We investigate the effect of the ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{Ca}\mathrm{Cu}}_2{\mathrm{O}}_{8+\delta }$ mesa sidewall on the spontaneous synchronization of intrinsic Josephson junctions and concomitant terahertz radiation. We develop a lithography technique to control the sidewall angles. Using a Fourier interferometer, we characterize the radiation emitted from a series of mesas with different sidewall angles. We determine that a uniform distribution of the oscillation frequencies is essential to produce coherent radiation outside the mesa. It is also noted that in the resonant state, the input excess energy is transferred to the excitation of the coherent state.

This paper reports tunable ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ artificial spin ice structures of various geometrical lattice arrangements as a function of film thickness. We achieve the magnetic tunability by three distinct methods namely, geometrical arrangements of nanomagnetic elements in the form of square, kagome, and triangular lattices with the variation in film thickness (20, 30, and 50 nm) for each geometry and the applied field orientations. Magnetic force microscopy reveals that the nanoelements are in single-domain states, obeying the spin ice rules for the 20-nm-thick spin ice structures. A combination of nanoelements in single-domain and vortex states is observed with the increase in thickness up to 30 nm. For the 50-nm-thick elements, vortex and flux closure states are in evidence. Broadband ferromagnetic resonance spectroscopy establishes the presence of distinct resonant modes that are spatially localized in the nanomagnets of different orientations and, hence, can be controlled by the applied field orientations. The role of shape anisotropy on the static and dynamic properties is investigated systematically and complemented by extensive micromagnetic simulations. The results show great potential towards designing reconfigurable magnonic crystals for microwave filter applications.

Benefiting from prominent performance in various scientific fields, metasurface research has been flourishing over the past decade. Huygens’ metasurface, as an emerging subcategory of metasurface, can theoretically achieve full control of electric field distribution within the subwavelength scale. Driven by its outstanding manipulation capacity, the three-dimensional holography utilizing broadband Huygens’ metasurface is demonstrated in the microwave regime in this paper. For the broadband working properties, two types of equivalent circuit are integrated into the design of Huygens’ meta-atom. Besides, for high image quality, the modified weighted Gerchberg-Saxton (GSW) algorithm is implemented for specific interfacial phase distribution. The proof-of-concept experiments show notable microwave holographic images, with an 86.2% transmittance efficiency, a 62.7% imaging efficiency, and an 88.1 signal-to-noise ratio at 12 GHz. The proposed holography extends the route to broadband microwave applications in security, data storage, and antenna systems.

If one folds a thin viscoelastic sheet under an applied force, a line of plastic deformation is formed that shapes the sheet into an angle. This study determines parameters that define this angle and shows that, no matter how much load one applies, it is impossible to make angles less than a certain minimum angle in a definite time. Moreover, it is shown that regardless of whether the sheet is released freely afterward or kept under load, a logarithmic relaxation process follows the first deformation. The slope of this logarithm is the same in both conditions and depends neither on the applied force nor on the thickness of the sheet, which indicates that it is directly a probe of the molecular mobility of the material. This intrinsic relaxation constant is measured at approximately $0.1$ and $6$ for Mylar and paper sheets, respectively. It is also suggested that the observed minimum angle of folding can be defined as a characteristic index for the plasticity of different materials.

Spin-orbit coupling (SOC) is a key interaction in spintronics, allowing electrical control of spin or magnetization and, vice versa, magnetic control of electrical current. However, recent advances have revealed much broader implications of SOC that is also central to the design of topological states with potential applications from low-energy dissipation and faster magnetization switching to high tolerance of disorder. SOC and the resulting emergent interfacial spin-orbit fields are simply realized in junctions through structural inversion asymmetry, while the anisotropy in magnetoresistance (MR) allows their experimental detection. Surprisingly, we demonstrate that an all-epitaxial ferromagnet/$\mathrm{Mg}\mathrm{O}$/metal junction with a single ferromagnetic region and only negligible MR anisotropy undergoes a remarkable transformation below the superconducting transition temperature of the metal. The superconducting junction has a MR anisotropy 3 orders of magnitude higher and could enable novel applications in superconducting spintronics. In contrast to common realizations of MR effects that require a finite applied magnetic field, our system is designed to have two stable zero-field states with mutually orthogonal magnetizations: in plane and out of plane. This bistable magnetic anisotropy allows us to rule out orbital and vortex effects due to an applied magnetic field and identify the SOC origin of the observed MR. Such MR reaches approximately $20\mathrm{\%}$ without an applied magnetic field and could be further increased for large magnetic fields that support vortices. Our findings call for a revisit of the role of SOC, even when it seems negligible in the normal state, and suggest an alternative platform for superconducting spintronics.

Spin angular momentum (SAM), a fundamental property of light, is associated with the right-hand and left-hand circular polarizations. It has never been trivial to engineer a light beam with desired SAM, and especially at the frequency regime other than the visible region. A widely used approach is to build periodic arrays of plasmonic nanostructures that host two orthogonal dipole resonances. As the unit cell, its structure design is crucial, but the design principle remains obscure. We present a model of two orthogonal resonant Lorentz dipoles to quantitatively describe the creation of SAM in such plasmonic quarter-wave plates. The equal amplitude and $\pi /2$ phase difference are essential. The requirements can be achieved by structure modulation and, in addition, the amplitude can be manipulated by varying the polarization angle of incident waves. In practice, the resonant frequency difference of two dipoles $\mathrm{\Delta }\omega =|{\omega }_A-{\omega }_B|$, and their damping rate ${\kappa }_A$ and ${\kappa }_B$, should meet a basic criterion, such as $\mathrm{\Delta }\omega ⩾\sqrt{{\kappa }_A{\kappa }_B}$. As an illustration, we design a cross-shaped circular polarization convertor, and show its structure and incident angle optimization. We find the optimal working frequency ${\omega }_{\mathrm{opt}}$ is roughly equal to $\sqrt{{\omega }_A{\omega }_B}$ at the critical condition $\mathrm{\Delta }\omega =\sqrt{{\kappa }_A{\kappa }_B}$. Our results provide good guidance on the design of SAM-enabled plasmonic devices for versatile applications.

High-gain and low-noise signal amplification is a valuable tool in various cryogenic microwave experiments. A microwave optomechanical device, in which a vibrating capacitor modulates the frequency of a microwave cavity, is one technique that is able to amplify microwave signals with high gain and large dynamical range. Such optomechanical amplifiers typically rely on strong backaction of microwave photons on the mechanical mode achieved in the sideband-resolved limit of optomechanics. Here, we observe microwave amplification in an optomechanical cavity in the extremely unresolved sideband limit. A large gain is observed for any detuning of the single pump tone within the cavity linewidth, a clear indication that the amplification is not induced by dynamical backaction. By being able to amplify for any detuning of the pump signal, the amplification center frequency can be tuned over the entire range of the broad cavity linewidth. Additionally, by providing microwave amplification without mechanical amplification, we predict that by using this scheme it is possible to achieve near-quantum-limited microwave amplification despite a large thermal occupation of the mechanical mode.

The successes of superconducting quantum circuits at local manipulation of quantum information and photonics technology at long-distance transmission of the same have spurred interest in the development of quantum transducers for efficient, low-noise, and bidirectional frequency conversion of photons between the microwave and optical domains. We propose to realize such functionality through the coupling of electrical, piezoelectric, and optomechanical resonators. The coupling of the mechanical subsystems enables formation of a resonant mechanical supermode that provides a mechanically mediated, efficient single interface to both the microwave and optical domains. The conversion process is analyzed by applying an equivalent circuit model that relates device-level parameters to overall figures of merit for conversion efficiency $\eta$ and added noise $N$. These can be further enhanced by proper impedance matching of the transducer to an input microwave transmission line. The performance of potential transducers is assessed through finite-element simulations, with a focus on geometries in $\mathrm{Ga}\mathrm{As}$, followed by considerations of the $\mathrm{Al}\mathrm{N}$, ${\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$, and $\mathrm{Al}\mathrm{N}$-on-$\mathrm{Si}$ platforms. We present strategies for maximizing $\eta$ and minimizing $N$, and find that simultaneously achieving $\eta >50\mathrm{\%}$ and $N<0.5$ should be possible with current technology. We find that the use of a mechanical supermode for mediating transduction is a key enabler for high-efficiency operation, particularly when paired with an appropriate microwave impedance-matching network. Our comprehensive analysis of the full transduction chain enables us to outline a development path for the realization of high-performance quantum transducers that will constitute a valuable resource for quantum information science.

DNA is the building block for most living organisms; hence, controlling the supramolecular self-assembly of DNA structures is important not only for a better understanding of its biological properties, but also for shedding light on the design of functional materials for biological engineering and materials science applications. However, it is still challenging to control DNA molecular self-assembly structures in a predesigned manner across multiple length scales. Here, we demonstrate that the orientational order of DNA molecules can be precisely controlled by using the photopatterning technique. This technique imprints various spatially varying patterns into a layer of liquid-crystalline polymer, which will be further used to control the DNA structures. It is demonstrated that DNA orientations can be patterned with a two-dimensional lattice of topological defects and arbitrary patterns through length scales from micrometers to millimeters. The resulting programmable and predesigned DNA self-assembly structures will open up opportunities in advanced materials and devices for optical and biological applications.

One of the most-important tools in modern science is the analysis of electromagnetic properties by spectroscopy. The various types of spectroscopy can be classified by the underlying type of interactions between energy and the material. In this paper we demonstrate a class of spectroscopy based on Casimir interactions between a solid investigated object and a reference surface embedded in an environmental liquid medium. Our main example is based on the measurement of Hamaker constants on change of the concentration of an intervening two-component liquid, where we demonstrate a possible reconstruction algorithm to estimate the frequency-dependent dielectric function of the particle investigated.

We report on an effort to improve the performance of superconducting radiofrequency cavities by using heat treatment in a temperature range sufficient to dissociate the natural surface oxide. We find that the residual resistance is decreased significantly, and we find an unexpected reduction in the Bardeen-Cooper-Schrieffer (BCS) resistance. Together these result in extremely high-quality factor values at relatively large accelerating fields $E_{\mathrm{acc}}$ ∼ 20 MV/m: $Q_0$ = 3–4 × ${10}^{11}$ at <1.5 K and $Q_0$ ∼ 5 × ${10}^{10}$ at 2.0 K. In one cavity, measurements of surface resistance versus temperature showed an extremely small residual resistance of just 0.63 ± 0.06 nΩ at 16 MV/m. Secondary ion mass spectrometry measurements confirm that the oxide is dissociated significantly, but they also show the presence of nitrogen after heat treatment. We also present studies of surface oxidation via exposure to air and to water, as well as the effects of very light surface removal via HF rinse. The study is performed on 1.3 GHz cavities, but the effect may be extendable to other frequencies as well. The possibilities for applications and the planned future development are discussed.

We study experimentally a chain of defect resonators in a phononic crystal slab and observe its collective resonances at ultrasonic frequencies of a few megahertz. A phononic crystal of cross holes is fabricated in a thin fused-silica plate by femtosecond-laser writing followed by $\mathrm{KOH}$ etching. A chain of 17 coupled resonators is defined with no definite spatial periodicity but similar coupling strength between nearest-neighbor resonators. The full phononic band gap ensures that only evanescent waves in the crystal can tunnel between adjacent resonators in the plane. The resulting evanescent-coupling strength decreases exponentially with distance. Collective resonances are excited by a frequency-driven piezoelectric vibrator attached at one end of the chain and imaged along the chain with a laser Doppler vibrometer. A discrete spectrum of resonances is observed and explained by a model representing the chain as a phononic polymer. The theoretical analysis is supported by finite-element simulations that agree well with experimental results. Chains of evanescently coupled microresonators forming phononic polymers could find applications in ultrasonic sensing, for implementation in topological phononics, and for the design of optomechanical resonator chains.

$\mathrm{Cu}$-$\mathrm{Ag}$-alloy nanoparticles (NPs) are synthesized from micropowders of pure $\mathrm{Cu}$ and $\mathrm{Ag}$ by two consecutive nonequilibrium processes based on plasma and lasers in liquids. The plasma process reduces the size of the particles forming the initial powders from micrometer size to nanometer size, at which the laser fluence is sufficient to melt them, making alloying possible. Measurements at macroscopic (solution absorption), microscopic (scattering of individual NPs), and nanoscopic (electron microscopy) scales confirm alloying of NPs and homogenization of size and composition. This has a noticeable effect on the final colloidal solution, which absorbs yellow-orange light (550–600 nm) after laser treatment. With a synthesis rate of 360 mg/h, this process opens up possibilities for nonequilibrium nanometallurgy of functional NPs.

Dielectric multilayer photonic-band-gap structures, called one-dimensional photonic crystals (1DPCs), have drawn considerable attention in the fields of physics, chemistry, and biophotonics. Here, experimental results verify the feasibility of a 1DPC working as a substrate for switchable manipulations of colloidal microparticles. The optically induced thermal convective force on a 1DPC can assemble colloidal particles that are dispersed in a water solution, while the photonic scattering force on the same 1DPC caused by propagating evanescent waves can guide these particles. Additionally, in the 1DPC, one internal mode can be excited that has seldom been noticed previously. This mode shows an ability to assemble particles over large areas even when the incident power is low. The assembly and guidance of colloidal particles on the 1DPC are switchable just through tuning the polarization and angle of the incident laser beam. Numerical simulations are carried out, which are consistent with these experimental observations.

We investigate the spin Hall magnetoresistance (SMR) at room temperature in thin-film heterostructures of antiferromagnetic insulating (0001)-oriented $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$ (hematite) and $\mathrm{Pt}$. We measure their longitudinal and transverse resistivities while rotating an applied magnetic field of up to 17 T in three orthogonal planes. For out-of-plane magnetotransport measurements, we find indications for a multidomain antiferromagnetic configuration whenever the field is aligned along the film normal. For in-plane field rotations, we clearly observe a sinusoidal resistivity oscillation characteristic for the SMR due to a coherent rotation of the Néel vector. The maximum SMR amplitude of $0.25\mathrm{\%}$ is, surprisingly, twice as high as for prototypical ferrimagnetic ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}/\mathrm{Pt}$ heterostructures. The SMR effect saturates at much smaller magnetic fields than in comparable antiferromagnets, making the $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3/\mathrm{Pt}$ system particularly interesting for room-temperature antiferromagnetic spintronic applications.

The absorption of airborne noise at frequencies below 300 Hz is a particularly vexing problem due to the absence of natural sound-absorbing materials at these frequencies. The prevailing solution for low-frequency sound absorption is the use of passive narrow-band resonators, the absorption level and bandwidth of which can be further enhanced using nonlinear effects. However, these effects are typically triggered at high intensity levels, without much control over the form of the nonlinear absorption mechanism. In this study, we propose, implement, and experimentally demonstrate a nonlinear active control framework on an electroacoustic resonator prototype, allowing for unprecedented control over the form of nonlinearity and arbitrarily low intensity thresholds. More specifically, the proposed architecture combines linear feedforward control on the front pressure through a first microphone located at the front face of the loudspeaker and nonlinear feedback control on the membrane displacement estimated through the measurement of the pressure inside the back cavity with a second microphone located in the enclosure. It is experimentally shown that even at a weak excitation level, it is possible to observe and control the nonlinear behavior of the system. Taking the cubic nonlinearity as an example, we demonstrate numerically and experimentally that in the low-frequency range (50–500 Hz), the nonlinear control law allows improvement of the absorption performance, i.e., enlarging the bandwidth of optimal sound absorption while increasing the maximal absorption coefficient value and producing only a negligible amount of nonlinear distortion. The reported experimental methodology can be extended to implement various types of hybrid linear and/or nonlinear controls, thus opening new avenues for managing wave nonlinearity and achieving nontrivial wave phenomena.

The continuous development of superconducting electronics is encouraging several studies on hybrid Josephson junctions (JJs) based on superconductor-ferromagnet-superconductor (SFS) heterostructures, as either spintronic devices or switchable elements in quantum and classical circuits. Recent experimental evidence of macroscopic quantum tunneling and of an incomplete 0-$\pi$ transition in tunnel-ferromagnetic spin-filter JJs could also enhance the capabilities of SFS JJs as active elements. Here, we provide a self-consistent electrodynamic characterization of $\mathrm{Nb}\mathrm{N}$/$\mathrm{Gd}\mathrm{N}$/$\mathrm{Nb}\mathrm{N}$ spin-filter JJs as a function of the barrier thickness, disentangling the high-frequency dissipation effects due to the environment from the intrinsic low-frequency dissipation processes. The fitting of the $I$-$V$ characteristics at 4.2 K and at 300 mK by using the tunnel-junction-microscopic model allows us to determine the subgap resistance $R_{\mathrm{sg}}$, the quality factor $Q$, and the junction capacitance $C$. These results provide the scaling behavior of the electrodynamic parameters as a function of the barrier thickness, which represents a fundamental step for the feasibility of tunnel-ferromagnetic JJs as active elements in quantum and classical circuits, and are of general interest for tunnel junctions other than conventional SIS JJs.