Papers

When a liquid drop impacts a solid surface, rebound and splashing are known to be suppressed by additives that induce elastic effects; however, the influence of elasticity on the maximum spreading radius remains debated. The difficulty lies in isolating elastic resistance from the enhanced spreading caused by viscous shear thinning. Here, we experimentally decouple these effects by investigating Boger fluid drops (constant-viscosity solutions with high elasticity) of polyethylene oxide (PEO) and polyacrylamide (PAAM). We demonstrate that elastic properties do not alter the maximum spreading ratio, even at high concentrations up to 1000 ppm. We formulate an energy balance that accounts for the inertial, capillary, viscous, and elastic contributions, and yields a dimensionless criterion ($\Gamma$) that estimates the degree of elastic effects. We show that $\Gamma \ll 1$ for all impact conditions tested, demonstrating that elastic effects are energetically negligible during droplet spreading, opposite to what Weissenberg and Deborah numbers would predict.

Energetic electrons create distinct cathodoluminescence (CL) angular distributions upon interaction with dielectric and plasmonic nanostructures, providing valuable information on coherences in the excitation pathways. A counterintuitive prediction is that the CL signals arising from the excitation associated with different lateral regions of an extended electron wave are mutually incoherent and do not interfere, while the signals originating from different structures within the electromagnetic field of a narrow electron beam are mutually coherent. We present conclusive experimental evidence of these effects by examining the angular CL emission profile from defocused electron-beam excitation of a thin silicon nitride film, which is shown to follow an incoherent sum of CL excitations within the electron beam spot. In contrast, CL interferences are observed for separated plasmonic scatterers excited within the evanescent field of a single electron. Coherence may be recovered through correlations between emitted light and post-selected electron states, for which we propose a measurement geometry that erases which-path information of the electron trajectory.

Hybrid magnonic system provides a versatile platform for coherent information exchange between spin excitations and other physical degrees of freedom. While strong coupling between magnons and spoof plasmons has been observed based on ferrimagnetic spheres and localized microwave resonators, it remains unexplored whether coherent magnon-plasmon coupling can be achieved in planar magnetic structures. Here we study the hybridization of antiferromagnetic (AFM) magnons and spoof surface plasmons in a planar heterostructure consisting of an AFM thin film, a dielectric spacer, and a structured metal surface. By analytically solving the coupled Maxwell and magnetization dynamics equation, we predict strong magnon-plasmon coupling in the terahertz regime, manifested by pronounced avoided crossings in the dispersion. The coupling originates from the spatial overlap between magnonic and plasmonic modes in the dielectric spacer, and can be efficiently tuned through geometric parameters of the system. The calculated cooperativity confirms that the hybrid system can operate in the strong coupling regime, enabling coherent information transfer between magnons and plasmons. Our results establish a planar platform for plasmon-magnon hybridization, which is more amenable to on-chip manipulation and integration.

Finite-memory optical tracers encode upstream transport histories rather than instantaneous local flow velocities. We introduce optical-memory transport (OMT) imaging, a framework in which finite memory couples internal-state relaxation to transport through memory kernels. Under structured illumination, these histories are converted into measurable complex spatial-frequency response, whose local transfer-function limit yields constant-velocity inversion. Fisher-information analysis establishes kernel-dependent information limits and design principles for finite-memory transport imaging.

Crystal anisotropy provides a powerful route for realizing direction-dependent transport in solid-state systems. While its influence on electronic transport is well established, the role of anisotropy in magnon spin transport in van der Waals magnets is largely unexplored. Here, in a nonlocal geometry, utilizing the monoclinic van der Waals antiferromagnet CrPS$_4$, we observe pronounced anisotropy in both electrically and in thermally excited magnon spin transport. Electrically generated magnons exhibit a magnon spin conductivity at least 2.2 times larger and a spin diffusion length at least 2.7 times longer for transport along the crystallographic-b axis compared to the crystallographic-a axis, where $\lambda_m^{a} \sim$ 211 nm and $\lambda_m^{b} \geq$ 575 nm. In comparison, at 8T, we find the nonlocal second-harmonic resistance associated with thermally excited magnons to be $\sim$7 times larger along the crystallographic-b axis at 25K. We further show that a magnon spin diffusion length cannot be reliably extracted from the nonlocal second-harmonic resistance, owing to the extended temperature profile within CrPS$_4$. Likewise, we show that the anisotropy in the spin Seebeck coefficients cannot be reliably estimated from the thermally excited magnon spin transport alone, as it is intertwined with the anisotropic heat conductivity of CrPS$_4$. Utilizing the electrically generated magnon spin transport, we demonstrate that intrinsic crystalline anisotropy serves as an effective control parameter for tuning magnon spin transport, opening new avenues for magnonic device engineering.

This study aims to unveil the physical properties of multifunctional Li5N electride under high pressure in the range of 150-350 GPa through first principles analysis within the density functional theory.

Excluded-volume interactions, arising solely from steric constraints, play a crucial role in determining the structure, dynamics, and phase behaviour of colloidal suspensions. This is particularly important for non-spherical particles, where orientation-dependent effects also become significant. In this study, we employ depletion-driven phase separation to develop a scalable, size-selective method for purifying spherical and non-spherical colloidal clusters that exhibit an interplay of concave and convex surface areas. Phase diagrams of charge-stabilised polystyrene spheres ranging in size from 267 to 1008 nm demonstrate that the mixing-demixing transition occurs across a range of surfactant concentrations rather than at a single threshold. Taking advantage of this transition width enables the purification of a single component from binary mixtures at size ratios as low as 1.6 in a single step. When the same approach is applied to tetrameric colloidal clusters, these are enriched fifteenfold relative to uncoordinated spheres. Importantly, the efficiency of sorting depends not only on the effective size but also on the geometry of the aggregate. For instance, anisotropic, weakly fused clusters separate more efficiently than spherical aggregates because their concave surface curvature is reduced compared to unfused clusters. These findings establish excluded-volume-driven sorting as a practical and scalable route for purifying colloidal building blocks for hierarchical assembly.

Hofstadter systems provide a lattice route to fractional quantum Hall physics, but their low-energy manifolds often lack simple wave-function descriptions. Here we present a composite-boson ansatz for a broad family of finite-size lattice-split Laughlin-quasihole manifolds in the low-flux Hofstadter–Bose–Hubbard model on a torus at generic fillings \(\nu<1/2\). Attaching two vortices to each boson yields reduced-flux orbitals from which we construct a many-body trial basis. Its translation-resolved rank reproduces the expected low-energy-manifold dimension and provides a composite-boson interpretation of the established quasihole counting previously inferred from generalized exclusion rules and thin-torus arguments. For smaller systems, diagonalization within the lowest-band-projected ansatz span closely reproduces the exact projected spectrum, while variational Monte Carlo extends the rank and energetic analysis to larger systems for which explicit subspace construction becomes costly. To probe the fractional quantum Hall character of these manifolds, we calculate their many-body Chern-numbers and show that localized added-flux excitations exhibit quasihole-like behavior, with fractional density depletion and an Aharonov–Bohm-free braiding phase that both track the effective filling. Together, these results establish a microscopic composite-boson framework for organizing a broad family of sub-half-filled fractional quantum Hall manifolds of lattice bosons.

We investigate piezomagnetism in higher-spin altermagnets with easy-plane single-ion anisotropy using a flavor-wave approach. We show that quantum fluctuations of higher-spin collective modes provide a microscopic origin of the piezomagnetic response. For integer spins, the relevant branch softens and evolves into a Higgs-like amplitude mode on approaching the large-$D$ transition, endowing the excitation with a sizable dipolar component and producing a pronounced enhancement of piezomagnetism. By contrast, in half-integer systems the higher-spin branches are progressively separated from the low-energy dipolar sector as the anisotropy increases, which suppresses their contribution to the response. This integer-half-integer contrast directly links macroscopic piezomagnetism to the low-energy fate of multipolar excitations. Our results establish piezomagnetism as a probe of higher-spin quantum dynamics and identify higher-spin altermagnets as a promising setting for quantum magnetoelastic responses.

This thesis utilizes a multiscale method by connecting molecular dynamics (MD) based information to hydrodynamic macroscopic calculations for investigating the shock response and spallation of metals. First, shock propagation in Cu, Al, and Ni single crystals is simulated up to $100$ GPa at strain rates $>10^6$ s$^{-1}$. Shock-Hugoniot ($U_s$-$U_p$) relations agree strongly with experiments (error $<6\%$); the Foiles EAM potential shows the least deviation for Ni. Second, a multiscale framework linking MD atomic void kinetics to hydrodynamic macro-calculations is established. Using particle swarm optimization (PSO), Nucleation and Growth (NAG) parameters are extracted for Cu, Nb, Mo, and Al, yielding free surface velocity (FSV) profiles matching experiments within $8\%$ for Al. Third, deformation across ten Al tilt (STGB) and twist (STwGB) bicrystals at rates of $10^{10}$-$10^{11}$ s$^{-1}$ proves that threshold spallation depends on boundary misorientation. Phase transitions near GBs lower spall strength at high $U_p$, whereas GB plasticity prolongs pull-back and delays spallation (e.g., $14.2^\circ$ STwGB). FSV methods are found to underestimate true peak tensile strength. Fourth, the framework is extended to polycrystals via 11 STGB and 12 STwGB configurations. Voids consistently nucleate at weakened GBs. Unique NAG parameters are fitted using PSO for all 23 bicrystals. An Average Void Growth in a Fluid Element (AVGFE) model is introduced to map these distinct boundary properties into 1D hydrodynamic codes. The combined model is validated against empirical Al flyer impacts at $518$, $1588$, and $2275$ m/s. The simulated temporal FSV curves mirror experiments, with spall strength deviations tightly bounded within $2.15\%$, $2.9\%$, and $6.0\%$, respectively, and spall thickness deviations within $2.4$-$4.0\%$.

These lecture notes provide an introduction to Bose-Einstein condensates with Raman-induced spin-orbit coupling. Owing to the interplay between the peculiar single-particle dispersion, featuring a double-minimum structure, and the two-body interaction, these systems possess a complex phase diagram. Three different quantum phases can be observed, i.e., a stripe, a plane-wave, and a single-minimum phase, each characterized by different broken symmetries. The condensate dynamics is also significantly affected by the spin-orbit coupling, as revealed by the behavior of the Bogoliubov spectrum in infinite systems and the behavior of the discretized collective mode frequencies in trapped configurations, especially close to the phase transitions. In turn, the superfluid and rotational properties are also deeply modified by the coupling between the motional and spin degree of freedom. Finally, a special attention is devoted to the stripe phase and its supersolid character, which can be clearly revealed by the study of its dynamic features.

Cathodoluminescence (CL) spectroscopy provides access to optical excitations with nanometer spatial resolution, but direct time-resolved measurements of optical resonances remain challenging. Here, we demonstrate that CL interferometry provides access to the temporal response, phase behavior, and modal spectral structure of resonant nanoscale scatterers without requiring ultrafast pump-probe schemes. We develop an analytical framework in which Fourier transformation angle- and frequency-resolved CL interferograms yields the decay time of optical resonances governed by the linear optical response. Multimode resonators exhibit characteristic temporal CL beating signatures associated with spectral mode splitting. By exploiting transition radiation emitted from a nearby metallic surface as a broadband reference, we further demonstrate phase retrieval and cross-correlation measurements between instantaneous and resonant emission processes. Experimental measurements on Au nanoparticles, broadband plasmonic emitters, Au nanostars, and Si nanospheres supporting multipolar Mie resonances confirm the theoretical predictions, and decay times in the range 1-10 fs are derived for each system. Our results establish CL interferometry as a powerful approach for accessing spectral, spatial, and phase information within a single nanoscale measurement with fs resolution.

We identify the spin rotatory strength—a chirality-odd, finite-frequency spin–dipole cross response—as the equilibrium observable for chiral-induced spin selectivity. Time-reversal symmetry forces the static response to vanish, while nonzero SU(2) Wilson-loop flux is an independent necessary condition. Exact diagonalization of a Kane–Mele–Hubbard model ($N{=}4,6,8$) reveals that gapped molecules robustly suppress the response, whereas near-degenerate systems show amplification at small $N$ whose persistence at larger sizes remains open.

In this work, we investigate the excitation dynamics of a Rabi-coupled dissipative Rydberg lattice with a time-dependent detuning. The system is analyzed using (i) a Lindblad master equation within a mean-field approximation and (ii) an effective non-Hermitian Hamiltonian framework. While the mean-field approach captures the emergence of an antiferromagnetic order in the Rydberg excitation profile, the non-Hermitian description provides direct insight into the complex energy spectrum and its avoided crossings, which govern the Landau$-$Zener dynamics. We identify a regime in which the sublattice population imbalance vanishes near the avoided crossing, resulting in identical Landau$-$Zener probabilities on the two sublattices. Beyond a critical effective blockade strength there is a dynamical crossover to another regime in which the sublattice population imbalance persists through the avoided crossing, giving rise to sublattice-dependent Landau$-$Zener probabilities. Furthermore, Rydberg interactions prolong the lifetime of Landau$-$Zener-induced excitations in the presence of weak dissipation and strong Rabi coupling. In contrast, for weak Rabi coupling, the Rydberg blockade inhibits excitation and suppresses the Landau$-$Zener transition probability.

We investigate the infrared magneto-optical response of n-doped epitaxial graphene on 4H-SiC in ultrahigh magnetic fields up to 560~T, utilizing single-turn coil and electromagnetic flux compression techniques. The measured absorption spectra are anomalously broad, strongly deviating from conventional cyclotron resonance. Angle-resolved photoemission spectroscopy (ARPES) reveals a distorted Dirac dispersion featuring a “camel-back" structure with an energy gap of $E_g \sim 0.2$~eV. Using the band parameters extracted via a generalized bilayer graphene model, we construct a Landau level (LL) fan chart that dictates a critical level crossing between the $N=0^+$ and $N=0^-$ states near 160–200~T. At this threshold, the optical transition mechanism undergoes a dramatic shift from an electron-dominated collective mode to a cooperative electron-hole collective excitation. Furthermore, the extreme-field absorption spectra under thulium fiber laser excitation ($\hbar\omega_0 = 0.636$~eV)—culminating in a massive resonance near 400~T with a shoulder at 200~T—are excellently reproduced by a collective Alfvén wave model. This analysis also evidences a magnetic-field-induced enhancement of the sublattice potential asymmetry parameter (from 0.10~eV to 0.12~eV). This directly signifies that the macroscopic electron-hole band asymmetry is further amplified by the applied magnetic field. Ultimately, the field-induced energy inversion generates a strongly interacting, fully compensated electron-hole plasma. The resonant excitation of Alfvén waves in this regime demonstrates that a pristine tabletop analog to the relativistic electron-positron plasmas found in astrophysical extremes can be elegantly realized within a 2D graphene system.

Group-IV color centers, such as the silicon-vacancy (SiV) defect, are highly promising for solid-state quantum technologies. However, nanodiamonds typically exhibit significant lattice strain and structural disorder, which degrade their optical properties and hinder the resolution of the fine spectral structure at cryogenic temperatures. High-pressure high-temperature (HPHT) annealing offers a potential route to relax internal strain, although the phase stability of diamond at the nanoscale under such conditions remains poorly constrained. Here, we investigate the structural evolution of nanodiamonds during HPHT annealing using a Paris-Edinburgh press coupled with in situ synchrotron X-ray diffraction at SOLEIL. A dedicated sample assembly combining nanodiamonds - NaCl - Pt enabled accurate pressure-temperature calibration and real-time monitoring of phase transformations. The diffraction data reveal that the onset of diamond-to-graphite transition occurs at approximately 1800 K at 2 GPa and 2120 K at 4 GPa under the applied HPHT heating protocol. These experimentally determined graphitization onsets define a practical pressure-temperature processing window for HPHT annealing of nanodiamonds while avoiding detectable graphitization and provide a calibrated framework for reliable off-beam annealing treatments that avoid graphitization. Photoluminescence measurements on samples annealed below the graphitization threshold show improved optical response, with partial resolution of the SiV fine structure at 12 K. These optical measurements suggest a relationship between nanoscale phase stability and the optical response of individual SiV-containing nanodiamonds following HPHT annealing. The experimentally established HPHT processing window provides a practical framework for the controlled processing of quantum nanodiamonds while avoiding graphitization.

Slow cyclic modulation of an open quantum system can generate a geometric contribution to its energy transfer statistics, separable from the dynamic background. In this work we construct an experimentally anchored four state open system model for a gate-tunable WSe2/WS2 moiré exciton manifold within a population level full counting statistics framework. We first drive the system uniformly through a closed gate and pump loop and separate the geometric contribution from the dynamic background by reversing the loop direction. We then examine how this response changes with environmental rates, exciton coupling, control conditions, and static spectral broadening. A shorter cycle period followed by nonuniform traversal of the driving loop substantially improves detectability while preserving the geometric response. Combined with enhanced phonon relaxation and reduced radiative loss, this gives about a fourteenfold fixed time signal to noise gain relative to the uniform loop. Our results show that the geometric phonon response remains robust against realistic variations in the system and its environment, and that we can improve its detectability more effectively by suppressing dynamical noise through frequency modulated driving.

Graphene exhibits extraordinarily high carrier mobility, making it a promising platform for next-generation electronics. Scalable growth on SiC, however, suffers from limited dielectric screening at the graphene-substrate interface, degrading electronic performance. In this work, we systematically enhance dielectric screening by intercalating a bilayer of indium at the graphene-SiC interface. Using graphene's plasmaronic signature observed in angle-resolved photoemission spectroscopy as a proxy for interaction strength, we quantitatively demonstrate strong dielectric screening arising from the interplay of both indium layers. Layer-resolved density functional theory shows that the first indium layer acts as a buffer that absorbs substrate interactions, enabling the second layer to form a nearly free-electron system that efficiently screens the graphene layer above. Experiments with only a single intercalated indium layer reveal reduced screening, confirming the essential role of the second layer. Our results establish 2ML indium intercalation as a powerful route for engineering dielectric environments in graphene.

In itinerant magnets governed by the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, the exchange coupling depends on both the moment-moment distance $r$ and the Fermi wavevector $k_{\mathrm{F}}$, yet in bulk synthesis the two are tightly coupled: a change in composition typically alters both. Here, we use a thin-film approach to tune these two variables independently in a single crystalline host. Using molecular-beam epitaxy (MBE), we stabilize either $2\times2\mathrm{R}0^\circ$ Cr$_{1/4}$NbSe$_2$ or $\sqrt{3}\times\sqrt{3}\mathrm{R}30^\circ$ Cr$_{1/3}$NbSe$_2$ within the same NbSe$_2$ host through separate growth windows. Controlled post-growth annealing performed across a series of temperatures then modifies the carrier density while leaving the Cr superstructure intact below a structural-transition threshold. The two as-grown phases are distinct in electronic structure, magnetic ground state, and transport. Along this annealing series, the Hall response evolves systematically while the magnetic response changes in a structurally insensitive manner, with ferromagnetic order emerging within the same $\sqrt{3}\times\sqrt{3}\mathrm{R}30^\circ$ structural class only above a critical annealing temperature, experimentally disentangling carrier density and moment geometry. The Hall magnitude and sign evolution point to a low-carrier-density system in which $k_{\mathrm{F}}$ is susceptible to modest external tuning. Cr-NbSe$_2$ thus realizes carrier-sensitive RKKY magnetism in a single crystalline host, within an MBE-plus-annealing approach extensible across the intercalated transition-metal dichalcogenide family.

We study the generalized one-dimensional (1D) quantum dissipative models corresponding to a Majorana wire which can possess more than one Majorana bound state at each end. The system consists of a 1D fermionic open quantum system whose dynamics is governed by a quadratic Lindblad equation. Using the adjoint Lindblad equation for the fermionic two-point correlations, we find the gaps in the damping and purity spectra of a generic 1D model. Then, using the symmetry-based classification, we show that a winding number as the topological invariant can be defined which distinguishes different steady states of the system in the presence of damping and purity gaps. Then we focus on certain models with different Lindblad quantum jump terms and explore their phase diagrams by calculating the damping and the purity gaps as well as the winding number. In particular, we show that by inclusion of quantum jumps between next-nearest-neighbor sites, higher winding numbers and, equivalently, more Majorana bound states can be achieved. Also, by introducing imbalanced couplings, we can switch between states with negative and positive winding numbers. Finally, we should mention that since our formulation is based on the fermionic correlations rather than the Majorana operators, it can be easily extended to the dissipative topological phases belonging to other symmetry classes.

Measurements of resistive breakdown in electronic systems under a DC electric field have shown that the threshold fields for the insulator-to-metal transition are significantly lower than predicted by single-electron excitation scenarios, such as the Landau-Zener theory. In this work, we propose an alternate mechanism of destabilizing ordered insulators under a DC electric field by fluctuations of the order parameters through the Goldstone mode excitation. The low-energy bosonic excitations receive energy from accelerated electrons and thus destroy the spontaneous symmetry breaking. Using the Keldysh Gree's function formalism, we numerically confirm that the Goldstone mode remains well-defined in the nonequilibrium steady state, while its nonequilibrium excitations are sensitive to the electric field. The effective temperature of the Goldstone mode increases much more rapidly than the electronic effective temperature, with the bosonic threshold field significantly smaller than the electronic one, which suggests that collective phase dynamics may further reduce the transition field to the experimental range via a purely electronic mechanism.

We consider fluctuations of the spin current in the stochastic XNOR process, a kinetically constrained hopping model in one spatial dimension. We formulate three conjectures with explicit amplitudes for the long-time current distributions: a Gaussian limit on the $t^{1/4}$ scale for homogeneous initial states with nonzero magnetization, a half-normal limit on the $t^{1/4}$ scale for domain-wall states with opposite magnetizations, and an M-Wright limit on the $t^{1/8}$ scale for homogeneous initial states at zero magnetization. Earlier work identified the tracer mechanism and anticipated the scaling exponents and limiting shapes in the domain-wall and zero-magnetization settings. Starting from the microscopic XNOR dynamics, we predict the missing amplitudes for the continuous-time process and extend the picture to homogeneous biased initial data. Simulations provide numerical support for all three conjectures without fitted parameters. A separate mathematical companion paper presents an extensively AI-generated candidate proof. Generative-AI tools were used in the research and writing workflow.

Strongly interacting quantum many-body systems subjected to non-Markovian dissipation pose a formidable challenge due to the interplay between strong correlation effects and memory effects. In this Letter, we develop a general theoretical framework to compute how a system observable responds to dissipation, which captures memory effects at short times and recovers the Markovian limit at longer times. Using this framework, we predict that, for a strongly correlated quantum critical state with critical exponent $\eta$, the short-time dynamics of a system observable always obeys a $t^{2\eta}$ scaling law. This emerges as a universal result from the interplay between strong correlation and memory effects, independent of the microscopic Hamiltonian of the system. We further reveal a crossover behavior of this scaling law to either $t^{2\eta-1}$ or linear-in-$t$ behavior beyond the memory time scale. We propose a concrete physical realization of a non-Markovian bath with tunable memory time using ultracold atoms, where our predictions can be straightforwardly verified in current experiments.

Ferroelectric thin films that are heterophased and polycrystalline possess strain sensitive piezoelectric behavior. However, a direct insight into polarization orientations within a given grain and how mechanical stresses reconfigures the ferro elastically coupled polarization orientations remains ambiguous. A polarization component resolved imaging in a Piezoresponse Force Microscope (PFM) was developed in combination with correlative structure and phonon studies that provide insights into grain orientation, domains and bending stress driven phase transitions. The method correlates the polarization invariant and the respective grain orientations present underneath. The technique facilitates an experimental inverse model approach to determine crystallographic grain orientation from the ferroelectric domain. A three point bending stage introduces a flexoelectric strain in Ba0.85,Ca0.15Zr0.1Ti0.9O3_BCZT thin films and simultaneous polarization imaging. This novel technique potentially captures the formation of new polarization invariant of a monoclinic phase that appears under high pressures. The experimental findings pave way for development of inverse modelling of heterophased and polycrystalline systems.

Topological quantum chemistry based on local charge profiles lacks predictive power for the crystalline cleavage of higher-order topological insulators (HOTIs). By cleaving an obstructed atomic insulator, we discover a topological phase characterized by e/2-fractional charges localized at precisely half of the corners, while the remaining empty corners host complementary vacancies of interstice charge. These zero-energy charge vacancies and topological corners form a spatially balanced geometry, separately localized at four corners. Crucially, we demonstrate that the emergence of corner zero modes dictates that specific dangling bonds acting as the mass of a Dirac fermion-must explicitly expose in, and subtly slope toward, the corner regions. This strict directionality is verified by the anisotropic evolution of the mass term within a (2+1) dimensional parameter space. Moreover, we find that the topological corners acquire lower entanglement entropy compared to the bulk, a behavior opposite to that of the real-space energy distribution which forms an energy-entropy compensation, essentially derived from the topological charge compensation. Our work paves the way for the local chemical environment at topological boundaries, and demonstrates the higher order quantum transport counterparts for high energy Dirac physics.

Atomically thin mechanical resonators have been realized predominantly in crystalline two-dimensional (2D) materials, such as graphene, where long-range crystalline order sets their elastic properties and defines their nonlinear resonant behavior. Extending these concepts to the amorphous 2D limit has remained largely unexplored. Here, we demonstrate that monolayer amorphous carbon (MAC) forms suspended membranes that support optothermal actuation and sensitive interferometric readout across both linear and nonlinear regimes of its resonant motion. We resolve thermomechanical motion, driven resonances, and multimode spectra in MAC nanodrums. The frequencies of fundamental vibration modes correspond to unusually low pretensions, placing monolayer MAC nanodrums in a regime where geometric nonlinearities, stress heterogeneity, and mode coupling emerge at comparatively low drive powers. Consistently, we observe pronounced nonlinear dynamics, including hardening, softening, and mixed Duffing responses, nonlinear damping, parametrically excited modes, and signatures of intermodal coupling. These results establish MAC as a robust nanoelectromechanical platform and open an experimental route to disorder-governed nanomechanics in the 2D amorphous limit.

Double perovskites (DPs) offer broad compositional tunability, but predicting the space groups (SGs) of stable structures remains difficult because available datasets are often strongly imbalanced toward dominant SG classes. We refer to dominant SG classes as major SGs and underrepresented classes as minor SGs. We introduce Dynamic and Diversity-enhanced Few-shot Retrieval and Rule-Guided Inference for Space-Group Prediction (DyRIS), an LLM-agent-based framework that predicts ranked SG candidates from a given DP composition. DyRIS uses diversity-enhanced dynamic few-shot prompting to retrieve relevant in-context examples while limiting the dominance of frequently represented SGs. It further incorporates rule-guided inference based on B/B' cation ordering, quantitative indicators, and major-SG bias control to refine and rank the final Top-3 SG candidates. We evaluate DyRIS on 3,528 thermodynamically filtered DP entries and compare it with composition-based and descriptor-based baselines. At a training-data ratio of 0.5, DyRIS achieves competitive overall accuracy while obtaining the best Overall Top-1 macro-F1 score and the best performance across all Minor-SG metrics. DyRIS improves Minor-SG Top-1 accuracy by 3.26 percentage points relative to CrabNet and achieves higher Minor-SG Top-3 accuracy than the strongest PyCaret-based baseline. Ablation studies show that diversity-enhanced retrieval, quantitative indicators, major-SG bias control, and B/B' ordering information each contribute to prediction performance. Additional experiments show that the final rule-guided inference step is not easily replaced by conventional classifier- or ranker-based models. These findings demonstrate the potential of combining retrieval-based LLM reasoning with crystallographic domain knowledge for SG prediction in imbalanced materials datasets.

The prediction of stable alloys forming solid-state solutions across large portions of the composition space is a serious theoretical challenge, since one has to evaluate the Gibbs free energy, including both configurational and vibrational contributions. This requires an energy theory capable of extremely high throughput. By taking the Ni-Pd system as prototype, we construct an efficient Jacobi-Legendre machine-learning potential based on density-functional-theory data, which provides accurate energies and forces across the entire composition space. Based on a cluster expansion up to three-body terms and only 873 trainable parameters, this allows us to compute the partition function by directly integrating all accessible microstates, differing for composition, atomic configuration and thermal agitation. We confirm that Ni and Pd are fully miscible, forming an $fcc$ solid-state solution. This is only metastable at room temperature, while becomes thermodynamically stable at around 600~K, with the stability achieved first at the Pd-rich end of the composition range. Interestingly, entropy and heat capacity analysis reveal a competition between the solid-state solution and two intermetallic phases with long-period L1$_0$ structure for NiPd and NiPd$_3$. All in all, our approach offers a powerful and high-throughput workflow for the study of disordered alloys, an approach that can be extended to multi-component systems such as high-entropy alloys.

We identify a unified thickness criterion for surface reconstruction in ultrathin metal sheets. The critical thickness is governed by the change in surface atomic density upon reconstruction: thinning always favors structural changes that increase this density. Thus, thinning suppresses the (1x2) reconstruction of 5d noble metal (110) sheets but promotes the quasi-hexagonal reconstruction of 4d noble metal (001) sheets. Density functional calculations validate these trends and show only minor corrections from surface stress and quantum-oscillation effects.

Lanthanum hydride (LaH$_{10}$) has been widely studied for its high superconducting critical temperature of 250 K at about 170 GPa pressure. Although the structural ${R\bar{3}m}$-to-${Fm\bar{3}m}$ transition under pressure connected to the emergence of the superconducting phase in this material is broadly understood, the detailed characterization of its nature and its order parameter are still missing. By applying the cluster multipole moment analysis to the hydrogen sublattice, we reveal that this transition is triggered by a quadrupolar $T_{2g}$ order parameter, and we provide evidence for its weak first-order nature. By performing path integral molecular dynamics coupled to a message-passing atomic cluster expansion (MACE) neural network potential, trained on Perdew-Burke-Ernzerhof (PBE) density functional theory configurations, we show that the collapse of the order parameter at the transition is simultaneously associated with the discontinuous softening of the optical $T_{2g}$ phonons. Their symmetry lets them carry a non-negligible electron-phonon coupling in LaH$_{10}$, while the weak first-order nature of the transition makes them soft. The presence of structural instabilities with low-frequency quadrupolar distortions can be a key ingredient to enhance superconductivity in superhydrides and provides guidance for the discovery of new high-$T_c$ superconductors in hydrogen-rich compounds.