Papers

We demonstrate how to build a robust phase space electronic Hamiltonian $\hat{H}_\text{PS}(\boldsymbol{R},\boldsymbol{P})$ that depends on nuclear position $\boldsymbol{R}$ and nuclear momentum $\boldsymbol{P}$ in the presence of ionic pseudopotentials. In particular, we show that in order to account for the non-local component of a pseudopotential while also conserving linear and angular momentum, one is forced to introduce a non-local one-electron operator $\hat{\boldsymbol{\Gamma}}^\text{nl}$ that couples electronic and nuclear momenta together. To test the validity of our ansatz, we derive a generalized form of Nafie's exact equality (which relates electronic momentum and electronic position) so as to include the presence of pseudopotentials. We then benchmark our proposed phase space electronic structure theory against this generalized Nafie-like result for a diverse set of diatomic molecules spanning a wide range of elements. We find excellent agreement across this ab initio test set, highlighting the strength of our method in capturing meaningful electronic momentum beyond the Born-Oppenheimer framework.

We study collective charge excitations in pseudospin-1 triple-point semimetals within the random-phase approximation, considering both the linearised model with a flat-band and its quadratic-corrected counterpart. We analyse their density response, Drude weights, screening, plasmon dispersion and damping, particle-hole continua, and Friedel oscillations from the long-wavelength to the arbitrary-momentum regime. The quadratic correction renders the flat-band dispersive and endows it with a Fermi surface, thereby affecting the overall response. Comparisons with Weyl and Hopf semimetals reveal how bandstructure and quantum geometry jointly govern collective charge dynamics. While the Drude weights are determined by the Fermi surface and band-velocities, interband screening, plasmon dispersion, and Friedel oscillations reflect the quantum geometry of the eigenstates.

The symmetric exclusion process (SEP) is a paradigmatic model of interacting particle transport. Its current–density correlations are governed by an infinite many-body hierarchy of equations. Only recently, this hierarchy was found to collapse at large scales onto a single closed equation. Is this remarkable simplification created by coarse graining, or does it reflect a deeper property already present in the microscopic dynamics? Here we show that the second scenario is realized. At arbitrary time on the lattice, the entire hierarchy collapses onto a single linear equation which is exactly equivalent to a persistence problem for a single auxiliary random walker. Thus an interacting many-body problem reduces exactly to a genuine one-body problem before any scaling limit is taken. This reduction determines the complete finite-time correlation profile, including during nonequilibrium relaxation. More broadly, the microscopic operator uncovered here opens a route to more general correlation functions in the SEP, and may point to a general organizing principle for nonequilibrium interacting particle systems.

Lattice vibrations govern the propagation of heat in materials, and investigating their dynamics through time-resolved phonon dispersion measurements would provide insight into these excitations and their interactions. However, time-resolved measurements that directly resolve the phonon dispersion at the nanoscale have not been previously demonstrated. Momentum-resolved vibrational electron energy loss spectroscopy (EELS) provides access to phonon energies and momenta with nanoscale spatial resolution. Here, we combine momentum-resolved vibrational EELS with pulsed laser heating and synchronised gated electron detection to observe the phonon dispersion of graphite during controlled heating and cooling on the microsecond timescale. Recording both the gain and loss spectra at defined times relative to laser excitation, we determine the temperature at each time delay and follow changes to the phonon branches as a function of temperature. The momentum-resolved spectra reveal a decrease in energy of the optical phonon branch with increasing temperature accompanied by an increase in peak width. These changes are consistent with temperature-dependent phonon renormalisation and scattering associated with anharmonic interactions. The approach is compatible with detector gating on timescales down to 50 ns, providing a route towards extending these measurements to faster dynamics. This work demonstrates time-resolved phonon dispersion spectroscopy using vibrational EELS and provides a route towards probing temperature-dependent phonon dynamics at the nanoscale with simultaneous energy and momentum resolution.

Mixed-anion semiconductors offer opportunities for bandgap engineering beyond conventional multication alloys, but competing phases and disorder complicate their synthesis and the identification of their electronic properties. Gallium oxynitride (GaON) could connect the technologically important GaN and Ga2O3 systems, yet establishing a clear relation between its crystal structure, composition and bandgap remains challenging. Here we report the direct growth of crystalline spinel gamma-GaON films by nitrogen-plasma-assisted pulsed-laser deposition. Varying the nitrogen and oxygen supply yields monoclinic beta-Ga2O3, predominantly disordered films and crystalline spinel GaON. Complementary diffraction, atomic-resolution microscopy and elemental analysis establish the spinel structure and nitrogen incorporation. Temperature-dependent photocurrent spectroscopy reveals a clear redshift of the crystalline gamma-GaON response, supporting assignment of a band-edge transition near 4.3 eV at room temperature. These results open opportunities to investigate mixed-anion wide-bandgap semiconductor physics and develop heterostructures.

Cu-C materials and interfaces are central to diamond thermal management, metallization, graphene growth and carbon-coating technologies, but atomistic simulations across these applications require a potential that describes metallic Cu, diverse carbon bonding, heterogeneous Cu-C interactions and close atomic encounters. Here we develop NEP-CuC, a transferable neuroevolution potential trained on a dataset of 2,727 uniformly relabelled configurations selected from a heterogeneous Cu-C candidate pool. Disagreement within an ensemble of five independently trained models provides an internal indicator of model sensitivity. A Ziegler-Biersack-Littmark (ZBL) correction describes short-range nuclear repulsion, while a runtime D3(BJ) correction supplements dispersion-sensitive calculations. Tests on source-derived held-out and independent external datasets, together with structural, elastic, defect, interfacial, vibrational and finite-temperature transport benchmarks, establish broad but property-dependent physical fidelity across elemental Cu, diverse carbon environments and heterogeneous Cu-C configurations. Large-scale simulations of amorphous-carbon formation and orientation-dependent shock compression of Cu further test transferability under strongly non-equilibrium conditions. For Cu/diamond interfaces, the same potential describes deposition, annealing and tensile response: preparation history leaves persistent differences in interphase structure, while the mean peak nominal tensile stress at 500 K decreases from $12.35\pm0.71$ to $6.65\pm0.98$ GPa as the incident Cu energy during the initial deposition stage increases from 1 to 50 eV. NEP-CuC provides an atomistic framework for linking processing, interfacial structure and physical response across Cu-C systems, with direct relevance to Cu/diamond thermal-management interfaces, diamond metallization and non-equilibrium Cu-C processing.

Kagome lattices provide a simple geometry for engineering electronic states that exhibit novel quantum behavior. In conventional kagome materials, however, the relevant states are often embedded in chemically complex three-dimensional crystals and are difficult to isolate or tune. Molecule-based kagome networks offer structural precision and tunability, but have largely been confined to metallic substrates incompatible with 2D devices. Here we report growth of single-layer Ni$_3$(HITP)$_2$ metal-organic frameworks (MOFs) on van der Waals substrates including graphene-based field-effect devices using metal-salt molecular beam epitaxy. Low-temperature scanning tunneling spectroscopy resolves kagome-derived flat-band and van Hove singularity-based spectral features consistent with first-principles calculations. Gating hybrid 2D MOF devices allows us to energetically shift kagome spectral features, thus establishing electrostatic control of chemically programmable 2D kagome electronic lattices.

We investigate the rotational properties of a zero-temperature Bose-Einstein condensed gas, which is confined in a hard-wall potential. For weak interactions the gas carries its angular momentum via vortices of multiple quantization. As the coupling increases and for sufficiently slow rotational frequencies of the trap, the multiply-quantized vortex states become unstable against a mixed state. For stronger couplings, as the angular frequency of the trap increases, there is a transition from a vortex lattice, to a vortex lattice with a hole at the trap center, and finally to a giant vortex. For weak effective attractive interactions we still have vortices of multiple quantization. These states become unstable towards states which break the axial symmetry of the problem and resemble center-of-mass excitation, as the coupling becomes more negative. Finally, for even more attractive forces, the system becomes unstable against collapse.

Strain gradients, unlike homogeneous strain, are odd under space inversion and unlock couplings that are strictly forbidden in the parent crystal. At the nanoscale, and in curved low-dimensional systems in particular, such gradients are readily attainable and often unavoidable, so that curvature acts as a symmetry-breaking field written into the lattice itself. This chapter reviews the resulting couplings to electric polarization and magnetism. After establishing the geometric relation between strain gradients and curvature, we review flexoelectricity as the better-established reference case: the bulk, surface and dynamic contributions that complicate its definition, its microscopic mechanisms, its manifestation in two-dimensional materials, and the first-principles methodology now available for its calculation. Using the magnetoelectric effect as a conceptual bridge, we then develop flexomagnetism in a broad sense, covering any coupling phenomena between magnetism and strain gradients, and specifically discuss the linear magnetization response to curvature and curvature-induced Dzyaloshinskii-Moriya interactions, beyond the established curvilinear treatment. Finally, we briefly describe some additional effects fitting under this broad umbrella of flexomagnetism, including nonlinear ones, inhomogeneous magnetoelectric and Rashba-type phenomena, and connections to altermagnetism.

Multiplayer social dilemmas on hypergraphs show a variety of emergent phenomena, which has been attributed to group interactions. Here we test whether pairwise dynamics can reproduce them as well. We derive the mesoscopic Langevin equation of a testbed model and find the operator content of absorbing phase transitions: a directed-percolation line, a tricritical point, and a first-order region whose spinodal is the explosive transition. In our analysis, three-player games only set the values of the Landau coefficients. We construct a strictly pairwise model with short-lived memory, in which every event involves at most two entities, that reproduces these coefficients term by term and has exactly the same mean-field fixed points. Simulations confirm that the two dynamics share mean-field critical and tricritical scaling and the size of the critical mass, and that a purely three-player game on a two-dimensional triangular lattice lies in the directed-percolation class. For these games, the explosive transition and the critical mass therefore do not require group interactions, and the critical behavior is that of the pairwise theory.

We develop a macroscopic fluctuation theory for diffusive classical lattice gases subject to continuous coarse-grained monitoring. Treating measurements in the typical-outcome (quenched) regime, we show that observation adds a quadratic confining term to the MFT action that pins the density to its hydrodynamic profile. We derive sufficient conditions under which, in the presence of monitoring, the current large-deviation function remains convex, the additivity principle holds, and dynamical phase transitions are excluded. For particle-hole-symmetric one-dimensional models we find that monitoring suppresses dynamical phase transitions and can change their order from second to first, as we demonstrate in the Katz–Lebowitz–Spohn model. In the strong-measurement limit, we find that the current distribution becomes Gaussian and determine the scaling of its cumulants: they follow simple power laws when the mobility remains nonzero throughout the system, but exhibit anomalous logarithmic scaling when the mobility vanishes at the boundaries.

Understanding why 2D materials remain suspended in solutions is essential to understanding the mechanisms of aggregation and exfoliation. These dynamics have been difficult to model because of the long timescales and large activation energies involved in these simulations. Here we describe an improved strategy for modelling the solvation and stability of 2D materials that uses the Gibbs free energy of solvation to accurately calibrate two disconnected potential energy surfaces for the fully desolvated and fully solvated 2D materials. By joining these surfaces using solvation energy, we obtain predictions for 2D material stability in various solvents that are qualitatively different than prior simulations and that have excellent agreement with experimental results. Our approach predicts a much higher barrier to full desolvation of the material, suggesting that materials that appear to be aggregated in fact still retain monolayers of solvent between adjacent layers of 2D materials. This work provides much needed understanding on the interactions between the solvent and 2D material that can guide future experimental work.

Yttrium oxyhydride (YHO) thin films are synthesised by reactive magnetron sputtering of e̱ta}-YHx precursor films onto single-crystalline yttria-stabilised zirconia (YSZ) (111) and (100) substrates at 200 {\deg}C, followed by post-deposition oxidation in air. For comparison, reference films are also prepared on amorphous SiO2 and soda-lime glass substrates at both 200 {\deg}C and room temperature (RT). The structural (X-ray diffraction and scanning electron microscopy), compositional (elastic recoil detection analysis), and optical properties, including photochromic behaviour, of the films are systematically investigated. The results reveal a strong influence of substrate orientation on the film microstructure and crystallographic texture, leading to epitaxial-like growth with a mosaic spread of ~3-4{\deg}. YHO deposited on YSZ(100) exhibits larger crystallite sizes (10-20 nm) than YHO grown on YSZ(111) (~8 nm) and exhibits residual in-plane compressive strain while remaining largely relaxed with respect to the substrate. Compositional analysis revealed that the O/Y and O/H atomic ratios ranged from 0.71 to 0.82 and from 0.33 to 0.44, respectively, for films deposited under optimised conditions. These films exhibit photochromic behaviour under solar simulator illumination, with relative transmittance changes ranging from 7 to 22 % after 10 min of illumination. Despite the pronounced structural differences, the epitaxial-like films show no systematic improvement in photochromic response, indicating that the effect is governed primarily by composition. The study shows that the bleaching time constant increases exponentially with increasing contrast reached during illumination, rather than representing an intrinsic material constant of YHO.

We identify exact altermagnetic ground states of a classical Heisenberg model on a quasicrystal. Considering the Ammann–Beenker tiling as an example, we determine the ground states by exploiting the parity structure of its parent four-dimensional hypercubic lattice. The ground state hosts coplanar altermagnetic order characterized by the preserved spin-group symmetry $[C_{2x}\parallel C_{8z}]$. Without translational symmetry, the momentum-space spin splitting that usually identifies altermagnets is not directly accessible. We instead couple the spins to itinerant electrons and show spin-resolved transport with $g$-wave symmetry, confirming the altermagnetic nature in a nonperiodic system. Our results establish a geometric route to altermagnetic order in quasicrystals, connecting exact magnetic ground states to their spin-resolved transport signatures.

Interdependent networks can be highly fragile because dependency links amplify local failures into cascades that trigger global collapse. Much of the theoretical understanding comes from geometric network models, where dependency range is imposed externally and coupling strength is distance independent, and it is unclear how these insights apply to real materials, where interdependence arises from physical transport. Here we study thermally coupled amorphous superconducting networks, in which dependencies emerge from current redistribution and heat-mediated interactions governed by thermal diffusivity. Using an experimentally calibrated model of resistively shunted Josephson junctions, we show the system reproduces the three canonical transition regimes: continuous, nucleation-dominated, and mixed-order. However, because heat-driven dependency simultaneously broadens and weakens with distance, long-range thermal coupling can stabilize the superconducting phase upon heating, in contrast with its destabilizing role in geometric models. Cascades are anisotropic, with one-dimensional front propagation. These results offer an experimentally testable perspective complementing the geometric framework.

We examine how the Curie–Weiss cell fluid model can be quantitatively related to real fluids by determining its microscopic parameters from experimental critical-point data for water, carbon dioxide, and three polyol ester lubricants (POE5, POE7, and POE9). The microscopic parameters of the model are determined from the experimental values of the critical temperature and critical density: the global attraction coupling constant is fixed by the critical temperature, and the cell volume by the critical density. The critical pressure then follows as an independent model prediction, deviating from experimental values by 10–41$\%$ across the studied substances. Varying the ratio of local repulsion to global attraction $f=J_2/J_1$ over a wide range has only a weak effect on this deviation. For $f\geq1$, the model's critical compressibility factor lays within a narrow range $Z_c\approx0.382-0.386$, remaining close to the mean-field van der Waals value $Z_c=3/8=0.375$ and consistently overestimating experimental values. The best agreement with experiment is obtained for the polyol ester lubricants and improves along the POE5–POE7–POE9 series with increasing molar mass, suggesting that multiple-occupancy cell fluid models are well suited to systems of large molecules, particularly soft-matter systems with bounded interaction potentials. We further show that generalizing the model by introducing a temperature- and phase-dependent effective attraction allows it to describe a triple point and to reproduce the broad range of critical-to-triple temperature ratios $T_c/T_{\mathrm{tr}}$ characteristic of real fluids.

Magnetic multilayers with structural inversion asymmetry, perpendicular magnetic anisotropy (PMA), and large Dzyaloshinskii-Moriya interaction (DMI) are widely studied for magnetic domain wall- and skyrmion-based data processing applications. In this work, we report a controlled, nonvolatile, but reversible local modification of such a system by electrically driven oxygen migration through the metallic film structure by using ionic liquid gating. Our findings provide direct evidence for the modification of the oxidation state at the heavy metal (HM)/ferromagnet (FM) interface. As a result, we observed changes in fundamental magnetic properties, such as an increase in the effective anisotropy constant (Keff) and coercive field (Hc) with oxidation, and a decrease with the reduction of oxygen ions. Positive gate voltages relative to the thin film extract oxygen ions from the magnetic layer, significantly reducing the domain nucleation field. In contrast, negative voltages drive oxygen ions into the magnetic layer, leading to a reversible increase in the extent of domain wall pinning near saturation. We observe a corresponding decrease in the magnetic moment and DMI, with negative voltage reducing both. This magneto-ionic modulation in fully metallic structures is beneficial for spintronic device applications, particularly in field-programmable domain wall and skyrmion devices.

Living supramolecular materials such as microtubules and actin filaments assemble and function in dynamic, heterogeneous environments, subject to chemical concentration gradients. Their rapid and precise response to such gradients—via aggregation, disassembly, or autonomous motion—underlies the fine spatiotemporal control typical of living systems. Reproducing such responsiveness in synthetic materials is a central challenge in materials science and requires a molecular-level understanding of how gradients couple to supramolecular structure and dynamics, which remains difficult to access experimentally. To this end, we combine implicit-solvent coarse-grained molecular dynamics (MD) with the constant chemical potential MD (C${\mu}$MD) technique to investigate, at molecular resolution, the coupling of two prototypical supramolecular polymer models with externally imposed ionic concentration gradients. Despite their contrasting responses to homogeneous ionic conditions, both systems undergo pronounced spatial reorganization under the gradient, generating regions of locally enhanced supramolecular activity that are inaccessible to homogeneous systems with the same overall content of self-assembling species. Crucially, the local supramolecular dynamics is largely determined by the local concentrations, consistent with the formation of local quasi-equilibria: this direct connection between spatial composition and supramolecular activity emerges as a common governing principle across the two models. These findings shed light on the spatially complex supramolecular response that can be triggered by chemical gradients, and show how a single gradient simulation can encode this response across a continuous range of local chemical environments, thus providing a general strategy to investigate and design materials operating under spatially heterogeneous conditions.

We identify the limit free energy of mean-field multi-species spin glasses with +/-1 spins, allowing for the presence of external fields, and without assuming any convexity property of the covariance function of the Hamiltonian. The limit is given by an "uninverted" variational formula over Brownian martingales. The proof consists in first identifying the limit free energy of configurations with a fixed magnetization. Once the magnetization is fixed, we can show the convergence of the enriched free energy to the solution of a Hamilton-Jacobi equation. The magnetization constraint is also used to show the convexity of the initial condition in this equation, and this yields a variational representation of the solution, as a Hopf formula. Convex duality then turns this formula into an optimization over martingales whose initial values are the prescribed magnetizations.

We demonstrate that the symmetry of magnetoelastic coupling governs the topological organization of composite defects and can qualitatively alter phase-ordering kinetics. In a two-dimensional theory of an in-plane magnetic vector coupled to elastic strain, we find that integer magnetic vortices bind pairs of elementary elastic half-defects. Isotropic magnetostriction produces a core-induced elastic winding independent of the magnetic charge, giving defect binding without charge locking and leaving the magnetic sector with essentially XY-like coarsening. In contrast, quadrupolar magnetoelastic coupling locks magnetic and elastic defect charges: continuous rotational symmetry favors $q_\phi=q_\theta$, whereas crystalline anisotropy can reverse the locking to $q_\phi=-q_\theta$. We reveal that both locking sectors display anomalously slow vortex annihilation: defect density shows a power-law decay $t^{-2/5}$, while the average defect-velocity scales as $t^{-4/5}$. These results are consistent with a dynamic exponent $z\simeq 5$. We show that this coarsening slowdown is associated with large anisotropic elastic friction. An adiabatic elimination of the elastic field reveals that isotropic magnetostriction merely renormalizes local magnetic interactions, whereas orientational coupling induces effective nonlocal interactions between magnetic spins. Our experimentally testable results thus establish magnetoelastic coupling symmetry as a means of controlling defect topology and ordering kinetics.

Deep neural networks that predict density functional theory (DFT) Hamiltonians from material structures offer a route to efficient electronic-structure calculations. However, extending localized atomic-orbital (AO) Hamiltonian learning to plane-wave (PW) calculations with hybrid functionals requires a compact AO representation that preserves the effects of nonlocal operators. Here we propose a projectability-guided construction of nonorthogonal AO Hamiltonians from a small, selected set of PW eigenstates and eigenvalues. High-projectability states are retained, and selected higher-energy states complete the AO subspace, avoiding an empirical shift and its arbitrary contribution to the learning targets. Because the construction uses PW eigenstates and eigenvalues, it incorporates nonlocal contributions present in the reference calculation without explicitly reconstructing their AO matrix elements. Benchmarks for MoS2 and sodium phases show accurate reproduction of PW bands with smaller AO bases than real-space reconstruction. The resulting PBE and HSE Hamiltonians can be learned by equivariant neural networks, connecting PW reference calculations with electronic-structure prediction. This approach broadens the range of PW DFT calculations available for AO Hamiltonian learning and enables compact, accurate training targets for developing more widely applicable electronic-structure models.

This work discusses and tests the potential of reaction graphs for material synthesis, in which events consist of reaction steps (actions) and their outputs (observations). The importance comes from the requirement to synthesize technologically useful materials, especially those that are kinetically stabilized. Often, it is a science that follows years of trial and error, culminating in (published) successful recipes, but is truly driven by far more (unpublished) failures. The entry into the era of AI provides an opportunity to use learning algorithms to encode rules from multi-dimensional synthesis pathways, regardless of their technological usefulness, and to decode both forward prediction and inverse learning modes. The main incentive is to accelerate material discovery by generating a global knowledge base that can be shared among data agents and contributed to by them. We will focus on several scenarios in the common synthesis process during solid-state synthesis, primarily because these reactions are kinetic in nature and require closer monitoring and control of the reaction history.

Achieving uniaxial magnetocrystalline anisotropy while preserving high magnetization and thermal stability remains a central challenge in the development of Fe-rich permanent magnets. YFe$_3$ is a promising candidate owing to its saturation magnetization and Curie temperature, but its intrinsic easy-plane anisotropy limits its potential for permanent-magnet applications. Here, we show that selective transition-metal substitution drives an easy-plane-to-easy-axis transition in YFe$_3$. Systematic first-principles screening identifies V, Nb, and Ta as effective dopants, with YFe$_{2.33}$Ta$_{0.67}$ exhibiting a large uniaxial magnetocrystalline anisotropy energy of 2.3~MJ/m$^{3}$. Calculated exchange interactions and atomistic Monte Carlo simulations show that the enhanced anisotropy is achieved while preserving robust ferromagnetic order and high thermal stability. Micromagnetic simulations further reveal that YFe$_{2.33}$Ta$_{0.67}$ exhibits the highest coercivity and strongest resistance to irreversible demagnetization, whereas YFe$_{2.33}$V$_{0.67}$ achieves a comparable maximum energy product at 300~K. Experimental characterization of V-alloyed YFe$_3$ shows that the YFe$_3$ phase can be retained at low nominal V concentrations (1-3 at.%) under the employed synthesis and heat-treatment conditions, whereas higher V contents lead to increasingly multiphase samples. Concentration-dependent MAE calculations reveal a sign reversal between approximately 11 and 14~at.% V, marking the transition from easy-plane to uniaxial easy-axis anisotropy. Consistent with this concentration dependence, electron backscatter diffraction and Kerr microscopy reveal in-plane magnetic domain structures in the experimentally accessible low-V regime. Therefore, our work offers a promising approach to tuning the magnetocrystalline anisotropy of YFe$_3$ while retaining high Curie temperatures.

Magnetic racetrack memory requires localized carriers that combine rapid motion, resistance to perturbations and a detectable signal. Here we show how a 360{\deg} domain wall in a hollow ferromagnetic tube combines these properties within a single continuous magnetic shell. Two successive magnetization reversals form a bound object whose surrounding domains point in the same direction. Analytical energetics and micromagnetic simulations establish its finite separation, recovery from tested perturbations and current driven transport without microscopic Dzyaloshinskii-Moriya interaction or a maintaining field. The texture's winding resists unwinding while radial rotation carries an energy cost, providing a specific control over stability. Relative rotation of the constituent spins accounts quantitatively for additional displacement during current onset. The wall supports motion at hundreds of metres per second, with transient velocities approaching one kilometre per second at stronger drive. A prepared seven-bit pattern retains its carriers and local readout contrast after pulsed transport and recovery. Curved-track and differential-current tests identify radial stiffness and drive uniformity as controls for intact motion. These results establish a physical basis for fast, locally distinguishable tubular magnetic bits and identify a continuous switching pathway that can be targeted by tailored excitation.

Dissipation dilution has driven a revolution in the quality factors ($Q$) of top-down nanomechanical resonators. Yet it has not been leveraged for van der Waals (vdW) materials. Here we report quality factors up to $372{,}000\pm37{,}000$ in monolayer MoS$_2$ drums at 4 K, nearly an order of magnitude beyond the previous best for any vdW material at this temperature, enabled by a clean, polymer-free exfoliation technique. We develop a dissipation-dilution model for circular drums and analyze the contributing intrinsic and extrinsic dissipation mechanisms. The MoS$_2$ monolayer exhibits a dilution factor of order $1,000$, establishing sub-nanometer-thin resonators as ultimate dilution materials. The intrinsic quality factor, however, is limited by surface losses at atomic thickness. Conversely, multilayer drums show a lower dilution factor but a high intrinsic quality factor, on par with established top-down materials of similar dimensions, both resulting from the increased thickness. A two-level-system analysis of the temperature-dependent damping confirms this bulk-versus-surface picture and provides first insight into its microscopic origin. Our results identify dissipation dilution as the governing mechanism for high-$Q$ mechanical vdW resonators. Combined with strategies such as soft clamping or stress engineering, they establish atomically thin resonators as a platform for ultrahigh-$Q$ quantum transduction and sensing.

The recent observation of superconductivity in untwisted multilayer graphene has sparked intense interest in its microscopic origin. As the displacement field and carrier density are varied, superconductivity emerges in several distinct regions with different temperature and magnetic-field responses. This behavior has been attributed to the presence of distinct electronic phases, raising the possibility that different superconducting regions originate from different microscopic mechanisms. While purely electronic pairing mechanisms have been extensively explored, an in-depth examination of phonon-mediated superconductivity is still missing. Here, we solve the coupled selfconsistent Migdal-Eliashberg equations using input from first-principles calculations and incorporating interaction-driven symmetry breaking of the electronic ground state. Varying the carrier density and displacement field, we reproduce the experimentally observed superconducting regions with comparable superconducting properties such as gap and $T_c$ and predict additional, as-yet undiscovered superconducting phases. Our findings exemplify that several superconductivity regions in rhombohedral graphene can be satisfactorily explained by phonon-mediated pairing.

Ultrafast laser excitation of carriers in semiconductors often results in the creation of fully symmetric coherent optical phonons, typically understood in terms of a thermalized transient carrier population. We test this understanding with systematic measurements and first-principles calculations of the photon-energy dependence of ultrafast-laser-driven coherent phonon generation in tellurium, using excitation wavelengths around the electronic band gap. We observe that, contrary to the expectations of models assuming a thermalized carrier population, the coherent amplitude of the fully symmetric $A_1$ mode changes only weakly when tuning wavelength across the band gap. The measured spectral dependence is instead reproduced by a transition-resolved prethermal force weighted by optical matrix elements and band- and momentum-dependent $A_1$ deformation potentials. Fitting this model to the data yields an excited transition state lifetime of a few femtoseconds. These results identify transition selectivity, rather than a thermalized total carrier density, as a key factor controlling coherent-phonon generation in semiconductors excited near a band gap.

We test the effective-gravity prediction of global thermodynamics using standard molecular dynamics of a two-dimensional Lennard-Jones fluid. Under weak heat conduction with the lower boundary hotter than the upper boundary, the transition between liquid below gas and liquid above gas shifts from zero to finite downward gravity. Using independently measured equilibrium saturation pressures, we calculate the shift predicted by global thermodynamics and find agreement with the observed transition shift. The transition occurs at zero effective gravity, where the hydrostatic pressure difference balances the saturation-pressure difference between the two boundaries. The hysteresis response under heat conduction also agrees with the equilibrium response when plotted against effective gravity. These results establish the predictive power of global thermodynamics for nonequilibrium structure formation.

We uncover an intrinsic gyrotropic spin current (IGSC) driven solely by an oscillating magnetic field, arising from the spin version of Zeeman quantum geometry. Using the density matrix formalism, we derive the IGSC in the low-frequency clean limit, in terms of the Zeeman spin quantum metric and the Zeeman spin Berry curvature. The effect is studied in a minimal Rashba-Dresselhaus model that also supports intrinsic gyrotropic charge currents from the Zeeman Berry curvature. The spin and charge currents exhibit a $\pi/2$ phase shift and are found to be perpendicular to each other for certain parameter ranges. This not only enables spin current detection but also opens pure spin current channels for energy-efficient spintronics. We further observe that these currents switch directions between longitudinal and transverse relative to the applied field, depending on the relative strength of Rashba and Dresselhaus interactions.

Atomistic simulations of minerals are limited by the accuracy and transferability of the force field. We introduce MINFF, a force field family for layered and non-layered oxides and hydroxides of M being Si, Al, Fe, Mg, Ca, Ti, Li and F. MINFF has no M-O bond terms. Instead M-O distances follow from electrostatics and dispersion, while a single harmonic angle term on all M-O triplets controls coordination geometry. Metal charges are DDEC6 charges from reference mineral structures, and oxygen charges are assigned by nearest-neighbour charge smearing, covering basal, apical, hydroxyl and edge sites and sites adjacent to isomorphous substitutions. The oxygen Lennard-Jones parameters are based on the OPC3 water model and change by less than 5% when re-optimised per mineral, so compatibility with OPC3 and related ion-pair potentials is measured rather than assumed. Metal Lennard-Jones parameters were fitted to unit-cell metrics, bond distances and angles, both synchronously across more than 30 reference minerals (general, GMINFF) and for individual minerals (tailored, TMINFF), each at four angle force constants (0, 250, 500 and 1500 kJ/mol/rad^2). With angle terms, MINFF reproduces experimental unit-cells metrics to within 0.5% and atom-type distances and angles to within 0.7-1.4% and 0.1-0.4%, with Global Instability Index values as low as 0.11, below those of CLAYFF (0.34) and INTERFACE (0.21). A moderate angle constant reproduces the stiff in-plane and soft shear elastic constants of phyllosilicates and improves the Kaolinite librational bands, and in hydrated Na-Montmorillonite MINFF gives the lowest residual factor against the 2W 00l pattern of the models tested. The general and tailored sets at four angle stiffnesses give direct control over the transferability-fidelity trade-off. Topologies can be generated with the atom (MATLAB) and atomipy (Python) libraries and at www.atomipy.io.