This paper proposes a design methodology for complex-amplitude reconfigurable metasurfaces (CRMSs). Low-coupling response criteria are established through detailed analysis of resonant structures, p-i-n diode placements, and gap parameter configurations. Amplitude modulation p-i-n diodes are positioned in regions with strong induced currents, achieving a 0.22–0.95 change range through ohmic effects. Meanwhile, phase modulation counterparts are located in low-current regions to minimize amplitude loss during 1-bit phase switching. Across 9.0–11.8 GHz, the amplitude-phase coupling coefficient is suppressed below 0.19. Integrated with the amplitude-phase Gerchberg-Saxton algorithm, an enhanced focusing effect with a 10 dB energy attenuation region of less than 0.60λ is achieved by CRMSs. Experimental validation confirms <5% measured simulated discrepancies, demonstrating robust design efficacy.

In microfluidics and other low-Reynolds-number systems, hydraulic conductivity often exhibits a continuous spatial gradation due to structural or external field effects; however, the lack of a predictive theory for such graded regions has forced hydrodynamic metamaterial design to rely on piecewise-constant approximations, which introduce parasitic perturbations at layer interfaces. Here, we introduce a continuous-gradient paradigm and establish a predictive forward-design theory. We derive exact analytical expressions for the effective hydraulic conductivity ($H_{\mathrm{eff}}$) of cylindrical graded regions with two canonical radial profiles—power law and linear—and rigorously validate them against finite-element simulations. Armed with these closed-form solutions, we demonstrate the on-demand forward design of devices with prescribed macroscopic responses, including hydrodynamic cloaks realized through two distinct continuous profiles. By inherently suppressing the interface-induced perturbations endemic to stratified designs while precisely replicating the target far-field behavior, our approach offers a pathway toward devices that are both physically robust and fabrication friendly. This work shifts the paradigm from numerical imitation of discrete, layered structures to the rational engineering of continuously tunable effective properties, opening a vast design space for applications in microfluidics, particle manipulation, and engineered porous media.

The resolution of conventional imaging systems is limited by the inherent diffraction limit, making the realization of enhanced-resolution imaging highly significant. This paper innovatively proposes a solid immersion square Maxwell’s fish-eye lens (solid immersion SMFEL). Through the solid immersion medium and boundary transition zone, the refractive index is ensured to vary continuously with thickness, thereby eliminating interface reflections. This results in a significant reduction of the full width at half maximum (FWHM) at the focusing position, overcoming the resolution limitations of conventional SMFEL. A series of numerical simulations were conducted to investigate the imaging performance of the solid immersion SMFEL over a wide frequency band and at different excitation points, as well as the wave-propagation characteristics at various times. The focusing effects of solid immersion SMFEL and conventional SMFEL were compared under multiple excitation sources. Subsequently, transient and steady-state analysis experiments were conducted. The proposed solid immersion SMFEL exhibits stable, wide-band, omnidirectional enhanced-resolution imaging in thin plate structures, providing a practical solution for high-resolution flexural wave-imaging applications and advancing the development of enhanced-resolution imaging technology in related fields.

Non-Hermitian photonic systems, where gain, loss, and nonlinear interactions interplay, offer a fertile ground for realizing complex dynamical behavior such as broken reciprocity, self-oscillations, and excitable dynamics. Here, we report experimental observations of phase-controlled hysteresis in a nonlinear, non-Hermitian silicon microring resonator with dynamically tunable coupling between counterpropagating modes. By integrating independent thermal phase shifters, we modulate the intermodal feedback phase in real time and access regimes with different energy stored in the cavity, allowing us to investigate conditions governed by thermo-optic and free-carrier nonlinearities. We observe non-Markovian memory effects in the form of path-dependent phase trajectories: forward and reverse phase sweeps lead to distinct steady or oscillatory states, despite identical boundary conditions. This hysteresis is underpinned by a nonlocal bifurcation, where the system transitions from a stable fixed point to a saddle-node annihilation, to finally ending in a distant limit cycle. Our results demonstrate coherent phase control as a tool for accessing previously unseen bifurcation structures in photonics, and they establish a scalable platform for exploring neuromorphic dynamics beyond classical excitability.

Hopping transport, characterized by carrier tunneling between localized states, is a key mechanism in disordered materials such as organic semiconductors, perovskites, nitride alloys, and two-dimensional-material- (2DM) based inks. Two main regimes are typically observed—variable-range hopping and nearest neighbor hopping—with a transition between them upon temperature variation. Despite numerous experimental observations, the modeling of this transition remain insufficiently explored and not fully understood. In this work, we present an in-house Monte Carlo random-resistor-network-based simulator capable of capturing both hopping-transport regimes. We demonstrate how material properties that define the network, such as localization length and the spatial and energetic distribution of sites, determine the dominant transport regime. The simulator has been successfully validated against experimental data, showing excellent agreement, reproducing the transition from one regime to the other and accurately capturing one-dimensional, two-dimensional, and three-dimensional variable-range hopping behavior, providing both a theoretical framework for interpreting experiments and a powerful tool for studying transport mechanisms.

Nanostructuring materials at small scales enables control over their physical properties, revealing behaviors not observed at larger dimensions. This strategy is particularly effective in two-dimensional materials, where surface effects dominate, and it is especially promising for energy conversion and thermal management. Here, we use multilayer graphene (4–6 nm thick) as a test platform to study the effect of nanomeshing on its thermoelectric coefficients. The nanomesh consists of a hexagonal array of holes with a measured diameter and neck width of approximately $360$ and $160$ nm, respectively. The multilayer graphene is integrated into field-effect-transistor-like devices supported by hexagonal boron nitride, allowing simultaneous electric and thermopower measurements, with nanomeshing applied to only part of the material. We use modulated thermoreflectance to investigate thermal transport in equivalent nanomeshed and pristine graphene flakes. Our results show a reduction in electrical conductivity that is in very good agreement with the classical Maxwell-Eucken model for porous media. In contrast, the observed reduction in thermal conductivity exceeds the value expected from geometrical modifications alone by a factor of 1.5, highlighting the different mean free paths of phonons and electrons. Moreover, we find an increased thermopower in the nanomeshed graphene region, which can be qualitatively attributed to filtering of low-energy charge carriers. These findings demonstrate that nanomeshing can significantly decouple the thermoelectric coefficients of multilayer graphene, paving the way for developing engineering strategies to achieve similar control across a wider range of 2D materials.

A minimalistic setup comprising a single homogeneous material, in bulk or two-dimensional form, is examined with respect to its ability to absorb visible light. The performance is assessed in terms of the Rozanov bound expressing the bandwidth-thickness balance, the average absorption indicating the broadband efficiency, and the minimal absorbance characterizing the self-camouflage ability. The materials used include ordinary lossy dielectric media, substances with ideal dispersion yielding perfect absorption across the whole visible spectrum, as well as their causal counterparts. The reported results show the optimal operating conditions of such a simple design, which may serve as a key component in absorption-based applications ranging from energy harvesting and medical imaging to photodetection and radar target concealment.

We propose a class of gaseous diffractive optical elements created by imprinting an entropy mode in a gas. Previous approaches to gaseous diffractive optics have relied on the simultaneous excitation of a standing acoustic wave and an entropy mode to produce one-dimensional periodic structures. However, the presence of acoustic oscillations in the gas imposes stringent constraints on some of the operational parameters of these optical elements, such as their lifetime and diffraction angle. In this work, we introduce an approach that eliminates the acoustic mode, relying solely on the entropy mode. This enables control of the lifetime and temporal profile of gaseous optical elements, and also allows the creation of arbitrary structures with greater contrast, including nonperiodic patterns such as chirped gratings or lenses. This approach should allow operation over a wider parameter space, including larger diffraction angles and compatibility with laser pulse durations ranging from femtoseconds to microseconds.

Hybrid magnonic systems have recently attracted significant attention due to their intriguing physics and potential applications in coherent information processing. In this regard, we have investigated magnon-magnon coupling in the all-oxide insulator garnet ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ (YIG)/${\mathrm{Tm}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ (TmIG) heterostructure. The presence of an avoided mode crossing region between the ferromagnetic resonance modes of YIG and TmIG indicates interfacial exchange coupling. This all-insulator system enables interfacial coupling via magnon-magnon interactions. The mode crossing occurs at $f_c=6.88$ GHz, corresponding to the minimal resonance separation between the two hybrid modes. The coupling strength is determined to be 78 MHz (or 2.8 mT), providing clear evidence of magnon-magnon coupling between the two Kittel modes in the YIG/TmIG insulator system at 200 K. These findings pave the way for engineering magnonic band structures, tunable coherent magnonic interactions, and nonreciprocal spin transport, which are crucial for advancing ultralow-power magnonic devices.

Single nitrogen-vacancy ($\mathrm{N}$-$V$) centers in diamond are excellent nano-NMR sensors with the ability to function in ambient conditions. However, the fluorescence signal detected from single $\mathrm{N}$-$V$ centers is weak and often requires measurement durations on the order of several hours to acquire enough signal for the conventional curve fit estimation (CFE) technique. In this work, we explore maximum-likelihood estimation (MLE) as an alternative method to process the fluorescence signal from single $\mathrm{N}$-$V$ centers in XY8-$k$ measurements, particularly for online and real-time applications. There are three key points of interest in this work. First, we present a closed-form analytical expression for $\mathrm{N}$-$V$ center electron phase accumulation in the time domain. Second, we provide an explicit derivation of the Fisher information and Cramér-Rao lower bounds for parameter estimators in XY8-$k$ data. Third, we study the use of MLE for direct parameter estimation in XY8-$k$ fluorescence data with single $\mathrm{N}$-$V$ centers in different environmental settings through simulations, as well as providing a demonstration of performance on real data. Our results show that MLE converges faster and is more robust than CFE in most conditions.

In this paper, we resolve a long-standing controversy: how and to what extent electron transport in the collector of a double-barrier resonant tunneling diode (RTD) affects its dynamics, particularly the rate of charge-relaxation processes and the RTD admittance. Here, we present a general analytical small-signal RTD admittance model that consistently incorporates space-charge effects in both the quantum well (QW) and the collector depletion region (spacer). If electron transport through the collector is sufficiently fast—this condition is met in contemporary subterahertz and terahertz RTDs under typical operating conditions—the general model reduces to a simple four-element $RLRC$ equivalent circuit with a certain charge-relaxation time constant ($\tau$), which, in general, largely deviates from the tunnel electron lifetime in the RTD QW. Collector space-charge effects influence both dynamic and static RTD characteristics. Specifically, in the negative differential conductance (NDC) region, RTDs exhibit increased $\tau$ and capacitance, resulting in slower operation. Additionally, the RTD $I$-$V$ curve tilts to the right and the NDC increases. However, collector space-charge effects are typically negligible when electrons travel ballistically through the collector—this outcome of our analysis is important for the practical modeling and design of RTDs. Nevertheless, these effects become significant in RTDs with long collector spacers, high current density, and electron transport at saturation velocity, though such RTDs are unusual at subterahertz and terahertz frequencies.

Resonator-based acoustic metamaterials are renowned for their ability to control wave propagation at low frequencies. Nevertheless, achieving band gaps at ultralow frequencies—critical for applications such as seismic protection—has been hindered by the need for excessively heavy resonator masses, often surpassing the weight of the structures they are designed to protect. In this study, we introduce an approach using inerter-based metamaterials that leverage translation-rotation coupling to achieve amplified inertia without the associated mass penalties. It enables band gaps in the subhertz to several hertz ranges while reducing the embedded mass by 3 orders of magnitude compared to resonator-based systems. Through a combination of analytical modeling, numerical simulations, and experimental validations, we demonstrate robust band-gap formation for both longitudinal (0.4–1.0 Hz) and transverse waves (4.6–6.2 Hz) using compact lightweight units. This paradigm shift breaks the long-standing trade-off between resonator mass and operational frequency in resonator-based metamaterials, paving the way for practical low-frequency wave attenuation in diverse engineering applications, including seismic shielding and aerospace vibration control.

Rydberg atoms, due to their large polarizabilities and strong transition dipole moments, have been utilized as sensitive electric field sensors. While their ability to detect modulated signals has been previously demonstrated, these studies have largely been limited to laboratory-generated signals tailored specifically to atomic detection. Here, we extend the practical applicability of Rydberg sensors by demonstrating the reception of real-world frequency-modulated (FM) audio transmissions using a consumer-grade handheld two-way radio operating in the UHF band. Detection is based on the ac Stark shift induced by the radio signal in a Rydberg atomic vapor, with demodulation performed using an offset local oscillator and lock-in amplification. We successfully demodulate speech signals and evaluate the audio spectral response and reception range. We show that all consumer-accessible radio channels can be simultaneously detected, and demonstrate simultaneous reception of two neighboring channels with at least 53 dB of isolation. This work underscores the potential of Rydberg atom-based receivers for practical, real-world FM signal detection.

We present a comprehensive study of planar $\mathrm{Nb}$-$\mathrm{Al}$-$\mathrm{Nb}$ Josephson junctions with submicrometer dimensions ($L\approx 100$ nm, active area of approximately $5\times {10}^4{\mathrm{nm}}^2$), where the intrinsic superconductivity of the aluminum weak link plays a crucial role in enhancing device performance. Through a combination of theoretical modeling and experimental characterization, we demonstrate that the aluminum interlayer significantly boosts the critical current $I_c\approx 50\text{μ}\mathrm{A}$ and the characteristic voltage $V_c\approx 1$ mV at $T=4$ K, while maintaining the nonhysteretic current-voltage characteristics essential for digital applications. Our microscopic model, based on self-consistent solutions of the Usadel equations, reveals that this enhancement originates from the coexistence of proximity-induced superconductivity and intrinsic pairing in aluminum, which is particularly pronounced at an optimal boundary resistance. Structural analysis confirms epitaxial $\mathrm{Nb}$-$\mathrm{Al}$ interfaces with minimal interdiffusion, enabling reproducible fabrication of these compact junctions. These results establish $\mathrm{Nb}$-$\mathrm{Al}$-$\mathrm{Nb}$ bridges as promising building blocks for high-density superconducting electronics operating at helium temperatures.

Semiconductor membranes are widely used in research fields that target medical, biological, environmental, and optical applications. Often such membranes derive their functionality from a nanopatterning, which challenges the determination of their optical, electronic, mechanical, and thermal properties. In this work, we demonstrate the noninvasive, all-optical thermal characterization of approximately-800-nm-thick and approximately-150-$\text{μ}\mathrm{m}$-wide membranes that consist mainly of wurtzite GaN and a stack of ${\mathrm{In}}_{0.15}{\mathrm{Ga}}_{0.85}\mathrm{N}$ quantum wells as a built-in light source. Because of their application in photonics, e.g., for vertical-cavity surface-emitting lasers, such photonic membranes are bright light emitters, which challenges their thermal characterization by optical means. We combine top-view two-laser Raman thermometry (2LRT) with time-resolved photoluminescence spectroscopy to extract the in-plane thermal conductivity ${\kappa }_{\text{in~plane}}$ of these membranes, which represents a notable difference from previous studies on epitaxial GaN films. Thus, we can disentangle the entire laser-induced power balance. Thermal imaging by Raman spectroscopy yields ${\kappa }_{\text{in plane}}={165}_{-14}^{+16}\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ for the best membrane. This result compares well with ${\kappa }_{\text{in plane}}=177\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ obtained by ab initio simulations based on a solution of the linearized phonon Boltzmann transport equation, including three- and four-phonon scattering, as well as phonon-isotope and phonon-boundary scattering. Furthermore, we study how ${\kappa }_{\text{in plane}}$ is affected by a roughening of the membrane’s back side and additional semiconductor layers. For the membrane with the roughest back side, we observe a reduction of ${\kappa }_{\text{in plane}}$ by almost 40%, which is accompanied by an anisotropy of ${\kappa }_{\text{in plane}}$ due to etch channel formation. Thanks to the 2LRT approach, such variations and anisotropies of ${\kappa }_{\text{in plane}}$ become accessible to the experimentalist via highly spatially resolved temperature maps.

Phase-contrast x-ray imaging overcomes low contrast in lightweight materials but suffers from an inherent tradeoff between spatial resolution (SR) and contrast-to-noise ratio (CNR). We resolve this conflict through a physics-constrained wavelet fusion framework. By integrating high-SR direct reconstruction and high-CNR phase retrieval, our method leverages single-level Sym4 wavelet decomposition to separate low-frequency contrast (governed by refractive index gradients) and high-frequency edges (dominated by Fresnel diffraction). The compact support and near-symmetry of Sym4 align with the spatial scales of x-ray propagation at 20 cm, minimizing spectral leakage while suppressing artifacts. For porous polyether ether ketone (PEEK), fused images achieve SR of 7.27 µm (140% enhancement over phase retrieval) and CNR of 8.33 (20.8× improvement over direct reconstruction). Validation on ordinary Portland cement achieves an SR of 10.81 µm and a CNR of 11.48, outperforming traditional Fourier fusion. This approach demonstrates artifact-free visualization of sub-10-µm pore networks, providing a robust pathway for high-fidelity nondestructive testing of lightweight materials in material science and biomedical diagnostics.

Spoof surface plasmon polaritons (SSPPs) were first developed in electromagnetics and later extended to acoustics, enabling deep-subwavelength confinement and efficient surface wave transport. Currently, unidirectional SSPP excitation is typically achieved by tailoring the excitation sources, such as with vortex waves carrying orbital angular momentum beams or by employing gradient metamaterials, though both approaches often face limitations in tunability, efficiency, and implementation complexity. Here, we propose and experimentally demonstrate a high-efficiency and tunable mechanism for directional SSPP excitation, achieved through structural symmetry breaking. Specifically, by introducing a rotational degree of freedom that breaks the intrinsic symmetry of the combined triangular elements and grating structures, distinct SSPP coupling efficiencies are induced on both sides under normal incidence, enabling directional excitation. Numerical and experimental results verify the stable, unidirectional propagation enabled by this approach. Compared with existing methods, our design offers superior efficiency, tunability, and simplicity, providing a robust and adaptable solution for directional acoustic energy transport and subwavelength device designs.