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Manipulating acoustic waves in wavevector domain by using nonlocal metasurfaces: Analog differentiation and extreme acoustic detection
Conventional acoustic metasurfaces have shown exceptional capability through spatial wavefront engineering, but the degrees of freedom in the wavevector domain remain to be unlocked. Here, we shift the manipulation paradigm from the spatial domain to the wavevector domain via nonlocal metasurfaces (NMSs). The proposed NMS consists of two sublayers of surface groove structures cascaded via a nonlocal channel, which enhances internal transverse energy flow. An inverse design framework integrating the genetic algorithm with numerical simulation is established for the NMS design. We find that the internal nonlocal energy flow dictates the wavevector-dependent transmissivity of NMSs. The nonlocal effect on the amplitude transmissivity results from the interaction between two sublayers, while the transmitted phase is dominated by the backward sublayer. Differentiations of 1st order on a Gaussian beam and a cylindrical wave are demonstrated and show agreement between theoretical and numerical results. Furthermore, we showcase the practical applications of NMSs in detecting deep subwavelength scatterers with diameters of 0.15 wavelengths, and isolating a weak source buried in a strong noise with a tenfold amplitude. Robustness analyses show that the transfer functions and detection and isolation effects of the proposed NMSs keep acceptably stable when thermoviscous loss, fabrication error, imperfect periodicity, structural defect, and background reverberation are considered. Our work elaborates the physical image of acoustic wavefront reshaping in the wavevector domain, paving the way for advanced applications in signal processing, imaging, and sensing and communication.
The effect of aging and charge variability on the detonation performance of a conventional plastic-bonded high explosive
Plastic-bonded explosives (PBXs) are pressed composites of energetic crystals (>90 wt. %), polymeric binder, and an internal porosity structure (1–2 vol. %). The binder ensures material stability, while porosity promotes more reliable reaction initiation. These microstructural features critically influence the bulk mechanical and detonation performance properties of the high explosive (HE), yet the connection between microstructure and bulk behavior remains incompletely understood, complicating both manufacture and characterization. Aging of HE constituents under varying environmental conditions introduces additional uncertainty. For PBXs composed of cyclotetramethylene–tetranitramine (HMX), it is commonly assumed that detonation performance, specifically detonation velocity and energy release, are insensitive to microstructural details and do not vary significantly over time. This assumption simplifies constitutive modeling choices at the engineering scale. Here, we analyze four high-precision cylinder expansion tests of an HMX-based PBX varying in molding powder lot, pressing method, final pressed density, and pressing age. These data support hydrocode-based model calibrations of the explosive product equation of state, and these are used to quantify the effect of the described material variability on energy release characteristics. The results indicate that the detonation velocity increases with density and may also increase with age, though further experiments would be required for confirmation. No significant variation in energy delivery was observed across the tests.
Analytical calculation of field enhancement factor of 2D structure graphene film
Field emitters are one of the promising electron sources for vacuum electronic devices operating in mm-wave and terahertz frequencies, where emission performance is critically governed by the field enhancement factor. While extensive analytical models exist for one-dimensional emitters like carbon nanotubes and Spindt tip, the corresponding framework for a thin-film (like two-dimensional) emitter remains lacking. In this work, an analytical field enhancement factor is derived using the floating-sphere and image-charge approach, based on a vertically oriented graphene sheet inside a closely spaced diode configuration. The model explicitly incorporates emitter dimensions such as height, width, thickness, and anode–emitter spacing. The proposed expression is validated by comparison with previously reported experimental data on reduced graphene oxide film based emitters. Good agreement between the emission current predicted via the proposed approach, and experimentally obtained data are observed for ultra-thin films, whereas a deviation in predicted and experimentally obtained data for films with higher thickness is observed. This deviation rises with increasing thickness, highlighting the limitations of the two-dimensional approximation. The proposed approach provides a useful analytical tool to estimate the field enhancement of graphene sheet field emitters for miniaturized THz vacuum electron device applications.
Weakly nonlocal thermoelasticity of type II: Rayleigh waves in coated half-spaces
It is well known that Eringen’s nonlocal thermoelasticity theory using the nonlocal Fourier law of heat conduction and its modifications has been widely applied to harmonic plane wave problems. However, it has recently been proven that a significant class of these problems such as Rayleigh wave propagation in layered nonlocal thermoelastic half-spaces is ill-posed under this theory in the sense of yielding no solutions because the number of required boundary conditions exceeds the number of constants to be determined. Therefore, it is necessary to develop nonlocal thermoelasticity theories under which the number of required boundary conditions and the number of constants to be determined are the same for all harmonic plane wave problems. In this paper, we introduce such a theory, called the weakly nonlocal thermoelasticity theory of Green–Naghdi type II (without energy dissipation). Employing this theory, we investigate Rayleigh wave propagation in a nonlocal type II thermoelastic half-space coated with a nonlocal type II thermoelastic layer. Departing from previous methodologies, we establish the explicit transfer matrix for a layer and the explicit surface impedance matrix of a half-space in the framework of this new theory. These results allow us to obtain directly the explicit secular equation of Rayleigh waves, which is a 3 × 3 determinant equation, along with the explicit H/V ratio formula. Based on these analytical results, we numerically examine the effects of nonlocality and material parameters on Rayleigh wave characteristics, focusing on both phase velocity and displacement polarization.
Higher-winding phases in one-dimensional non-Hermitian topological superconductors
Non-Hermitian topological superconductors provide a setting in which point-gap topology, non-Hermitian skin effects, and Majorana zero modes are strongly intertwined. In this work, we adopt a coefficient-based approach for computing winding numbers and deriving analytical expressions for phase boundaries in one-dimensional non-Hermitian topological superconductors characterized by point-gap topology with Z invariants. We apply this approach to two non-Hermitian topological superconducting lattice models, with and without sublattice degrees of freedom, including longer-range hoppings, thereby accessing a much broader parameter space. These extensions generate higher-order polynomials and support phases with higher winding numbers, reflecting the underlying Z topology. We further clarify how a weak perturbation suppresses the non-Hermitian skin effect while preserving the sublattice-symmetry-protected invariant associated with Majorana zero modes. The predicted winding numbers are verified by open-boundary spectra, where one or multiple pairs of zero-energy boundary modes appear consistently with the bulk invariant. We also examine the stability of these modes against onsite disorder by examining the zero-mode energy, the bulk gap, and the inverse participation ratio. Our results provide a systematic and efficient route to constructing topological phase diagrams for higher-winding non-Hermitian topological superconductors.
Dilute Pb in Ge materials fabricated by ion implantation and pulsed laser melting
Germanium lead (GePb) alloys have shown promising potential as a material platform for fabricating mid-infrared photodetectors, where the Pb content enables tuning of the bandgap. However, fabricating such devices using GePb is challenging because the equilibrium solid solubility of Pb in Ge is in the parts per million range. Here, we synthesize the metastable GePb alloy by Pb implantation into Ge, followed by pulsed laser melting. By varying the ion implantation and melting conditions, we identify a processing window that yields GePb alloy films of high crystalline quality, with a substitutional Pb amount of at least 1.6 × 1015 Pb atoms/cm2, which is equivalent to a Pb concentration of around 0.36 at. %, more than 3 orders of magnitude above the equilibrium solubility. These results establish a pathway to fabricating GePb for mid-infrared photodetection applications using non-equilibrium ion implantation, ultra-rapid melting, and solidification.
A sector-shaped acoustic metamaterial for broadband and wide-angle sound absorption
Maintaining stable absorption performance at large oblique incidence while achieving broadband sound absorption remains a major challenge for conventional sound-absorbing materials. To address this issue, a sector-shaped acoustic metamaterial composed of two-dimensional gradient waveguides and a porous backing cavity is proposed to achieve broadband and wide-angle sound absorption. By arranging the entrances of the two-dimensional gradient waveguides in a fan-shaped configuration spanning different azimuthal directions, incident sound waves from various directions can be efficiently guided into the structure, which reduces the dependence of absorption performance on the angle of incidence. Meanwhile, the multiple narrowband resonant responses induced by the gradient waveguides are coupled and smoothed through the damping effect of a porous backing cavity, enabling continuous broadband absorption. Numerical simulations demonstrate that the proposed structure maintains stable and high absorption over a broad frequency range of 500–3400 Hz for incidence angles from 0° to 75°, and remains effective even under near-grazing incidence at 80°. Comparative results further demonstrate that, under large oblique incidence, the proposed metamaterial maintains higher absorption levels across a wide frequency range than conventional porous absorbers and sonic black hole structures. These findings provide an effective design strategy for compact broadband sound absorbers with enhanced angular robustness.
Electric-field dependence of cycle endurance in HfO2-based ferroelectric capacitors
The cycle endurance characteristics of HfO2-based ferroelectric (FE-HfO2) capacitors were systematically investigated in terms of area, temperature, film thickness, and ferroelectric polarization. Cycle endurance exhibited distinct electric-field dependent behavior, which is classified into low, middle, and high field regimes. For area, the electric-field dependence does not change with area. The endurance cycle followed the Weibull distribution, and the Weibull slope is small at low field. For temperature, the electric-field dependence does not change with temperature. Thermal activation energy is almost constant with electric field. The trap generation rate is large at low field. For thickness, endurance and remanent polarization (Pr) had high correlation in electric-field dependence. Thicker ferroelectric capacitors show lower inflection points in electric-field dependence between low-field and middle-field. For polarization, cycle endurance has a universal relationship with Pr, comprehending electric field and temperature. Taking the analysis above into account, the cycle endurance of FE-HfO2 capacitors can be described by Pr and relevant oxygen vacancies. At low field, cycle endurance is determined by the initial oxygen-vacancy rich region non-uniformly generated in the fabrication process. At middle field, dipole pinning is released, and oxygen vacancies are migrated and redistributed by polarization switching. The breakdown path is formed through the redistributed oxygen vacancies. At high field, the initial oxygen vacancy rich region causes high leakage current and accelerates the breakdown. It is a practical method to evaluate cycle endurance vs Pr for reliability assessment of FE-HfO2 capacitors.
Angle-dependent magnetotransport and quantum interference effect in type-II topological Dirac semimetal PtSe2
We report the angle-dependent magnetoresistances (MRs) of platinum diselenide (PtSe2) in the Dirac semimetal phase. The negative longitudinal MR observed in parallel fields persists up to ∼50 K, which is quantitatively consistent with the chiral anomaly of Dirac fermions. When the field is perpendicular to the current, a low-field transition from positive to negative transverse MR is observed between 2 and ∼20 K, which is closely related to the quantum interference between time-reversed scattering paths, as well as the spin–orbit coupling strength. Our results reveal that the small-energy-transfer electron–electron scattering dominates the dephasing process in our PtSe2 films, providing experimental evidence for quantum interference transport in type-II Dirac fermion systems.
From drop impact to cellular response: Transient interfacial force fields, contact-line physics, and mechanotransduction in complex biofluids
Drop impact is a classical problem in fluid mechanics, yet its implications for biological systems remain largely unexplored. Upon impact, droplets generate transient interfacial force fields composed of localized pressure, shear, and extensional stresses that evolve over microsecond-to-millisecond timescales. In complex biofluids and at soft interfaces, these stresses are not simply dissipated, but are redistributed and transformed through structure–flow coupling, dynamic wetting, contact-line motion, and interfacial compliance. This Perspective develops a multiscale physical framework linking drop-impact hydrodynamics to microstructural dynamics in complex fluids and to the transmission of mechanical signals across soft biological interfaces. Particular emphasis is placed on the physics of stress localization near the advancing contact line, the role of classical and soft-matter dimensionless groups in governing impact response, and the conditions under which transformed stresses may perturb cellular mechanosensitive pathways. To quantify this coupling, an impact–mechanotransduction number is introduced as a dimensionless measure relating transmitted impact stress to characteristic cellular prestress. Within this framework, drop impact is recast not only as a transport and deformation process, but also as a source of impulsive mechanical forcing in soft matter and biointerface systems. These ideas define a new direction, impact-driven mechanobiology, and establish a physically grounded basis for future theoretical, experimental, and translational studies of fluid–biological interactions.
Pressure-dependent electron heating and discharge localization in an electronegative CF4 ICP reactor with RF substrate bias
A two-dimensional axisymmetric direct-implicit particle-in-cell/Monte Carlo collision model is used to study pressure-dependent electron heating and discharge localization in an electronegative CF4 plasma sustained by an inductive source with RF substrate bias. Under fixed absorbed inductive and bias powers, increasing the pressure from 20 to 200 mTorr transforms the discharge from a relatively diffuse state into a strongly localized and highly electronegative regime. The plasma contracts toward the dielectric window, while the downstream bulk becomes strongly electron depleted. This behavior is traced to a pressure-induced redistribution of electron energy: energetic electrons are able to penetrate into the bulk at low pressure, but become increasingly confined near the inductive heating zone at high pressure and cool rapidly during transport. Consequently, ionization becomes sharply localized near the dielectric window, whereas dissociative attachment is enhanced over a broader surrounding region. The results reveal a spatial decoupling between ionization-capable and attachment-favorable electron populations and clarify the kinetic origin of pressure-dependent discharge localization in electronegative CF4 inductively driven plasmas.
Temperature-bias noise and quantum shot noise as probes of pairing symmetry in iron pnictides
Quantum noise has long served as a powerful probe of quantum transport in mesoscopic junctions. Recently, temperature-driven noise, or ΔT noise, has attracted growing interest due to its presence even in the absence of average charge current. In this work, we investigate a normal metal–insulator–iron-pnictide junction and demonstrate how zero-temperature quantum shot noise, finite-temperature quantum noise, and ΔT noise can discriminate between s++ and s+− pairing symmetries, which are relevant to iron-based superconductors. We introduce ΔT noise as a novel probe for distinguishing between the two pairing symmetries. In contrast to conductance, which exhibits a single peak for both s++ and s+− states with only a difference in magnitude, the ΔT noise reveals qualitatively distinct features: a twin-peak structure for the s++ pairing symmetry and a single-peak profile for the s+− state. A similar symmetry-dependent contrast is observed in both zero-temperature quantum shot noise and finite-temperature quantum noise, where the s++ state consistently exhibits a twin-peak structure, while the s+− state shows a single-peak response. Our results demonstrate that noise-based measurements form a mutually reinforcing set of probes that enables reliable identification of superconducting gap symmetry in iron-pnictide superconductors.
Spatially asymmetric switching under spin–orbit torque and Dzyaloshinskii–Moriya interaction
Efficient spin–orbit torque (SOT) switching of perpendicular magnetization is of crucial importance for the magnetic random-access memory. In this work, we study the ultrafast switching of a perpendicular ferrimagnetic alloy by the SOT and an external field (Hx) along the current direction. We find that the magnetization reversal occurs first at the corner of the sample and then propagates to the whole sample through domain-wall motion. We show that, in the absence of field-like SOT, the location of this anti-domain nucleation corner exhibits left-right and top-down asymmetries, as determined by the polarities of current and Hx. By varying the magnitude and sign of field-like SOT, we establish that it significantly affects the switching process but is not necessary for such switching asymmetries. These results are fully explained using a consistent torque analysis framework. Our work improves the understanding of the physics behind SOT switching.
High-sensitivity optical fiber magnetic field and current sensor based upon two cascaded Mach-Zehnder interferometers
In this article, we have designed a highly sensitive S1 that can measure magnetic field (MF) and current. S1 consists of two Mach-Zehnder interferometers (MZIs) cascaded together, namely, MZI1 and MZI2. MZI1 and MZI2 have simple structures and are fabricated by directly tapering single-mode fiber. MZI1 and MZI2 with tapered structures are sensitive to axial strain and temperature. MZI1 is pasted into Terfenol-D microgroove with magnetostrictive properties, and the MF acting on Terfenol-D corresponds to acting the strain to MZI1, so MZI1 has high sensitivity to MF. MZI2 is pasted onto a copper rod, which generates abundant heat, which is absorbed by MZI2 and causes the resonance wavelength drift, making MZI2 very sensitive to current. The experiment reveals that the MF sensitivity of MZI1 is −97.47 pm/mT, and the sensitivity of the current square of MZI2 is −45.44 pm/A2. S1 is a Vernier effect sensor composed of MZI1 and MZI2 cascaded together, which can improve the sensitivities of MZI1 and MZI2. The experiment reveals that S1 has the MF sensitivity of −1011.98 pm/mT and the sensitivity of the current square of 439.36 pm/A2, which increases the sensitivities of MZI1 and MZI2 by 10.4 and 9.7 times, respectively. The manufacturing of sensor S1 only requires fiber tapering, fiber cleaving, and material bonding. Therefore, this sensor boasts advantages such as simple structure, easy manufacturing, low cost, durability, and high sensitivity, providing a novel scheme for simultaneously measuring MF and current.
Zr concentration-dependent sub-lattice phase-field model of Hf1− <i>x</i> Zr <i>x</i> O2: Analysis of phase composition and polarization switching
We develop a sub-lattice phase-field model of Hf1−xZrxO2 incorporating zirconium (Zr) concentration (x)-dependence. Our framework expands the time-dependent Ginzburg–Landau equation to the sub-lattice level and incorporates x-dependent interaction parameters and gradient coefficients. Our experimentally calibrated model captures the evolution of charge–voltage (Q–V) characteristics for x ranging from 0.5 to 1.0. The sub-lattice formulation explains the thermodynamic preference and kinetic transition barriers of competing orthorhombic phase (o-phase) and tetragonal phase (t-phase), while the phase-field framework enables spatially resolved analysis of polarization (P) and electric-field (E-field) profiles, allowing multi-domain (MD) P and mixed-phase states to emerge naturally. Our model reproduces the experimentally observed ferroelectric (FE)-to-anti-ferroelectric (AFE) transition as x increases from 0.5 to 1.0. At low Zr concentration (x = 0.5–0.6), the o-phase dominates, yielding distinct FE behavior. At high concentration (x ≥ 0.9), the t-phase is stabilized, leading to AFE transitions. A key finding of our work is the unique behavior at intermediate Zr concentrations (x = 0.7–0.8). Here, the o- and t-phase energies are comparable, making the system strongly influenced by local variations in the electric field (E-field), which arise from stray fields near the domain walls. This non-uniform field distribution results in a mixed-phase composition and spatially staggered P reversal, which manifests as a more gradual Q–V evolution (compared to other values of x). By linking energy landscapes to spatial field effects, the model provides insights into the FE-to-AFE crossover in Hf1−xZrxO2.
Hysteretic excitation in non-collinear antiferromagnetic spin-torque oscillators: A terminal velocity motion perspective
We present a novel theoretical framework for non-collinear anti-ferromagnetic spin torque oscillators by unifying spin dynamics under the Poisson bracket formalism. By shifting from traditional torque-based descriptions to a continuous operational symmetry perspective, we develop two complementary viewpoints: a vector perspective that identifies infinite degenerate Rigid Body Precessional (RBP) states—arising from the fact that exchange energy is solely a function of the Rigid Body Rotational Transformation (RBRT) generator (i.e., total magnetic momentum)—and a particle perspective that decomposes the dynamics into Center-of-Mass (CM) translation and Relative Motion (RM) oscillation. Utilizing time-dependent RBRT and rigid body uniform translational transformation techniques, we analytically resolve the rapid (∼10 ps) transient evolution into a stable RBP state driven by spin–orbit torques (SOTs) and damping. We further demonstrate that the out-of-plane anisotropy component of the uniaxial crystalline anisotropy lifts the exchange degeneracy, triggering a long-term (∼1 ns) oscillatory decay toward a finalized steady state s, characterized by uniform spin z-components and a 120° inter-spin locking angle. The dynamics of this state are accurately governed by our proposed terminal velocity motion model for CM variables [H.-H. Chen et al., arXiv:2305.11020 (2023)], in which exchange coupling is effectively transformed into kinetic energy with a light effective mass, leading to a transient excitation time of approximately 10 ps—nearly two orders of magnitude shorter than that of typical ferromagnetic systems (∼1–2 ns). This model precisely predicts SOT-driven transients, hysteretic excitation process, and the dynamic phase diagram across the full current range. Finally, we account for the theoretical mismatch in the sub-critical current regime by identifying a “rigid-body breaking” effect: a surge in effective friction caused by the self-resonance of RM variables induced by the translation of the CM variable, as mediated by the in-plane anisotropy component of the uniaxial crystalline anisotropy.
Layer-resolved pump absorptance in spintronic/orbitronic terahertz emission modeling: A transfer matrix Poynting flux analysis method with sample-specific parameter fittings
Quantitative interpretation of thickness-dependent spintronic/orbitronic terahertz (THz) emitter (STE/OTE) experiments requires reliable knowledge of how pump energy is distributed among individual layers. However, this distribution is often approximated using tabulated optical constants or simple thickness-weighted estimation, which may not represent actual thin-film spectral parameters. Here, we develop a sample-specific optical-analysis workflow based on transfer-matrix modeling combined with Poynting-flux evaluation. The workflow supports forward calculation and thickness-dependent modeling with retrieval of effective optical constants. Using representative Sub/Pt/NiFe, Sub/W/NiFe, and Sub/Ta/NiFe series, we show that thickness-dependent reflectance, transmittance, and absorptance data can be self-consistently reproduced using a single set of effective optical constants for the varying layer, from which layer-resolved pump absorptance is obtained. Comparison with thickness-weighted partitioning further shows that, although simple rules may capture qualitative trends, rigorous sample-specific investigation provides a more reliable description of pump-energy deposition for quantitative STE/OTE analysis.
Using the recurrent neural networks to predict the results of classical molecular dynamics modeling of crystalline solids
In this article, on an example of modeling the equilibrium state of crystalline copper, the possibility of predicting the atomic configuration at the next time step using data on atomic configurations at several previous time steps by a bidirectional recurrent neural network trained on classical molecular dynamics data is shown. A network with a minimum number of hidden layers (the number of layers is three) is used, which corresponds to the required number of nodes for calculating velocity and acceleration when integrating particle motion equations using the finite difference method. The figure of merit of the simulation is based on a comparison of the dynamic structural factor of the system, calculated from the initial molecular dynamic trajectories, and the one calculated from the molecular trajectories predicted by the recurrent neural network. The graphs of the radial distribution function, as well as the histograms of the distribution of the first-order differences of coordinates, constructed from the initial data on the arrangement of atoms and from the data predicted by the neural network, show a good match. Both the graphs of the radial distribution function and the histograms of the distribution of the first-order coordinate differences do not undergo significant changes during the simulation of the equilibrium state (180 ps), which indicates an adequate representation of statistical patterns in molecular trajectories predicted by a recurrent neural network.
Electrostatic rectification of Li+ transport in amorphous TiO <i>x</i> thin films grown by mist CVD
Amorphous metal oxide interlayers are widely used to stabilize Li+ transport at battery interfaces, yet the underlying transport mechanisms remain unclear. Here, Li+ transport in amorphous TiOx (a-TiOx) thin films prepared by mist chemical vapor deposition was investigated by comparing electrochemical lithiation with concentration-driven Li+ insertion induced by LiPF6 exposure. Electrochemical lithiation enables redox-assisted, dynamically activated Li+ diffusion accompanied by partial Ti4+ reduction, whereas LiPF6 exposure results in diffusion-limited Li+ transport without significant electronic reduction. Depth-resolved glow discharge optical emission spectroscopy and spectroscopic ellipsometry clearly distinguish these two regimes. In addition, dielectric contrast between the electrolyte, a-TiOx, and graphite is proposed to generate internal electric fields that directionally bias Li+ transport. A Drude-like sub-gap optical response originates from field-induced polarization and localized electronic states rather than metallic conduction. These results highlight the importance of dielectric-field effects in amorphous oxide interlayers for improving interfacial stability and rate performance in lithium-based batteries.
A tetragonal Cu20Bi9 intermetallic compound phase discovered in Cu75Sn13Bi12 alloy
This study reports the discovery and characterization of a previously unknown intermetallic compound phase, Cu20Bi9, within Cu75Sn13Bi12 alloy solidified both onboard China’s Space Station and under ground-based conditions. Combined with selected-area electron diffraction (SAED), atomic-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and energy-dispersive x-ray spectroscopy elemental mapping, its crystal structure was identified to be tetragonal (P4¯, No. 81) with lattice parameters a = b = 17.648 Å and c = 10.534 Å. A crystallographic model consisting of 80 Cu and 36 Bi atoms in a single unit cell was proposed, and its dynamic stability was validated by density functional theory-based molecular dynamics simulations. SAED patterns and HAADF images simulated based on this model perfectly reproduce the experimentally observed diffraction and imaging characteristics. Theoretical calculations of the formation and cohesive energies suggest that Cu20Bi9 is thermodynamically metastable, which is further supported by isothermal annealing experiments.