Materials Science
Second-Harmonic Imaging of Magnetic Domains in Thin Film Hematite
Holger Mirkes, Johannes Schmuck, Katharina Müller et al. (+7 more)
Hematite is an
antiferromagnetic oxide and candidate altermagnetic
insulator whose Néel order reorients from an easy-axis to an easy-plane phase at the Morin transition. Interpreting altermagnetic transport and
symmetry sensitive optical responses requires knowledge of the Néel vector orientation relative to the
crystal axes and of the domain structure within the probed device. Here, we show that polarization-resolved second-harmonic generation (SHG) microscopy resolves
magnetic symmetry and domains in epitaxial (0001)-oriented hematite films. Across the Morin temperature, the SHG polarization anisotropy evolves from an approximately sixfold pattern consistent with the easy-axis orientation to pronounced twofold patterns consistent with the easy-plane orientation. A
symmetry analysis based on
magnetic-dipole and electric-quadrupole contributions reproduces this
evolution. Importantly, the interference between SHG amplitudes that are odd and even under reversal of the
magnetic order renders opposite Néel-vector orientations optically distinguishable. Consistently, opposite directions of an applied in-plane
magnetic field produce distinct SHG responses in our experiments. Using this
magnetic contrast, we image micrometer-scale domains, their reorganization across the Morin transition, and their reconfiguration under
magnetic and thermal cycling, including a remanent change after cycling through the
spin-flop transition. These results establish SHG microscopy as a local probe of
magnetic symmetry, Néel-vector orientation, and domain
evolution in hematite films.
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All authors Holger Mirkes, Johannes Schmuck, Katharina Müller, János Papp, Paul Seifert, Matthias Althammer, Hans Huebl, Stephan Geprägs, Alexander W. Holleitner, Christoph Kastl
High Energy Physics (Theory)
Superloop Equations and Minimal Surfaces I: Confining minimal surface in $4D, N=1$ SYM
Alexander Migdal
We formulate the loop equations of pure $4d, N=1$ super Yang–Mills (SYM) theory in a finite
geometric form. The usual equal-point loop derivatives are singular because the order of gauge-field insertions is lost when contour points coincide. Our path-ordered operator calculus (POOC) keeps the insertions in distinct ordered slots, forms the graded commutators and Jacobi combinations, and only then takes the coincidence limit. This removes the spurious kinematical singularities without introducing a cutoff; the genuine ultraviolet contact remains a separate physical distribution. We apply POOC to the exact Itoyama–Takashino superloop hierarchy and construct a Lorentzian supersymmetric Hodge-dual (SHD) surface functional. Its Hodge-resolved area derivative is annihilated by the local
chiral and anti-
chiral loop operators. Exact additivity under surface-geodesic sewing shows that the exponential of this zero mode multiplies any solution of the complete finite-$N$ hierarchy without changing the equations. For planar contours the SHD functional is the
geometric area. In particular, for a long rectangular Wilson loop, $W[C_{T,L}]\sim\exp[-i\sigma_kLT]$ and $E_k(L)=\sigma_kL>0$. Thus the construction gives an exact nonperturbative confining area-law factor in $ N=1$ SYM. After Euclidean continuation, the same SHD factor is an exact fixed point of the deterministic zero-noise SYM gradient flow. Its interpretation as a dynamically selected
equilibrium still requires stability in the long-flow-time, large-volume, and zero-noise limits, but this does not affect the exact zero-mode and finite-$N$ dressing
theorems. The complete planar Wilson-loop solution, including the undressed fluctuation factor and excitation spectrum, will be developed in the next papers of this series.
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Strongly Correlated Electrons
Pressure-Driven Evolution of Electronic and Magnetic Correlations in Bilayer Nickelate La3Ni2O7
Jian Zhou, Rui Song and Haiyan Lu
The recent discovery of high-temperature superconductivity in pressurized
bilayer La3Ni2O7 has sparked intense research interest, yet the microscopic mechanism governing its pressure-dependent superconducting transition temperature (Tc) remains elusive. In this work, we investigate the electronic and
magnetic correlations of La3Ni2O7 under high pressure using a combination of density-functional theory (DFT), constrained random phase approximation (cRPA), and dynamical mean-field theory (DMFT). We find that while hydrostatic pressure enhances the interlayer hopping and the bare superexchange energy scale (4t2/U), it simultaneously drives the system toward a more itinerant regime by reducing the relative correlation strength (U/W). Crucially, our results reveal a distinct orbital-selective
evolution: the Ni dx2-y2 states become increasingly itinerant, whereas the Ni dz2 orbitals retain a more localized character. This pressure-induced itinerancy significantly enhances the hybridization between the two, leading to a dramatic amplification of the Kondo-like screening of the local dz2 moments by the itinerant dx2-y2 electrons. Consequently, the effective
magnetic exchange coupling (Jeff), which serves as the pairing glue, is suppressed in the high-pressure regime. Our findings suggest that the monotonic decrease of Tc at high pressures is driven by the dominance of Kondo screening over superexchange interactions, providing a coherent microscopic explanation for the dome-shaped superconducting phase diagram in La3Ni2O7.
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Mesoscale and Nanoscale Physics
Valley-controlled chiral magnetism in transition metal dichalcogenide monolayers
Igor S. Krivenko, Vladimir N. Mantsevich and Dmitry S. Smirnov
We put forward the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in transition metal dichalcogenide monolayers as a tool to create and control a
chiral magnetic texture. We show that in the
spin-valley locking regime, the RKKY interaction acts as a Dzyaloshinskii-Moriya coupling with an effective
spin rotation period exactly equal to the tripled
lattice constant. Using mean field theory and classical Monte Carlo simulations, we demonstrate that this interaction qualitatively reshapes the phase diagram of atomically thin antiferromagnets. It destroys the chirality-related phase transition by selecting a single chirality value even when the RKKY interaction is small. At the same time, it shifts the Berezinskii-Kosterlitz-Thouless transition associated with
spins orientation to higher temperatures. We argue that the valley degree of freedom of electrons mediating the RKKY interaction provides a powerful control knob for exploring non-universal phase transitions and
quantum spin liquid states in two-dimensional van der Waals
heterostructures.
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General Relativity and Quantum Cosmology
Hidden Symmetry of Kerr-deSitter from Manifest Symmetry of Painlevé VI
Stefan Hollands, Akihiro Ishibashi and Jochen Zahn
We show that the recently discovered “mass
symmetries" of the radial Teukolsky equation for Kerr-deSitter black holes can be understood from a corresponding
symmetry of the Painlevé VI equation via the classical theory of “isomonodromic deformations". It is known that a subset of the mass
symmetries transforms the Teukolsky equation to a wave equation on a “dual" Lorentzian spacetime. We find that this dual spacetime again represents a black hole, and use this insight to re-obtain a previously known partial mode stability result in a
geometric manner. Further special
geometric features of the dual spacetime are pointed out.
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Optics
Direct Wafer Bonding of Crystal-Ion-Sliced GaP Thin Films for Photonic Applications
Hossein Esfandiar, Emanuel Glück, Fabian Ganss et al. (+11 more)
Gallium phosphide (GaP) is a promising material platform for integrated photonics because of its high refractive index, broad optical transparency, and strong second-order nonlinear response. Here, we demonstrate GaP-on-
insulator thin films fabricated by
crystal ion slicing and direct wafer bonding, using fused silica and SiO$_2$/Si/Si thermally oxidized silicon substrates as representative platforms. Unlike GaP thin-film platforms that rely on heteroepitaxial growth or sacrificial-layer release, the presented approach enables the flexible integration of crystalline GaP thin films, independent of both donor and target substrates. Following post-transfer annealing, the films exhibit near-bulk crystalline quality with low residual strain, smooth surfaces suitable for nanophotonic fabrication, and homogeneous bonding interfaces. Furthermore, annealing restores the linear optical dispersion (n and k) approaching that of epitaxially grown GaP with estimated plane wave absorption loss of 0.9 dB/cm at 1550 nm in the telecom C-band. The demonstrated approach establishes a scalable pathway toward high-quality GaP thin-film photonics compatible with versatile heterogeneous integration and back-end-of-line CMOS processing.
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All authors Hossein Esfandiar, Emanuel Glück, Fabian Ganss, Ulrich Kentsch, Dennis Arslan, Jana Paeschke, Sebastian Ritter, Andreas Ihring, Muyi Yang, Isabelle Staude, Stefan Facsko, Falk Eilenberger, Carolin Rothhardt, Sebastian W. Schmitt
Optics
Phase-Drift Limits and Adaptive Quadrature Readout in Programmable Photonic Processors
Gökhan Elmas, Igor A. Litvin and Janis Nötzel
Phase fluctuations between optical inputs limit programmable photonic processors because their output powers depend on coherent interference. We study the phase-drift penalty that arises when sine and cosine quadratures are measured sequentially rather than simultaneously. The analysis is motivated by measurements from an eight-mode programmable photonic processor, including 35 free-running recordings of 300 s acquired at approximately 125 samples per second per channel. These recordings provide an empirical route for estimating the phase-increment variance at a selected reconfiguration interval. The estimate is defined at the time of the second measurement. For fixed quadrature order, perturbation of the atan2 reconstruction gives $e_{C\to S}=-\delta_\tau\sin^2\phi_0+O(\delta_\tau^2)$ and $e_{S\to C}=-\delta_\tau\cos^2\phi_0+O(\delta_\tau^2)$. Writing $Q_\tau=\operatorname{Var}(\delta_\tau)$, uniform phase averaging gives the first-order drift mean-square error $3Q_\tau/8$. A phase-predicted ordering rule measures the locally less informative quadrature first and the more informative quadrature second. Its uniform first-order penalty is $(3/8-1/\pi)Q_\tau$, which is 84.9 percent below the fixed-order value. We also derive an increment-aware
estimator from a local state-space model. Marginalizing the unknown phase increment increases the variance of a stale phase observation by $Q_\tau$, reducing its Fisher information from $I$ to $I/(1+IQ_\tau)$. For ideal balanced Poisson detection, the Fisher information of each quadrature equals its detected signal-
photon number. This yields dimensionless architecture boundaries in spatial information and phase-increment variance. Nonlinear Monte Carlo simulations validate the perturbative laws, quantify robustness to prediction error, and compare simultaneous, fixed-order, increment-aware, and adaptive receivers under a common noise model.
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Nuclear Theory
Probing Quadruple Deformation in Transitional Nuclei via Angular Momentum Projection
Xian-Zhi Zhao, Sheng-Nan Wang and Yu Zhang
Within the interacting
boson model (IBM), a
geometric analysis of transitional
nuclei is carried out through angular momentum projection of the intrinsic coherent state. The results indicate that $K$-mixing effects in the calculations are typically negligible, validating the use of $K$-fixed projection for semiclassical analyses of the
spin dependence of quadrupole deformation in the IBM. Further analysis indicates that in a rotating transitional system, quadrupole deformation is stretched with increasing angular momentum, providing a geometrically intuitive perspective on the commonly observed Jacobi-type transitions, as exemplified by the case studies of $^{160}$Gd and $^{162}$Dy. The method is additionally applied to the yrast states of $^{170}$Os to probe quadrupole deformation changes linked to the observed low-
spin $B(E2)$ anomaly behavior, demonstrating the capability of IBM-based angular momentum projection in interpreting exotic collective phenomena.
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Accelerator Physics
Beam energy measurement at the European XFEL with high-performance trajectory fitting
Lars Fröhlich
This contribution presents the method used for beam energy monitoring at the European XFEL. It relies on high-performance trajectory fitting of beam position monitor data against an online model of the accelerator
lattice. Unlike most other methods, it can be applied to virtually any section of the
lattice with sufficient dispersion without the need for manual adaptation. Our implementation is fast enough to measure the energy of many thousands of bunches per second in realtime on conventional x86 hardware shared with other processes. A short outline of the technique is presented and illustrated with data from the accelerator.
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Quantum Physics
Quantum computer-based simulation of Stark many-body localization in a 1D Fermi-Hubbard model
Abdul Kalam, Prasenjit Deb, Akitada Sakurai et al. (+3 more)
Many-body localization (MBL) is a dynamical phenomenon that describes the non-ergodicity of isolated
quantum many-body systems. In contrast to thermalization, this phenomenon leads to a long-lived
memory of initial states of local systems and slow growth of
entanglement. In this work, we study Stark MBL in a 12-
qubit correlated fermionic system described by the one-dimensional
Fermi-Hubbard model using
Hamiltonian simulation on an IBM superconducting
qubit quantum computer. To enable such a computation on current-day noisy hardware, we combine a series of compilation steps, including the use of the
spin-resolved Jordan-Wigner transformation, employing SWAP networks, and integrating a tensor-network-based
quantum circuit optimization routine on top of a standard
circuit optimization pipeline. As a result, there is approximately an 88$\%$ and 87$\%$ reduction in two-
qubit gate count and
circuit depth, respectively. Through such simulations of the real-time dynamics using Trotterized
quantum circuits, we exhibit a crossover from thermalizing dynamics of the system at a weak tilt of the field to a strongly localized behavior at large tilt with short
evolution times. We also
benchmark our obtained results with respect to those from exact simulations.
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All authors Abdul Kalam, Prasenjit Deb, Akitada Sakurai, Tapan Mishra, V.S. Prasannaa, B. P. Das
Materials Science
Polaron-mediated metal-insulator transition and proton conduction in hydrogenated nickelate perovskites
Hang Ma, Tianxing Ma and Ying Liang
Nickel-based perovskites, owing to their spontaneous hydrogen uptake and the dramatic increase in resistivity upon hydrogenation, have emerged as promising candidates for
proton-conducting fuel
cell electrolytes. However, the mechanism of the hydrogen-induced metal-
insulator transition (MIT) in rare-earth nickelates remains under debate, particularly regarding whether the doped electrons occupy Ni e$_g$ states or O 2p ligand hole states. Here, we reveal a comprehensive MIT mechanism using first-principles calculations on NdNiO$_3$: the electrons introduced by hydrogen doping occupy the O 2p ligand hole states of the Ni-O hybridized d$_8$L configuration, promoting electron-polaron formation. The resulting electron polarons, together with
proton polarons, weaken the Ni-O hybridization and thereby drive the originally itinerant Ni e$_g$ electrons toward localization. This generates a local d8 (t$_{2g}$$^6$e$_g$$^2$) electronic configuration, leading to a Mott transition. In addition, we also find that compared with NdNiO$_3$, SmNiO$_3$ with a smaller A-site ionic radius more readily absorbs hydrogen but exhibits weaker
proton diffusion capability. Hydrogenation promotes
proton permeation along the [001] direction via the intraoctahedral transfer, whereas the overall
proton diffusivity is reduced. These results provide guidance for experimental screening of strongly correlated
oxides as electrolyte materials and offer theoretical insights for enhancing
proton conductivity in rare-earth nickelates.
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Mesoscale and Nanoscale Physics
Proximity effects of chiral magnetization on transition metal dichalcogenides monolayers
Vladimir N. Mantsevich, Igor S. Krivenko and Dmitry S. Smirnov
We consider the proximity effects of a commensurate
chiral $120^{\circ}$ Néel
magnetic structure on the transport and optical properties of a transition metal dichalcogenide monolayer (TMD ML). The enlarged
magnetic unit
cell leads to the folding of the Brillouin zone and enables efficient intervalley
spin-flip scattering. Starting from a six band tight binding model, we develop an effective $k\cdot p$ model, which describes the coupling between charge carriers in the TMD ML and the
chiral magnetization. We predict the anomalous
antiferromagnetic Hall effect (AHE) for conduction electrons and describe it accounting for the interplay between anomalous velocity, side jump, and skew scattering contributions. The proximity of the
chiral magnetization also leads to the mixing and splitting of the
exciton resonances in the two valleys which are related by the time reversal
symmetry despite zero net magnetization. Finally, we demonstrate the possibility to measure the distribution of in-plane orientation of the
chiral magnetization through Faraday rotation and the ellipticity of incident linearly polarized light.
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Solar and Stellar Astrophysics
Towards understanding stellar variability at the sub m/s level: granulation-induced variability across the optical spectrum
Cis Lagae, Ginger Frame, Heather M. Cegla et al. (+5 more)
Detecting the radial velocity signal of Earth-mass
exoplanets requires the characterisation and removal of granulation-induced radial velocity variability from spectroscopic observations. By coupling three-dimensional (3D) hydrodynamic (HD) simulations to a radiative transfer code, we can isolate and study the effect of granulation on
stellar lines. In this study we isolated the impact of granulation on spectral line shapes and shifts for the largest and most diverse synthetic spectral line sample to date. Our aims were twofold. First, we quantified how granulation affects the temporal
evolution of shapes and shifts of 72 unblended spectral lines in two wavelength regions: 5500-5600 Å and 6100-6200 Å, from disc centre to the
stellar limb. Second, we investigated if spectral lines behave coherently in their line shape variability. We find that weak lines show the largest radial-velocity variability due to granulation, up to 40 m/s at disc centre and 50 m/s at the
stellar limb. On the other hand, strong lines exhibit larger variability in equivalent width than weak lines across the
stellar disc. In addition, the equivalent width and line depth of a spectral line are strongly linearly correlated with its radial velocity. While granulation affects all three of these quantities, planetary Doppler shifts only affect radial velocities, opening the door to new granulation-mitigation methods. Lastly, we find that the radial velocity and equivalent width of most spectral lines in our sample evolve coherently in time, with the Fe I and Ca I lines behaving the most similarly. Due to the coherency, line blends will not significantly affect the temporal behaviour of RV and line shape, as induced by granulation. Besides, the coherency between spectral lines offer the opportunity to create disc-integrated spectra of many lines simultaneously, which will be explored in future work.
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All authors Cis Lagae, Ginger Frame, Heather M. Cegla, Veronika Witzke, René Holzreuter, Sergiy Shelyag, Christopher Watson, Alexander Shapiro
Plasma Physics
Mass Spectrometry Studies of Hydrogen Ions Energy Distributions in an ECR- based Large Volume Plasma Source
Bibekananda Naik, Ramesh Narayanan, Debaprasad Sahu et al. (+2 more)
Plasma is produced in a Large Volume
Plasma Source (LVPS; dia. = 1 m, height = 1m) using CW microwaves (= 400 - 600 W, 2.45 GHz), in a compact ECR
plasma source (CEPS) attached to LVPS, at hydrogen gas pressures = 1 - 3 mTorr.
Plasma expands along the CEPS
magnetic field into LVPS. A Hiden Analytical HPR 60 molecular beam mass spectrometer (MBMS) is used to measure the H^- ion energy distribution functions (IEDFs) in the downstream
plasma. Previous
plasma characterization studies in LVPS indicated favourable downstream
plasma conditions for volume production of H^- ions. Measurements conducted with the MBMS probe aligned facing the
plasma flow = 80 cm downstream, gave typical H^- count rates = 3 x 10^5 counts /s, at = 400 W, = 1 mTorr, along with a distinct high energy tail (<= 20 eV). These and other results are analyzed in detail. The positive ion spectrum showed the H_3^+ count to be consistently high in all cases (= 60-70 %); the counts for H_2^+ and H^+ were =30-35 % and a =few %. Combining the Langmuir probe (LP) and MBMS data it is possible to determine the approximate densities in front of the MBMS probe aperture. At = 500 W and = 2 mTorr, one finds: n_(H^+) = 9.6 x 10^9 cm^(-3), n_(H_2^+) = 1.7 x 10^10 cm^(-3) and n_(H_3^+) = 4.3 x 10^10 cm^(-3). The corresponding H^- density, = 80 cm downstream is n_(H^-) = 3.9 x 10^8 cm^(-3). Accounting for all H^- losses due to scattering and destruction, one finds the effective mean free path for H^- loss to be = 12.4 cm. Noting that H^- formation takes place about = 10 - 30 cm downstream of the source exit, the approximate average H^- density in the formation zone is determined as = 5.5 x 10^10 cm^(-3). This value is remarkably encouraging for H^- production in volume mode, considering the large chamber volume and area, as well as the very moderate power used for the experiments.
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All authors Bibekananda Naik, Ramesh Narayanan, Debaprasad Sahu, Mainak Bandyopadhyay, Ashish Ganguli
Materials Science
Ab initio High-Pressure Phase Diagrams of Al-Mg Alloys in the Low Solute Concentration Limit
Shambhu Bhandari Sharma, Shailesh Mehta and Dario Alfè
Binary
alloy phase diagrams at high pressure are essential for understanding solidification and chemical partitioning in both engineered materials and planetary interiors, yet their experimental determination becomes increasingly challenging under extreme conditions. We apply a fully ab initio approach [J. Chem. Phys. 162, 184502 (2025)], based on density-functional theory, to compute the dilute-limit phase diagram of the Al-Mg system from ambient conditions up to 150 GPa. As a first step, we calculate the melting curves of pure fcc Al and pure hcp/bcc Mg, including the hcp-bcc phase boundary and triple point of Mg, all of which agree closely with available experimental data. The binary phase diagram is then constructed at both compositional extremes. On the Al-rich side, Mg consistently favours the
liquid throughout the entire pressure range, with this preference strengthening monotonically under compression. On the Mg-rich side, Al partitions preferentially into the
liquid at ambient pressure but undergoes a complete reversal above ~60 GPa, becoming solid-favouring as the Mg host transitions from hcp to bcc. This pressure-driven reversal inverts the
topology of the Mg-rich coexistence field from a conventional downward-sloping to an upward-sloping phase boundary, and has direct implications for models of planetary differentiation and interior chemical stratification.
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Optics
A subsurface array of photonic crystal slabs produces green stripes in a scarab beetle
Laura Ospina-Rozo, Nicola S. Kubzdela, Zezheng Zhu et al. (+4 more)
Vivid colours in nature often arise from photonic nanostructures that have inspired diverse technologies. Yet most known examples fall within a limited set of structural themes. Here, we describe a biologically and optically novel structure in the bright green, violin-shaped stripes of the fiddler beetle Eupoecila australasiae. The green colour is produced by a composite, hierarchical structure comprising dense arrays of microscopic, fin-like elements located beneath the cuticle. Each vertical fin, patterned with complementary
lattices of nanospheres and indentations, can be approximated by two photonic
crystal slabs mounted on a solid central core. Optical modelling shows that the fins are strongly iridescent, reflecting light with longer wavelengths near the normal and light with shorter wavelengths at oblique angles. However, disorder in fin orientation and filtering by the overlying cuticle converts the opaline cyan appearance of the fins into the bright diffuse green seen externally. Our work expands the known diversity of biological photonic nanostructures and offers new inspiration for biomimetic designs.
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All authors Laura Ospina-Rozo, Nicola S. Kubzdela, Zezheng Zhu, James A. Hutchison, Mia Wansbrough, Nanfang Yu, Devi Stuart-Fox
Nuclear Theory
An exact time-dependent generator coordinate method with projection for spontaneous fission reactions
N.-W. T. Lau, G. Scamps, P. Tan et al. (+1 more)
Microscopic descriptions of fission dynamics through the barrier rely on different theoretical frameworks depending on the fission regime, with the time-dependent generator coordinate method (TDGCM) commonly used for induced fission and semiclassical approaches such as the Wentzel-Kramers-Brillouin (WKB) method widely employed for spontaneous fission. In this work, we develop a fully microscopic approach to spontaneous fission based on an exact formulation of the TDGCM, avoiding both the Gaussian overlap approximation and semiclassical treatments. By combining the exact TDGCM with new projection tools and a quasistatic description of spontaneous fission, we derive spontaneous fission half-lives from a one-dimensional potential energy surface. A detailed analysis of the model parameters shows that they do not introduce uncontrolled phenomenological effects. Remaining discrepancies with experimental half-lives are related to possible limitations of the underlying microscopic interaction and to the choice of basis states in the generator coordinate method. The new framework provides a microscopic description of spontaneous fission with reduced empirical input and offers a pathway toward improved predictions through future developments of
nuclear interactions, collective coordinates, and the handling of many-body dynamics.
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All authors N.-W. T. Lau, G. Scamps, P. Tan, R. N. Bernard
Classical Physics
Solving the Dissipation Inequality not as a constitutive restriction
Maximiliano Larrain Silva and Amit Acharya
A solution procedure is formulated and solved for treating the nonlinear Dissipation Inequality as a constraint equation within continuum mechanics, and allowing for incomplete knowledge of constitutive behavior. The scheme is demonstrated in the context of the rate-dependent, elastoplastic response of a bar, resulting in a nonlinear problem of constrained optimization. Both closed form and computational results are developed. The computational solutions utilize a sequence of convex optimization problems, and are shown to be accurate. In the example considered, the approach is shown to automatically correct an (intentionally) faulty constitutive specification, resulting in the solution to be in accord with the fundamental postulates of continuum mechanics.
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Statistical Mechanics
Renormalization-Group Stability Does Not Determine Front Selection
Ko Okumura
The Fisher-Kolmogorov-Petrovsky-Piskunov (FKPP) equation provides a paradigmatic example of front propagation and asymptotic-state selection. Using a unified renormalization-group (RG) framework, we show that its traveling-wave solutions form a continuous family of RG fixed points and that all fronts with v >= 2 are locally RG-stable. The resulting RG stability criterion reproduces the classical linear-stability analysis of Canosa, according to which all fronts with v >= 2 are stable. Nevertheless, the asymptotically selected front is v=2, determined by the leading-edge structure of the initial condition rather than by RG stability. The FKPP equation thus provides an explicit example in which RG fixed-point stability does not determine asymptotic-state selection, demonstrating that stability and selection constitute distinct aspects of RG behavior.
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Soft Condensed Matter
Direct visualization of local electric fields in a layer of a ferroelectric nematic liquid
Anej Sterle, Natan Osterman, Calum J. Gibb et al. (+4 more)
Ferroelectric nematic
liquids exhibit complex ferroelectric domains shaped by competing elastic and electrostatic interactions. Using fluorescence and polarizing optical microscopy, we investigate domain formation and
evolution under different anchoring conditions. Charged fluorescent ions map the electrostatic potential, revealing that electric fields are localized near domain walls and material surfaces. Upon cooling, domain walls transform from Ising- to Néel-type configurations, lowering the electrostatic potential, and reversibly recover upon heating.
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All authors Anej Sterle, Natan Osterman, Calum J. Gibb, Jordan Hobbs, Richard J. Mandle, Nerea Sebastián, Alenka Mertelj
Geophysics
Thermo-Hydro-Mechanical Modeling of a TBM Tunnel in Opalinus Clay: Thermal Coupling Effects on Long-term Lining Pressures and Excavation Damage Zone Development
Saeed Tourchi, Martin Ziegler and Arash Alimardani Lavasan
Tunnels in argillaceous formations such as Opalinus Clay (OPA) develop a coupled thermal, hydraulic, and mechanical response. This study examines the New Belchen Tunnel (STB), excavated by tunnel boring machine through faulted OPA shale. Field measurements show a strong relation between lining temperature and radial pressure. We use a two-dimensional plane-strain THM model to examine excavation, construction heat, seasonal temperature cycles, pore-pressure transients, and stress redistribution. The model reproduces the phasing and approximate magnitude of the seasonal pressure cycles and shows how the thermal expansion mismatch between the lining, grout, and OPA modifies lining load and near-field pore pressure. It underestimates the monotonic long-term pressure increase at several sensors. Comparison with radial extensometer measurements indicates that moisture-driven swelling, local geological structure, grout or interface damage, and three-dimensional construction effects also contribute. The model therefore supports a thermal interpretation of the cyclic response while defining the processes required for a fuller long-term back-analysis.
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Atmospheric and Oceanic Physics
Arctic bimodality reflects enhanced variability in the clear-cloudy transition rather than bistability
Nadja Omanovic, J. Antoon van Hooft, Valentina Zeni et al. (+1 more)
The wintertime Arctic boundary layer is characterized by two distinct states, radiatively clear (cloud-free) and radiatively opaque (cloudy), which is reflected in observations as a bimodal distribution. Previous studies hypothesized that these regimes are related to an underlying bistability of the system's dynamics. We apply a drift-
diffusion framework based on the two leading terms of the Kramers-Moyal expansion to observations from 15 winter periods in Ny-Alesund, Norway. Our model captures the bimodality; we find a single stable point for the deterministic drift, however, which questions the existence of bistable deterministic dynamics. Instead, the observed regimes can be attributed to state-dependent
stochastic fluctuations with maximum amplitude close to the clear-cloudy transition. The position of the stable point depends on the meteorological conditions. Controlling for synoptic variability does not remove the state-dependence of
diffusion, however. The cloudy regime is associated with southwesterly winds, high specific humidities, and uplifting motion, the latter two being conducive for cloud formation, while the cloud-free regime occurs under drier conditions and northeasterly winds. Through an illustrative example, we suggest a possible process-based interpretation of our statistical analysis. The nonlinear onset of cloud formation, once atmospheric humidity reaches saturation, could map state-independent fluctuations in humidity to state-dependent fluctuations in cloudiness.
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All authors Nadja Omanovic, J. Antoon van Hooft, Valentina Zeni, Franziska Glassmeier
Earth and Planetary Astrophysics
Accretion across scales: streamers, surface-layer transport, and rapid replenishment in young protoplanetary discs
Christian Granzow Holm, Michiel Lambrechts, Michael Kuffmeier et al. (+3 more)
Protoplanetary discs evolve around newly-formed
stars through an interplay of infall from surrounding turbulent cloud material,
accretion towards the young
star, and
outflow driven mass-loss. It has been challenging to determine if discs are fed predominantly through infall along the disc midplane, or along the poles, and if
accretion occurs in a steady or burst-like fashion. Here, we present a suite of 3D ideal magnetohydrodynamical simulations of protoplanetary disc formation and
evolution in a dynamic, large-scale molecular cloud environment using the adaptive mesh refinement framework DISPATCH. We focus on nine
stellar systems, where we resolve discs down to a scale of 0.8 au. Across the sample,
stellar accretion proceeds at rates of $\sim$10$^{-5}$ M$_\odot$ yr$^{-1}$ over 10$^{5}$ yr, with significant variability. Discs grow to 100 au scales and remain gravitationally stable in time, with disc-to-
star mass ratios below 10 %. Transient high-density streamers, with 10 kyr infall times, can drive anisotropic mass delivery at rates comparable to the background
accretion flow. Their interaction with discs typically results in a temporary reduction of the disc size by half, and disc mass by 40 %. During later quiescent disc
evolution stages ($t\gtrsim$50 kyr),
accretion predominantly occurs through the midplane and disc surface layers. This is associated with the development of a toroidal
magnetic field morphology, which includes field reversals across both disc surfaces. In this way, the full disc mass reservoir is replenished on 10 kyr-timescales. These findings support that the outer parts of very young discs, when well-ionised and close to the ideal MHD regime, are not yet conducive to
planet formation, due to high replenishment rates, strong
turbulence, and disruptive streamer infall events.
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All authors Christian Granzow Holm, Michiel Lambrechts, Michael Kuffmeier, Anders Johansen, Troels Haugbølle, Åke Nordlund
Applied Physics · Cross-listed from eess.AS
MEMS Microphones as Ultrasonic Transducers: Nonlinear Electrostatic Actuation and a Parametric Array Prototype
Xiaoyu Niu, Zihuan Liu, Ehsan Vatankhah et al. (+2 more)
This paper investigates commercial-style capacitive MEMS microphone dies as air-coupled ultrasonic transmitters under nonlinear pull-in and snap-back actuation and demonstrates a compact parametric-array prototype. A single die produces large diaphragm displacement and measurable ultrasonic pressure in air. A 28-die array driven at 83 and 93 kHz generates a directional component at the 10 kHz difference frequency. Measurements are compared with analytical radiation theory and finite-element modeling, and the effects of aperture, fill factor, device uniformity, and receiver nonlinearity are discussed.
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All authors Xiaoyu Niu, Zihuan Liu, Ehsan Vatankhah, Yuqi Meng, Neal A. Hall
Cosmology and Nongalactic Astrophysics
A refined method for measuring cosmological distances using variability and proper motions in AGN with VLBI-detected counter-jets
Jeffrey A. Hodgson, Anthony Carr, David Parkinson et al. (+6 more)
In a previous paper, we described a `standard speed-gun' (SSG) distance that uses the speed of light to standardize a ruler under the assumption that the
radio variability seen in blazars is causally limited. The apparent size is then measured with Very Long Baseline Interferometry in order to derive the angular diameter distance. A key limitation of this method is that it requires knowledge of the relativistic Doppler factor. Previously, we estimated the distance to the bright
radio source, 3C 84 at the center of the Perseus cluster assuming a Doppler factor of \delta ~ 1. In this paper, we aim to describe how a detected counter-jet and approaching jet proper motions can be used to remove the need for knowledge of the Doppler factor when measuring cosmological distances in this way. Under the assumption of a disk (or spherical) geometry and parameterizing the relationship between the physical emitting region and the variability timescale via a causality correction factor (kappa), we estimate a refined angular diameter distance to 3C 84 (z=0.0178) with statistical errors. Assuming kappa=1, we derive distances of D_A,disk = 78.9(-9.8+11.0) Mpc (or D_A,sphere = 71.2(-8.8+9.7) Mpc). Comparing these results to literature
benchmarks, we find that the spherical assumption yields a distance consistent with local Type Ia
supernovae calibrated to the SH0ES H0, while a disk-like geometry aligns with expectations from a lower H0 cosmology. Ultimately, this demonstrates that utilizing jet and counter-jet kinematics successfully removes the Doppler-factor dependence from the standard speed-gun method, providing a viable independent distance estimate once the
geometric structure of the jet is resolved.
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All authors Jeffrey A. Hodgson, Anthony Carr, David Parkinson, Matteo Statti, Jaehyeon Myeong, Benjamin L'Huillier, Arman Shafieloo, Ioannis Liodakis, Se Heon Oh
Solar and Stellar Astrophysics
Performance of radio-based detection to operational monitoring M5+ class solar flares
Julia van Ravenswaaij, Ines Wilms, Ivan Ricardo et al. (+1 more)
Early detection of major
solar flares is critical for defense operations due to their potential to disturb radar and
radio systems. Typically, soft X-ray flux is used to monitor and classify
solar flares, but since this flux has to be measured in space, it means that its availability itself is dependent on space weather conditions. For this reason, in this paper, we investigated the feasibility of using ground
radio observations to monitor major (M5+ class)
solar flares. We made use of
datasets from the GOES-16 satellite and the
Radio Solar Telescope Network in the time range between March 2023 and March 2025. An elastic net regularized logistic regression model was trained on this data, optimized through a grid search and with incorporated class weighting for class imbalance. It was found that especially higher frequencies (8800 MHz) had a reasonable ability in monitoring and predicting major
flares (precision and recall for
flare events are 53% and 65%, respectively - implying that roughly one third of
flares were not detected - with signals appearing, on average, 3 to 4 minutes before the M5 threshold is exceeded).
Radio measurements at super high frequencies can thus serve as an alternative method to monitor major
solar flaring activity.
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All authors Julia van Ravenswaaij, Ines Wilms, Ivan Ricardo, Michaela Brchnelova
General Relativity and Quantum Cosmology
Charged Black Holes with a Lorentz–Violating Kalb–Ramond Background
Jia-Hui Yang, Xin-Yu Guo, Jia-Zhou Liu et al. (+1 more)
We investigate exact static, spherically symmetric electrically charged black hole solutions in a gravitational theory with spontaneous Lorentz-
symmetry breaking induced by a background Kalb–Ramond field. In contrast to previous analyses that retained only one nonminimal
curvature coupling, we include the combined effects of the two independent nonminimal
curvature couplings and obtain charged black hole solutions both with and without a cosmological constant. Using the Iyer–Wald covariant phase-space formalism, we derive the corrected thermodynamic quantities and analyze the Joule–Thomson expansion, including the inversion curve and the cooling/heating regions. We further apply the topological approach to black hole thermodynamics to characterize the van der Waals-like phase transition and show how the thermodynamic critical temperature and pressure are encoded in the corresponding topological defect curve. These results clarify the thermodynamic and topological signatures of electrically charged black holes in
gravity with a Lorentz-violating Kalb–Ramond background.
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All authors Jia-Hui Yang, Xin-Yu Guo, Jia-Zhou Liu, Yu-Xiao Liu
Instrumentation and Methods for Astrophysics
The Wetterstein Millimeter Telescope: A New German Facility for Astronomy and Geodesy
Alexander Neidhardt, Matthias Kadler, Anne-Kathrin Baczko et al. (+7 more)
The Wetterstein Millimeter
Telescope (WMT) is a planned broadband (1.2-120 GHz)
radio telescope to be established near the Environmental Research Station Schneefernerhaus (UFS) on Germany's highest mountain, the Zugspitze. Developed by a consortium of German research institutes and partners, the WMT is conceived as a multidisciplinary research infrastructure supporting
radio astronomy, geodetic VLBI, satellite communications, space situational awareness, and technology development. The
telescope is designed to operate within international VLBI networks, including the European VLBI Network, the Global mm-VLBI Array, and future ngVLA and SKA-VLBI observations. This contribution summarizes recent progress in the WMT project, including the
evolution of the
antenna design, and highlights the potential of the WMT to support future astronomical and geodetic VLBI.
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All authors Alexander Neidhardt, Matthias Kadler, Anne-Kathrin Baczko, Guido Dietl, Urs Hugentobler, Matthias Schartner, Tobias Ullmann, Till Rehm, Jompoj Wongphechauxsorn, for the WMT consortium
Earth and Planetary Astrophysics
A JWST Study of Stardust. I. Infrared Spectroscopy of Comet 81P/Wild 2 and Overall Composition
Nathan X. Roth, Stefanie N. Milam, Diane H. Wooden et al. (+11 more)
We report observations of comet 81P/Wild 2, target of the Stardust sample return mission, on UT 2023 March 20 and 24 at a heliocentric distance ($r_H$) of 1.85 au using the NIRSpec and MIRI integral field unit spectrographs on board the James Webb Space
Telescope (JWST). This study is the first compositional comparison between JWST remote-sensing spectroscopy of a
solar system object against terrestrial analysis of its returned samples. We securely detected molecular emission from H$_2$O, CH$_4$, C$_2$H$_6$, CH$_3$OH, CO, CO$_2$, $^{13}$CO$_2$, OCS, HCN, and CN and find molecular abundances consistent within $2\sigma$ with those reported during previous perihelion passages. The water ortho-to-para ratio was $2.76\pm0.05$, and the $^{12}$CO$_2$/$^{13}$CO$_2$ ratio was $85\pm4$. Thermal emission from the
nucleus and
dust was detected and modeled, providing an effective
nucleus radius of $1.77\pm0.04$ km and a
dust composition (relative mass fraction of the submicron grains) of $\sim36\%$ amorphous carbon, $\sim25\%$ amorphous Mg:Fe olivine, $\sim23\%$ Mg-rich crystalline olivine, and $\sim15\%$ amorphous Mg:Fe pyroxene. The crystalline mass fraction of the sub-micron grains in the coma was $0.362\pm0.003$. Comparison of the JWST-derived thermal model against the fine-grained materials in Stardust returned samples demonstrates complementarity between the missions, with each most sensitive to a different population of the coma
dust grains.
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All authors Nathan X. Roth, Stefanie N. Milam, Diane H. Wooden, Charles E. Woodward, Dominique Bockelee-Morvan, Michael S. P. Kelley, Steven B. Charnley, Simon J. Clemett, Martin A. Cordiner, Perry A. Gerakines, David E. Harker, Els Peeters, Ella Sciamma-O'Brien, Geronimo L. Villanueva
Quantum Physics
A Standard Quantum Mechanical Treatment to Rationalize the Delayed-Choice Quantum Eraser
Vipul Badhan, Pranvi, Samreet Dhillon et al. (+1 more)
Ever since the proposal of delayed choice
quantum erasure and subsequent realization in the experiment by Kim et al., the interpretation and implications of delayed-choice experiments have remained a subject of intense foundational debate. This paper resolves the apparent paradox attached to the experiment using standard
quantum mechanics. Using an extended Mach-Zehnder interferometer which captures every operational feature of the original experiment, we show that choosing between which-path and erasure detectors is simply a choice of measurement bases, which does not rewrite a
photon's past. Furthermore, by mapping the experiment to a two-way Stern-Gerlach framework, we prove that
quantum erasure is an expected result of measuring entangled states, not a physical anomaly. Ultimately, through a pedagogical game, we illustrate that the illusion of retrocausality arises from asking illegitimate questions, and that a forward-in-time description is entirely sufficient to explain the logic.
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All authors Vipul Badhan, Pranvi, Samreet Dhillon, Bindiya Arora