability of xDRESP charges to reproduce the electrostatic potential, as well as molecular multipoles, against the performance of fixed point-charge models commonly used in force fields. Moreover, we highlight cases where DRESP atomic multipoles can provide valuable information about chemical systems, such as indicating when polarization plays a significant role, and chemical reactions, in which xDRESP atomic multipoles can be used as an on-the-fly analysis tool to track changes in electron density.
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All authors Andrea Levy, Andrej Antalík, Jógvan Magnus Haugaard Olsen, Ursula Rothlisberger

Biological Physics · Cross-listed from q-bio.BM

Machine Learning for RNA Secondary Structure Prediction: a review of current methods and challenges

Giuseppe Sacco, Giovanni Bussi and Guido Sanguinetti

Predicting the secondary structure of RNA is a core challenge in computational biology, essential for understanding molecular function and designing novel therapeutics. The field has evolved from foundational but accuracy-limited thermodynamic approaches to a new data-driven paradigm dominated by machine learning and deep learning. These models learn folding patterns directly from data, leading to significant performance gains. This review surveys the modern landscape of these methods, covering single-sequence, evolutionary-based, and hybrid models that blend machine learning with biophysics. A central theme is the field's "generalization crisis," where powerful models were found to fail on new RNA families, prompting a community-wide shift to stricter, homology-aware benchmarking. In response to the underlying challenge of data scarcity, RNA foundation models have emerged, learning from massive, unlabeled sequence corpora to improve generalization. Finally, we look ahead to the next set of major hurdles-including the accurate prediction of complex motifs like pseudoknots, scaling to kilobase-length transcripts, incorporating the chemical diversity of modified nucleotides, and shifting the prediction target from static structures to the dynamic ensembles that better capture biological function. We also highlight the need for a standardized, prospective benchmarking system to ensure unbiased validation and accelerate progress.
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2511.02622 · 4 Nov · 22 pages, 3 figures. Updated version of the article published in RNA 32(4):443-456 (2026); the Foundation Models section has been revised to reflect developments since publication. The remainder of the manuscript is unchanged apart from formatting

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Instrumentation and Detectors · Cross-listed from cond-mat.mtrl-sci

Exploring mechanisms leading to composition errors in monazite (CePO4) analysed with atom probe tomography

Tom Veret, Fabien Delaroche, Ivan Blum et al. (+6 more)

Monazite (CePO4) is widely used in U-Th-Pb geochronology due to its reliable age determinations, although isotopic disturbances often require nanoscale investigation to better understand the mechanisms at play. Atom Probe Tomography (APT) offers unique capabilities for nanoscale chemical analysis and 3D atomic reconstruction but presents challenges for insulating materials such as CePO4, particularly due to oxygen loss during field evaporation. This study investigates the effects of laser wavelength, energy, metallic coatings and detection device on mass spectrum optimization and compositional accuracy in synthetic CePO4 samples. Results show that shorter laser wavelengths (260 nm) enhance peak resolution, particularly when combined with advanced reflectron configurations, as demonstrated with the LEAP 6000 XR. Chromium coatings further improve thermal dissipation and reduce noise levels. However, compositional measurements reveal systematic underestimation of oxygen and overestimation of P and Ce, likely influenced by preferential low-field element evaporation. These findings highlight the need to carefully tune experimental parameters to mitigate quantification biases and enhance the reliability of APT analyses for geological materials.
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All authors Tom Veret, Fabien Delaroche, Ivan Blum, Jonathan Houard, Benjamin Klaes, Isabelle Mouton, Frederic De-Geuser, Anne-Magali Seydoux-Guillaume, François Vurpillot

Fluid Dynamics

Generalizable super-resolution turbulence reconstruction from minimal training data

Wu Haokai, Cao Yong, Chen Yaoran et al. (+4 more)

Fully resolving turbulent flows remains challenging due to turbulent systems' multiscale complexity. Existing data-driven approaches typically demand expensive retraining for each flow scenario and struggle to generalize beyond their training conditions. Leveraging the universality of small-scale turbulent motions (Kolmogorov's K41 theory), we propose a Scale-oriented Zonal Generative Adversarial Network (SoZoGAN) framework for high-fidelity, zero-shot turbulence generation across diverse domains. Unlike conventional methods, SoZoGAN is trained exclusively on a single dataset of moderate-Reynolds-number homogeneous isotropic turbulence (HIT). The framework employs a zonal decomposition strategy, partitioning turbulent snapshots into subdomains based on scale-sensitive physical quantities. Within each subdomain, turbulence is synthesized using scale-indexed models pre-trained solely on the HIT database. SoZoGAN demonstrates high accuracy, cross-domain generalizability, and robustness in zero-shot super-resolution of unsteady flows, as validated on untrained HIT, turbulent boundary layer, and channel flow. Its strong generalization, demonstrated for homogenous and inhomogenous turbulence cases, suggests potential applicability to a wider range of industrial and natural turbulent flows. The scale-oriented zonal framework is architecture-agnostic, readily extending beyond GANs to other deep learning models.
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All authors Wu Haokai, Cao Yong, Chen Yaoran, Laima Shujin, Chen Wenli, Zhou Dai, Li Hui

Computational Physics · Cross-listed from cs.IT

Redundancy Maximization as a Principle of Associative Memory Learning in Hopfield Networks

Mark Blümel, Andreas C. Schneider, Valentin Neuhaus et al. (+5 more)

Associative memory, traditionally modeled by Hopfield networks, enables the retrieval of previously stored patterns from partial or noisy cues. Yet, the local computational principles which are required to enable this function remain incompletely understood. To formally characterize the local information processing in such systems, we employ a recent extension of information theory – Partial Information Decomposition (PID). PID decomposes the contribution of different inputs to an output into unique information from each input, redundant information across inputs, and synergistic information that emerges from combining different inputs. Applying this framework to individual neurons in classical Hopfield networks we find that below the memory capacity, the information in a neuron's activity is characterized by high redundancy between the external pattern input and the internal recurrent input, while synergy and unique information are close to zero until the memory capacity is surpassed and performance drops steeply. Inspired by this observation, we use redundancy maximization at each neuron as an information-theoretic learning goal. This dramatically increases the network's memory capacity to 1.59, a more than tenfold improvement over the 0.14 capacity of classical Hopfield networks, and also outperforming recent state-of-the-art implementations of Hopfield networks. Overall, this work establishes redundancy maximization as a new design principle for associative memories and opens pathways for new associative memory models based on information-theoretic goals.
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All authors Mark Blümel, Andreas C. Schneider, Valentin Neuhaus, David A. Ehrlich, Marcel Graetz, Michael Wibral, Abdullah Makkeh, Viola Priesemann

Optics

Routes for Light Management in Monolithic Perovskite/Silicon Tandem Solar Cells

Michel Gaglioni Rocha and Emiliano Rezende Martins

Fully-textured perovskite/silicon tandem solar cells have emerged as promising candidates for next-generation photovoltaics. The optical functions of full texturing, however, are not yet fully understood. A key challenge is the requirement for perovskite layer texturing, which often leads to increased electrical losses. Here, we elucidate the distinct optical roles of front and rear textures in tandem configurations using optical simulations and use these insights to propose a new architecture that eliminates the need for perovskite surface texturing. We demonstrate that our proposed structure achieves optical results comparable to those of fully-textured devices, while its planar perovskite layer has the potential to reduce electrical losses. The high optical performance also results in higher efficiency if a texture-induced voltage loss as low as 50 mV is assumed, which is about six times lower than the loss of fully-textured devices, thus enabling higher efficiencies within a simplified design. Our results show that perovskite texturing is not essential for optimal light management, thus opening the way to combine efficient light management with high electrical performance.
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Chemical Physics

Single-particle detection of a semiconductor-to-metal transition by scanning dielectric microscopy

Ruben Millan-Solsona, José A. Ruiz-Torres, Carlos Moya et al. (+5 more)

Hybrid nanostructures that combine semiconducting and metallic components offer great potential for photothermal therapy, optoelectronics, and sensing, by integrating tunable optical properties with enhanced light absorption and charge transport. Boosting the integrated performance of these hybrid systems demands techniques capable of probing local variations of the physical properties inaccessible to bulk analysis. Here, we report the single-particle dielectric characterization of hybrid, semiconducting bismuth sulfide (Bi$_2$S$_3$) nanorods (NR) decorated with metallic Au nanoparticles (NP), employing scanning dielectric microscopy, which uses electrostatic force microscopy in combination with finite-element numerical simulations. We reveal a pronounced enhancement in the local dielectric response of Bi$_2$S$_3$ upon Au decoration, attributed to interfacial polarization and electron transfer from Au to the Bi$_2$S$_3$ matrix, thus suggesting a semiconductor-to-metal-like transition at the single-particle level. Numerical simulations show that the response is dominated by the vertical component of the permittivity and that the decorating metallic Au NP produce only moderate shielding of the semiconductor Bi$_2$S$_3$ NR core, indicating that the large increase in the dielectric response originates primarily from intrinsic modifications within the NR. Overall, these findings provide direct insight into structure–property relationships at the single-particle level, supporting the rational design of advanced hybrid nanostructures with tailored electronic functionalities.
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All authors Ruben Millan-Solsona, José A. Ruiz-Torres, Carlos Moya, Arantxa Fraile Rodríguez, Adriana I. Figueroa, Gabriel Gomila, Amílcar Labarta, Xavier Batlle

Fluid Dynamics · Cross-listed from cond-mat.quant-gas

Polarization-controlled pattern formation in antiparallel dipolar binary condensates

Zhijun Zhang, Weijing Bao, Changjian Yu et al. (+3 more)

We investigate non-equilibrium pattern formation in an antiparallel two-component dipolar Bose-Einstein condensate by varying the polarization angle and the trap aspect ratio. At finite tilt, the condensate supports stripe order. Quenching the angle to zero triggers a roton-assisted, mushroom-like corrugation that destroys translational order and drives the system into labyrinthine textures, whereas a slow linear ramp produces long-lived curved stripes that ultimately converge to labyrinths. Population imbalance strongly biases the evolution: the minority component preferentially fragments into a stable droplet array while the majority remains comparatively diffuse; once formed, the droplet crystal is robust under polarization hysteresis with largely reversible shape changes and unchanged lattice topology. The trap aspect ratio controls both the initial stripe number and the instability timescale, with tighter axial confinement accelerating corrugation and yielding denser labyrinths at late times. All behaviors arise within a quasi-two-dimensional mean-field regime where beyond-mean-field corrections are negligible; accordingly, the droplets reported here are not self-bound in free space. The observed textures (such as stripes, curved stripes, and labyrinths) mirror the taxonomy and instability pathways of nuclear "pasta" morphologies (rods and slabs) known from neutron-star and supernova matter, highlighting polarization angle, trap geometry, and population imbalance as practical, experimentally accessible controls for selecting and steering patterns in dipolar mixtures.
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All authors Zhijun Zhang, Weijing Bao, Changjian Yu, Jinbin Li, Gentaro Watanabe, Kui-Tian Xi

Instrumentation and Detectors

Pulse shape simulation for the reduced charge collection layer in p-type high-purity germanium detectors

P. Zhang, W. Dai, Q. Zhang et al. (+8 more)

$P$-type high-purity germanium (HPGe) detectors are widely used across many scientific domains, and current data analysis methods have served well in many use cases. However, applications like low-background experiments that search for rare physics, such as dark matter, neutrinoless double-beta decay, and coherent elastic neutrino-nucleus scattering, could profit a lot from a more detailed understanding of the detector response close to the surface. The outer $n^+$ electrode of the $p$-type HPGe detector forms a layer with reduced charge collection, and events originating here can be a critical background source in such experiments. If the difference in detector pulse shape between detector surface and bulk events is known, it can be used to identify and veto these background events. However, a faithful simulation of the detector response in this surface region is difficult and has not been available as a standard method so far. We present a novel three-dimensional pulse shape simulation method for this reduced charge collection (RCC) layer. We have implemented this method as a new feature in the open-source simulation package \emph{SolidStateDetectors$.$jl} and show a validation of the numerical simulation results with analytical calculations. An experimental study using a $p$-type HPGe detector also validates our approach. The current implementation supports $p$-type HPGe detectors of fairly arbitrary geometry, but is easily adaptable to $n$-type detectors by adjusting the impurity density profile of the layer. It should also be adaptable to other semiconductor materials in a straightforward fashion.
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All authors P. Zhang, W. Dai, Q. Zhang, F. Hagemann, O. Schulz, C. Alvarez-Garcia, L. Yang, Q. Yue, Z. Zeng, J. Cheng, H. Ma

Instrumentation and Detectors

Neutron Interaction Properties of Structural Materials for Multi-Grid Neutron Detectors

A.Backis, C.-C.Lai, M.Aouane et al. (+5 more)

The T-REX neutron time-of-flight spectrometer at the European Spallation Source will use Multi-Grid Technology, which relies on thin B4C coatings on the Al blades of the grids to detect scattered thermal neutrons. Following a Monte Carlo study of internal shielding to suppress neutron multiple scattering in T-REX, the neutron transmission and scattering properties of 12 shielding-material samples have been measured at the ISIS spallation neutron source. Neutron transmission was measured on the EMMA beam line at wavelengths 0.5-4.7 A, using a 2D-position-sensitive, neutron GEM detector, while neutron scattering was measured for 6 of the samples at the Merlin spectrometer, at wavelengths 0.72, 1.28, 1.85 and 2.41 A. The present tests show that a B4C/Al composite material, plated with Ni to stop intrinsic alpha background, is an effective neutron absorber, suitable for incorporation in the Multi-Grid structures which detect the neutrons in inelastic neutron spectrometers .
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All authors A.Backis, C.-C.Lai, M.Aouane, P.P.Deen, K.G.Fissum, J.R.M.Annand, K.Livingston, D.Raspino

Biological Physics · Cross-listed from cond-mat.soft

Vorticity-induced surfing and trapping in porous media

Pallabi Das, Mirko Residori, Axel Voigt et al. (+2 more)

Microorganisms often encounter strong confinement and complex hydrodynamic flows while navigating their habitats. Combining finite-element methods and stochastic simulations, we study the interplay of active transport and heterogeneous flows in dense porous channels. We find that swimming always slows down the traversal of agents across the channel, giving rise to robust power-law tails of their exit-time distributions. These exit-time distributions collapse onto a universal master curve with a scaling exponent of $\approx 3/2$ across a wide range of packing fractions and motility parameters, which can be rationalized by a scaling relation. We further identify a new motility pattern where agents alternate between surfing along fast streams and extended trapping phases, the latter determining the power-law exponent. Unexpectedly, trapping occurs in the flow backbone itself – not only at obstacle boundaries – due to vorticity-induced reorientation in the highly-heterogeneous fluid environment. These findings provide a fundamentally new active transport mechanism with direct implications for biofilm clogging and the design of novel microrobots capable of operating in heterogeneous media.
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All authors Pallabi Das, Mirko Residori, Axel Voigt, Suvendu Mandal, Christina Kurzthaler

Chemical Physics

Unlocking n-alk-1-ynes Conformers: Quantum "Trigger Finger" versus "Stiff Joint" Conformations

Ioan Bâldea

Molecular conformation in n-alk-1-ynes (CnA) is conventionally simplified to an all-planar structure. We report a comprehensive quantum chemical analysis revealing two near-isoenergetic rotamers at the acetylenic terminus: planar (C$_s$) and skewed (C$_1$). The high, symmetric rotational energy barrier ($\approx 150$\,meV) arises from unique steric relief near the $\mathrm{sp}$ center coupled with electronic stabilization of C$_1$. This creates a unique kinetic profile: a Quantum “Trigger Finger” ($\alpha$ rotation) that enforces an $\approx 50\%:\,50\%$ $\mathrm{C}_s/\mathrm{C}_1$ ensemble, sharply contrasting with the thermodynamically biased “Stiff Joint” ($\delta$ rotation) of the alkyl chain. This structural degeneracy necessitates ensemble averaging for spectroscopic data interpretation, while the slow interconversion permits kinetic trapping and intentional conformer enrichment during synthesis and molecular junction fabrication. Our work redefines the alkyne anchor, providing a blueprint for accurate interpretation of spectroscopic data and achieving conformational control in molecular electronics.
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Instrumentation and Detectors

Demonstration of Sub-Percent Energy Resolution in the NEXT-100 Detector

NEXT Collaboration: M. Pérez Maneiro, M. Martínez-Vara, S. Torelli et al. (+110 more)

NEXT-100 is a high-pressure xenon time projection chamber with electroluminescent amplification, designed to operate with up to approximately 70.5 kg at 13.5 bar. It is the most recent detector developed by the NEXT collaboration to search for the neutrinoless double-beta decay ($\beta\beta 0\nu$) of Xe-136. The NEXT gas TPC technology offers the best energy resolution near the Q-value of the decay ($Q_{\beta\beta}$ = 2458 keV) among xenon detectors, which is set by design to be <1% FWHM. We report here the high-energy calibration of the detector using a Th-228 source, demonstrating linear response and an energy resolution of $(0.90 \pm 0.02)$% FWHM at the Tl-208 photopeak (2615 keV). This performance extrapolates to a resolution at the double-beta decay end-point of $R(Q_{\beta\beta})$ = $(0.93 \pm 0.02)$% FWHM, confirming the detector's capability for precision energy measurement in the search for $\beta\beta 0\nu$.
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All authors NEXT Collaboration: M. Pérez Maneiro, M. Martínez-Vara, S. Torelli, G. Martínez-Lema, P. Novella, J.A. Hernando Morata, J.J. Gómez-Cadenas, C. Adams, H. Almazán, V. Álvarez, A.I. Aranburu, L. Arazi, I.J. Arnquist, F. Auria-Luna, S. Ayet, Y. Ayyad, C.D.R. Azevedo, K. Bailey, F. Ballester, J.E. Barcelon, M. del Barrio-Torregrosa, A. Bayo, J.M. Benlloch-Rodríguez, F.I.G.M. Borges, A. Brodoline, N. Byrnes, A. Castillo, E. Church, L. Cid, M. Cid, X. Cid, C.A.N. Conde, C. Cortes-Parra, F.P. Cossío, R. Coupe, E. Dey, P. Dietz, C. Echeverria, M. Elorza, R. Esteve, R. Felkai, L.M.P. Fernandes, P. Ferrario, F.W. Foss, Z. Freixa, J. García-Barrena, J.W.R. Grocott, R. Guenette, J. Hauptman, C.A.O. Henriques, P. Herrero-Gómez, V. Herrero, C. Hervés Carrete, Y. Ifergan, A.F.B. Isabel, B.J.P. Jones, F. Kellerer, L. Larizgoitia, A. Larumbe, F. Lopez, N. López-March, R. Madigan, R.D.P. Mano, A. Marauri, A.P. Marques, J. Martín-Albo, A. Martínez, R.L. Miller, K. Mistry, J. Molina-Canteras, F. Monrabal, C.M.B. Monteiro, F.J. Mora, K.E. Navarro, D.R. Nygren, E. Oblak, J. Palacio, B. Palmeiro, I. Parmaksiz, A. Pazos, J. Pelegrin, M. Querol, J. Renner, I. Rivilla, C. Rogero, L. Rogers, B. Romeo, C. Romo-Luque, E. Ruiz-Chóliz, P. Saharia, F.P. Santos, J.M.F. dos Santos, M. Seemann, I. Shomroni, A.L.M. Silva, P.A.O.C. Silva, A. Simón, S.R. Soleti, M. Sorel, J. Soto-Oton, J.M.R. Teixeira, S. Teruel-Pardo, J.F. Toledo, C. Tonnelé, J. Torrent, A. Trettin, P.R.G. Valle, M. Vanga, P. Vázquez Cabaleiro, J.F.C.A. Veloso, J.D. Villamil, J. Waiton, A. Yubero-Navarro

Optics · Cross-listed from cond-mat.other

Deterministic generation of single B centers in hBN by one-to-one conversion from UV centers

Andrés Núñez Marcos, Christophe Arnold, Julien Barjon et al. (+3 more)

Among the variety of quantum emitters in hexagonal boron nitride (hBN), blue-emitting color centers, or B centers, have gathered a particular interest owing to their excellent quantum optical properties. Moreover, the fact that they can be locally activated by an electron beam makes them suitable for top-down integration in photonic devices. However, in the absence of a real-time monitoring technique sensitive to individual emitters, the activation process is stochastic in the number of emitters, and its mechanism is under debate. Here, we implement an in-situ cathodoluminescence monitoring setup capable of detecting individual quantum emitters in the blue and ultraviolet (UV) range. We demonstrate that the activation of individual B centers is spatially and temporally correlated with the deactivation of individual UV centers emitting at 4.1 eV, which are ubiquitous in hBN. We then make use of the ability to detect individual B center activation events to demonstrate the controlled creation of an array with only one emitter per irradiation site. Additionally, we demonstrate a symmetric technique for heralded selective deactivation of individual emitters. Our results provide insights into the microscopic structure and activation mechanism of B centers, as well as versatile techniques for their deterministic integration.
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All authors Andrés Núñez Marcos, Christophe Arnold, Julien Barjon, Stéphanie Buil, Jean-Pierre Hermier, Aymeric Delteil

Computational Physics · Cross-listed from cond-mat.mtrl-sci

Ultrafast magnetic moment transfer and bandgap renormalization in monolayer FeCl$_2$

Yu-Hui Song, Huan-Cheng Yang, Kai Liu et al. (+1 more)

The microscopic origin of laser-induced ultrafast demagnetization remains an open question, to which the non-thermal electronic distribution plays a vital role at the initial stage. Herein, we investigate the connection between the non-thermal electronic distribution and the ultrafast spin dynamics as well as the electronic structure evolution in ferromagnetic FeCl$_2$ monolayer using real-time time-dependent density functional theory (rt-TDDFT) with self-consistent Hubbard $U$ correction. Our simulations reveal that femtosecond laser pulses induce ultrafast magnetic moment transfer from Fe to Cl atoms. More importantly, through a comprehensive analysis of orbital-resolved electronic structure, we elucidate the microscopic origin of this transfer, attributing it to specific intra-atomic and inter-atomic charge transfer pathways driven by non-thermal excitations. The extent of demagnetization of Fe atoms exhibits a non-monotonic dependence on the laser photon energy, reaching a maximum at the resonant excitation. In addition, the dynamical evolution of the band structure was studied based on the eigenstates of the instantaneous Hamiltonian. Under resonant excitation, the bandgap reduction reaches up to $41\%$ within tens of fs. These findings provide fundamental insights into ultrafast spin control and suggest a strategy to optically engineer the magnetism in two-dimensional magnetic materials.
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All authors Yu-Hui Song, Huan-Cheng Yang, Kai Liu, Zhong-Yi Lu

Optics

Demonstration of on-chip all-optical switching of magnetization in integrated photonics

Pingzhi Li, Gijs W.A. Simons, Tianyu Zhang et al. (+7 more)

Ultrafast all-optical magnetization switching (AOS) holds great promise for nextgeneration spintronic memory and hybrid spintronic-photonic systems. However, most implementations to date rely on bulky free-space optical setups, limiting scalability and practical integration. As a critical step toward integrated applications, we demonstrate single-pulse AOS within a silicon nitride (Si3N4) photonic integrated circuit. Using trains of femtosecond laser pulses guided through on-chip waveguides, we achieve deterministic toggle switching in a sub-micron out-of-plane Co/Gd Hall cross patterned directly atop the photonic waveguide. Electrical readout via the anomalous Hall effect reveals a switching contrast of up to 90% for 500 nm-wide devices. In larger Hall crosses, the contrast decreases and switching becomes stochastic, consistent with spatially non-uniform optical absorption as confirmed by finite-element simulations. This behavior is hypothetically attributed to domain wall relaxation and thermally assisted (de)pinning processes within partially switched regions. Our results highlight the critical role of device scaling in achieving robust on-chip AOS and establish a foundation for ultrafast, energy-efficient, and fully integrated spintronic-photonic platforms.
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All authors Pingzhi Li, Gijs W.A. Simons, Tianyu Zhang, Philip P.J. Schrinner, Sohrab Kamyar, Ronald Dekker, Diana C. Leitao, Reinoud Lavrijsen, Yuqing Jiao, Bert Koopmans

Chemical Physics

Vertical Excitation Energies of Embedded Systems: The Vertical Excitation Model (VEM) within Polarizable QM/MM

Chiara Sepali, Piero Lafiosca, Linda Goletto et al. (+2 more)

Polarizable Quantum Mechanics/Molecular Mechanics (QM/MM) approaches based on fluctuating charges and dipoles (QM/FQ(F$\mu$)) are formulated within the state-specific Vertical Excitation Model (VEM) to compute vertical excitation energies of solvated systems. This methodology overcomes the limitations of the widely used Linear Response (LR) approach. While LR can capture the dynamic response of the solvent to the QM transition density, it neglects the solvent reorganization that follows solute relaxation upon electronic excitation. In contrast, the VEM framework explicitly accounts for this effect. Benchmark calculations of vertical excitation energies using QM/FQ(F$\mu$) are reported for a representative set of solutes - acrolein, acetone, caffeine, p-nitroaniline, coumarin 153, doxorubicin, and betaine-30 - comparing VEM with LR, corrected LR (cLR), and cLR 2 schemes. The results reveal notable variations in solvent response depending on the character of the electronic transition and demonstrate that optimal accuracy can be achieved by selecting the most appropriate model for each specific system and excitation.
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All authors Chiara Sepali, Piero Lafiosca, Linda Goletto, Tommaso Giovannini, Chiara Cappelli

Geophysics

Hydrogen site-dependent physical properties of hydrous magnesium silicates: implications for water storage and transport in the mantle transition zone

Zifan Wang, Yu He, Ho-kwang Mao et al. (+1 more)

The Earth's mantle transition zone (MTZ) is widely recognized as a major water reservoir, exerting significant influence on the planet's water budget and deep cycling processes. Here, we employ crystal structure prediction and first-principles calculations to identify a series of stable hydrous magnesium silicate phases under transition zone conditions. Our results reveal a pressure-induced hydrogen substitution mechanism in wadsleyite, where H+ preferentially migrates from Mg2+ sites to Si4+ sites near 410 km depth. This transformation leads to a substantial decrease in electrical conductivity, consistent with geophysical observations. We estimate the water content in the MTZ to be approximately 1.6 wt%, aligning with seismic and conductivity constraints. Furthermore, using machine learning-enhanced molecular dynamics, we discover double superionicity in hydrous wadsleyite and ringwoodite at temperatures exceeding 2000 K, wherein both H+ and Mg2+ exhibit high ionic mobility. This dual-ion superionic state has potentially profound implications for mass transport, electrical conductivity, and magnetic dynamo generation in rocky super-Earth exoplanets.
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All authors Zifan Wang, Yu He, Ho-kwang Mao, Duck Young Kim

Classical Physics

Characterization Of Cyclic Hygrothermal Swelling And Shrinkage Behavior Of Balsa Wood And Gfrp-Balsa Sandwich Structures

Yuan Wu, Pascal Casari, Jamal Fajoui et al. (+2 more)

The objective of developing bio-based composite sandwich structures with greener core materials is to facilitate the decarbonization of industries such as aviation and maritime. This field of research has received increasing attention over the past decades. For example, balsa wood has emerged as a highly promising alternative to foam or honeycomb cores, offering a lightweight, rapidly renewable and cost-effective solution. However, plant fibers such as balsa wood and flax often display high hydrophilic behavior, which could affect their mechanical performance and long-term durability. It is therefore imperative to promote further research into the characterization of the cyclic hygrothermal aging behavior of balsa wood core sandwich structures, in particular the identification of moistureinduced strains and internal stresses in the skins and cores, as well as the investigation of moisture desorption processes and the associated thermal shrinkage phenomena in wood fibers, resins and glass fibers. Accordingly, this work employs two complete moisture absorption-desorption cycles to characterize the moisture diffusion behavior of specimens comprising three different materials, including the pure balsa wood, resin-infused balsa and balsa core sandwich structures with two Glass-Fiber-Reinforced-Polymer (GFRP) skins. The changes in moisture content and hygroscopic strains in the thickness, length and width directions of all specimens were investigated with a view to identifying the hygroscopic swelling and thermal shrinkage behaviors exhibited during long-term aging cycles.
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All authors Yuan Wu, Pascal Casari, Jamal Fajoui, Sylvain Fréour, Mouna Bouziane

Plasma Physics

Simulation of multi-species kinetic instabilities with the Numerical Flow Iteration

Rostislav-Paul Wilhelm and Manuel Torrilhon

Kinetic instabilities are one of the most challenging aspects in computational plasma physics. Accurately capturing their onset and evolution requires fine resolution of the high-dimensional distribution functions of each relevant species, which quickly becomes computationally prohibitively expensive. Additionally, plasma dynamics is an inherently multi-scale phenomenon due to the vast separation of scales between heavy ions and light-weight electrons. In previous work the Numerical Flow Iteration (NuFI) was suggested as a high-fidelity alternative with reduced memory complexity making it an interesting candidate to simulate complicated kinetic instabilities. In this work we extend NuFI to non-periodic boundary conditions and demonstrate how it is possible to reduce the computational complexity to allow for longer simulation periods.
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Instrumentation and Detectors

Yield and performance validation of the Monolithic Stitched Sensor (MOSS), the first wafer-scale prototype for the ALICE ITS3 upgrade

Marius Wilm Menzel

The ALICE Inner Tracking System upgrade (ITS3) will employ stitched, wafer-scale Monolithic Active Pixel Sensors (MAPS) for the first time in high-energy physics, achieving a material budget of only 0.09$\,$%$\,$X$\mathrm{_{0}}$ per layer. Its first stitched prototype, the Monolithic Stitched Sensor (MOSS), underwent serial testing confirming sensor yield compliance with ITS3 requirements. In-beam tests show the device meets the ITS3 efficiency requirement of >$\,$99$\,$% while maintaining a fake-hit rate below 0.1$\,$hits/pixel/s, with performance sustained up to irradiation levels of 4$\,$kGy and $4\times10^{12}$1MeV$\,$n$\mathrm{_{eq}}\,$cm$\mathrm{^{-2}}$. The sensor demonstrates excellent charge-collection properties and linearity between time-over-threshold and deposited energy in the 1.8 - 6.5$\,$keV range in response to soft X-ray emissions. This article provides an overview of the validation steps and characterisation results.
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Plasma Physics

Laser diagnostics for negative ion source optimization: insights from SPIDER at the ITER Neutral Beam Test Facility

R. Agnello, M. Barbisan, R. Pasqualotto et al. (+4 more)

The ITER Heating Neutral Beams (HNBs) require large, high-energy H/D atom beams (285/330 A/m^2 extracted current density, and 1/0.87 MeV acceleration energy, respectively for H and D). To address the associated challenges, the SPIDER negative ion RF beam source at the Neutral Beam Test Facility (NBTF) in Padova (Italy) serves as a full-scale source prototype with a 100 kV triode accelerator, for design validation and performance verification. SPIDER is equipped with two advanced laser diagnostics to monitor key plasma parameters; Cavity Ring-Down Spectroscopy (CRDS) is used to measure H$^-$\slash D$^-$ ion densities, while Laser Absorption Spectroscopy (LAS) tracks caesium neutral density in the source. These measurements are essential for optimizing negative ion production and meeting ITER source targets. We present diagnostic upgrade details, recent experimental results, and correlations with other machine parameters. Since CRDS relies on a single 4.637-meter-long optical cavity, the longest used in such sources, it has demonstrated sensitivity to alignment. Based on recent experimental experience, structural improvements are being implemented to enhance both stability and measurement reliability. LAS has mainly been employed as a tool to monitor the caesium conditioning status of SPIDER. Additionally, due to a distributed measurement over four lines of sight, LAS has proven effective in monitoring the caesium distribution within the source. This work demonstrates the essential role of laser diagnostics in developing ITER-relevant plasma sources and informs ongoing efforts to improve measurement accuracy in challenging environments.
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All authors R. Agnello, M. Barbisan, R. Pasqualotto, B. Pouradier-Duteil, E. Sartori, A. Tiso, B. Zaniol

Applied Physics · Cross-listed from quant-ph

Temporal filtered quantum sensing with the nitrogen-vacancy center in diamond

Florian Boehm, Yan Liu, Chengliang Yue et al. (+5 more)

Nitrogen vacancy centers in diamond are among the leading solid state quantum platforms, offering exceptional spatial resolution and sensitivity for applications such as magnetic field sensing, thermometry, and bioimaging. However, in high background environments,such as those encountered in in vitro diagnostics, the performance of NV based sensors can be compromised by strong background fluorescence, particularly from substrates such as nitrocellulose. In this work, we analytically and experimentally investigate the use of pulsed laser excitation combined with time gating techniques to suppress background fluorescence and enhance the signal to noise ratio in NV based quantum sensing, with an emphasis on spin enhanced biosensing. Through experimental studies using mixed ensembles of silicon vacancy and NV centers in bulk diamond, as well as fluorescent nanodiamonds on NC substrates, we demonstrate significant improvements in NV spin resonance visibility, demonstrated by an increase of the SNR by up to 4x, and a resulting measurement time reduction by 16x. The presented technique and results here can help significantly increase the readout efficiency and speed in future applications of NV centers in high background environments, such as in IVD, where the NV centers are used as a fluorescent label for biomolecules.
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All authors Florian Boehm, Yan Liu, Chengliang Yue, Xianqi Dong, Huaxue Zhou, Dong Wu, E Wu, Renfu Yang

Instrumentation and Detectors

Status of the HENSA collaboration at the Canfranc Underground Laboratory: results from two years of measurement of the neutron flux in hall B

N. Mont-Geli, A. Tarifeño-Saldivia, G. Cortés et al. (+29 more)

Thiswork deals with the characterization of the neutron flux in hall B of the CanfrancUnderground Laboratory (LSC) employing the High Efficiency Neutron Spectrometry Array (HENSA). The ultimate goal of this measurement is to set a limit on the corresponding effects of the neutron flux in the background of the ANAIS-112 experiment. The preliminary neutron counting rates of two years of measurement are reported. Various data analysis techniques, including pulse shape discrimination, are discussed. The first results on the spectral reconstruction of the neutron flux are also presented.
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All authors N. Mont-Geli, A. Tarifeño-Saldivia, G. Cortés, J. L. Tain, M. Grieger, A. Quero-Ballesteros, M. Pallàs, J. Agramunt, A. Algora, J. Amaré, D. Bemmerer, F. Calviño, D. Cano-Ott, S. Cebrián, D. Cintas, I. Coarasa, A. De Blas, I. Dillman, L. M. Fraile, E. García, R. Garcia, A. M. Lallena, M. Martínez, T. Martínez, E. Nacher, S. E. A. Orrigo, Y. Ortigoza, A. Ortiz de Solórzano, T. Pardo, J. Plaza, J. Puimedón, M. L. Sarsa

Applied Physics

Monochromatic Electron Emission from Graphene-Insulator-Semiconductor-Structured Electron Source Utilizing Interference Efficets

Takao Koichi, Shogo Kawashima, Hiroshi Miyake et al. (+4 more)

The graphene-insulator-semiconductor-structured electron source has garnered significant attention due to its high electron emission efficiency and highly monochromatic electron emission. Graphene, with its c-axis orientation and well-defined interlayer spacing, exhibits electron interference effects that can influence the properties of emitted electrons. In this work, motion of an electron wave packet is numerically calculated to discuss the energy spread of the zero-order and first-order diffracted electron waves by mono- and multilayer graphene. It is found that the effects of multiple reflections of electron between the layers broaden the energy spread especially for the incident energy of 13.4 eV, and that highly monochromatic electron emission can be achieved by using diffracted electron wave with a small aperture.
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All authors Takao Koichi, Shogo Kawashima, Hiroshi Miyake, Satoshi Abo, Fujio Wakaya, Masayoshi Nagao, Katsuhisa Murakami