Papers

In one dimension, Anderson localization by a disordered potential sets in at any strength, whereas localization by a quasiperiodic potential in the Aubry-André model occurs through a transition at a critical strength. Disordered photonic time crystals exhibit a temporal counterpart of this Anderson localization, in which light, instead of decaying in space, stops propagating and grows in time. Whether a counterpart of the Aubry-André transition exists in photonic time quasicrystals remains an open question. Here we show that it does, and that the transition occurs at mobility edges in momentum rather than in energy. These edges arise even under impulsive modulation, where the field obeys the self-dual almost-Mathieu equation exactly, and for general analytic modulations Avila's global theory reveals the condition under which they form. The Aubry-André transition thus extends from spatial lattices to the time domain, where it sorts light by wave number into components that propagate and components that stop and grow.

The pronounced chiral asymmetry of biomolecules is a defining feature of living systems, yet the mechanisms by which such asymmetry emerged remain unresolved. Chiral symmetry breaking may have occurred under prebiotic conditions in systems with sufficiently small molecular populations for intrinsic fluctuations to play an important role. Here, we investigate how finite-population fluctuations affect chiral-state selection, the characteristic time for symmetry breaking, and stochastic switching between chiral states in a system driven by autocatalysis and mutual antagonism. We determine how these dynamical processes scale with particle number and derive an analytical expression for the probability of selecting either chiral state as a function of the initial enantiomeric bias. We further calculate the mean selection time for different initial biases and show that, for weak mutual antagonism, fluctuations can induce transitions between opposite chiral states. These results characterize how finite-population fluctuations control both the emergence and stability of molecular chirality in autocatalytic chemical systems.

The structure of high-entropy alloys, which include 5 or more components in equimolar proportions, is proposed to be described in the mathematical language of Latin squares. This model is fundamentally discrete and allows for a quantitative description of ideal mixing, in which any given alloy element is guaranteed not to have an identical element as its nearest neighbor. For the two-dimensional case, the model possesses four axes of translational symmetry, which makes it possible to tile the plane with a single Latin square and, based on the properties of this square, describe the properties of macroscopic material samples. The model makes it possible to make quantitative estimates of the suitability of a particular atomic structure (configuration) for implementation in a perfectly mixed high-entropy alloy with maximum mixing entropy. A condition has been obtained for acceptable fluctuations in the concentration of components at which the thermodynamic stability of the alloy is maintained. The possibility of identifying superstructures in high-entropy alloys based on group theory, as applied to the description and construction of Latin squares, is discussed. Based on the proposed model, the probability of forming a multicomponent alloy with ideal mixing is estimated. For a five-component alloy, this probability is no more than 2.6*10^{-10}.

Semi-Markov networks provide a natural framework for describing stochastic transitions between coarse-grained states with non-exponential dwell times, with applications ranging from biophysics and neuroscience to epidemiology and finance. Here, it is shown that finite semi-Markov networks admit explicit combinatorial representations of their Laplace-transformed occupation probabilities and hitting-time distributions as sums over weighted spanning trees and forests of an augmented graph. These representations yield asymptotic results, including a generalization of the Markov Chain Tree Theorem to semi-Markov networks, in which the rate constants replaced by pseudo-rates given by the inverse mean sojourn time weighted by the exit probability through this channel, as well as the long-time scaling of hitting-time survival probabilities in the presence of infinite-mean sojourn times. They also extend recently derived combinatorial formulas for hitting-time moments to the semi-Markov setting. In particular, the mean hitting-time formula coincides with that of a Markov network with the corresponding pseudo-rates, which also yields a short proof of the constancy of Kemeny's constant for finite-mean semi-Markov networks. Finally, we use the same framework to show that weak ergodicity breaking occurs generically for time-additive state observables that are nonconstant on the support of the limiting distribution in heavy-tailed semi-Markov networks.

The Ba-atoms in BaFe12O19 were substituted by Eu-atoms to prepare the material of composition Ba1-xEuyFe12O19. The Eu atoms occupied at the sites of Fe atoms. The atomic ratio of Eu/Ba were varied from 0 to 0.33 to control the secondary phase (hematite) and M-type hexaferrite. Raman spectra provided complimentary support for a systematic increase of the hematite phase on increasing the Eu/Ba ratio. X-ray photoelectron spectroscopy informed the presence of oxygen deficiency and surface defects, and charge state of Ba and Fe/Eu ions close to +2 and +3, respectively. The material showed direct optical transitions with band gap in the range of 2.25-3.09 eV. The increase of Eu/Ba ratio systematically increased the saturation magnetization from 84.44 emu g-1 to 57.68 emu g-1 at 3 K and 67.09 emu g-1 to 43.42 emu g-1 at 300 K, along with remarkable enhancement of the coercivity (914- 3656 Oe at 3 K and 1996-4862 Oe at 300 K). Electrical conductivity increased from 10-11-10-10 Sm-1 at 30 K to 10-5 -10-4 Sm-1 at 300 K. The electrical conductivity analysis reveals the Efros-Shklovsky-type variable-range hopping mechanism at the low-temperature region, whereas the Mott variable range hopping mechanism is applicable near to room temperature. The analysis of current-voltage characteristics provided electrode to sample interfacial barrier height of 0.27-0.74 eV. The material exhibited novel magneto-electronic properties (bi-stable electronic switching and its transformation in the temperature scale, magnetoresistance and magnetoelectric coupling) which are highly useful for spintronic devices. This work demonstrates that controlled Eu/Ba atomic ratio in the stoichiometric and non-stoichiometric lattice structure could be an effective strategy to widely tune the magnetic, optical and magneto-electronic properties in M-type Ba hexaferrite material.

The effect of mechanical stresses and deformations upon the behavior and properties of cells and tissues is a topic of paramount interest in the field of biophysics. Its understanding is essential for deepening our comprehension of cellular responses to environmental stimuli, with implications in fields ranging from embryogenesis to tumor development. For boosting the understanding in this field, it is important to develop devices for the application of simple deformations in order to probe the cellular response to the basic mechanical transformations. While a number of stretching devices have been developed, in-plane shearing deformation has been little investigated. Here, a new device is introduced that allows the application of homogeneous in-plane shear upon a cell monolayer while imaging the sample with a commercial optical microscope. A description of the faced experimental challenges is reported and a full characterization is presented. It is demonstrated the capability of the device to apply reproducible, controlled and homogeneous shear of both single cells and confluent cellular monolayers.

Twisted van der Waals heterobilayers are a promising material platform for studying collective exciton many-body phenomena, but near-aligned structures often exhibit a local, anisotropic atomic reconstruction that compromises lateral homogeneity. The present study describes how atomic-scale rearrangement in adjacent regions of hBN-encapsulated, near-aligned MoSe$_2$/WSe$_2$ heterobilayers is controlled by the presence of a mono- or bilayer hBN spacer between the two monolayers. High-angle annular dark-field STEM directly resolves the atomic alignment in both layers and shows that the spacer suppresses the reconstruction and strongly increases the structural uniformity of the heterobilayers. 4D-STEM quantitatively maps local rotation, dilation, and heterostrain, revealing that the separated regions remain consistent with rigid moiré superlattice simulations, whereas without the spacer the structural parameters have two to three times broader distributions. By suppressing reconstruction, ultrathin hBN spacers therefore provide an effective route to enhance lattice homogeneity in MoSe$_2$/WSe$_2$ heterobilayers targeting collective excitonic and optoelectronic phenomena.

Altermagnets combine compensated magnetic order with momentum-dependent spin splitting, which makes them promising for future spintronic and magnonic applications, but their macroscopic responses can be strongly reduced by domain averaging. In hexagonal $\alpha$-MnTe, three symmetry-related in-plane Néel-vector orientations and their time-reversal counterparts form six magnetic domain states, complicating both magnetic structure determination and measurements of the chiral magnon response. Using single-crystal neutron diffraction, we show that an in-plane field applied along the $[-1,1,0]$ direction produces a common magnetic domain orientation that saturates near $\mu_0H=2$ T. A constrained refinement of 61 nuclear and magnetic reflections collected at 2 K and 2 T yields $\mathbf{M}\parallel[1,1,0]$, an ordered moment of $4.62(8)~\mu_\mathrm{B}$ per Mn, and an orientational domain population at $r_A:r_B:r_C=0.97:0.03(5):0$ that is compatible with a nearly complete alignment of orientational domains. Furthermore, an abnormal behaviour in the temperature dependence of the selected reflections is observed in 60-88 K, its microscopic origin is discussed within the context of possible intrinsic piezomagnetic or magnetoelastic effects. Because unpolarized diffraction neither distinguishes domain repopulation from continuous Néel-vector rotation nor resolves time-reversal antiphase domains, the field-prepared state is a near-single-orientation state rather than a truly single-domain state. This non-contact domain control provides a practical complement to strain and field-cooling approaches for preparing well-defined magnetic states in bulk $\alpha$-MnTe.

Micro- and nanostructures fabricated by focused ion beam (FIB) milling invariably deviate from input designs due to systematic and stochastic effects such as ablation-rate fluctuations, and redeposition. As such, nominally identical iterations of a given process yield a distribution of non-identical fabrication outcomes, leading to variations in the physical (optical, mechanical) properties of fabricated structures. Existing models of the milling process typically predict a single deterministic fabrication result, neglecting this variability. Here we present a conditional diffusion model that learns the statistical distribution of process outcomes conditioned on input design, enabling it to predict a realistic distribution of possible output sample structures. These predictions accurately reproduce edge morphology, linewidth variations, and defect probabilities observed in fabricated samples, enabling statistical analysis of milling performance and the identification of dominant structural and process parameter-dependent deformation modes. The work establishes a probabilistic modelling framework for fabrication variability analysis and fabrication-aware design optimization.

Efficient simulations of grain growth are essential for investigating the process-structure-property relationships in polycrystalline materials. We introduce a two-dimensional von Neumann-Mullins-based graph grain growth simulation (VN-GraphGG), which couples the grain-scale kinetics with microstructure reconstruction. The polycrystalline microstructure is represented as a graph with grain and junction nodes. The grain-area evolution on the grain graph is governed by the von Neumann–Mullins (VN) law, while a graph neural network is trained to reconstruct the microstructure from the graph. This separation allows kinetic coefficients to be varied without retraining the neural reconstruction model. Topological changes during grain growth such as disappearance of grains and changes in neighbor relations are handled straightforwardly through reconstruction and postprocessing. Simulations demonstrate accurate predictions of VN kinetics and coarsening statistics, and significant speedup over the phase-field simulations. The proposed method provides a foundation for efficient grain growth simulation based on grain-scale kinetics, opening the way to incorporate a broader range of physical mechanisms. An application example is presented for abnormal grain growth, in which kinetic heterogeneity significantly influences the grain microstructure evolution.

Josephson junctions are the central nonlinear element of superconducting qubits, yet their standard description is reached through a chain of approximations. We propose a purely quantum-mechanical model of the junction, formulated directly in Hilbert space: a charged particle moves on a one-dimensional loop, and the junction is a point at which the wave function obeys self-adjoint boundary conditions, labelled by a coupling strength $\lambda$, which controls the transparency of the junction, and a phase jump $\delta$, which plays the role of the superconducting phase difference. For a loop with a single junction we solve the spectral problem and show that the ground-state momentum expectation, identified with the supercurrent, factorises exactly as $\langle\hat{p}_0\rangle = I_c(\delta,\lambda)\sin\delta$. For opaque junctions $I_c$ becomes independent of $\delta$ and the first Josephson relation $I=I_c\sin\delta$ is recovered; for strongly attractive coupling, where the ground state is bound to the junction, the $\sin\delta$ law is also recovered, but with an exponentially suppressed amplitude. For more transparent junctions, however, the model predicts deviations from the pure $\sin\delta$ law: $I_c$ acquires a dependence on $\delta$ already at order $\lambda^{-2}$, compatible with the higher Josephson harmonics recently found necessary to describe superconducting qubit spectra, and a fully transparent contact yields a current linear in $\delta$. When the phase varies in time, a gauge transformation shows that the voltage drop across the junction is proportional to $\dot\delta$, so that the second Josephson relation emerges without being imposed. The boundary-condition approach thus reproduces both Josephson relations from first principles and predicts corrections to them, offering a route towards higher-fidelity models of superconducting qubits.

Specific heat of graphite at high temperatures demonstrates significant deviation from the “3R” Dulong-Petite law. It can be explained by accumulation of defects with formation energy as low as 1.45 eV. Based on the density functional theory calculations, we propose a possible candidate of topological defects, whose energy is comparable to the growth activation energy.

The $S=1/2$ Kitaev model provides an exactly solvable setting in which spin fractionalization produces itinerant Majorana fermions coupled to an emergent $\mathbb{Z}_2$ gauge field. In realistic Kitaev magnets, however, non-Kitaev interactions break integrability and make their finite-temperature dynamics difficult to calculate. We develop a finite-temperature parton mean-field theory based on the Abrikosov-fermion representation and incorporate the effects of exchange interactions through the random phase approximation to calculate the dynamical spin structure factor. For the pure Kitaev model, the method reproduces a strong, nearly dispersionless peak at a finite low energy together with a broad continuum at higher energies. It also reproduces the momentum dependence of the dynamical spin structure factor and its temperature evolution, including the downward shift of the low-energy spectral weight, in qualitative agreement with continuous-time quantum Monte Carlo calculations. Within the present theory, the contraction of the continuum is traced to the temperature-induced reduction of the bond amplitudes, which narrows the parton bands and compresses the two-parton phase space. For ferromagnetic Kitaev coupling, the energy of the low-energy peak is minimized at the $\Gamma$ point for a ferromagnetic Heisenberg interaction and maximized there for an antiferromagnetic interaction. In the ferromagnetic Kitaev-$\Gamma$ model, the static response develops a finite-momentum softening, indicating an instability toward the period-three magnetic order reported in numerical studies. For uniform-ferromagnetic states selected by a $[111]$ magnetic field, we find that a broad parton continuum coexists with magnonlike dispersive structures, producing spectral features consistent with a spinon-to-magnon crossover.

How can human researchers use artificial intelligence (AI) to make progress on difficult mechanics problems while retaining control of physical significance, mathematical rigor, and validation? We explore this opportunity through a quantitative stability problem rooted in the Eshelby conjecture. For a uniform dilatational eigenstrain in a homogeneous isotropic solid, we establish a nonlinear two-sided relation between whole-interior strain heterogeneity and a geometry-only distance from the ellipsoid family, with half-order Sobolev scaling that captures morphological length scale. We then develop a complementary finite-shape theory: ellipsoidal subtraction yields an exact residual-field budget from which systematically convergent upper and lower bounds are obtained for a prescribed geometry. Applied to protruded, indented, and necked inclusions, the bounds agree with independent displacement-based finite-element calculations. The study also documents a human-led, AI-assisted research process in which researchers select consequential problems, shape targets, audit arguments, require independent checks, and interpret mechanics, while AI broadens analytical exploration and supports computation. This experience also led us to develop Open Problems in Mechanics, a versioned community-facing map that makes selected mechanics questions, their known/open boundaries, and criteria for progress explicit.

Nanomaterial properties are governed by atomic structure, and driving structural changes on demand could enable materials with programmable properties. Pulsed light is the most controllable route: wavelength, fluence, polarization and pulse timing can each be tuned to inject energy with nanometre and picosecond precision and mould atomic positions. Yet the spatiotemporal dynamics of these transformations have remained hidden, inferred only from before-and-after snapshots. Here we track gold nanorods in a transmission electron microscope under pulsed optical excitation, quantifying the structural transition frame by frame. The rods enter an unexpectedly dynamic regime: material redistributes within and between particles, twin boundaries nucleate and propagate, rods hundreds of nanometres apart reshape in concert, and individual rods almost vanish before recovering their original shape, indicating a structural memory. Driving and following these transformations with pulse-synchronized in situ electron microscopy could turn light-induced reshaping into a tool for setting structure, and consequently properties, on demand.

YbZn2GaO5 has recently emerged as a structurally ideal triangular-lattice antiferromagnet and a promising candidate for hosting a U(1) Dirac quantum spin-liquid (QSL) ground state. However, signatures of broadened crystal electric field (CEF) excitations have raised questions about potential site disorder and its impact on the intrinsic spin dynamics. In this study, we employ 71Ga nuclear magnetic resonance (NMR) and muon spin relaxation (muSR) to microscopically probe both the structural and magnetic properties of YbZn2GaO5. NMR spectra reveal two inequivalent 71Ga sites and a broad distribution of quadrupolar frequencies, providing clear evidence of Ga$^{3+}$/Zn$^{2+}$ site mixing and local CEF randomness. The NMR spin-lattice relaxation rate exhibits, down to 1.3~K, a power-law temperature dependence, consistent with persisting spin dynamics below the exchange energy scale in a frustrated magnet. Complementary muSR measurements further show that the spin dynamics persist down to 30mK, with no signs of spin freezing. Together, these results establish that YbZn2GaO5 presents substantial structural disorder, while the persistence of dynamic spin fluctuations down to the lowest temperatures may indicate the survival of QSL-like excitations despite such disorder.

We show that H–F edge complexes in biphenylene nanoribbons act as intrinsic atomic resonators, flattening low-frequency phonon branches. With increasing wave vector, flexural and twisting vibrations concentrate at the edges while motion of the carbon backbone is suppressed. Displacement profiles and edge-mass tuning identify a local-resonance mechanism, an atomic counterpart of a tuned mass damper. Combining machine-learned interatomic potentials, frozen-phonon calculations, and density-functional tight binding, we find that weakly dispersive modes contribute substantially to thermal band-gap narrowing. Zero-point motion shifts the calculated gap closure toward the experimentally observed ribbon widths. A hexagonal boron nitride substrate preserves the principal spectral features while reducing thermal renormalization. These results establish edge chemistry as a route to nearly flat phonon bands and connect a local atomic resonance to the electronic response of an entire nanoribbon.

Ultrafast laser-assisted field emission from metallic nanotips is a promising route for generating coherent electron pulses. However, existing theoretical models often neglect many-body strong correlation effects in the emitter's electronic structure and its response to the optical field. In this work, we propose a theoretical framework based on the non-equilibrium Green's function formalism to simulate the out-of-equilibrium electron dynamics across a strongly driven matter-vacuum interface, in a one-dimensional model. Treating the tip-vacuum coupling perturbatively, we find that the interplay between strong-field emission and multi-photon emission regimes can be described in terms of a filtering of the emitter's local density of occupied states through field-dressed vacuum propagators. By including electron-electron interactions via the second-Born approximation, we show that correlation-induced modifications in the electronic structure are directly transferred to the far-field spectrum. Finally, by self-consistently solving the Dyson equation at the interface, we uncover a dynamic back-action regime driven by the optical field, characterized by a periodic polarization of the emitter, which reshapes the far-field spectrum. This shows that the non-equilibrium Green's functions approach provides a versatile framework for exploring and analyzing field emission of correlated electrons.

The Zak phase provides a fundamental geometric characterization of one-dimensional band structures and, when quantized by symmetry, serves as a bulk indicator of polarization and boundary phenomena. Conventionally, its exact quantization is tied to a global symmetry of the Bloch Hamiltonian, such as inversion or reflection symmetry. Here, we demonstrate a distinct mechanism by which the Zak phase remains exactly quantized even when the corresponding protecting symmetry is explicitly broken at the level of the full Hamiltonian. The mechanism is based on local support symmetry and destructive interference: symmetry-breaking degrees of freedom are coupled to a topological parent system in such a way that the relevant Bloch states cannot leak into them. The preserved states therefore retain their parent wave functions and inherit their quantized Zak phase exactly, despite the absence of the protecting global symmetry. We establish this mechanism for general one-dimensional insulators and demonstrate it in an inversion-broken minimal model and a reflection-broken armchair nanoribbon, where a quantized $\pi$ Zak phase and associated boundary-localized states persist. We further show that perturbations violating the exact destructive-interference condition continuously dequantize the Zak phase, while a finite regime with a near-$\pi$ Zak phase and boundary response can survive. Our results establish wave-function support, rather than global symmetry alone, as a mechanism for protecting quantized quantum geometry in one-dimensional systems.

Excitons are bound electron-hole pairs in semiconductors whose interactions influence optical properties and determine their collective behavior and emergent correlated phases. Despite the theoretical and experimental significance of these phenomena, a microscopic theory of exciton-exciton interactions that takes into account the full composite nature of these quasiparticles is lacking. Here, we present a general theory of exciton-exciton interactions that builds upon our previous publication [Physical Review B 113, 155440 (2026)], which applied only to conventional semiconductors with weak band hybridization. By contrast, the theory presented here is valid in virtually any crystalline semiconducting system and can be applied to the study of biexciton formation and correlated excitonic phases in systems where band topology, quantum geometry, and moiré effects play a significant role. In addition to the analytical theory, we also present results in simple systems with flat bands with a nontrivial quantum metric and show that the biexcitonic spectrum differs strongly from that in the case without quantum geometry. Our theory paves the way for accurate quantitative calculations of biexciton spectra and excitonic many-body phases in modern condensed-matter systems.

We study how a neural network reorganizes its learned function as training proceeds and as previously unseen parity data accumulate. The trained model is itself a Boolean function on binary strings of finite length. We then evaluate it on all data, inside and outside the training set, and read off its complete sign table. Its $\pm1$ entries are the amplitudes of a normalized state, dubbed the function-state, whose inverse subsystem purity $K_f=1/\textrm{Tr}(\rho_A^2)$ is an effective Schmidt rank. We find that small data additions broaden the Schmidt spectrum, whereas larger additions reconcentrate it in the target mode. The former is called differentiation because the model distinguishes inputs more sharply. The latter is called target-selective recoherence, where the model settles on the single rule shared by the added data. As the dataset grows, the connectivity of the constraint graph defined by the training set increases monotonically, whereas the learned inverse purity changes nonmonotonically. On a fixed connected dataset, as learning proceeds, the Schmidt spectrum begins to reorganize, followed by gains in target alignment and later by improvement in predictive accuracy. This ordering distinguishes three aspects of learning: constraint identifiability, function-state organization, and predictive accuracy. At fixed data size, a function that has already been learned can re-differentiate, an event we call retreat, without changing graph connectivity. Recovery reconcentrates the Schmidt spectrum in a similar target-selective pattern, without exact recurrence of the Boolean state. Thus the percolation of data constraints fixes the identifiable support, while the reduced state produced by training continues to reorganize even after that support stops changing.

Matter-based two-level quantum systems are fundamental building blocks of quantum technologies, underpinning applications in quantum computing, simulation, communication, and sensing. Today, most of these two-level quantum systems, including Rydberg atoms, trapped ions, superconducting circuits, molecules, and quantum dots, involve transition frequencies in microwave or optical domains. However, extending their transition frequency to the THz spectral range could provide numerous benefits, leveraging the unique properties of THz radiation. Here, we show that an hBN-encapsulated graphene double quantum dot realizes a two-level system with a transition frequency in the THz spectral range. Using low-temperature transport spectroscopy in the dark combined with modeling based on nonequilibrium Green's function formalism, we demonstrate the formation of an artificial molecule, featuring bonding and antibonding states separated by an energy of up to 0.6 meV, corresponding to a resonance frequency of 0.145 THz. This approach provides direct access to important parameters of open double quantum dot systems, including tunneling rates, offering a practical alternative to conventional techniques such as photon-assisted tunneling, which are challenging to implement at THz frequencies. The realized 2D-material-based THz two-level system, compatible with direct on-chip integration, could serve as a key building block for future THz quantum technologies. Furthermore, by involving a single-electron transition, coupling these devices to a THz resonator could enable the exploration of ultra-strong light-matter interactions at the fundamental limit of a single transition coupled to a single cavity, beyond the reach of existing THz quantum systems based on collective transitions.

We investigated the equal-spin Andreev reflection phenomenon in an altermagnet/super\-conductor/altermagnet (AM/SC/AM) junction, focusing on the roles of the crystal orientation angle and the Néel vector. The crystal orientation angle in the AM effectively determines the spin-dependent transport channels for both electrons and holes, leading to orientation-dependent local and crossed Andreev reflection in the AM/SC/AM junction. We studied how and under what conditions this equal-spin Andreev reflection occurs. Rotating the Néel vector in the AM substantially increases spin-flip channels for both electrons and holes, giving rise to equal-spin Andreev reflection. When the Néel vector $\theta=\pi/2$, the spin-dependent transmission channels for crystal orientations $\alpha=0$ and $\alpha=\pi/2$ are completely the same, the Andreev reflection coefficients remain different, reflecting the distinct roles of the Néel vector in spin space and the crystal orientation in real space. By tuning the crystal orientation angle and the Néel vector, orientation-dependent conventional and equal-spin Andreev reflection can be realized. This study reveals that Néel vector rotation is the direct cause of equal-spin Andreev reflection in AM/SC/AM junctions and provides a viable pathway for realizing spin-dependent superconducting transport phenomena in AM heterojunctions.

Understanding volume changes in high-voltage spinel cathodes is essential for mitigating mechanical degradation and improving cycling stability. However, linking these changes to cation-specific redox processes remains challenging. Here, we combine operando X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) to investigate the LiCoxMn2-xO4 spinel system, which exhibits a cubic structure and isotropic lattice response, in order to correlate the evolution of the local and long-range structure. Five compositions (x = 0, 0.25, 0.5, 0.75, and 1.0) were synthesized and electrochemically characterized, with x = 0, 0.5, and 1.0 examined in detail under identical cycling conditions. XAS at the Mn and Co K-edges reveals distinct Mn4+/Mn3+ and Co4+/Co3+ redox processes, with Mn redox activity dominating below 4.7 V and Co redox triggered at higher potentials. Chemometric tools for XAS data analysis further resolve the evolution of local structure during cycling. Both XRD and XAS capture consistent trends in volume evolution, despite probing different structural length scales. Increasing Co content progressively decreases the overall volume change, from 5.0 % to 1.6 % by XAS and from 5.8 % to 2.1 % by XRD. These results demonstrate that Co substitution suppresses electrochemically induced structural strain and establish a direct link between cation-specific redox activity and volumetric evolution. The correlative operando XRD/XAS approach provides a framework to investigate newly designed low-strain, high-energy cathodes with improved cycling stability.

The imbibition of milk into a biscuit provides an example of a broader class of processes in which a liquid invades a porous material, dissolving components of the solid and thereby modifying its own rheology. This coupling between imbibition, dissolution, and evolving fluid rheology also occurs in food processing, filtration, and reactive porous media. While the resulting changes in fluid viscosity are known to affect imbibition, a quantitative description of how this evolving rheology determines the imbibition dynamics is still lacking. Here, we establish such a description for dissolution-driven fluid thickening. For a capillary tube in the well-mixed limit, we derive a generalized Washburn law showing that the evolving viscosity can be incorporated through a rescaled time given by the accumulated inverse viscosity. This predicts a collapse of the imbibition dynamics for different dissolution rates, which we confirm numerically using coupled free-surface and solute-transport simulations. When diffusion is slower, concentration and viscosity become spatially heterogeneous, resulting in a weaker retardation of the advancing liquid than predicted by the well-mixed theory. We then consider disordered porous media and quantify how dissolution-driven thickening and variations in pore geometry affect the dynamics. Our results extend the classical Washburn description to imbibition with evolving fluid properties and provide a quantitative basis for understanding fluid uptake when interactions with the solid progressively modify the rheology of the invading liquid.

The degree of oxygen vacancy in A-site-doped layered double perovskite oxides can lead to anion vacancy ordering, which subsequently results in distinct superstructures. We have studied oxygen deficient double perovskite oxide, NdBaCo$2$O$_{5+\delta}$ ($\delta \sim$ 0.65), utilising X-ray absorption near edge structure (XANES) spectroscopy complemented by multiple scattering and first-principles calculations based on density functional theory (DFT+U). The present results establish a direct correlation between oxygen-vacancy distribution, magnetic inhomogeneity, and charge transport in layered cobaltates. Our investigations on the Co K, Ba, and Nd $L_{\mathrm{III}}$ edges suggest that the near-edge spectra, based on the number and shape of the spectral features, indicate the value of $\delta$ for the compound under study lies closer to 0.75. The analysis of the Ba $L_{\mathrm{III}}$ edge spectrum confirms the +2 oxidation state for Ba ions. The Co K-edge near-edge spectra suggest the possibility of oxygen vacancies arising at the basal sites in addition to the apical sites. This is counterintuitive to the common understanding that oxygen vacancies usually occur at the apical sites, i.e., in the lanthanide (Nd) layer in these compounds. Such a distribution of oxygen vacancies naturally explains the Griffith phase and the conduction mechanism of variable range hopping observed in the compound. The vacancy distribution, when at the optimum level, can also bring about easier oxygen ion mobility and a more sensitive and faster oxygen sensor. We believe that our results will help in tailoring oxygen-ion mobility and enhancing oxygen-sensing performance.

Rydberg excitons in atomically thin semiconductors offer a sensitive view of dielectric screening and electronic structure. As their spectra become increasingly well resolved, a central question is how much material information an effective Hamiltonian can predict beyond the states used to determine it. Using the 1s, 2p and 2s levels to determine a scalar Rytova-Keldysh Hamiltonian, we test its transfer to the excluded 3p state. The transfer deviations have opposite signs: the observed 3p lies 7.38 meV below the prediction in MoSe2 and 5.58 meV above it in WS2; the opposite signs persist across the complete reported +/-2-sigma peak-error boxes. In a separate high-field-calibrated benchmark, RK removes 66.8% of the orbital error of a pure two-dimensional Coulomb reference, making the remaining state-selective deviations particularly informative. After separating gap and common-scale contributions, the residuals reveal distinct material-dependent orbital patterns and constrain simple multichannel descriptions. For WS2, the measured 2p/3p curvatures yield a parameter-fixed prediction, Q4p=+4.08 meV, for a future same-platform measurement. Together these results show how a well-performing spectral model can be tested for transferable physical information, with the next unmeasured state providing an independent experimental check.

Two-dimensional (2D) superconducting systems have recently emerged as a frontier in condensed matter physics, driven by their unique physical properties and potential applications. Using first-principles calculations, we show that monolayer ZrX$_2$ (X = Cl, Br, I), which is a family of 2D semiconducting electrides, hosts phonon-mediated superconductivity under both electron and hole dopings. Electron doping in ZrX$_{2}$ can achieve high superconducting transition temperatures at very low concentrations, with ZrBr$_2$ reaching $T_c = 30.0$ K at 0.01 e/f.u., followed by ZrCl$_2$ (22.5 K at 0.05 e/f.u.) and ZrI$_2$ (18.1 K at 0.01 e/f.u.), for which the high $T_c$ originates from the flat conduction band minimum, with Van Hove singularities nearby enhancing the density of states. In contrast, hole doping requires higher concentrations (0.2–0.25 h/f.u.) to activate superconductivity, yielding $T_c \sim 2$ K, and approaches a magnetic instability at elevated doping levels. By comparing with InSe and LaBr$_2$, we identify the spatial location and orbital character of excess electrons as key factors determining the strength of hole-doped superconductivity and the nature of competing orders. These findings establish monolayer ZrX$_2$ as a platform for bipolar superconductivity in a 2D electride and provide insights into flat-band engineering for high-$T_c$ superconductors.

The phase of an electron wave is sensitive to the local electrostatic environment and can therefore provide information about atomic-scale structural variations. In electron ptychography, however, specimen thickness, multiple scattering and projected atomic overlap can complicate the quantitative interpretation of the reconstructed phase. Here, we use a twisted trilayer WS2 thickness staircase containing monolayer, bilayer and trilayer regions as an internal reference, with all regions measured under identical experimental conditions. The mean W-column phase increases by approximately 13.2% from the monolayer to the bilayer region, compared with only 4.7% from the bilayer to the trilayer region, revealing a nonlinear thickness dependence. W-S overlap has little effect on the W-column phase, whereas short-range projected W-W overlap increases it by approximately 8-9%. These results provide a benchmark for evaluating quantitative phase measurement in multilayer WS2 and for assessing phase-based mapping of local electrostatic potential, charge-density and three-dimensional atomic-scale polarization.

We report the experimental investigation of the quaternary Heusler alloy NiRuMnGa, complemented by first-principles calculations. The energetically favorable crystal structure was identified from first-principles calculations and subsequently used as the structural model for refinement of the powder X-ray diffraction data. The refinement shows good agreement with the experimental pattern and reveals substantial B2-type disorder involving Ni/Ru and Mn/Ga site intermixing. The dc magnetic response exhibits pronounced ZFC–FC irreversibility near $\sim 48$ K, with the irreversibility temperature shifting toward lower temperatures under increasing magnetic field, indicating a field-sensitive glassy state. The isothermal magnetization remains unsaturated up to 7 T, reaching only $\sim 0.4\,\mu_{\mathrm{B}}$/f.u., accompanied by pronounced hysteresis, suggesting competing exchange interactions and frustrated magnetic moments. AC susceptibility, together with magnetic relaxation and memory measurements, confirms slow spin dynamics characteristic of a cluster glass state. The lack of a discernible heat-capacity anomaly near the irreversibility temperature further supports the absence of conventional long-range magnetic order. Collectively, these results demonstrate that competition between ferromagnetic and antiferromagnetic interactions in NiRuMnGa leads to magnetic frustration and stabilizes a cluster glass state.