Papers

We study finite-time quantum Otto cycles whose working medium is a harmonic oscillator undergoing a quantum Brownian motion described by the Caldeira-Leggett model when the oscillator is in contact with heat baths in isochoric processes. The time evolution of the Otto cycle is studied by analytically solving the exact Heisenberg-Langevin equations for the system variables and the interaction energy between the system and the bath. This enables us to investigate non-Markovian strong-coupling effects on the quantum Otto cycle. We obtain cyclic steady states and study the thermodynamic properties of the Otto cycle for various values of the parameters describing the heat baths and the coupling between the system and the bath. We compare our results with those obtained in the Markovian limit, where the time evolution is described by the Lindblad equation. We find that the change in the interaction energy during the isochoric process contributes to both work and heat and plays a crucial role in determining the thermodynamic behavior of the cycle. This is in contrast to the behavior of the state observables of the working medium, which show relatively small change compared to the Markovian counterparts. We find that non-Markovian effects only become significant when we consider thermodynamic fluxes such as work and heat with the system-bath interaction fully taken into account. We also compare our results with the power-efficiency trade-off relation recently proposed for the Markovian quantum Otto engine.

Hydrogen embrittlement and tritium leakage pose critical challenges for fusion reactor structural components, rendering {\alpha}-Al2O3/Fe interfaces vital as tritium permeation barriers. Here, the thermodynamic stability, trapping energetics, and hydrogen-induced decohesion at the {\alpha}-Al2O3 (0001)/Fe(110) interface were systematically investigated using density functional theory. Single-hydrogen incorporation reveals that the Fe-hollow site is the most stable trapping region, owing to local free volume and heterogeneous interfacial bonding. Multi-hydrogen analysis demonstrates that trapping behavior is concentration-dependent; increasing hydrogen concentration progressively reduces the available free volume and increases local lattice distortion. As a result, simulated cleavage processes show a monotonic decrease in cleavage energy with accumulation. At high hydrogen concentrations, cleavage energy turns negative, indicating spontaneous interfacial exfoliation. These quantitative insights clarify the atomistic degradation mechanisms of protective oxide scales, offering a theoretical framework for optimizing high-performance permeation barriers in fusion-relevant steels.

Integer quantum Hall effect, which is the Hall effect quantized into integer times $e^2/h$ ($e$: elementary charge, $h$: Planck's constant) observed first in two-dimensional electron gases in strong magnetic fields, is reviewed from both theoretical and experimental standpoints. Basic physics underlying the phenomenon is explained. Specifically in this new edition we have a fresh look at how the quantum Hall effect is captured in a perspective of topological systems, since, while the quantum Hall effect is historically the first realization of the topological systems, the field has been delved into a much wider realm of physics of topological systems. We also mention diverse advances such as the quantum Hall effect (QHE) in various materials and contexts that include graphene, oxides and narrow-gap semiconductors, a relation with the fractional quantum Hall effect, and the quantum Hall effect as the resistance standard and further roles in the new SI system. We also expound the Floquet topological insulator (a light-matter coupled system) as a new paradigm in nonequilibrium topological systems, where an anomalous quantum Hall effect in zero magnetic field is realized as theoretically predicted to occur in graphene illuminated by a circularly-polarized laser and experimentally verified recently.

Recent experiments simulating two-dimensional few-fermion systems have observed emergent hydrodynamic behavior, i.e., interaction-driven elliptic flow by adding fermions two at a time [S.~Brandstetter et al., Nat. Phys. (2025)]. Due to the curse of dimensionality and strong correlations, capturing such phenomena beyond two particles remains challenging. Here, we use the ab initio time-dependent explicitly correlated Gaussian (TDECG) method to quantitatively reproduce these experimental observations. With only a moderate number of correlated Gaussian basis functions, our approach obtains converged dynamical observables for systems up to six particles. Furthermore, real-time access to the many-body wavefunction and two-point correlation functions enables us to visualize the transformation from a strongly interacting gas to a stream of paired molecules, i.e., a dynamical BCS-BEC crossover.

The doping and temperature dependencies of the electronic structure and the dynamic spin susceptibility of the Hubbard model on a square lattice are studied within cluster perturbation theory (CPT). The most general features of both electronic and spin spectra qualitatively agree with the experimental data on cuprates. Generalized mean-field calculations of the electronic structure using static short-range magnetic correlations from CPT are also implemented and compared with the results of CPT, allowing us to discuss the role of short-range antiferromagnetism in the formation of the pseudogap.

We explore the nonequilibrium dynamics of a density-ordered dipolar Bose gas in a finite one-dimensional optical lattice following a negative interaction quench, using the numerically exact multiconfigurational time-dependent Hartree method for bosons. The interaction sign reversal, effectively driving a crossover from long-range to short-range interactions, generates rich intra- and interwell tunneling dynamics spanning superfluid, Mott-insulating, and fragmented regimes. A striking finding is the robustness of the underlying crystal-state correlations against the quench, despite the strong dynamical response. We identify emergent excitation modes, including local breathing and dipole-like oscillations, via real- and momentum-space observables, and quantify tunneling through site-resolved position variance. One- and two-body Glauber correlation functions further uncover a direct connection between tunneling and correlation dynamics. Moreover, we show that combining interaction quenches with lattice-depth ramping enables controllable dynamical engineering, establishing dipolar lattice systems as a promising platform for nonequilibrium quantum simulation.

This paper demonstrates the significance of the recently proposed time-convolutionless mode-coupling theory (TMCT) in capturing the dynamics of glass-forming liquids. The origin of the primary differences between ideal MCT and TMCT is comprehensively explored from a unified perspective. First, we review two distinct projection operator methods in the Heisenberg picture: the time-convolution (TC) formulation proposed by Mori and the time-convolutionless (TCL) formulation proposed by Tokuyama and Mori. We show that the appropriate choice between these frameworks fundamentally depends on the space-time scales of the relevant variables. In TMCT, the TC formulation is applied to the current density, whereas the TCL formulation is applied to the number density because the latter operates on a significantly longer space-time scale. In contrast, ideal MCT applies the TC formulation to both densities. Consequently, the governing equation in TMCT is timeconvolutionless, whereas the ideal MCT equation features a time-convolution form. This fundamental difference significantly affects various physical quantities near the glass transition. Finally, the full TMCT equation is transformed into a simplified recursion equation to facilitate numerical analysis, and the key predictions of TMCT are compared with those of ideal MCT

Recent experiments and simulations provide compelling evidence for the emergence of a non-phononic flat band in the dynamical structure factor of two- and three-dimensional amorphous solids. This feature has been suggested to be connected to the excess in the reduced vibrational density of states of glasses, commonly known as the boson peak, and displays several apparently universal characteristics. First, it is nearly dispersionless, with an energy close to the boson-peak frequency. Second, its intensity is negligible below a critical wave vector of the order of the first diffraction peak. Third, its reduced intensity exhibits a strong correlation with the static structure factor. Here, we revisit the resonant-coupling model, a single-mode harmonic realization of the soft-potential scenario in which acoustic phonons interact with single frequency quasi-localized vibrations. We show that, under minimal phenomenological assumptions, this framework naturally reproduces the main features of the observed flat band and clarifies its connection to the boson peak.

A locking between propagation direction $\hat{\bf q}$, spin $\hat{\bf S}$, and surface or interface normal $\hat{\bf n}$ – a phenomenon broadly termed chirality – pervades evanescent or surface waves in optics, magnetism, plasmonics, and acoustics. Yet, it is not known whether the phenomenon is universal or bound to conditions. Here, we unveil that any source-free vector field that propagates along $\hat{\bf q}$ and is evanescent along $\hat{\bf n}$, the existence of a spin automatically enforces a rigid, right-handed locking among $\hat{\bf q}$, $\hat{\bf S}$, and $\hat{\bf n}$, that is characterized by a chirality index $C_{\bf q}\equiv \hat{\bf n}\cdot(\hat{\bf S}\times \hat{\bf q})>0$. For an arbitrary propagation direction defined by $\hat{\bf q}\cdot \hat{\bf S}\equiv \eta\in [-1,1]$, i.e., not necessarily transverse spin, we derive a fundamental upper bound $C_{\bf q}\le \sqrt{1-\eta^2}$. The universal absence of left-handed evanescent (source-less) vector fields underscores the fundamental physical non-equivalence of mirror-image configurations – a principle echoed by parity violation, the natural excess of enantiomers in chiral molecules, and the fixed chirality of DNA.

We introduce the tandem exclusion process (TEP), a one-dimensional stochastic lattice model motivated by tandem running in ants. Particles evolve through two cooperative local transitions, $110\to101$ at rate $\alpha$ (leader advancement) and $101\to011$ at rate $\beta$ (follower recovery). We prove that the stationary measure on the dynamically active sector is the Gibbs measure $\pi\propto q^{H(\eta)}$, where $q=\beta/\alpha$ and $H(\eta)$ counts neighboring occupied pairs, and derive exact closed-form expressions for the stationary current and spatial correlations using transfer-matrix methods. The current is asymmetric under particle–hole exchange $\rho\mapsto1-\rho$, with its maximum occurring at densities strictly larger than $1/2$, in contrast to the symmetric current $\rho(1-\rho)$ of the totally asymmetric simple exclusion process (TASEP). For $q>1$, cooperative dynamics enhances the current above the TASEP value and generates strong spatial clustering; in the limit $q\to\infty$, the current approaches $J\to\alpha\rho$, corresponding to nearly unconstrained collective transport. These results suggest that tandem coordination alone can substantially enhance collective transport efficiency at moderate and high densities, even without pheromone-mediated long-range communication.

Coherent electron shuttling is a key requirement for realizing scalable silicon quantum computing architectures. However, in silicon qubits, the existence of nearly degenerate conduction-band valleys poses a significant challenge because non-adiabatic transitions to excited valley states cause spin dephasing via spin-valley mixing. In this paper, we propose a smooth velocity shuttling protocol to suppress these valley excitations. By mapping the time-domain design of the shuttling velocity profile onto the design problem of window functions in signal processing, we establish an analytical and intuitive design guideline that does not require computationally expensive numerical optimization. We demonstrate that the high-frequency sidelobes of the shuttling velocity spectrum can be effectively suppressed by applying a frequency-modulated gate voltage based on the Tukey window. Through statistical numerical simulations incorporating realistic spatial randomness of the valley landscape, we show that the proposed smooth velocity control significantly reduces the average spin infidelity in the moderate-to-low disorder regime ($|\Delta_0|/\sigma_\Delta \simeq \mathcal{O}(1)$). Our results underscore that this simple, control-level velocity shaping provides a robust pathway toward high-fidelity spin transport in large-scale silicon quantum processors.

Hole spin qubits in germanium (Ge)-based heterostructures have demonstrated their potential for scalable quantum information processing using all-electrical gate operations. Furthermore, the emerging material platform of germanium-tin (GeSn) can feature a direct bandgap, which makes it promising for establishing spin-photon interfaces for quantum networking. Here, we perform magneto-photoluminescence measurements of a Ge0.88Sn0.12/Si0.02Ge0.89Sn0.09 double quantum well using the double modulation Fourier transform infrared-based photoluminescence spectroscopy. Our measurements reveal theoretically expected diamagnetic shift at low magnetic fields as well as the linear trend of zeroth-level Landau quantization at higher fields and Zeeman-induced polarization-dependent energy shifts at +/- 12 T. We extract an effective g-factor of ~ 2 and an excitonic reduced mass of ~ 0.04 me consistent with previous estimations for heavy-hole {\Gamma}-valley excitons. The observation of sizable Zeeman splitting is consistent with strong spin-orbit interaction in Ge-based hole systems, which can enable electrically driven spin control. Our analysis can be adopted for studying and evaluating group-IV semiconductor heterostructures as hosts for hole spin qubits toward scalable quantum information processing.

MnF$_2$ is widely regarded as a candidate altermagnet, but the magnitude and implications of its altermagnetic band splitting remain debated. Using electronic-structure calculations, we construct minimal models that capture the magnetic and electronic properties of MnF$_2$. These models show that the parameters governing the chiral magnon splitting and the spin splitting of the electronic bands are relatively small. Moreover, the electronic system lies in the strong-coupling regime, where most magnetic properties are controlled by the ratio $t/U$ between the characteristic hopping amplitude $t$ and the large on-site Coulomb repulsion $U$. Consequently, all exchange interactions scale as $1/U$, so a small altermagnetic hopping $\delta t$ produces only a proportionally small exchange term. Upon doping, the altermagnetic contribution to the anomalous Hall effect is likewise suppressed, being smaller than the conventional (non-altermagnetic) contribution by a factor of order $\delta t/U$. In contrast, the behavior of the conductivity tensor $\hat{\sigma}(\omega)$ at $\hbar \omega \sim U$ differs qualitatively, because $\delta t$ enters the energies of interband optical transitions directly rather than through the reduced ratio $\delta t/U$. This contribution strongly reshapes $\hat{\sigma}(\omega)$, leading to a dramatic enhancement of the magneto-optical response.

The exact ground state of the two-dimensional Hubbard model is critical for understanding cuprate superconductivity. Previous numerical studies on narrow cylinders found insulating, static stripes that inherently suppress superconductivity. Here, using constrained-path auxiliary-field quantum Monte Carlo on isotropic lattices up to $24 \times 24$ sites, we show static stripes are boundary artifacts. The true 2D thermodynamic limit yields a topologically melted fluid of dynamically fluctuating magnetic pockets. Furthermore, we reveal the microscopic real-space origin of cuprate particle-hole asymmetry. Hole doping actively melts the magnetic background, driving a Lifshitz transition that unleashes macroscopic $d_{x^2-y^2}$ phase coherence at an optimal $x \approx 0.150-0.200$. Conversely, electron doping preserves rigid antiferromagnetic domains, confining carriers to narrow fault lines that optimally saturate early at $x \approx 0.100$. By extracting the macroscopic off-diagonal long-range order across both regimes, we perfectly recover the skewed phenomenological superconducting dome. Our parameter-free theoretical curve aligns with empirical Uemura and Božović scaling relations, capturing the underdoped emergence, distinct optimal peaks, the 1/8 anomaly suppression, and overdoped collapse. These results prove that robust d-wave superconductivity is the intrinsic ground state of the pure Hubbard Hamiltonian. Finally, we propose the Topological Magnetic Fluctuation Model (TMFM) as the exact real-space microscopic mechanism of the cuprate superconductors.

The point-charge approximation is one of the most successful idealizations in molecular biophysics, but it becomes strained in strong fields, confined geometries, and crowded aqueous environments. We develop a minimal Extended Structural Dynamics (ESD) model in which charged entities are treated as finite, deformable objects with an internal breathing mode rather than as structureless points. Starting from a Hamiltonian description and a controlled coarse-graining procedure, we derive an effective generalized Langevin equation for the center-of-mass motion. The reduced dynamics contain a memory kernel with three physically distinct contributions: finite-size causal delay, inertial deformation, and crowding-induced deformation. The derivation rests on explicit assumptions of small deformation, local dielectric screening, one dominant internal mode, and adiabatic elimination of the fast structural coordinate. Parameters are determined by independently measurable inputs – ionic radius, charge, mass, and the high-frequency dielectric constant of water – with one exception: the dimensionless coupling lambda governing crowding-induced deformation, discussed in detail in the paper. Two primary predictions follow. First, transport through confined geometries should show dynamical deviations from point-charge baselines scaling with ionic deformability, beyond static potential-of-mean-force predictions. Second, polarization response should preserve ionic-radius ordering across alkali ions. Two secondary consequences are identified: a field-dependent effective charge radius and a deformation-dependent correction to near-surface mobility. Amplification of these effects in confined settings is treated as a plausible extension rather than a derived result. The framework recovers standard electrostatic models as limiting cases.

The Longest Increasing Subsequence problem - a classic combinatorial challenge with deep connections to statistical mechanics- exhibits a rich thermodynamic landscape. Introducing a temperature we identify two distinct energy scales: A Schottky-like crossover at T_cross and a condensation transition at T_cond, below which the number of maximum-length configurations becomes sub-exponential in system size. We also show that despite the existence of polynomial-time dynamic programming algorithms for the ground state, local Monte Carlo dynamics, after sudden quenches at low temperatures, become trapped in metastable state configurations displaying characteristic glassy signatures: two-step relaxation, persistent dynamical overlaps and aging. On the other hand, logarithmic annealing tracks equilibrium down to the ground state. These results establish that thermodynamic sparsity - not energetic barriers - can render local search dynamically intractable, positioning the LIS problem as a bridge between exactly solvable optimization and glassy spin-glass phenomenology.

Scientific discovery is not only answer generation but revision of the representational regime in which evidence, artifacts, operations, and verifiers are typed. We develop a category-theoretic account of agentic discovery for materials science. In a fixed regime b with schema category S_b, the system state is a copresheaf I_t: S_b -> Set, and provenance is the category of elements \int_{S_b} I_t. Fixed-regime operation is an update on such states, endofunctorial only when provenance-preserving refinements are specified and preserved. Discovery is instead a verified regime transition u: S_b -> S_b': old artifacts are preserved, transported by the left Kan extension Lan_u I_t, and compared with the post-transition state to identify residual content beyond functorial transport. This separates retrieval, search, and discovery without subjective novelty. We instantiate the framework in two systems. In Builder/Breaker, a protein-mechanics world model is revised under a Minimum Description Length gate; the accepted law expresses within-chain flexibility as all-mode elastic compliance conditioned by slow collective-mode participation, or mode-conditioned compliance. In CategoryScienceClaw, typed skills, artifacts, open needs, workflow mutation, gates, stress tests, and public discourse become a proof-carrying knowledge-computation graph. A fiber-network example records candidate models, rejected alternatives, an AIC gate, perturbation tests, and an accepted orientation-tensor anisotropic stiffness surrogate over an isotropic fiber-count descriptor. Together, the cases show how category theory can be both a mathematical language for discovery and an engineering specification for self-revising AI discovery systems.

We investigate the quantum thermal conductivity (TC) of two-dimensional monolayer amorphous carbon (MAC). We employ three distinct amorphization algorithms to generate various possible MAC configurations, ranging from Zachariasen-type continuous random networks to nanocrystallites embedded in random networks. The local bond order parameter, q3, is used to quantify the amorphousness of the structures, and TC is computed as functions of q3 and temperature. This framework enables us to assess how structural topology, degree of amorphization, and quantum statistics contribute to heat conduction in a two-dimensional amorphous solid. At room temperature, TC values are predicted to range between 3.5 to 10 W/m/K, in agreement with recent experiments. Analysis of vibrational modes reveals that, while the modes of these 2D amorphous structures fall into the usual categories, namely, propagons, diffusons, and locons, their polarization characteristics display distinct behavior. Owing to the fully quantum mechanical framework, we examine both low- and high-temperature characteristics of this 2D amorphous system. By examining the classical limit, we show that classical treatments substantially overestimate the TC of MAC; namely, the quantum TC is less than half of the classical value at room temperature and up to nearly an order of magnitude lower at low temperatures.

We here explore the emergence of orbital and spin Hall effects, originating beyond the $L$-$S$ coupling, and investigate the interplay between inter-orbit hybridization, relativistic Rashba spin-orbit coupling (SOC), and non-relativistic SOC, namely altermagnetic (AM) order, in a two-dimensional model Hamiltonian. The orbital (spin) Hall responses are remarkably found to be quantized within a window of Fermi energy when the strength of AM order (Rashba SOC) exceeds (falls below) the scale set by $sp$-hybridization. Importantly, orbital and spin Hall quantizations are independent of Rashba SOC and AM order, respectively, while the uniform profiles of finite orbital and vanishingly small spin moments of bands around the Fermi energy. The microscopic origin of such quantization comes from the Fermi surface-activated orbital and spin Berry curvatures. The extent of the quantized regime is strongly controlled by the intra-orbital coupling strength. As the temperature increases, the quantization is significantly compromised in the spin Hall case. We extend our analysis to the orbital and spin Nernst coefficients where the pronounced dip-peak structures signal the existence of the quantization leading to experimental relevance.

The pressure-induced transformation between low-density amorphous ice (LDA) and high-density amorphous ice (HDA) is a prototypical polyamorphic transition, yet its microscopic mechanism - and in particular the nature of intermediate amorphous (IA) states - has long remained unresolved. We present the first characterisation of a flat LDA||HDA interface, determining its equilibrium thickness and showing its link to medium-density amorphous ice (MDA). Interestingly, the thickness of the interfacial layer remains constant under compression, while its position shifts reversibly into the LDA region - an elastic response that exhibits kinetic hysteresis upon decompression, reminiscent of memory effects. For high-precision discrimination of amorphous ices, we use a neural network classifier based on SOAP (Smooth Overlap of Atomic Positions) descriptors. The systematic description of the local structure emphasizes the importance of orientational information from the hydrogen bond network. Furthermore, this approach enables molecular dynamics analysis of the LDA-to-HDA transformation, directly mapping the spatial distribution of intermediate structures relative to growing HDA domains and the surrounding LDA matrix, and revealing that MDA-like IA configurations are not a distinct bulk phase but rather localise at the LDA-HDA interface.

We investigate the combined effect of a far - infrared cavity field and Rashba spin - orbit interaction on the band structure and transport properties of artificial graphene composed of quasi-2D InAs/GaAs quantum dots. The coupling to cavity photons is modeled by constructing a complete basis as the tensor product of the electronic Hilbert space and the Fock space. Our numerical calculations for the system embedded in a linear cavity predict the existence of both type-I and type-II Dirac points which can be distinguished by their response to Rashba interaction. Namely, Rashba coupling opens a gap at type-II Dirac points, while type-I Dirac points remain gapless. The possibility of gap-opening for type-II Dirac points is demonstrated analytically as well. For both cylindrical and linear cavities, we demonstrate the formation of electron - photon hybrid states and Rabi splittings between energy minibands. Multiple crossings, and anticrossings between Dirac-band replicas produce pronounced modifications of the spin-Hall conductivity, including strong anisotropy and oscillatory behavior controlled by cavity geometry and polarization of photons. Our results show that the interplay between Rashba and cavity couplings governs Dirac-point physics and provides a route toward tunable polaritonic spin-transport in engineered nanostructures.

Raman scattering is a powerful spectroscopic technique widely employed to investigate light-matter interactions and lattice dynamics in two-dimensional materials. Here, we investigate the temperature-dependent resonant Raman response of bilayer 3R-MoS$_2$. The study combines multi-wavelength Raman spectroscopy, photoluminescence measurements, and density functional theory calculations to track the evolution of excitonic transitions and resonance conditions. We observe contributions from both zone-centre and finite-momentum phonons, a pronounced quenching of the Stokes intensity at low temperatures followed by saturation, the emergence of anti-Stokes scattering above 130~K, and a strong deviation of the effective phonon temperature from the lattice temperature induced by resonance effects. These results demonstrate that the Raman response is governed by the interplay between incoming and outgoing resonance processes, providing deeper insight into exciton-phonon coupling in van der Waals materials.

Complex oxide interfaces, such as $\mathrm{SrTiO_3}$ and $\mathrm{KTaO_3}$ based heterostructures, host rich correlated phenomena with strong potential for advanced device applications. However, these interfaces are extremely susceptible to contamination and defect formation during nanofabrication, which often compromises device performance. Here, we present a solvent-free method for patterning oxide interfaces by employing high-resolution transferable thin metal masks in conjunction with oxygen-enriched $\mathrm{Ar^+}$ ion milling, which enables a clean and well-controlled nanofabrication process. Transport measurements demonstrate that the fabricated devices preserve their intrinsic properties, including high carrier mobilities, with negligible degradation compared to the pristine interfaces. This technique offers a convenient and robust route for engineering high-performance oxide electronic devices with precisely tailored transport characteristics.

We investigate size difference driven segregation in dense granular flows of multicomponent mixtures down a periodic chute using continuum model and Discrete Element Method (DEM) simulations. A previously developed particle force-based segregation model for binary mixtures is systematically extended to mixtures comprising three or more particle species differing in size. The generalized model accounts for inter-species interactions by computing the net force on each component in the presence of all others, without relying on empirical percolation velocity. This segregation model is coupled with a mixture rheology model and incorporated into the species transport and momentum balance equations to develop a continuum model that predicts the spatial and temporal evolution of species concentration and velocity fields. The continuum model predictions are found to be in agreement with DEM simulation data for ternary and quaternary mixtures over a wide range of mixture compositions and chute inclinations at moderate size ratios for well-mixed and small-near-base configurations. For larger size ratios, the one dimensional model predictions capture the qualitative segregation trend while showing relatively larger quantitative differences from DEM data. For an initial configuration, having large particles near base and small particles near the free surface, a Rayleigh-Taylor like instability at early times is observed. Due to the presence of this instability, two dimensional evolution of the species concentration fields is present for initial part of the flow. Predictions of such features requires the extension of the one dimensional continuum model to two dimensions.

Orbital currents in light metals offer large orbital Hall conductivities, yet translating this into practical spin-orbit torque efficiency is hindered by fundamental limitations. In this work, we introduce a Gd interlayer between a Ti orbital source and a Co ferromagnet to enhance the orbital torque efficiency. Ferromagnetic resonance-based spin (orbital) pumping measurements identify an optimal Gd thickness of around 4 nm, where the orbital-to-spin conversion efficiency reaches its maximum. The Ti-thickness dependence of the inverse orbital Hall effect signal confirms a bulk orbital Hall origin in Ti and yields a qualitative orbital diffusion length exceeding 20 nm. Spin-torque ferromagnetic resonance measurements demonstrate a fivefold enhancement of the SOT efficiency in Ti(20 nm)/Co compared to a Gd(4 nm)/Co reference. Interestingly, the trilayer Ti/Gd/Co architecture exhibits a spin (orbital) torque efficiency greater than 1, which is higher than that of the bilayer Ti/Co and Gd/Co structures, irrespective of Ti thickness. These results establish rare-earth interlayer engineering as a viable route to enhanced orbital torque efficiency for next-generation spin-orbitronic devices.

The CALPHAD framework provides a rigorous basis for thermodynamic modeling, yet its ability to predict new chemistries is restricted by limited data and by functional forms that rely heavily on composition alone. Here, we show that machine learning (ML) can address these challenges through a hybrid strategy that learns Redlich-Kister (RK) interaction coefficients directly from physically informed elemental descriptors. Using formation energies of 14-element FCC alloys generated by a universal machine-learning interatomic potential (MLIP), we benchmark three classes of models: (1) composition-based RK and ML models, (2) descriptor-based ML models, and (3) a combined ML-augmented RK approach (ML4RK). Leave-one-element-out tests highlight complementary strengths. RK models, class (1), remain the most data-efficient when binary information is available, while descriptor-based ML models, class (2), enable genuine zero-shot extrapolation to elements absent from the training set. By embedding elemental descriptors into the RK framework, the hybrid approach unifies these regimes and enables prediction of interaction parameters for otherwise unknown or data-scarce binaries, class (3). This work demonstrates a physically grounded and data-efficient route to extend CALPHAD models by combining the transferability of ML with the physical grounding, interpretability, data efficiency, and robustness of thermodynamic formalisms.

The Granovskii-Zhedanov (GZ) states are exact scar states of the spin-S XYZ chain for S >= 1. As a result, local quantum information encoded in a GZ state remains preserved under the unitary dynamics of the XYZ Hamiltonian; thus, these states evade thermalization and violate ergodicity despite the system being otherwise nonintegrable and chaotic. However, in realistic experimental settings, the realization of an ideal XYZ Hamiltonian is not possible, as perturbations are inevitable. These perturbations ultimately lead to the decay and thermalization of the GZ state. We study the stability and dynamics of GZ states in the presence of generic perturbations and propose physically realistic mechanisms to stabilize them. We show that the product structure of the GZ state allows its lifetime to be enhanced in the presence of an external helical magnetic field, which slows down thermalization but does not prevent it at long times. We further demonstrate that the inclusion of effective non-Hermitian spin relaxation processes can substantially stabilize the GZ states, leading to a nonequilibrium steady state with finite fidelity with GZ state. Such dissipative processes can naturally originate from mechanisms such as Purcell-enhanced spontaneous emission or spin-lattice relaxation in the presence of the helical magnetic field. Using infinite time-evolving block decimation and exact time evolution, we systematically analyze the dynamics and robustness of the GZ states in the perturbed non-Hermitian XYZ model. To connect with experimental platforms, we introduce a Hubbard model that maps onto the XYZ spin system and propose that ring-shaped optical lattices may provide a viable route for realizing and stabilizing GZ states. Finally, we present an equivalent Lindblad description of the effective non-Hermitian dynamics.

Adding a polymer to a sessile water droplet not only lowers its freezing point but also suppresses the tip singularity that forms during its freezing on cold substrates. Here, we employ synchrotron X-ray and Raman imaging to elucidate the spatiotemporal mechanism underlying tip suppression in an aqueous polyvinyl alcohol (PVA) solution, a model polymer solution. As the polymer concentration increases, we observe slower propagation of the freezing front, reduced bubble entrapment, and a progressively more rounded apex across the volumes and molecular weights examined. X-ray tomography reveals that frozen PVA droplets retain low X-ray transmittance domains in their interiors and at the surface, and Raman spectral mapping confirms that these domains correspond to PVA-enriched regions, providing direct evidence of freeze-induced polymer segregation. These findings indicate that PVA is redistributed heterogeneously during water solidification rather than shifting bulk properties homogeneously, providing a spatially resolved framework for interpreting the observed tip blunting and the suppression of discrete bubble entrapment. Our work identifies freeze-induced polymer segregation as a pathway by which a dissolved polymer regulates both the external shape and the internal structure of a freezing droplet, and these findings shed light on potential applications in freezing-based processes such as freeze-casting and cryopreservation.

Representative elementary areas and volumes provide the scale bridge between resolved granular microstructure and continuum-scale material properties, yet they are still commonly selected from the apparent stabilization of a single scalar observable. Such plateaus can be false indicators of representativeness when statistically incompatible regions are averaged together or when long-wavelength structural correlations remain unresolved. We introduce a general representative-support framework for granular materials based on three sequential requirements: statistical admissibility of the sampled domain, persistent convergence of the apparent field mean and the low-wavenumber covariance spectrum, and validation against independent effective properties. The concept is tested on seven large-area backscattered-electron images of Arabian dune sands and mineral-resolved QEMSCAN maps. The structure-only criterion identifies a representative elementary area of $1536$ pixels, corresponding to approximately $2.01~\mathrm{mm}$. Without property-specific fitting or recalibration, the same physical scale transferred to the QEMSCAN grid $(\approx 2.04~\mathrm{mm})$ coincides with the onset of weak size dependence in apparent thermal conductivity, elastic stiffness, and directional Young's moduli. Thus, the representative scale inferred from long-wavelength granular organization independently predicts the convergence of distinct constitutive responses. The results show that representative support should be assigned only after both statistical compatibility and long-range structural convergence have been established. Although demonstrated here on two-dimensional dune-sand sections, the criterion is formulated for granular materials generally and has a direct mathematical extension to three-dimensional voxelized volumes.

We investigate collective excitations in flat-band superfluids by incorporating the coupled dynamics of pairing (phase and amplitude) and density fluctuations. We demonstrate that for any time-reversal symmetric superfluid system with an isolated flat band, only a single low-energy collective mode emerges in the long-wavelength limit. In contrast to the linearly dispersive Goldstone mode in conventional superfluids, this hybridized mode is gapless at zero momentum but exhibits a quadratic dispersion ($\omega \propto q^2$) at small momenta. We show that the dispersion coefficients of this collective mode are governed by the normal-state quantum metric of the flat band. These analytical predictions are in excellent agreement with numerical calculations. Our results are applicable to any generic $s$-wave flat-band superfluid, provided the flat band is energetically well separated from other dispersive bands.