Papers

In epithelia, how do collective cell migration and tissue spatial organization feedback on each other? We address this question through large-scale numerical simulations of the cellular Potts model. By accounting for both cell morphology and cytoskeletal activity, we uncover a remarkably rich phase diagram featuring multiple types of orientational order, either as distinct phases or coexisting across length scales. We identify a specific pathway in parameter space along which a gradual increase in the actin polymerization rate drives a phase transition into a long-range flocking state. Simultaneously, quasi-long-range nematic order emerges at length scales much larger than the cell size due to the combined effects of directed motion and lateral cell-cell interactions. At length scales comparible to cell size, however, cells adopt an approximatively hexagonal morphology, resulting in hexanematic order, similar to that observed in reconstituted Madin-Darby Canine Kidney (MDCK) cell monolayers. With further increases in actin polymerization, nematic order becomes fully long-range, while hexatic order remains quasi-long-range and confined to short length scales, but independent of cytoskeletal activity. When noise is sufficiently low to allow crystallization at finite actin polymerization rate, cycling the cell-monolayer across the melting transition yields an example of phenotypical hysteresis, reminiscent of that observed across the epithelial-mesenchymal transition.

Pattern formation in soft, active, and biological matter is described by two ostensibly distinct continuum frameworks: phase-field theories driven by chemical-potential gradients, and mass-conserving reaction-diffusion (McRD) dynamics governed by local interconversion kinetics. Here we establish a constructive, equation-level duality valid in the nonlinear, far-from-equilibrium regime. McRD is the broader class: every chemical-potential theory with conserved order parameters embeds as the slow dynamics on an attracting manifold of an McRD system; conversely, every McRD with attractive nullcline admits an exact chemical-potential representation in the fast-interconversion limit, with the constitutive relation set by the nullcline. The construction resolves the generic non-invertibility of the chemical-potential as a function of density in phase-separating regimes by embedding it as an attracting manifold in an extended two-field description with conserved total density. Gradient stiffness maps faithfully onto an intrinsic reaction-diffusion length set by the auxiliary field, yielding a diagonal-diffusion normal form whose interface profile matches the original Cahn-Hilliard model by construction. The duality yields an explicit dictionary for phase coexistence: the Maxwell equal-area construction is exactly equivalent to the reactive turnover-balance condition. It extends to weakly nonconservative dynamics, unifying reaction-arrested coarsening and mesa splitting, and to multicomponent theories with broken Maxwell symmetry. As a concrete payoff, the dual sharp-interface picture yields a closed-form velocity law for traveling waves in nonreciprocal Cahn-Hilliard dynamics, in quantitative agreement with simulations.

We show that the low-energy states of non-Abelian topological orders possess extensive magic which is long-ranged, and cannot be eliminated by a constant-depth local unitary circuit. This refines conventional notions of complexity beyond the linear circuit depth which is required to prepare any topological phase, and provides a new resource-theoretic characterization of topological orders. A central technical result is a no-go theorem establishing that stabilizer states–even up to constant-depth local unitarie–cannot approximate low-energy states of non-Abelian string-net models which satisfy the entanglement bootstrap axioms. Moreover, we show that stabilizer-realizable Abelian string-net phases have mutual braiding phases quantized by the on-site qudit dimension, and that any violation of this condition necessarily implies extensive long-range magic. Extending to higher spatial dimensions, we argue that any state obeying an entanglement area law and hosting excitations with nontrivial fusion spaces must exhibit extensive long-range magic. This applies, in particular, to ground-states and low-energy states of higher-dimensional quantum double models.

Ultrafast diffraction is the cutting-edge technique to extract the atomic temperature at femtosecond timescales, and further related quantities - in particular, electron-phonon coupling strength at elevated electronic temperatures. The present work demonstrates limitations of such an analysis, emphasizing the importance of careful evaluation of the evolution of the Debye temperature. It is shown that, due to the sensitivity of the Debye-Waller analysis to this parameter, neglecting its changes under electronic excitation may lead to significant deviations of the atomic temperature extracted from its true values.

Efficient and selective excitation of lattice vibrations is central to controlling energy flow at the nanoscale, yet remains challenging under conventional optical excitation. Here, we introduce a mid-infrared-assisted phonon amplification approach, termed MIRAPA, that enables efficient energy injection directly into vibrational bonds. Using surface-enhanced resonant Raman scattering in few-layer $\mathrm{MoS_2}$, we exploit strong exciton–phonon coupling to monitor phonon populations. When mid-infrared (MIR) light is introduced, it couples directly to out-of-plane lattice vibrations, leading to room-temperature phonon amplification exceeding $80\%$. Crucially, MIRAPA bypasses electronic excitation pathways, allowing the MIR power density to be nearly $300\times$ lower than that required for visible excitation to achieve comparable enhancement. The resulting phonon modulation is robust, persisting over more than $2800$ on/off cycles and exceeding $15$ hours of continuous-wave laser illumination without degradation. Quantitative analysis yields an effective noise-equivalent power of approximately $0.3\,\mathrm{nW}/\sqrt{\mathrm{Hz}}$ for MIR detection, highlighting the sensitivity of the approach. By combining vibrational selectivity, low-power operation, and long-term stability, MIRAPA provides a robust platform for probing and amplifying phonons in two-dimensional semiconductors. These results open new opportunities for nanoscale vibrational sensing, mid-infrared detection, and phonon-based coherent devices, including routes toward phonon lasing.

We consider the displacement contribution to photoresistance in overlapping Landau levels at radiation frequencies much smaller than the cyclotron frequency. We show that in the limit of short-range disorder and high radiation power, this contribution leads to a new class of magneto-resistance oscillations. These oscillations, which we call radiowave-induced resistance oscillations (RIROs), are distinct from the well known microwave-induced resistance oscillations in the following aspects: (i) their amplitude is independent of power, (ii) their period is controlled by the radiation electric field, rather than by the radiation frequency, and (iii) they can be either $1/B$ or $1/B^2$-periodic, depending on $B$, with the crossover point linked to the width of the cyclotron resonance absorption curve. We also show that RIROs should be readily observed in experiments.

Crystallization during droplet evaporation gives rise to complex, self-organized structures, yet the mechanisms underlying the emergence of ordered functional phases remain poorly understood. In this study, we present a comprehensive, multi-scale investigation into the crystallization dynamics of NaCl during droplet evaporation on a germanium (001) substrate, relevant for its IR applications. Through systematic microscopic characterization, we identify the formation of diverse microstructures, including 1D photonic crystal nanostructures formed within hybrid crystal-glass photonic system. To enable quantitative comparison across experimental conditions, we introduce the NaCl equivalent height as a unified metric to describe and classify the evolution of crystalline morphology. Our results reveal that diffusion anisotropy, rather than growth kinetics, primarily governs the maximal attainable structure size. Quantitative thin film interference analysis demonstrates the presence of discrete thickness layers in the film. Controlled evaporation experiments yield homogeneous crystallization patterns across the entire droplet area, facilitating the emergence of ordered photonic structures. Time-series dynamics analysis of height profiles uncovered the spatiotemporal evolution of the crystallization front, providing insights into the details of underlying physical mechanisms. Together, these results establish a robust experimental framework for understanding and predicting crystallization behavior in evaporating droplets, with potential applications in materials synthesis, photonics, and microscale pattern formation.

We present an $\mathcal{O}(L^3)$ algorithm for evaluating contracted Clebsch–Gordan tensor products in $\mathrm{O}(3)$-equivariant machine learning potentials at fixed Canonical Polyadic (CP) rank. Mapping the angular integral to a structured Gauss–Legendre and Fourier tensor-product grid decouples the radial channel contractions from the angular transforms. The antisymmetric parity-odd Clebsch–Gordan channels, unreachable by the symmetric pointwise product on a scalar $S^2$ grid, are recovered through the surface-curl pairing $\hat r \cdot [\nabla_{S^2} A \times \nabla_{S^2} B]$, the spherical Poisson bracket, which supplies the $L=1$ angular momentum on the grid while preserving rotational equivariance. The construction extends to parity-aware equivariant message passing in atomic-cluster-expansion-style architectures and is verified by direct numerical quadrature. The full uncontracted Clebsch–Gordan tensor product remains subject to the $\mathcal{O}(L^4)$ output-size lower bound. A benchmark shows wall-clock scaling empirically as $L^2$ across the practical $l_{\max}$ range. For the on-site contraction this is pre-asymptotic, giving way to $L^3$ at large $l_{\max}$. For message passing it is structural and the runtime is memory-bandwidth bound on $L^2$-sized grid tensors.

Actively tunable nanophotonic platforms that control light-matter interactions enable reconfigurable optical systems and programmable photonic integrated circuits. Hydrostatic pressure provides a noninvasive and material-agnostic mechanism for modulating the refractive index and resonance conditions without introducing free carriers or structural damage. Here, we demonstrate multiple pressure-dependent functionalities in silicon nitride nanostructures, including resonance tuning, refractive index modulation, and polarization state conversion. Applying a pressure of up to 5 GPa, we observe a Fabry-Pérot resonance shift of up to 30 nm and a relative refractive index decrease of up to 4%. Based on the results, we design and examine, to the best of our knowledge, the first extreme-pressure-tunable, polarization-converting metasurface, which tunes the ellipticity and orientation angle of the output light. These findings establish pressure-controllable silicon nitride as a viable platform for reconfigurable photonics and extreme-environment nanophotonic systems, including deep-ocean exploration, planetary interiors, and space applications.

We study dynamical scaling in the quantum-critical fan of the pseudogap-metal to Fermi-liquid transition of the two-dimensional Hubbard model. Using a four-patch dynamical cluster approximation with the numerical renormalization group as a cluster impurity solver, we access real-frequency dynamics over several decades at arbitrary temperatures. Close to the critical doping, the local spin and cluster-current susceptibility spectra exhibit $x=\omega/T$ scaling of the form $\chi''(\omega,T)\sim \tanh(x/2)$, and the cluster contribution to the optical conductivity obeys $T\sigma'_{\mathrm{cl}}(\omega,T) \sim \tanh(x/2)/x$, implying a $1/T$ cluster dc conductivity. In the scaling regime, the vertex contribution to the cluster optical response is much larger than the bubble contribution. We further find evidence for a marginal-Fermi-liquid nodal self-energy. This, together with the $1/T$ vertex contribution to the conductivity, implies strange-metal optical transport in the quantum critical region. Our results describe several qualitative aspects of several experimental observations.

We study the normal-state, doping-driven phase diagram of the square-lattice Hubbard model using the dynamical cluster approximation combined with the numerical renormalization group as a cluster solver, which gives direct access to real-frequency dynamics at essentially zero temperature. In a parameter regime relevant for cuprates, $U=7t$ and $t'=-0.3t$, we find a critical doping $p^{\ast}$ that marks a continuous quantum phase transition between a pseudogap metal and a normal Fermi liquid. The transition is identified by a continuous collapse, from both sides, of the Fermi-liquid scale extracted from charge, spin, and $d_{x^2-y^2}$-wave pairing susceptibilities. This collapse produces a non-Fermi-liquid regime at intermediate energy scales, which appears to extend to arbitrarily low scales at $p^{\ast}$. As $p^{\ast}$ is crossed from the normal Fermi liquid at $p>p^{\ast}$ into the pseudogap metal at $p<p^{\ast}$, the coherent low-energy spectral weight in the antinodal region is lost and replaced by a narrow, metallic pseudogap, while the nodal region evolves smoothly and remains comparatively coherent. This gives rise to Fermi arcs in the pseudogap metal at $p<p^{\ast}$, since the zero-frequency spectral weight remains large in the nodal region but is strongly suppressed in the antinodal region.

We propose a geometric mechanism for fractional quantum Hall states based on impurity-induced correlations within a Landau level. A correlated distribution of ionized impurities partially modifies the Landau-level degeneracy through coherent coupling between cyclotron orbits, generating fractional energy sublevels. The odd-denominator hierarchy emerges naturally from the intrinsic guiding-center quantization and the correlated cyclotron motion. The resulting spectrum reproduces the principal experimentally observed fractional sequences and predicts a strong dependence of fractional-state stability on impurity geometry and layer separation. The absence of an incompressible Hall plateau at filling factor 1/2 follows from cancellation of the geometric correlations responsible for odd-denominator states. These results suggest that impurity-induced geometry may constitute an additional organizing principle in quantum Hall systems.

Scintillators convert ionizing radiation into visible photons, enabling applications from cosmic ray detection to medical imaging. Two independent strategies for improving scintillator performance via nanoscale patterning have recently been demonstrated: engineering material properties to enhance absorption of ionizing radiation and integrating nanophotonic structures to enhance the spontaneous emission rate ("nanophotonic scintillators"). Here, we propose a nanophotonic scintillator that simultaneously enhances both the initial energy conversion and the spontaneous emission rate, by periodically stacking a fast-emitting scintillator and a visible-light-transparent material with strong X-ray attenuation ("stopping layer") to form a one-dimensional (1D) photonic crystal (PhC) scintillator. Photoelectric absorption in the stopping layer increases the number of photoelectrons that deposit energy in neighboring scintillator layers and contribute to scintillation. At the same time, the spontaneous emission rate is enhanced by the nanophotonic structuring itself. We design a 1D PhC comprising an organic scintillator and indium tin oxide (ITO) as the stopping layer and numerically simulate the enhancement in scintillation yield and decay rate. The total detected light output is enhanced by up to a factor of 700 compared to a bulk organic scintillator of equal thickness. We further investigate a 1D PhC structure integrating inorganic and organic scintillators for time-of-flight positron emission tomography (TOF-PET): replacing the non-scintillating stopping layer with an inorganic scintillator further increases the light yield, and the coincidence time resolution (CTR) is enhanced up to 3.5 times compared to a bulk inorganic scintillator of equal thickness. Our work presents a unified approach to improve key scintillation parameters within a single nanophotonic structure.

By implementing the Bogoliubov-de Gennes (BdG) formalism of population-imbalanced atomic Fermi gases with pairing interactions in a thin spherical shell, we characterize the Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) state in such a compact geometry. We first construct a phase diagram showing where uniform solutions of spin-polarized Fermi superfluid from the BdG equation cease to exist due to the vanishing order parameter. Near the boundary, various LOFF states with spatially modulating order parameters and density profiles can survive as convergent solutions to the BdG equation. When both uniform and LOFF solutions are present, we compare their grand potentials to determine the energetically favorable state and find that the LOFF states with multiple nodes in the order parameter become more stable at higher spin polarization. However, the LOFF state only survives close to the phase boundary where the uniform solutions vanish, indicating fragility of the LOFF state on a spherical surface. We also briefly discuss possible implications.

We study the current-induced magneto-optical Kerr effect (MOKE) in Bi$_{1-x}$Sb$_x$ semi-metalic alloys. The MOKE signal is found to be the largest in pure Bi ($x=0$), exceeding that of transition metals by nearly four orders of magnitude, and decreases monotonically with increasing Sb concentration. We find the MOKE signal scales with the resistivity ($\rho$) as $\rho^{1.7 \pm 0.6}$ and with the mobility ($\mu_\mathrm{c}$) as $\mu_\mathrm{c}^{2.0 \pm 0.2}$. Model calculations show that such exponent can be accounted for if the Dirac electrons are responsible for the generation of spin current. This is in contrast to the $\rho^{2}$ and $\mu_\mathrm{c}^{-2}$ scaling of the MOKE signal induced by the free electrons in parabolic band. The scaling of the MOKE amplitude with the resistivity also partly accounts for the order of magnitude differences of the signal observed between metals, semimetals, and semiconductors. These results demonstrate that current induced MOKE serves as an effective means to characterize the nature of spin current in materials with diverse electronic structures.

We show that anisotropic spin interactions do not merely break spin-space group (SSG) symmetries, but instead twist them through cohomology invariants, yielding symmetry classes beyond subgroups of $ O(3)\times \operatorname{Isom}(\mathbb{R}^3) $. This requires redefining the spin-only group $ S_0 $ in terms of proper spin rotations. Based on this unitary $ S_0 $, we formulate a twisted SSG (tSSG) theory that captures the complete set of spin-space symmetries. We then study a spin-1 model with tSSG symmetry using linear flavor wave theory and find $\mathbb{Z}_2$ topological quadrupolar excitations defined on a spin Brillouin Klein bottle. Specifically, the quadrupolar excitations possess a momentum-space glide-reflection symmetry and the edge states exhibit a nonlocal momentum twist. These results establish the symmetry language required for interacting spin systems, whether realized in magnetic materials or on programmable quantum simulators, and open a route to unconventional magnetism.

We apply the Worldvolume Hybrid Monte Carlo (WV-HMC) method [arXiv:2012.08468] to the two-dimensional Hubbard model, which is known to suffer from a severe sign problem when the system is doped (away from half filling). We show that the method predicts physical observables with controlled statistical errors on an $8 \times 8$ lattice at temperature $T/t = 1/6.4 \approx 0.156$ and interaction strength $U/t = 8.0$ ($t$ is the hopping amplitude), for which the standard determinant quantum Monte Carlo fails.

In a Scanning Tunneling Microscope (STM), when a tunneling electron treated as a point charge enters the barrier region between the tip and the sample, it induces image charges on the conducting surfaces, which modifies the shape of the potential barrier it sees. In this paper, the effect of the modification in the barrier potential due to these induced charges on the tunneling current density and currents in an STM,is studied as a function of the tip-sample distance $d$ and the Bias Potential $eV_b$. The image potential is found to reduce the height and the effective width of the potential barrier, leading to a huge increase in the tunneling current densities. This huge increase (by several order of magnitudes) is however unreasonable, prompting a revisit of the assumption that the electron in the barrier region is a point particle.

Resonant cooling of the nuclear spin system of a semiconductor by spin-polarized charge carriers under pumping with helicity-modulated polarized light is considered theoretically. It is shown that in the case of strong Knight field of charge carriers, exceeding local fields of the dipole-dipole interaction of nuclear spins, the Overhauser field arising as a result of resonant cooling can considerably modify the overall shape of magnetic-field dependences of charge carrier spin polarization, experimentally observed as the Hanle effect.

Biological neural networks can operate in qualitatively distinct dynamical regimes, and transitions between these regimes are thought to underlie changes in computation and behavior. The seminal work of Sompolinsky, Crisanti, and Sommers (SCS) showed that random recurrent networks undergo a transition from quiescence to asynchronous chaos, establishing a paradigmatic link between random connectivity, dynamical instability, and internally generated fluctuations in neural circuits. Here, we extend this framework to two-population firing-rate networks with segregated excitatory and inhibitory neurons and target-specific inhibitory couplings that break excitation–inhibition balance. Using dynamical mean-field theory, we derive self-consistent equations for the macroscopic mean activities and autocorrelations, together with stability criteria distinguishing mean-driven and fluctuation-driven instabilities. We show that target-specific inhibition organizes the phase diagram into three qualitative classes: inhibition-dominated or strictly balanced networks display only quiescent activity and asynchronous chaos; excitation-dominated networks display persistent activity together with either synchronous chaos with non-vanishing mean activity or coherent oscillations, depending on the stability-matrix eigenvalues. Crucially, coherent oscillations do not coexist with chaotic fluctuations around the periodic mean trajectory; rather, their onset suppresses the chaotic component, reminiscent of input-induced suppression of chaos. These results generalize SCS theory to recurrent networks with explicit excitatory–inhibitory structure and identify target-specific inhibition as a key control parameter for large-scale neural dynamics.

We study numerically the evolution of one-dimensional FKPP fronts initiated from steep initial conditions in the presence of a quenched random growth rate. Compared to both the homogeneous case (with velocity $v_0$) and deterministic disorder, quenched randomness increases the average propagation speed. We show that the velocity shift relative to the homogeneous case scales linearly with the disorder variance $\sigma^2$, with a universal prefactor – independent of the specific distribution of the disorder – such that $v = v_0 + a \sigma^2$, with $a \approx 0.02432 \pm 0.00002$. Moreover, the front position exhibits diffusive fluctuations across disorder realizations. The corresponding effective diffusion coefficient scales quadratically with $\sigma$, $D = \frac{b^2 \sigma^2}{2}$, with $b \approx 0.223 \pm 0.002$. These results suggest a universal statistical response of FKPP fronts to quenched heterogeneity.

We observe an enhanced visibility of charge-density-wave correlations in a cold-atom realization of the attractive Hubbard model following a rapid boost of the interaction strength. The interaction boost associates nonlocal pairs into doublons which mark the center of mass of the original pairs. The enhancement is largest in the strongly correlated regime where pairing is nonlocal. We distinguish the unpaired Fermi liquid from the pseudogap phase of preformed pairs by analyzing atom-resolved spin-charge correlations after the ramp. The technique we establish here may facilitate the observation of exotic forms of pair order in spin-imbalanced systems, and of stripe order in the dual case of the doped repulsive Hubbard model.

Establishing structure-property linkages in polycrystalline materials requires representative two- (2D) and three- (3D) dimensional microstructural inputs for full-field simulations. A core objective of microstructure characterization and reconstruction is the generative synthesis of 2D and 3D microstructures that reflect a target statistical ensemble using limited 2D data as a reference. This work introduces an orientation-based differentiable microstructure characterization and reconstruction framework, implemented in MCRpy, to perform reconstructions of voxelized images. Unit quaternions in combination with symmetrized hyperspherical harmonics are utilized to derive a continuous, symmetry-invariant representation of crystallographic orientations to overcome the numerical singularities and discontinuities associated with traditional Euler-based methods. The descriptor-based reconstructions are driven by a set combining two-point spatial correlations, a novel hybrid three-point variogram, and a mean variation regularizer to capture both global texture and local interfacial topology. The framework's efficiency is demonstrated by reconstructing 3D realizations from 2D orientation data of an aluminum alloy after thermo-mechanical processing, successfully recovering both morphological features and crystallographic distribution. Systematic benchmarking indicates that second-order gradient-based optimization, utilizing the L-BFGS-B algorithm, effectively navigates the complex loss landscape to generate high-fidelity realizations with minimal residuals. This methodology provides a versatile, open-source framework for the digital synthesis of polycrystalline representative volume elements to facilitate the rapid development of microstructure-informed materials design workflows.

We study Lévy-like and truncated Lévy-like flights with step probability distribution of the form $r^{-1+\nu}$ for negative, positive, and zero $\nu$, focusing on the appearance of fractal geometry characteristics in the generated point sets. Forming ensembles of such point sets with fixed multiplicity, we develop simulation techniques leading to the desired value of correlation dimension in a vast continuous interval of scales. In particular, we demonstrate the possibility to produce ensembles of data sets with a low number of points with the needed properties. Furthermore, we show that the positive $\nu$ distributions, apart from a region near the upper scale limit, show fractal behaviour that extends to infinitesimally low scales. As an example, we apply our findings to producing simulations relevant to the search for critical fluctuations, related to QCD critical endpoint, in heavy-ion collision experiments.

Matter under irradiation may enter unusual transient states, outside of its equilibrium phase diagram. One of such states is a superionic-like state, in which one sublattice of a compound liquifies, whereas another one remains solid. Here, we study theoretically post-transition metal oxides under ultrafast excitation of its electronic system, identifying which compounds produce such a superionic state. It is shown that oxides with sufficiently sparce metallic sublattices (e.g. corundum structure) generally form transient superionic states via nonthermal phase transition. More closely packed lattices (such as the zinc-blend structure in ZnO and CdO) do not exhibit superionicity. Tl and Pb oxides only enter thermally-produced superionic states (induced by the atomic heating via electron-phonon coupling), but not nonthermal ones. Sn and Bi oxides demonstrate states that cannot be clearly classified, in which oxygen subsystem diffuses significantly more and faster than the metallic one, but the metallic one is not stable as it would be in a truly superionic state.

Numerical methods for modeling thin-film magnetization are primarily focused on computing the current density distribution. The highly nonlinear current-voltage characteristic of type-II superconductors significantly complicates the accurate computation of the electric field. The T-E formulation-based mixed finite element method, previously derived for flat superconducting films, enables the simultaneous, accurate determination of both variables. Another advantage of this method is that the computational domain is limited to the film itself: no meshing of the surrounding space is required. The thin-shell approximation reduces the problem to a two-dimensional one. This work extends the T-E formulation and numerical method to non-flat superconducting shells with a metal substrate. We validate the method with several test examples, including modeling the magnetization of a sphere. The method is then applied to a realistic model of a cylindrical magnetic dynamo pump, and the generated open-circuit voltage is computed.

Ruddlesden-Popper bilayer nickelates provide an emerging platform for studying high-temperature superconductivity, yet the superconducting pairing symmetry remains under debate. Here, we use atomic-resolution scanning tunnelling microscopy and spectroscopy to investigate superconducting 1.5-unit-cell (La,Pr)3Ni2O7 films grown on SrLaAlO4. A cryogenic ultrahigh-vacuum (UHV) sample transfer preserves an ordered sqrt(2) * sqrt(2) surface and yields reproducible U-shaped spectra with two gap scales of ~14 and ~20 meV and extended flat zero-conductance bottoms. By contrast, samples exposed for a longer time in UHV without cooling during transfer show V-shaped spectra despite retaining the surface reconstruction and a transport superconducting transition onset above 40 K. Wide-energy-range spectra indicate that oxygen loss can mix density-wave-related spectral weight. Our measurements provide an atomic-scale observation of the intrinsic nodeless superconducting gap in bilayer nickelate ultrathin films.

We investigate the melting behavior of calcium oxide (CaO) under extreme conditions, a problem that remains poorly constrained due to experimental limitations despite its relevance for geophysical and technological applications. We develop a Machine Learning Interatomic Potential (MLIP) for CaO with PANNA 2.0 and the LATTE descriptor, training it on a dataset of $\sim$12,000 configurations including solid, liquid, interfacial, and void-containing structures, extracted from ab-initio molecular dynamics data employing PBEsol exchange-correlation functional. We perform large-scale molecular dynamics simulations to compute the melting temperature at ambient pressure using both the void-nucleated melting (VNM) and two-phase coexistence (TPC) methods, obtaining $T_m=3055\pm11$ K and $T_m=2847\pm15$ K, respectively.\\ We calculate an enthalpy of fusion of $\Delta H_f\sim73$ kJ/mol, in agreement with thermodynamic assessments and ab initio calculations. We also reproduce the thermal expansion and obtain a volume increase of $\sim$29% at Tm, consistent with the corresponding decrease in density extracted from spatially resolved number density profiles. Finally, we calculate the high-pressure melting curve of CaO up to 20 GPa, providing one of the very few computational determinations of this quantity to date. The results confirm that the overheating ratio $\eta$ is not constant under pressure, increasing from 17% at ambient pressure to 24% at 20 GPa, confirming previous findings and ruling out the assumption of a fixed overheating ratio. Our results establish MLIP-based simulations as a robust and efficient framework for investigating phase stability in ionic oxides and provide new insight into the melting behavior of CaO under extreme conditions.

The thermal expansion of natural FeWO$_4$ (ferberite) and synthetic FeWO$_4$:Fe$_2$WO$_6$ (7:1) was investigated over the 2-1123 K temperature range combining single-crystal and powder X-ray diffraction together with neutron powder diffraction. High-precision lattice parameters were obtained for both samples. The temperature dependence of the unit-cell volume was analysed using physically based thermodynamic models, including the Kroll and Berman approaches as implemented in EoSFit7. All datasets are well reproduced within their respective temperature intervals. However, significant differences are observed between the behavior of ferberite and FeWO$_4$:Fe$_2$WO$_6$, which has a \~40% smaller thermal expansion coefficient and a reduced reference volume. Possible origins, including microstructural and phase-coexistence effects, are discussed. The results provide a comprehensive description of the thermal expansion behavior of FeWO$_4$ across a wide temperature range.

Exciton-polaritons provide a versatile platform for the study of a wide range of phenomena, including polariton lasers, topological polaritons, and bosonic condensation. Transition metal dichalcogenide monolayers host excitons with large oscillator strength and binding energies constituting a robust matter constituent that forms polaritons from cryogenic to room temperature when embedded in optical microcavities. Plasmonic nanoparticles arranged in lattice geometries offer strong field-confinement and high quality factors. However, the high sensitivity of monolayer excitons to strain and dielectric disorder necessitates encapsulation in atomically flat hBN to ensure a high optical quality, rendering plasmonics more challenging. Here, we employ our recently developed fabrication method for embedding gold nanodisk arrays into van der Waals heterostructures and compare two samples with opposite layer order. We observe that strain and etching-induced surface contamination can reduce the exciton quality and thus the light-matter interaction strength significantly. Our fabrication approach reduces interfacial irregularities and enables homogeneous large-area polariton lattices for a wide range of applications, such as polarization-control or topological polaritonics.