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Physics

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Wednesday 10 June

Soft Condensed Matter

Perspective: The Physics of Active Solids – From Hamiltonians to Active Matter Models

Antik Bhattacharya, Jürgen Horbach and Smarajit Karmakar

The physics of active matter, wherein constituent particles consume energy to generate autonomous motion, has revolutionized non-equilibrium statistical mechanics. While a large body of work has successfully elucidated the behavior of dilute active systems, the dense regime – characterized by “active glasses and active solids” – presents profound challenges that defy conventional theoretical frameworks. Recent observations reveal two striking features in these dense systems: an apparent enhancement of Mermin-Wagner-Hohenberg (MWH) fluctuations leading to anomalous long-wavelength density fluctuations, and a remarkable correspondence between activity-induced annealing and annealing via oscillatory shear. In this perspective article, we propose a novel approach toward a deeper understanding of dense active matter: by developing active Hamiltonian models as equilibrium reference frameworks, we map out pathways toward non-equilibrium active systems. This strategy allows us to elucidate both the correspondence between driven and active systems and the enhanced MWH fluctuations, which likely arise from a strong coupling between spatially random active forces and long-wavelength density (phonon) modes. We outline a comprehensive roadmap employing complementary approaches, including the active Hamiltonian formalism, comparative studies of oscillatory shear in active and passive solids, and investigations of chiral active matter. Establishing this activity-oscillatory shear correspondence across diverse systems is essential to demonstrate its universality, reveal the underlying large-scale emergent physics, and place our hypothesis on a firmer theoretical ground.
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Quantum Physics

Controlled ion-ion interactions and cavity-enhanced emission of a coherent dinuclear Eu$^{3+}$ complex

Evgenij Vasilenko, Vishnu Unni Chorakkunnath, Barbora Brachnakova et al. (+4 more)

Molecular rare-earth-ion complexes offer unique opportunities for quantum technologies by combining the intrinsic coherence properties of rare-earth ions with chemically tunable molecular environments. A crucial capability is the realization of multi-qubit architectures with defined qubit couplings to enable two-qubit quantum gates. Here, we investigate the optical coherence properties and excitation-induced interactions of two Eu$^{3+}$-based molecular complexes, comparing a mononuclear reference system with a dinuclear analogue in which two Eu$^{3+}$ ions are positioned at a well-defined intramolecular distance of about 7 Angstrom. Using cryogenic ensemble spectroscopy, including spectral hole burning, free-induction decay, and photon echo measurements at temperatures down to 100 mK, we demonstrate long optical coherence times $T_{2,\text{o}}$ of up to 9 $\mu$s. As a key step toward scalable multi-qubit architectures, a control-target sequence was implemented to probe conditional ion-ion interactions, revealing a stronger interaction-induced dephasing in the dinuclear complex. Finally, we show the integration of the dinuclear complex into a fiber-based optical microcavity, and observe an 380-fold emission enhancement of the $\mathrm{}^5\mathrm{D}_0\rightarrow\mathrm{}^7\mathrm{F}_0$ transition. Together, these results position molecular rare-earth complexes as versatile and chemically tunable building blocks for scalable quantum technologies.
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All authors Evgenij Vasilenko, Vishnu Unni Chorakkunnath, Barbora Brachnakova, Nicholas Lester Jobbitt, Senthil Kumar Kuppusamy, David Hunger, Mario Ruben

Physics Education

A Thematic Analysis of A-level Physics Examiner Reports on Gravity

Corey McInerney

Examiner reports from six major UK exam boards published between 2017 and 2025 are analysed using a mixed-methods thematic analysis. Focusing on questions relating to gravity, the objective is to understand where students commonly drop marks. Findings reveal that the source of difficulty is dependent upon topic and question style. Mathematical errors account for the majority of lost marks in calculation-type questions, while a lack of conceptual understanding commonly results in lost marks on questions relating to fields, energy and gravitational potential. Pedagogical strategies for teaching gravity must emphasise algebraic skills for orbital mechanics topics while prioritising qualitative modelling and precise definitions for field theory.
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General Relativity and Quantum Cosmology

Critical Coupling Surfaces in $\kappa(R,T)$ Gravity: Regularity, Gravitational Screening, and Phase Transitions

Ginés R. Pérez Teruel

We investigate the critical regime $\kappa(R,T)=0$ in $\kappa(R,T)$ gravity. While most studies assume a non-vanishing effective gravitational coupling, the existence of critical hypersurfaces where $\kappa$ vanishes is a generic feature of many admissible coupling functions. We show that the apparent singularity of the non-conservation equation is an artifact of a rewritten form of the conservation law and that the fundamental equations remain regular at $\kappa=0$. We further analyze the structure of critical hypersurfaces, derive the associated compatibility condition $(\nabla^\mu\kappa)T_{\mu\nu}=0$, and discuss their interpretation as gravitational screening surfaces separating attractive and repulsive gravitational phases. The existence of critical coupling hypersurfaces also obstructs a global Einstein-frame description, distinguishing $\kappa(R,T)$ gravity from theories based solely on algebraic redefinitions of the energy-momentum tensor. Possible cosmological and astrophysical consequences are briefly explored.
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Applied Physics

Enhancement of nitride-based solar cells using graphene as transparent contact layer

Miriam Cadenas, Mireia Martínez, Kerly Sánchez et al. (+5 more)

The effect of using a graphene layer as a semitransparent contact layer is studied in solar cells based on AlInN on Si (100) substrates. The devices consist of AlxIn1-xN layers deposited on p-type Si (100) substrates incorporating a thin amorphous silicon (a-Si) buffer layer to improve the heterointerface quality. Three aluminum contents are studied, namely: x=0.22, 0.35 and 0.43. Subsequently, a monolayer graphene film was transferred onto the front surface of the devices using a simple and low-temperature transfer process, acting as a semitransparent conductive contact. The photovoltaic characteristics were then evaluated under illumination and dark conditions in devices with and without the graphene layer. The results show that the incorporation of graphene leads to a clear improvement in the short-circuit current density, fill factor, and overall power conversion efficiency for all studied compositions, while the open-circuit voltage remains largely unaffected. These findings demonstrate the potential of graphene as an effective transparent conductive contact for nitride-based solar cells.
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All authors Miriam Cadenas, Mireia Martínez, Kerly Sánchez, Jordi Ibáñez, Sergi Hernández, Sirona Valdueza-Felip, Ana M. Diez-Pascual, Fernando B. Naranjo

Optics

Self-Pulsing Microring Resonator Networks for Bandwidth-Efficient Event Detection in an Optical Fiber Sensor

Alessio Lugnan, Yonas Seifu Muanenda, Ilya Auslender et al. (+4 more)

The native processing of time-dependent signals from optical sensors by integrated photonic circuits can potentially bring significant advantages in terms of energy consumption, latency and processing power, as it allows skipping or reducing the use of fast digital electronics and directly exploiting optical degrees of freedom and parallelism. However, due to a short memory, optical operations usually struggle to directly process optical signals with relatively slow (<MHz) dynamics from optical sensors. In this work, we experimentally show that these limitations can be overcome by exploiting the self-pulsing dynamics in a microring resonator (MRR) network. In particular, we demonstrate that such dynamics can expand and retain information about perturbations sensed by a fiber sensor. This reduces the minimum sampling rate for the digitization of the sensor signal by at least one order of magnitude. The reduction is achieved by combining fiber sensing measurements at two different perturbation locations and frequencies with MRR network measurements at multiple output ports, input power levels and laser wavelengths. This work represents a first step in bridging time-dependent optical processing and optical sensing at sub-{\mu}s time scales.
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All authors Alessio Lugnan, Yonas Seifu Muanenda, Ilya Auslender, Stefano Biasi, Claudio J. Oton, Fabrizio Di Pasquale, Lorenzo Pavesi

High Energy Astrophysical Phenomena

Detection of a parsec-scale, compact, and fading ejecta from an accreting massive black hole

Chao Li, Ning Chang, Jun Yang et al. (+2 more)

Dwarf galaxies, characterized by their low luminosities and masses, are excellent candidates for searches for intermediate-mass black holes (IMBHs), particularly when they show strong accretion and ejection activity. The dwarf galaxy SDSS J101747.09+393207.7 has recently been found to display a very high X-ray luminosity and an X-shaped optical structure, possibly caused by a dwarf–dwarf merger. To explore its potential IMBH ejection activity, we performed very long baseline interferometry (VLBI) observations at 4.9 GHz. In this work, we present the detection of a milliarcsecond-scale, compact, sub-microjansky radio component near the optical centroid. According to some existing radio sky survey data, the radio component was not detected until 2015; it displayed an optically thin steep radio spectrum and declining flux densities across 0.8–5 GHz from 2019 to 2025. Therefore, we identify it as a short-lived and rarely seen ejecta that was produced by unstable accretion onto a massive black hole and likely faded away in a few decades. These results indicate that short-lived, episodic jet activity from accreting IMBHs in dwarf galaxies might exist.
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All authors Chao Li, Ning Chang, Jun Yang, Lang Cui, Luis C. Ho

Soft Condensed Matter

Visualizing Transient Ordering Phenomena in Dense Nanoparticle Clouds

Rieke von Seggern, Jasmin Pongratz, Christine Ziegler et al. (+1 more)

The dynamics of nanoparticles within nanoscale liquid environments exhibit a range of complex phenomena driven by the interplay of processes at varying length scales. While these dynamics have profound technical implications, such as in nanoscale catalytic kinetics, ion-transport pathways in energy storage, and macromolecular crowding in biological systems, real-space imaging of dense, confined nanoparticle assemblies remains a significant challenge. Here, we present a liquid-phase transmission electron microscopy approach in which dense clouds of gold nanoparticles are formed within microfluidic channels, rendering the particle ensemble visible in bright-field electron imaging. This strategy enables direct imaging of different density-dependent particle ordering phenomena, including a local structuring of the colloidal liquid in nanoscale spaces, disordered dynamic clouds at high nanoparticle densities and the reversible formation of superlattice structures. Our results provide a unique window into the complex processes of colloidal self-organization at the nanoscale.
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All authors Rieke von Seggern, Jasmin Pongratz, Christine Ziegler, Sascha Schäfer

High Energy Physics (Phenomenology)

Thermal contact and direct detection in a broken $Z_4$ Majorana dark matter model

XinXin Qi and Hao Sun

We consider a broken $Z_4$ Majorana dark matter model in which the fermion mass is generated by a real singlet scalar. For small scalar mixing, freeze-out is dominated by $\chi\chi\to h_2h_2$, whereas momentum exchange with the Standard Model bath becomes inefficient. In this region, the usual assumption $T_\chi=T$ is not always adequate. We therefore evolve the dark matter abundance and kinetic temperature simultaneously. Although $T_\chi$ is still close to the bath temperature around chemical freeze-out, the later departure from kinetic equilibrium reduces the residual $p$-wave annihilation rate and leaves a larger relic abundance. In the sub-TeV region considered here, the difference between the two-moment and single-temperature calculations reaches $37.1\%$ at fixed parameters. Refitting the Yukawa coupling to reproduce $\Omega_\chi h^2=0.12$ increases the spin-independent scattering cross section by up to $18.6\%$. A momentum-resolved Fokker–Planck calculation gives a similar shift, $17.7\%$, at a representative point. The LZ upper limit on the scalar mixing changes by less than $0.3\%$, since kinetic equilibrium is already well maintained in that part of parameter space. The lower mixing boundary obtained from the comparison of the two relic calculations therefore indicates where the common-temperature approximation loses accuracy; it is not an experimental lower bound. These results apply to the specified low-reheating broken-phase cosmology and to the region where threshold and strong nonrelativistic-potential effects remain small.
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Cosmology and Nongalactic Astrophysics

Nonminimal couplings and preheating effects in $R^2$-Higgs inflation after ACT and SPT data

Haneesh Gonuguntla, Tanmoy Modak and Arnab Samanta

We study the effects of dimension-four and dimension-six nonminimal Higgs couplings to the Ricci scalar $R$ in the $R^2$-Higgs inflation model in light of the recent ACT and SPT observations. We show that the dimension-six operators $|\Phi|^2 R^2$ and $|\Phi|^4 R$ can accommodate the enhanced scalar spectral index $n_s$ preferred by the combined CMB+BAO analyses. Using a doubly covariant formalism, we find that the same region of parameter space that explains the observed value of $n_s$ can also induce rapid preheating through the production of the Goldstone modes. If thermalization proceeds efficiently through this preheating mechanism, it may help match the inflationary scale with the CMB reference scale.
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Materials Science

Spin-Polarized Electronic Structure and Chemical Bonding Data for 2,500+ Halide Double Perovskites

Luc Walterbos, Alex McEwan, Ravindra Shinde et al. (+2 more)

Halide double perovskites (A$_2$BB'X$_6$) are a long-known class of materials that has recently been rediscovered for diverse applications, including photovoltaics, photocatalysis, and radiation detection. Their doubled unit cell provides immense chemical tunability, allowing the incorporation of magnetic ions and enabling access to a wide range of electronic-structure features, including different band-edge characters, alignments, and symmetries. Magnetic elements may further introduce spin degrees of freedom and magnetic behaviour, thereby broadening the functional landscape of these compounds. Here, we present the first comprehensive database of spin-polarised electronic-structure data for all halide double perovskites predicted to be stable by the recently introduced $\tau$ tolerance factor by Bartel et al. The dataset focuses on the Cs$_2$BB'X$_6$ family, with X = I, Br, Cl, and F, and includes density of states (DOS) for $>$2,500 compounds, calculated using hybrid-functional density functional theory. Among these, 719 compounds exhibit band gaps in the visible range and 118 display half-metallic character. In addition, we provide chemical-bonding analysis using lobster, which provides insights into orbital interactions across the dataset. To facilitate exploration, we further offer UMAP-based visualisations and an interactive app for systematic investigation of chemical composition, electronic structure, and magnetic properties.
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All authors Luc Walterbos, Alex McEwan, Ravindra Shinde, Janine George, Linn Leppert

Solar and Stellar Astrophysics

Building three-dimensional giant stellar models for common envelope simulations

Ron Schreier, Shlomi Hillel and Noam Soker

We build a three-dimensional (3D) red supergiant (RSG) stellar model by transporting a 1D stellar model to a 3D numerical grid, mimicking core nuclear power by depositing energy into an inner shell, and mimicking stellar emission by cooling grid cells with densities below the photospheric density. The goal is to use such models for common envelope evolution (CEE) and grazing envelope evolution simulations. We do not relax the model; rather, we let it perform its natural pulsation. We find that when we mimic photospheric emission by cooling low-density grid cells, the oscillations decay slowly on a timescale much longer than without photospheric cooling. When we mimic both nuclear energy production, by depositing the stellar luminosity in an inner shell above the inert core of the stellar model, and photospheric cooling, the oscillations do not decay; instead, their amplitude slowly increases with time. The main pulsational period is about 1 year, comparable to the stellar dynamical time, suggesting a fundamental radial pulsation mode. The non-spherical structure of the stellar model and rapid low-amplitude temporal variations in the average stellar radius tentatively hint at the presence of non-radial oscillation modes on top of the fundamental radial mode. We also obtain convection, as RSG stars should have. We conclude that energy deposition in the inner envelope at the stellar luminosity and the cooling of the outer low-density numerical cells are a way of preparing a pulsating giant star to simulate CEE and grazing-envelope evolution. This procedure requires no relaxation of the stellar model.
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High Energy Astrophysical Phenomena

Gamma-Ray Constraints on Heavy Axion-Like-Particle Decays from Fermi-LAT and H.E.S.S. Blazar Spectra

A. Acharyya, F. Aharonian, M. Backes et al. (+118 more)

The propagation of very-high-energy (VHE; $E_{\gamma} \geq 100$ GeV) gamma rays from extragalactic sources is affected by interactions with photons of the extragalactic background light (EBL), resulting in pair production that attenuates the intrinsic gamma-ray flux. This interaction renders the Universe increasingly opaque to VHE photons at high energies and redshifts. New physics scenarios involving axion-like particles (ALPs) could modify this expected optical depth. In particular, ALPs with masses $m_a \sim 10$ eV can decay into two photons over cosmological timescales, thereby contributing to the diffuse EBL. If such ALPs constitute a significant fraction of the dark matter density, their decay would enhance the EBL intensity and consequently increase the gamma-ray optical depth. In this study, we investigate this scenario using a large sample of gamma-ray spectra observed with the High Energy Stereoscopic System (H.E.S.S.) and the Fermi Large Area Telescope. We model the contribution of decaying ALPs to the EBL and assess their impact on the spectra of blazars across redshifts. By comparing these observations with standard EBL models, we place constraints on the properties of heavy ALPs, specifically their mass and photon coupling, and evaluate their viability as a dark matter candidate capable of modifying the gamma-ray transparency of the Universe. From the combined analysis, and under the assumption that ALPs constitute the entire dark matter density, we derive 95% confidence exclusion limits on the photon-ALP coupling down to $g_{a\gamma} \sim 7 \times 10^{-12}$ GeV$^{-1}$ for masses $m_a\sim 15$ eV. These constraints are competitive with existing astrophysical bounds and provide complementary sensitivity to other techniques, closing a previously unconstrained region of parameter space in the $m_a \sim 2.5$-$20$ eV range.
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All authors A. Acharyya, F. Aharonian, M. Backes, R. Batzofin, Y. Becherini, S. Bisero, M. Böttcher, C. Boisson, J. Bolmont, F. Brun, C. Burger-Scheidlin, T. Bylund, S. Casanova, D. Cecchin Momesso, M. Cerruti, A. Chen, M. Chernyakova, J.O. Chibueze, O. Chibueze, T. Collins, B. Cornejo, G. Cotter, G. Cozzolongo, J. de Assis Scarpin, M. de Naurois, E. de Oña Wilhelmi, A. Deka Baruah, A. Dmytriiev, K. Egberts, K. Egg, C. Escañuela Nieves, K. Feijen, M.D. Filipović, G. Fontaine, S. Funk, S. Gabici, Y.A. Gallant, M. Genaro, P. Geneste, J.F. Glicenstein, P. Goswami, C. Grimaud, L. Heckmann, B. Heß, J.A. Hinton, W. Hofmann, T.L. Holch, M. Holler, M. Jamrozy, F. Jankowsky, I. Jaroschewski, I. Jung-Richardt, D. Kerszberg, B. Khélifi, N. Komin, D. Kostunin, R.G. Lang, S. Lazarević, M. Lemoine-Goumard, J.-P. Lenain, P. Liniewicz, A. Luashvili, J. Mackey, D. Malyshev, D. Malyshev, V. Marandon, M.G.F. Mayer, A. Mehta, M. Meyer, A.M.W. Mitchell, R. Moderski, L. Mohrmann, A. Montanari, E. Moulin, J. Niemiec, L. Olivera-Nieto, M.O. Moghadam, M. Panter, R.D. Parsons, D. Pastuszka Malek, P. Pichard, S. Pita, S. Porras-Bedmar, T. Preis, G. Pühlhofer, M. Punch, A. Quirrenbach, A. Reimer, O. Reimer, H.X. Ren, B. Reville, F. Rieger, G. Roellinghoff, G. Rowell, B. Rudak, K. Sabri, V. Sahakian, A. Santangelo, M. Sasaki, F. Schüssler, J.N.S. Shapopi, W. Si Said, Ł. Stawarz, R. Steenkamp, S. Steinmassl, T. Tanaka, A.M. Taylor, G.L. Taylor, R. Terrier, Y. Tian, T. Unbehaun, C. van Eldik, M. Vecchi, J. Vink, V. Voitsekhovskyi, T. Wach, S.J. Wagner, A. Wierzcholska, M. Zacharias, A. Zech, W. Zhong

High Energy Astrophysical Phenomena

Spectral study of X-ray sources in some galaxies recently observed by Chandra

Amom Lanchenbi Chanu and Anoubam Senorita Devi

With the aim to study the spectral properties of some X-ray sources from recently observed Chandra data, 9 galaxies which have been observed by Chandra ACIS-S during the year 2018 to 2022 have been considered for the present work. 27 sources with net source counts $ \ge$ 100 have been considered. The spectra of all the sources were fitted using two empirical models – an absorbed powerlaw and an absorbed disk blackbody. From their estimated bolometric luminosities, the 27 X-ray sources are categorized as 6 X-ray binaries (XRBs) and 21 Ultraluminous X-ray sources (ULXs). All the six XRBs are found to be in the spectrally hard state ($\Gamma \sim$ 1.52-2.29) which indeed may be due to thermal comptonization. Only one ULX, CXOUJ032251.2-370950 (X-5), was found to be spectrally soft while the remaining 20 ULXs were spectrally hard. The spectral parameters of X-5 with an inner disk temperature (kT$_{in}$) $\sim $ 0.5 keV and an estimated bolometric luminosity, L$_X \sim$ 3.26 $\times$ 10$^{39}$ erg s$^{-1} $ requires a black hole of mass, M$_{BH} \sim$ 137.86$^{+66.62}_{-47.41}$ M$_\odot $ accreting at $ \sim$ 0.19 times its Eddington limit. 8 ULXs, X-4, X-8, X-9, X-10, X-11, X-12, X-20 and X-21, were found to be in the Extremely luminous X-ray sources (ELXs) regime with even their lower limit of luminosity $>$ 10$^{40}$ erg s$^{-1}$. Softening/Hardening of spectra with or without changes in the luminosity were also observed in some ULXs/ELXs. In the hard ELX, X-8, spectral softening with almost consistent luminosity was observed. While in the ULXs X-20 and X-25 spectral softening with increasing luminosity was observed. However spectral hardening with increase in luminosity were observed in the ULXs X-21 and X-26.
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Quantum Gases

Quantum tidal locking in orbiting Bose-Einstein condensates

Yaoyuan Fan, Shuoyu Shi, Lang Cao et al. (+7 more)

Angular momentum coupling manifests widely in diverse physical systems, underpinning the emergent properties and collective dynamics across different scales. The tidal locking, which originates from the synchronization of rotational and orbital motions, has far-reaching impacts in celestial mechanics, reflecting fundamental processes of angular momentum transfer, energy dissipation, and evolution toward dynamical equilibrium. However, its counterpart in mesoscopic quantum fluids has remained largely unexplored. Here we demonstrate the emergence of quantum tidal locking in Bose-Einstein condensates undergoing central force motion in an anharmonic potential. The condensate follows a well-defined orbital trajectory in a static trap and experiences an effective rotating potential induced by the trap anharmonicity. The sustained geometric squeezing continuously deforms the condensate and drives a self-organized synchronization process, in which the intrinsic rotation gradually locks to the orbital motion. Numerical simulations further reveal the formation of a ring-shaped vortex array over longer timescales, arising from the coherent evolution of the rotating matter wave during the locking dynamics. Our findings establish quantum tidal locking in mesoscopic systems as a robust self-organized mechanism for generating and stabilizing circulating states.
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All authors Yaoyuan Fan, Shuoyu Shi, Lang Cao, Ziyue He, Qiuxin Zhang, Dong Hu, Yu Wang, Qing Wang, Tianwei Zhou, Xiaoji Zhou

High Energy Physics (Phenomenology)

Femtoscopy-driven searches for saturated gluonic matter in inclusive photonuclear processes

S. Ragoni, P. Chakraborty, A. Kisiel et al. (+2 more)

We present femtoscopy as a new way to search for saturated gluonic matter in inclusive photonuclear processes, such as inclusive ultraperipheral collisions at the Large Hadron Collider (LHC) and the inclusive photonuclear reactions at the Electron-Ion Collider (EIC). As the femtoscopic approaches are sensitive to the space-time structure of the particle emitting source, they are ideal in providing insights also about the initial stage of the collision, where the gluon distributions may impact the effective size of the dipole the quasireal photons oscillate into. This technique demonstrates its capabilities in isolating nuclear shadowing and gluon saturation effects. Finally, we show how a femtoscopic approach is highly sensitive to sub-fermi scale structures typically observed in ultraperipheral collisions, such as gluonic hot spots.
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All authors S. Ragoni, P. Chakraborty, A. Kisiel, G. Kornakov, S. Pulawski

Mesoscale and Nanoscale Physics

Robust Spin Logic Enabled by Generalized $\mathrm{SU}(2)$ Symmetry in $p$-Wave Magnets

Hao-Kun Ke, Gong Zhao, Siqing Li et al. (+2 more)

Unconventional magnets combine the vanishing stray fields of antiferromagnets with the strong spin-splitting of ferromagnets, offering a unique material platform for spintronics. However, a critical challenge in realizing functional spin-logic devices lies in preserving long-range spin coherence against momentum-degrading scattering and gate-induced dephasing. Here, we demonstrate that the intrinsic momentum-dependent exchange field of a three-dimensional $p$-wave magnet can be precisely tuned against gate-induced Rashba spin-orbit coupling to establish a generalized $\mathrm{SU}(2)$ spin-rotation symmetry. This emergent conservation law generates a symmetry-protected Persistent Spin Helix (PSH), effectively integrating the high energy scales of 3D bulk magnetic exchange with the macroscopic coherence of symmetry protection. By modeling a synergistic $p$-wave magnetic spin field-effect transistor (spin-FET), we reveal high-visibility Datta-Das conductance oscillations controlled purely by electrical gating. Crucially, our quantum transport simulations confirm that this symmetry-engineered transport regime exhibits exceptional resilience against strong non-magnetic Anderson disorder and geometric variations. These results establish a synergistic paradigm for non-magnetized spintronics, demonstrating how the active integration of spin-orbit coupling and unconventional magnetism can yield disorder-resilient spintronic logic.
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All authors Hao-Kun Ke, Gong Zhao, Siqing Li, Ruixiang Chen, Chui-Zhen Chen

Solar and Stellar Astrophysics

Protostellar Outflows at the EarliesT Stages (POETS). IX. Magnetohydrodynamic disk winds traced by SO and SO$_2$ in luminous protostars

L. Moscadelli, H. Beuther, A. Sanna et al. (+13 more)

We investigate two massive young stellar objects (YSOs), IRAS21078+5211 and G035.02+0.35, where evidence for magnetohydrodynamic (MHD) disk winds (DWs) has been obtained at scales of 10-100 au through measurements of the 22GHz water maser velocity distribution within the Protostellar Outflows at the EarliesT Stages (POETS) survey. We employ IRAM Northern Extended Millimeter Array and archival Atacama Large Millimeter Array observations of IRAS21078+5211 and G035.02+0.35, respectively, to study kinematics and physical conditions of the corresponding protostellar winds on scales of 100-1000 au using the same molecular tracers. In IRAS21078+5211, the emissions of several molecules, particularly SO, SO2, CH3CN and CH3OH, are distributed along the axis of the radio jet, and present a LSR velocity (Vlsr) gradient transversal to the jet axis. Position-velocity (PV) plots of the SO lines show patterns consistent with Keplerian rotation. The SO2 emission comes from high velocity gas flowing close to the jet axis, while CH3CN and CH3OH present larger radial extension than the S-bearing species. In G035.02+0.35, the same molecules are instead distributed along the major axis of the rotating disk, and their Vlsr gradients consistently trace the disk rotation. The corresponding PV plots present Keplerian profiles. SO is the only molecular species whose emission extends well outside the disk. In both YSOs, the spatial and velocity distributions of SO are consistent with a rotating wind magneto-centrifugally launched from the YSO disk. The comparison with models of molecule formation and excitation in shocks indicates that the different radial extension of the molecular species observed in the protostellar wind of IRAS21078+5211, as well as the lack of molecules, except SO, in the G035.02+0.35's wind, can be explained in terms of a radially extended MHD DW, rather than a compact X-wind.
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All authors L. Moscadelli, H. Beuther, A. Sanna, M.T. Beltrán, C. Gieser, Th. Henning, P.D. Klaassen, R. Kuiper, S. Leurini, T. Möller, A. Palau, R. E. Pudritz, Á Sánchez-Monge, D. Semenov, J.S. Urquhart, H. Zinnecker

Mesoscale and Nanoscale Physics

Intrinsic Nonreciprocity in Electron-Phonon Interaction Driven Thermoelectric Diodes

Hao-Kun Ke, Lie-Run Tian, Pei-Hao Fu et al. (+3 more)

We study an electron-phonon interaction driven thermoelectric diode. The nonreciprocity in this diode arises from the asymmetry between the probabilities of phonon emission and absorption in the electron-phonon interaction, as well as the structural reflection asymmetry. We reveal the intrinsic nature of this nonreciprocity, as the forward and backward electron transport remains asymmetric even when the applied temperature difference is not reversed. This intrinsic nonreciprocity gives rise to two novel transport phenomena. One is a novel thermoelectric effect which is driven by the temperature difference between the leads and the central device region, rather than the conventional temperature difference between the two leads. The second, and more significant, phenomenon is the suppression of electronic backscattering in the load resistor. This suppression decreases the resistance of the load resistor, which leads to the breakdown of Ohm's addition law. Under suitable conditions, the presence of electron-phonon interaction can yield a larger thermoelectric current compared to the case without it. This intrinsic nonreciprocity opens up a new pathway for low-power electronics besides topology and superconductivity, and for nonreciprocal thermoelectric devices.
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All authors Hao-Kun Ke, Lie-Run Tian, Pei-Hao Fu, Jun-Feng Liu, Jun Wang, H. Xu

High Energy Astrophysical Phenomena

A Jet from a Nearly Dormant Black Hole

Xiaopeng Cheng, Hai Yang, Jun Yang et al. (+11 more)

Most galaxies host supermassive black holes (SMBHs) that remain weakly accreting or dormant for much of their lifetimes. At the lowest accretion rates, these systems may represent the transition between active nuclei and dormant black holes, but whether they can still launch collimated jets remains unclear. The nuclei in our Galaxy (\sgra) and M31 are key examples of this regime, although no clear jet structure has yet been detected in either source. Here we report multi-frequency very long baseline interferometric observations of \Msixty\ (NGC~4649), a nearby elliptical galaxy hosting a nearly dormant SMBH with an Eddington ratio of $\sim10^{-8}$. We detect a compact two-sided jet with an unusually steep synchrotron spectrum, demonstrating that collimated outflows can persist even under nearly dormant accretion conditions. The apparent radio core exhibits an unprecedentedly steep frequency-dependent position shift toward the SMBH, locating the central engine only $\sim57\,\mu$as, corresponding to a projected distance of $\sim10$ Schwarzschild radii, upstream of the 8.37-GHz core. The observed jet morphology and steep core-shift behaviour are reproduced by general relativistic magnetohydrodynamic and radiative-transfer simulations, indicating a magnetically dominated, non-equipartition jet-launching region that departs from the standard conical equipartition picture. These results provide direct observational evidence that jet production can survive near the dormant SMBHs and establish \Msixty\ as a unique laboratory for probing jet formation on event-horizon scales in the lowest-accretion SMBH regime.
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All authors Xiaopeng Cheng, Hai Yang, Jun Yang, Xiaofeng Li, Feng Yuan, Rusen Lu, Hyunwook Ro, Bong Won Sohn, Lulu Fan, Yihang Zhang, Wen Chen, Niu Liu, John E. Conway, Taehyun Jung

High Energy Physics (Phenomenology)

Final-state rescattering mechanism of doubly-charmed baryon decays: $\mathcal{B}_{cc}\to\mathcal{B}_{c}V$

Xiao-Hui Hu, Fu-Sheng Yu and Ye Xing

We study the non-leptonic weak decays of doubly charmed baryons (${\cal B}_{cc}$) into singly charmed baryons (${\cal B}_c$) and vector mesons ($V$), denoted as ${\cal B}_{cc}\to{\cal B}_{c}V$. The short-distance contributions are calculated within the naive factorization hypothesis, while the long-distance final-state interaction effects are modeled via hadronic triangle diagrams. Unlike previous approaches, which compute only the imaginary part using the Cutkosky cutting rule, we evaluate the complete loop integrals to obtain both the real and imaginary parts of the amplitudes. These provide the nontrivial strong phases essential for CP violation. The model parameters are determined using experimental data. With this improved calculation method, we predict the branching ratios and decay asymmetry parameters for various decay channels, as well as $CP$ violations for short-distance dominated and singly Cabibbo-suppressed channels. This strengthens our theoretical framework for future study of doubly charmed baryons. Certain decays, primarily driven by long-distance effects, have been calculated; their observation in future experiments could help clarify the role of final-state interactions in charm baryon decays. Therefore, our calculation of ${\cal B}_{cc}\to{\cal B}_{c}V$ provides crucial predictions for branching ratios, decay asymmetry parameters, and $CP$ violation, which are essential for guiding experimental study at LHCb.
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Statistical Mechanics

Universal Information-Theoretic Structure of the Quasi-Stationary Domany–Kinzel Automaton

Hyun-Yong Lee, Kenji Harada and Naoki Kawashima

We characterize the quasi-stationary distribution (QSD) of the bond directed-percolation line of the Domany–Kinzel automaton using a matrix-product-state representation of the probability distribution, obtained by projecting out the absorbing state and iterating the transfer matrix. Unlike moment- or sampling-based methods, this yields the full conditional distribution and direct access to information-theoretic diagnostics. The spatial structure of the QSD changes sharply across the transition: the active phase is bulk-like with finite density, whereas in the inactive phase the surviving activity collapses into a single flock – the smallest interval containing all active sites – occupying a vanishing fraction of the chain. Throughout the inactive phase the bipartite mutual information of the QSD equals the entropy of a single binary choice – whether the flock lies to the left or right of the cut – so the surviving clusters together encode just one bit of positional information, corresponding to a single effective cluster.
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Quantum Physics

Tensor-Network Algorithm for Many-Body Trace Norms

Seunghun Lee and Eun-Gook Moon

Trace norms are fundamental to quantum information theory, yet in many-body systems their evaluation remains a major computational bottleneck, as it generally requires diagonalizing exponentially large operators. Here, we overcome this bottleneck by introducing a controlled tensor-network algorithm for estimating the trace norm of matrix product operators without full diagonalization. The key idea is to combine Zolotarev's rational approximation to the sign function with a variational formulation solved using a density-matrix-renormalization-group-like algorithm. The resulting approximation is systematically improvable, with its accuracy controlled by the rational approximation parameters and the spectral weight near zero. Beyond the reach of exact diagonalization, we demonstrate controlled trace-norm calculations for entanglement negativity, quantum fidelity and quantum Fisher information, achieving substantially improved accuracy over polynomial-based Lanczos approaches. Our results establish trace-norm-based quantities as practical tensor-network observables, opening a route toward tensor-network studies of quantum information in mixed states.
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Fluid Dynamics

Thin-film drainage becomes singular at saddles

Simeon Djambov, Alice Marcotte, François Gallaire et al. (+1 more)

From coating curved parts to creeping lava, thin-film gravitational drainage over complex surfaces can produce abrupt accumulation, usually associated with sharp edges or defects. Here, experiments, simulations and asymptotics show that a smooth saddle alone generates a logarithmically singular ridge, regularized within a dynamic region where drainage balances hydrostatic pressure and capillarity. In a Newtonian lubrication picture, this mechanism can inform redistribution in manufacturing and geophysics, motivating extensions to complex rheology and interacting geometric features.
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All authors Simeon Djambov, Alice Marcotte, François Gallaire, Pier Giuseppe Ledda

Materials Science

Sonochemically Boosted Hydrogen Evolution Activity of Janus TMD Monolayers

Rayantan Sadhukhan, Md Tarik Hossain, Julian Picker et al. (+5 more)

2D electrocatalysts that enable hydrogen evolution at low overpotentials offer an attractive alternative to expensive platinum-based systems. Here, we report the growth of Janus transition metal dichalcogenide (TMD) monolayers (MLs), SeMoS and SeWS, on Au foils using chemical vapor deposition, and systematically compare their catalytic properties in the context of hydrogen evolution reaction (HER) with those of their parent TMDs. The Janus MLs exhibited significantly enhanced catalytic performance relative to the parent TMDs. Furthermore, these MLs on Au foils were subjected to sonochemical treatment in polar and non-polar solvents, in which the treatment with polar solvents led to a substantial improvement in the HER activity of Janus MLs. In particular, SeMoS MLs treated with water showed a low overpotential of ~63 mV, a Tafel slope of ~42 mV/dec, and an exchange current density of ~10$^{-3}$ mA cm$^{- 2}$, approaching that of platinum. Analyses indicate that enhanced electrocatalytic activity is associated with tensile strain induced by Au surface restructuring and the formation of defects in Janus MLs, as shown by experimental observations and by density functional theory calculations. The enhancement in catalytic performance due to sonochemical treatment emphasizes the importance of our results for developing novel catalytic systems for HER based on Janus 2D materials.
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All authors Rayantan Sadhukhan, Md Tarik Hossain, Julian Picker, Mahdi Ghorbani-Asl, Christof Neumann, Arkady V. Krasheninnikov, Tharangattu N. Narayanan, Andrey Turchanin

Astrophysics of Galaxies

Distinct Gas and Stellar Circular Rotation Curves in the Milky Way Galaxy

Alistair H. Nelson, Yoshiaki Sofue and Peter R. Williams

The rotational velocity of interstellar gas in the Milky Way, and other galaxies, has been taken to represent the circular velocity of a test particle in the Galaxy gravitational field, and hence an indicator of the Galaxy mass. The derived circular velocity is found to be too high for the gas to be gravitationally bound to the galaxy given the observed Galaxy mass in stars and gas, and consequently an extra component of mass in the Milky Way and other galaxies, namely dark matter, has been postulated. However recently the observational satellite Gaia, has been carrying out ground-breaking astrometric observations to accurately measure, inter alia, the three dimensional velocities of stars in the vicinity of the Sun and beyond. This has revealed that the circular velocity derived from the stellar population is much less than that of the gas, and the rotation curve, circular velocity versus radius, is distinctly declining with radius, whereas the gas rotation curve is not declining. By combining results from multiple observations of the gas velocity, averaging the velocities in radial bins, we establish that there is a grand average rotation curve. This can be compared directly with a grand average of the published Gaia rotation curves, and the confidence level in the difference between the two estimated by statistical analysis. The difference is shown to have a high degree of confidence, and increases with galactocentric radius. The lower circular rotation curve from the stellar velocities has resulted in significantly reduced estimates of the dark matter mass fraction of the Milky Way. The higher rotation of the gas lacks an explanation, but it is unlikely to be an accurate indicator of the kinematic mass of the Galaxy. This also has significant consequences for the mass of external galaxies based on gas rotation curves.
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Materials Science

Modelling magnetic material properties with uncertainty-aware neural networks

Clemens Wager, Heisam Moustafa, Alexander Kovacs et al. (+10 more)

Machine learning is increasingly used to accelerate materials discovery across large compositional and structural design spaces, but limited and heterogeneous data make reliable uncertainty estimation essential. In this work, we investigate uncertainty quantification for permanent magnet modeling across three complementary studies. First, on a public Curie temperature surrogate dataset, we benchmark Gaussian process regression, random forest bagging, and dropout-based Bayesian neural networks and show that calibration, sharpness, and confidence curve diagnostics reveal differences in uncertainty quality that are not visible from point-prediction metrics alone. Second, we transfer this framework to the prediction of intrinsic magnetic properties in Nd2 Fe14 B-based magnets. Third, we extend the same uncertainty-aware perspective to coercivity prediction from microstructural information using a graph neural network. Together, these studies show that uncertainty quantification improves the trustworthiness of magnetic material property predictions and can be transferred from composition-based surrogate models to more complex structure-sensitive learning tasks.
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All authors Clemens Wager, Heisam Moustafa, Alexander Kovacs, Qais Ali, Harald Oezelt, Hayate Yamano, Masao Yano, Noritsugu Sakuma, Hyuga Hosoi, Akihito Kinoshita, Tetsuya Shoji, Akira Kato, Thomas Schrefl

Earth and Planetary Astrophysics

Strong and variable stratospheric CO emission from lava-planet 55 Cnc e observed with NIRCam/JWST

Ignas Snellen, Yamila Miguel, Leoni Janssen et al. (+4 more)

Some rocky planets orbit so close to their host stars that stellar heating melts their surfaces. They offer a rare glimpse of planets in a magma-ocean state, providing an observable analogue to processes that likely shaped the early Earth and other terrestrial planets during their infancy. Recent JWST observations of five eclipses of the prototypical lava planet 55 Cnc e have confirmed earlier hints that it exhibits highly variable thermal emission, with low-resolution spectroscopy pointing to a possible volatile-rich atmosphere likely rich in CO and CO2. Here we report on an analysis of the same JWST datasets but at their native spectral resolution, utilizing cross-correlation techniques. An unambiguously strong ~8 sigma signal from CO in emission is recovered during one out of five epochs, with potential ~3 sigma detections during two others. The strongest observed cross-correlation signal is difficult to reconcile with a hydrostatic atmosphere, requiring a steep and strong thermal inversion at the right pressure level (~1-10 mbar) and a relative abundance of CO2 that is at least 3 orders of magnitude lower which would otherwise mask the CO signal. Self-consistent atmospheric modelling indicates that this is most readily achieved in a hydrogen-rich atmosphere, which produces the steepest inversions and highest CO/CO2 ratios. The pronounced epoch-to-epoch variability suggests that the CO signal does not trace a static atmosphere alone, but may reveal a transient, dynamically active component, potentially linked to variable atmospheric outflow.
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All authors Ignas Snellen, Yamila Miguel, Leoni Janssen, Dario Gonzalez Picos, Sam de Regt, Natalie Grasser, Lars Klijn

Mesoscale and Nanoscale Physics

Ferroelectric Altermagnetic Chern Insulator in magnetic field: electrical control of the Chern number

Meysam Bagheri Tagani and Carmine Autieri

We investigate electrically controllable Chern topology in a two-dimensional compensated (d)-wave altermagnet described by a lattice-regularized Bernevig–Hughes–Zhang model. In the altermagnetic reference state, the two Kramers sectors acquire momentum-dependent spin splitting and opposite sector Chern numbers, while the combined $C_{4z}\mathcal T$ symmetry enforces a vanishing total charge Chern number. We show that this hidden topological structure can be activated by orbital-selective magnetic coupling and independently tuned by ferroelectric orbital hybridization. The magnetic coupling removes the sector cancellation and generates $C=\pm1$ and $\pm2$ phases, whereas the polar distortion shifts the Dirac gap closing away from high-symmetry momenta and enables electrical transitions such as $C=0\rightarrow-1$ and $C=1\rightarrow2$. The resulting phases exhibit the expected chiral edge-state multiplicity and quantized anomalous Hall conductivity. Their topology is further reflected in the orbital magnetization through the in-gap relation $\partial_\mu \widetilde M_z=-C$. Finally, we show that the Chern phases remain robust against transverse Kramers-sector mixing and symmetry-allowed inversion-asymmetric spin–orbit coupling. These results establish a symmetry-based route to electrically tunable Chern insulating phases in compensated altermagnets.
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Space Physics

Extreme, transient bursts of energy in the auroral ionosphere. II. A magnetotail dipolarization event

Magnus F Ivarsen, Yukinaga Miyashita, Brian Pitzel et al. (+5 more)

We report ground-based coherent VHF radar observations of extreme turbulent field-structures detected in coincidence with a magnetospheric substorm-associated magnetotail dipolarization. The field-structures are observed by the ICEBEAR radar, in the form of Farley-Buneman (FB) waves in the auroral electrojets, and the field-structures themselves move an order of magnitude faster than the saturation speed of the underlying FB waves, implying transient electric field sources up to 330 mV/m in strength. The field-structures are identified and automatically tracked using an unsupervised clustering & tracking algorithm, applied to clutters of ICEBEAR radar backscatter targets, a method that turns the Doppler radar into a tracking radar capable of measuring the ionospheric ExB-drift by proxy. We place this finding in a coordinated multi-instrument context. Three THEMIS spacecraft observed the dipolarization event in-situ in the near-Earth plasma sheet. In the ionosphere, Swarm A, crossing through the guilty auroral arc at the onset of the dipolarization event, recorded clear signatures of propagating Alfvén waves threading the relevant flux tube. We interpret the ICEBEAR transients as the natural ionospheric foot signature of a shear Alfvén pulse launched by the bipolar space-charge (Hall) electric field of the thinned current sheet, with amplification along the converging flux tube, partial reflection at the ionospheric boundary, and spatial sharpening by precipitation-produced Pedersen-conductance gradients on the auroral arc edges. A one-dimensional wave-transmission analysis recovers the observations. Our results elucidate a tightly controlled coupling between magnetotail processes and meter-scale auroral plasma turbulence, and demonstrate the capability of ICEBEAR to resolve extreme, transient electric-field enhancements in the ionosphere.
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All authors Magnus F Ivarsen, Yukinaga Miyashita, Brian Pitzel, Jean-Pierre St-Maurice, Jaeheung Park, Devin R Huyghebaert, Yangyang Shen, Glenn C Hussey