Papers

A ferroelectric surface in contact with an ionic or molecular reservoir is intrinsically a ferroionic state in which polarization and compensating surface charge are thermodynamically coupled. Surface chemical compensation is known to control the magnitude and sign of ferroelectric polarization, yet the competing instability toward domain formation has usually been treated separately. Here we develop a static theory in which polarization, electrochemical surface charge, and finite-wave-vector domain formation are analyzed within a single thermodynamic framework for uniaxial polarization orientation. The central quantity is the differential chemical capacitance, which determines how strongly the surface charge can respond to a spatial modulation of polarization and therefore differs fundamentally from the equilibrium screening charge. We derive the homogeneous equation of state, the finite-wave-vector stability kernel, analytical domain-onset wavelengths and thickness scalings, and weakly nonlinear stripe and checkerboard solutions for both second- and first-order ferroelectrics. For a first-order transition, a finite-amplitude stripe state can become thermodynamically favorable before the homogeneous linear spinodal when the effective quartic coefficient is negative; this pre-spinodal window closes as the biased background polarization increases. Dense numerical phase maps confirm the analytical structure and show how chemical potential and film thickness reorganize weakly polar, monodomain, and polydomain states. Numerical analysis for BaTiO3 realization illustrates the corresponding temperature, oxygen-pressure, and thickness scales and identifies experimentally testable regimes in which chemical screening stabilizes the homogeneous state against the columnar 180{\deg} instability considered here or domain formation becomes the preferred route for depolarization-energy reduction.

Metallic altermagnets remain rare, particularly in low-symmetry three-dimensional crystals where spin-split electronic bands and chiral magnon excitations can coexist. We report a family of metallic $d_{yz}$-wave altermagnets in the orthorhombic ternary borides XCoB$_2$ (X = Ta, Zr, Hf), which crystallize in the centrosymmetric $Pnma$ structure with G-type collinear magnetic order. Symmetry analysis within the magnetic space group $Pnm'a'$ (BNS No.~62.447) predicts a nonrelativistic spin splitting proportional to $k_yk_z$, with symmetry-enforced degeneracy on the $k_y$ and $k_z$ nodal planes, consistent with first-principles calculations. On the $k_x=0$ plane, the momentum-averaged spin splitting reaches 88.4, 52.3, and 70.6~meV at the Fermi level in TaCoB$_2$, ZrCoB$_2$, and HfCoB$_2$, respectively, with maxima exceeding 200~meV in all three compounds. Exchange analysis shows that the altermagnetic magnon splitting originates from symmetry-inequivalent sixth-neighbour inter-sublattice interactions. The chirality splitting reaches 1.51, 2.03, and 3.10 meV below 50 meV in TaCoB$_2$, ZrCoB$_2$, and HfCoB$_2$, respectively, making it accessible to inelastic neutron scattering. Monte Carlo simulations yield N'eel temperatures of $67\pm1.1$, $330\pm5.7$, and $307\pm5.0$~K, placing ZrCoB$_2$ and HfCoB$*2$ above room temperature. With spin-orbit coupling included, all three compounds host symmetry-protected Weyl points near the Fermi level, Fermi-arc surface states and sizable intrinsic anomalous Hall conductivities $\sigma*{zx}$ of $+342$, $-392$, and $-221$~S/cm at the Fermi level, reaching maximum magnitudes of $763$, $942$, and $924$~S/cm for TaCoB$_2$, ZrCoB$_2$, and HfCoB$_2$, respectively. $X$CoB$_2$ therefore provides a single compensated platform carrying both magnonic and electronic chirality, one in the spin waves and the other in the Berry curvature, without any stray field.

Buckled colloidal monolayers constitute a versatile soft-matter platform for engineering artificial spin lattices, with each particle serving as a single Ising spin. While the average Ising coupling energy has been approximately derived for perfect particle lattices, extracting the complete set of coupling parameters from real samples remains inaccessible. Here, we apply an inverse method to reconstruct all nearest-neighbor effective Ising coupling energies from measured colloidal spin configurations. We design multiple experimental protocols to control the thermodynamic state of the colloidal system, from isotropic compression and shear deformation to modulation of interparticle attraction, each giving rise to distinct spin configurations. Using spin configuration data, we reconstruct all nearest-neighbor effective Ising coupling energies using maximum likelihood estimation. To assess inference reliability without ground-truth model parameters, we propose to use the convergence of the standard deviation of the estimated couplings as a practical, ground-truth-free criterion, and validate its reliability using simulation data with known parameters. The extracted spatially resolved couplings reveal how each control protocol influences the sign, magnitude, statistical distribution, and spatial arrangement of the microscopic coupling parameters: isotropic compression strengthens antiferromagnetic couplings and enhances quenched disorder; shear deformation generates direction-dependent anisotropic couplings; and increased interparticle attraction drives a crossover from antiferromagnetic to paramagnetic and then to ferromagnetic couplings. This work establishes a practical inference framework for estimating effective model parameters of colloidal artificial spin lattices.

Altermagnets combine compensated magnetic order with momentum-dependent spin splitting, providing spin-polarized electronic states without a net magnetization. Metallic $d$-wave altermagnets are particularly promising because they can support time-reversal-odd spin currents in linear response, yet experimentally validated bulk realizations remain scarce. Here, we use high-throughput density-functional-theory data to relate the magnitude of altermagnetic band splitting to compositional, structural, and DFT-derived magnetic descriptors. An interpretable gradient-boosted model identifies two candidate-prioritization criteria: compact unit cells and magnetic sublattices that sustain sizable local moments. Guided by these trends, we screen tetragonal $A_2XY$ Heusler compounds in space group $P4/mmm$. Among 307 structures, symmetry identifies 169 altermagnetic arrangements, of which 157 remain metallic altermagnets in DFT. Sixteen realize an altermagnetic collinear ground state, of which 15 are dynamically and mechanically stable and 10 also lie on or below the calculated thermodynamic hull. Six candidates exceed the CrSb splitting obtained under the same computational protocol, led by Co$_2$AlSc ($\Delta_\mathrm{max}=2.24$~eV) and Fe$_2$AlGe ($2.07$~eV). A Julliere-model estimate gives a tunneling magnetoresistance of up to $203\%$ at the Fermi level for Co$_2$AlSc. These results identify a chemically tunable family of metallic $d$-wave altermagnets and demonstrate how interpretable machine learning can guide targeted first-principles searches.

We analyze how an arbitrary observation mask on a finite periodic ring of equally spaced sensors affects the posterior covariance, Fourier-mode coupling, and normalized posterior trace in Gaussian-process reconstruction. Under a rotationally stationary prior and homogeneous independent measurement noise, complete observation gives independent scalar posterior formulas for the Fourier modes. For an arbitrary mask, however, the matrix $Q_M=F D_MF^\ast$ is generally non-diagonal; its off-diagonal entries are finite Fourier components of the realized mask and couple modes in the posterior precision. Consequently, masks with the same unavailable-channel fraction can have different normalized posterior traces because their geometries differ. A dimensionless 64-channel synthetic benchmark illustrates this finite-matrix effect. A circumferential array of equally spaced wall-mounted microphones at a fixed axial station of a circular fan or compressor duct provides one concrete mechanical-engineering interpretation: failed, saturated, corrupted, or dropped-out channels form the observation mask. The analysis is a finite-dimensional reference calculation under the stated rotational-stationarity and common-noise assumptions, not a performance claim for a nonuniform or unequally instrumented operating duct.

Nonreciprocal many-body dynamics can develop a swap phase characterized by spontaneous global oscillations far from equilibrium. To determine how local nonreciprocal interactions predict global oscillations and how broadly this prediction applies, we compare mean-field theory, independent-node theory, and nearest-neighbor spin-coupling theory for a two-spin nonreciprocal Ising model on networks of fixed coordination number (\(z=4\)). Nearest-neighbor spin-coupling theory retains nine independent joint edge probabilities. Monte Carlo benchmarks show that it predicts the oscillation amplitude, angular momentum, and period on edge-swapped networks with a 2.1% aggregate mean absolute relative error. We then extend the square lattice to degree-preserving edge-swapped networks and find sharply different behavior. With increasing system size, the oscillation amplitude and angular momentum decay strongly on the periodic square lattice but remain nearly size independent on edge-swapped networks. These results show that identical local parameters do not determine the macroscopic phase. The contrasting finite-size trends identify network geometry as a key determinant of collective oscillations at fixed local interaction parameters.

We propose a new product entropy, defined as the Rényi (or von Neumann) entropy of a normalized product operator constructed from two density matrices. We establish a duality showing that the SVD entanglement entropy of a subsystem for two pure states is exactly equivalent to the product entropy of the complementary subsystem. This connection provides both a transparent physical interpretation in terms of the spectral diversity of the subsystem state product and a computationally efficient route that bypasses the reduced transition matrix. For low-lying eigenstates, we derive analytical expressions for the subsystem product entropy between the ground state and primary excitations in two-dimensional conformal field theories, explicitly verified against the critical Ising chain. In quantum quench dynamics, the quasiparticle picture yields time evolution in the scaling limit: following a global quench, the subsystem product entropy exhibits distinct sequences of thermalization and revivals, whereas under a local operator quench, it develops characteristic plateaus whose constant values are determined by the inserted operator. Extensive numerical calculations on the critical Ising chain confirm the analytical predictions with excellent accuracy.

We study the retrieval dynamics of an $n$-body asymmetric dense associative memory model, in which sequential retrieval is implemented by shifting one pattern index in the higher-order Hebbian interaction. The model exhibits sequential retrieval of the stored patterns, and the retrieval state corresponds to a stable limit-cycle attractor. The storage capacity is defined as the maximum loading rate for which this limit cycle remains stable. Using generating functional analysis, we derive the dynamical equations describing the sequential retrieval state. The generating functional analysis reveals that the retarded self-interaction term vanishes in the asymmetric model, and the resulting overlap dynamics is reproduced by an Amari-Maginu-type signal-to-noise analysis. Also, we find that for the interaction order $n\ge 3$, the normalized storage capacity decreases monotonically with increasing interaction order, in contrast to symmetric Modern Hopfield models.

Mixed-halide perovskite nanocrystal electrodes fail in supercapacitors through field-driven halide segregation. In undoped $\mathrm{CsPbBr_2I}$, this appears as a capacitance that climbs to 218% of its first-cycle value by cycle 1378 and then collapses to 39% by cycle 2500, with complete loss of the iodine signal from the cycled electrode. This work tests whether sodium incorporation suppresses that failure mode. Na-doped $\mathrm{CsPbBr_{3-x}I_x}$ ($x = 0, 1, 2$) nanocrystals were prepared by ligand-assisted reprecipitation at a Na/Pb precursor ratio of 1.25:1.00 and compared with undoped analogues in 0.1 M tetrabutylammonium tetrafluoroborate in anhydrous dichloromethane. Sodium contracts the pseudocubic lattice parameter of $\mathrm{CsPbBr_3}$ from $5.908 \pm 0.029$ to $5.851 \pm 0.019$ $\mathring{\mathrm{A}}$ after correction for specimen displacement. Specific capacitance at 0.3 A g$^{-1}$ rises for every composition, from 42 to 75, from 63 to 96, and from 56 to 84.5 F g$^{-1}$. Na-$\mathrm{CsPbBr_2I}$ gives the lowest charge-transfer resistance at 175 $\Omega$ and the highest ion diffusion coefficient at $1.6 \times 10^{-16}$ m$^2$ s$^{-1}$, and power-law exponents between 0.33 and 0.45 at all potentials examined show that charge storage is limited by ion transport through the pore network rather than by the interfacial process. In the sodium-containing (Na-$\mathrm{CsPbBr_2I}$) electrode, the capacitance rise reaches only 115% at cycle 600, no collapse follows, and 97% is retained at 2500 cycles, the excess above the first-cycle value being reduced by a factor of 7.9. Iodine is retained at unchanged binding energy, and the Br:I ratio measured by elemental mapping is 2.30 after cycling against 2.25 before.

Electrides are an unconventional class of materials in which electrons are localized in crystallographic void spaces rather than solely around atomic nuclei, giving rise to appealing properties such as low work functions, strong electron-donating character, and even superconductivity. Here, we use ab initio methods to investigate metal-organic framework (MOF) electrides, a new class of materials that combines the interstitial electrons of electrides with the permanent porosity and chemical tunability of MOFs. These materials host pore-confined electrons: occupied electronic states localized in the pore space and with bands slightly below or crossing through the Fermi level. Using density functional theory calculations, we establish several design rules for stabilizing pore-confined electrons in MOFs via an anion-electron exchange process and identify candidate MOF electrides. As a proof-of-concept, we also demonstrate that the pore-confined electrons can directly facilitate chemical reactions, substantially lowering the activation barrier for H2 dissociation without requiring adsorption at a surface site. We envision that pore-confined electrons in nanoporous materials may enable a fundamentally new type of catalysis in which chemical reactions take place in the pore space, driven by electron-centered active sites.

Magnetic ground states are commonly predicted using spin Hamiltonians whose interaction terms are selected a priori, potentially overlooking the microscopic interactions that govern complex magnetic order. Here, we introduce a general framework for the unbiased first-principles construction of symmetry-complete tensorial spin Hamiltonians and its automated implementation in AMATIS. The framework constructs the Hamiltonian directly from density-functional theory while rigorously enforcing quantum spin algebra and crystallographic symmetry. Applied to representative two-dimensional van der Waals magnets, the framework reproduces established magnetic interactions and uncovers hidden physics beyond conventional spin models, including chiral interactions that stabilize metastable skyrmions, higher-rank tensorial interactions that reconstruct the magnetic phase diagram and establish stabilizing competing multi-Q phases, and an emergent p-wave altermagnetic electronic structure. Our results demonstrate that unbiased tensorial Hamiltonian construction provides a predictive alternative to the conventional practice of manually selecting spin-model interactions, enabling first-principles discovery of unconventional magnetic phases.

Recent studies have shown that classical LiF simulations can reproduce low-temperature experimental spectra when performed at a simulation temperature $T^*$ higher than the physical temperature $T$. We show that the characteristic scale of this rescaling follows naturally from quantum vibrational statistics. An effective temperature $T_{\rm eff}(T)$ is obtained by matching classical and quantum harmonic energies and is evaluated using an analytic acoustic-optical model and a first-principles LiF vibrational density of states $D(\varepsilon)$. The resulting temperature reproduces the low-temperature scale of the reported spectral temperature and approaches the physical temperature in the classical regime. Our results identify zero-point motion and Planck-Bose-Einstein statistics as the origin of the reported temperature scale.

We develop a systematic algebraic approach, based on the Wei–Norman factorization method, to the normal ordering of exponential bosonic operators and apply it to derive analytical excitonic form factors in two-dimensional semiconducting materials. By introducing an auxiliary parameter, the normal-ordering problem is reduced to a system of ordinary differential equations determined by the commutation relations of the underlying closed Lie algebra. The approach is first illustrated for exponential operators associated with the Heisenberg–Weyl and $su(1,1)$ algebras, and is then extended to two-mode bosonic operators involving $su(2)$ and a six-generator closed algebra that contains two coupled $su(1,1)$ subalgebras. For the excitonic application, the Levi–Civita transformation maps the two-dimensional exciton problem onto an oscillator representation, providing a natural formulation in terms of bosonic creation and annihilation operators. Combined with the Laplace and Fourier representations of the Rytova–Keldysh potential, this formulation reduces the interaction matrix elements to the evaluation of exponential bosonic form factors. The isotropic problem is governed by a three-generator $su(1,1)$ algebra, whereas the anisotropic case requires the full six-generator algebra together with an additional $su(2)$ factorization. Explicit analytical expressions for both form factors, $\langle e^{-rt}\rangle$ and $\langle e^{i\mathbf q\cdot\mathbf r}\rangle$, are obtained, providing useful building blocks for matrix-element calculations in two-dimensional excitonic systems and potentially in other quantum problems involving exponential bosonic operators.

Vortex dynamics govern the dissipation and magneto-resistive properties of type-II superconductors. At large transport currents, the current-voltage ($I$-$V$) characteristics of a superconductor in the mixed state usually exhibit a nonlinear upturn followed by an abrupt jump occurring due to a flux-flow instability. However, other transition behaviors are also possible, including the formation of phase-slip lines and normal domains. Which mechanism dominates depends on the sample uniformity, its dimensions relative to the coherence length and penetration depth, and the rates of electron energy relaxation and heat removal. Here, based on the time-dependent Ginzburg-Landau equation, we present the results of numerical modeling of the $I$-$V$ curves of superconducting films with various types of disorder. For a grain-boundary defect mesh, we find multiple voltage transitions overlaid with a nonlinear upturn of the $I$-$V$ curves. For randomly arranged elongated defects, the $I$-$V$ curves exhibit voltage steps, whereas for L-shaped defects oriented perpendicular to the transport current, the $I$-$V$ curves show extended linear regimes separated by voltage transitions. We analyze the evolution of the order parameter along the $I$-$V$ curves and discuss the experimental accessibility of the revealed dynamics regimes.

Open quantum systems describe quantum systems that interact unavoidably with their environments. These notes introduce the physical origins of decoherence and dissipation in realistic settings, developing the theoretical framework of reduced dynamics and quantum master equations within the connection to thermodynamics in the quantum regime. Additionally, a set of relevant exercises are proposed to reinforce the acquisition of knowledge. The text equips readers with the tools to model and analyze open quantum dynamics.

We study rare nonresonant regions in a canonical one-dimensional disordered quantum spin chain by directly implementing the iterated Schrieffer-Wolff construction underlying the recent work of De Roeck, Giacomin, Huveneers and Prosniak on subdiffusive transport. For finite systems, we compute the probability that a disorder realization remains nonresonant through successive scales of the flow, while separately monitoring operator proliferation and the spatial localization of dressed local observables. The survival probability decays at most exponentially with system size over the numerically accessible regime. Resolving this decay scale by scale yields failure rates associated with successive Schrieffer-Wolff steps. The first rate is obtained analytically in excellent agreement with numerics, while higher-scale rates decrease rapidly throughout the regime studied. These results support the summability mechanism required for exponentially rare but parametrically long nonresonant regions, which provide the insulating bottlenecks responsible for subdiffusive transport. At the smallest couplings studied, the survival probability under our conditions exceeds the rigorous lower bound by six to seven orders of magnitude, demonstrating how conservative the constants required by the proof are while confirming that its underlying physical mechanism is quantitatively visible at accessible scales. More broadly, our results show how direct numerical implementations can provide an independent and physically transparent test of technically demanding constructive proofs, a methodology that may become increasingly useful as machine-assisted proofs become more common.

Conventional transport and optical responses, such as the Hall effect, can only distinguish material phases with substantially different symmetries. However, many quantum materials, such as candidate altermagnetic materials, host competing phases with similar structures, making it difficult to differentiate them using conventional transport or optical measurements. Here, guided by symmetry principles, we introduce a B-type quadratic planar Hall effect (B2-PHE) as a sensitive probe of magnetic structures. B2-PHE features a planar Hall current that scales quadratically with the applied magnetic field. This response originates from the interplay among external magnetic fields, intrinsic magnetic order, and quantum geometric properties of the electronic bands. We investigate B2-PHE in two altermagnetic candidates, KV2Se2O and RuO2, whose ground-state magnetic orders are under intense debate. Remarkably, B2-PHE emerges in their altermagnetic phases but is symmetry-forbidden in their antiferromagnetic (nonmagnetic) phases. We also show that B2-PHE should be detectable under a moderate magnetic field on the order of 1 Tesla. These findings establish B2-PHE as an experimentally convenient and potentially unambiguous probe of altermagnetic order, which is otherwise difficult to realize.

We investigate the thermodynamic geometry of an ideal quantum gas obeying inclusion statistics, characterized by a negative statistical parameter $g < 0$. In this framework the grand-canonical partition function admits a finite maximum fugacity, and the thermodynamic scalar curvature $R$ is strictly positive for all $g < 0$, reflecting effective attractive statistical interactions analogous to those of a bosonic system. As the fugacity approaches its maximum value, $R$ diverges, signaling a phase transition of the Bose-Einstein condensation type. A key distinction from the ordinary ideal Bose gas is that the condensation temperature is elevated relative to the bosonic case, and finite-temperature condensation occurs even in the dimensional regime $1/2 < D/\sigma \leq 1$ where standard bosons do not condense, while for $D/\sigma \leq 1/2$ the transition temperature vanishes. Three independent criteria; divergence of $R$, the maximum fugacity singularity, and the non-analytic cusp in the specific heat, coincide at the same condensation point, confirming the thermodynamic consistency of the transition.

We develop a surrogate-assisted workflow for millimeter-scale transport of a $^{87}$Rb Bose–Einstein condensate (BEC) on a multi-wire atom chip. Gradient-based inverse optimization generates 42 current schedules spanning seven regularization strengths and six transport durations. A low-cost Gaussian phase-space model ranks these schedules by endpoint overlap at three atom numbers. A Thomas–Fermi scaling (Ermakov) model estimates cloud dimensions for case-specific moving-grid construction. We then evaluate selected schedules in detail with the three-dimensional Gross–Pitaevskii equation (GPE). At $N=10^3$ and $T=0.5$ s, the surrogate predicts a larger axial center-of-mass (COM) excursion than at longer durations. The GPE confirms this prediction and reveals sloshing that persists through delivery, with an endpoint fidelity $F_{3D}=0.9244$. For all five longer transports, the surrogate predicts near-unit endpoint overlap for the top-ranked schedules, and GPE propagation using these schedules gives $F_{3D}>0.9997$. At $N=10^4$ and $T=2.0$ s, the surrogate-selected schedule similarly gives $F_{3D}=0.999932$. These results demonstrate that the surrogate estimates provide a useful low-cost basis for candidate screening, while GPE propagation resolves the transport dynamics and the delivered condensate state.

The hybridization of magnons and excitons would combine magnetic and optical degrees of freedom in a single composite quasiparticle. Such a hybridization is however difficult to achieve, because of their inherent energy mismatch. We propose that in biased bipolar ferromagnetic electron–hole bilayers the excitons and magnons can be brought into resonance, with the exciton energy lowered through the voltage bias to match the magnon energies. We demonstrate the linear hybridization of magnons and spin-flip excitons in this regime, starting from the microscopic exchange interactions between electrons and localized magnetic moments. We show that further increasing the gate voltage softens the hybrid magnon–exciton mode and realizes a magnon–exciton condensate, which manifests in both the magnon and exciton sectors and is associated with spin-superfluid transport. Ferromagnetic electron–hole bilayers therefore provide a new platform for the study of composite magnon–exciton quasiparticles and the realization of spinful condensates and associated spin superfluidity.

Interferometry is a powerful method for studying many fundamental phenomena ranging from gravitational waves to anyon excitations. Besides loss of coherence in the interferometer paths, quantum mechanics sets an incompressible bound for linear interferometry arising from the quantum noise of the light beam, called the shot noise limit. Here, we implement a non-linear quantum interferometer that uses a microwave cavity and a magnetic field resilient anharmonic superconducting quantum circuit made of granular aluminum. The circuit enables interferometry beyond the shot noise limit. A direct application of our findings is the detection of dark matter (axions or dark photons), high-frequency gravitational waves or astronomical masers.

We investigate the capability of variational quantum circuits in detecting a topological phase transition within the toric code model subjected to a uniform magnetic field. The detection is carried out via shot-based computations of both the ground state energy and the global entanglement. We begin by employing well-established renormalization techniques to construct a quantum circuit that accurately represents the pure toric code under periodic boundary condition. This circuit is subsequently parameterized to enable a shot-based variational simulation of the ground state in the presence of the magnetic field. Our results demonstrate that even for the minimal lattice sizes and a finite number of measurement shots, the ground state energy exhibits a distinct singularity at the transition point which can be reliably approximated through finite-size scaling analysis. Furthermore, we introduce a secondary variational circuit designed to compute the global entanglement of the generated ground state. We observe that both global entanglement and its conditional counterpart display the expected qualitative behavior at the transition point, consistent with the topological nature of the phase transition. To evaluate the practical viability of our variational approach on real quantum hardware, we systematically examine the detrimental effects of gate noise on the analysis. We find that the topological phase exhibits a notable robustness against noise, manifesting as a linear decrease in the transition point with increasing noise strength.

Studying the multistability of origami structures presents challenges due to the nonlinearity of their kinematics and the high-dimensional configuration spaces that are difficult to visualize and explore exhaustively. To address this, we utilize the Lagrangian framework for origami to exploit symmetries and obtain reduced-dimensional slices of the configuration space. Our analysis of degree-6 vertices with reflection symmetry reveals topological transitions in their kinematic space as sector angles are varied, with implications for the number of symmetry-constrained minima and the emergence of metastable regions. These lower-dimensional slices are amenable to exhaustive search and visualization. A subsequent full-space stability analysis shows that 18 of 41 degree-6 and 14 of 45 degree-8 symmetry-constrained minima remain minima when all locally compatible perturbations, including those that break symmetry, are admitted. The metastable regions, which would likely be overlooked by numerical optimization alone, are influenced by the interplay between the boundaries of admissible kinematic space and crease mechanical properties. We extend our analysis to cone-like vertices with higher symmetry and one-degree-of-freedom kinematics, exploring symmetry-breaking phenomena, combinatorial structure, and their consequences for branchwise stability. The stability landscapes uncovered have potential applications in mechanical metamaterials, mechanical computing, origami-based robotics, and structures designed to self-deploy and retain their shape.

The design of quantum materials to manipulate dimensionality and electronic correlations is a central focus in the exploration of emergent phenomena. We propose a new correlated quantum material platform for realizing a layer- and orbital-selective Mott transition (LOSMT) in a nickelate heterostructure by combining bilayer and monolayer LaNiO$_3$ separated by a monolayer LaAlO$_3$ spacer under compressive strain from the LaAlO$_3$ substrate. The LOSMT emerges from the layer-dependent dimensional confinement of the apical Ni($d$)-$z^2$ orbital and strain-induced lifting of the orbital degeneracy. The monolayer LaNiO$_3$ exhibits an orbital-selective Mott insulating phase with a Mott gap in the Ni($d$)-$z^2$ orbital, whereas the bilayer LaNiO$_3$ exhibits a multi-orbital metallic phase, triggering the orbital-selective Mott transition upon cooling $via$ inter-layer hybridization of the Ni($d$)-$z^2$ orbitals. Calculations within the density functional theory plus dynamical mean-field theory (DFT+DMFT) framework reveal that the LOSMT drives a dimensional crossover by enabling out-of-plane electronic transport through the metallization of the localized apical Ni($d$)-$z^2$ orbital, while the planar Ni($d$)-$x^2-y^2$ orbital remains itinerant across the transition. The emergence of the LOSMT provides a new pathway for engineering correlated quantum materials toward unconventional superconductivity and Mott-transistor functionalities.

We consider two canonical market-microstructure regularities: the long-memory of trade signs and the square-root law of meta-order impact. The point is not to propose new empirical laws, but to separate the clocks on which existing laws are defined. The sign-memory law is an event-time statement about the ordering and fragmentation of hidden orders. The square-root impact law is an operational-time statement about front motion in a locally linear latent order book. Starting from a discrete-time random-walk bid/ask reaction–diffusion order book with a separate event clock, we identify an event-time imbalance reduction, derive the operational-time front and impact equations in the locally linear regime, and then subordinate both sign and impact observables to calendar time. Fractional or tempered clock effects enter through this event-to-calendar projection, not through a different operational-time impact mechanism. This gives a compact clock-aware framework in which event-time sign persistence, operational-time square-root impact, and anomalous calendar-time effects appear as distinct but compatible consequences of a common order-book representation.

Silicon, which is highly reflective and has negligible absorption at the microwave 2.45 GHz range, can be heated when it is turned into black-Si with a surface texture of nano-needles made by SF6/O2 plasma etching. Microwave heating of flat Si and of black-Si with vertical and with tilted (oriented) nano-needles was compared under identical conditions in a cylindrical TM010 resonator. Samples were placed horizontally on a 150-micrometer-thick cover glass, which standardized their height and position inside the cavity and allowed a common calibration of the radiation thermometer against a K-type thermocouple. Under a stepwise protocol of only 2-3-4 W of microwave power (60 s per step), black-Si with vertical needles reached ~ 260 C, systematically exceeding flat Si (~ 190 C), while black-Si with oriented needles showed a delayed but abrupt onset of heating at 3 W. In situ monitoring of the cavity resonance revealed a 2-3 MHz downshift of the resonance frequency f for all samples, with the drift consistently appearing once the sample temperature exceeded ~ 120 - 150 C, consistent with thermally activated carrier generation in Si. At a given temperature, each sample loads the cavity at a different f and quality factor Q, indicating an orientation-dependent effective permittivity of the nano-needle array, in line with the strong form birefringence of tilted black-Si. Application potential and challenges in the quantitative temperature and permittivity determination are discussed.

Substrate surface preparation is a key step in the fabrication of electronic devices. In III–V semiconductor platforms, e.g. used in HEMTs and lasers, removal of the native substrate oxide is extremely important, where improper removal will negatively affect end-of-line device performance. However, the impact of substrate preparation in hybrid superconductor–semiconductor (S–Sm) systems relevant to quantum information applications remains poorly understood. This study compares three surface preparations for the deposition of sputtered Nb films on InP: (i) no intentional oxide removal (control), (ii) in-situ $\mathrm{Ar}^{+}$ milling, and (iii) S-passivation. In-situ $\mathrm{Ar}^{+}$ milling reduces the O concentration at the metal–substrate (MS) interface, but also roughens the InP surface, increasing the effective thickness of the Nb–InP interface and promoting O incorporation through extended defects in the Nb film. S-passivation suppresses interfacial O more effectively while preserving a sharper and smoother buried interface. It also yields Nb films with higher superconducting transition temperatures and less structural damage than the $\mathrm{Ar}^{+}$-milled samples. Despite these materials improvements, the microwave response is comparable across the three preparations. At single photon powers, the highest internal quality factors, $Q_i$, are approximately $1.30\times10^{5}$ ($130\mathrm{k}$) for the control resonators, $9.7\times10^{4}$ ($97\mathrm{k}$) for the S-passivated resonators, and $8.4\times10^{4}$ ($84\mathrm{k}$) for the $\mathrm{Ar}^{+}$-milled resonators. These results suggest that the present devices are not primarily limited by dielectric loss at the buried Nb–InP interface.

Thixotropic and viscoelastic materials both retain their deformation history and are difficult to distinguish. However, a stationary linear response obeys the Kramers-Kronig relations. A structure that evolves during a sweep renders the spectrum inconsistent with them, so the residual from one chirp and no model measures nonstationarity. It survives the small-amplitude limit, returns to its baseline at any stationary state, and, for bounded restructuring, peaks near the structural time. We verify this on eight models and demonstrate it on published spectra of a thixotropic silica suspension.

The kagome material has rapidly established itself as a research frontier in condensed matter physics, owing to its distinctive geometric structure and the rich array of unconventional physical phenomena. In the kagome AV3Sb5 (A = K, Rb, Cs) family, the charge-ordered state exhibits a remarkable characteristic, i.e., anomalous symmetry-breaking, which is tied to the topological nature of the electronic band structure. Here, we report the third-order nonlinear longitudinal and Hall responses that persist stably up to room temperature in the kagome material CsV3Sb5. Notably, the nonlinear responses demonstrate significant enhancement below the charge density wave (~ 77 K) order and anomalous symmetry-breaking (~ 39 K) state. The scaling analysis indicates that the third-order nonlinear transport is governed jointly by quantum geometric contribution and extrinsic scattering. This study realizes a giant third-order nonlinear response and provides a distinct method to detect anomalous symmetry-breaking in CsV3Sb5.

Ferrons are collective excitations of polarization fluctuations that can enable terahertz communications and quantum transduction due to long propagation lengths. Although ferrons have been experimentally demonstrated in van der Waals ferroelectrics and relaxor ferroelectrics, there is no direct (sub)nanoscale experimental evidence of ferrons in three-dimensional ferroelectrics. Here, we detect two types of ferrons, Higgs and pseudo-Goldstone, at the (sub)nanoscale in lead titanate by measuring vibrational signals due to polarization fluctuations. By harnessing momentum transfer in electron energy loss spectroscopy (EELS), we directly distinguish between soft-phonons and ferrons. We observe that the Higgs mode originates from the soft optical phonon parallel to the polar axis, whereas the pseudo-Goldstone mode originates from the soft optical phonon perpendicular to the polarization axis. Together with Landau theory, Raman spectroscopy measurements, and EELS, we observe that Higgs group velocities, in the bulk limit, are eight times greater than those of out-of-plane soft phonons and the pseudo-Goldstone ferrons have group velocities six times greater than in-plane soft phonons due to long-range dipole interactions. We further show that the domain size confinement effects lead to doubling of the respective bulk ferron group velocities, reaching up to approximately 15 km per second (almost 15 times higher than the out-of-plane soft phonon modes). Overall, this study opens a pathway to the detection of ferrons in three-dimensional ferroelectrics with domain engineering as a promising avenue for terahertz communication and transduction.