Surface-acoustic-wave (SAW) devices form an important class of acoustofluidic devices, in which acoustic waves are generated and propagate along the surface of a piezoelectric substrate. Despite their widespread use, only a few fully three-dimensional (3D) numerical simulations have been reported in the literature. In this paper, we present a 3D numerical simulation taking into account the electromechanical fields of the piezoelectric SAW device, the acoustic displacement field in the attached elastic material, in which a liquid-filled microchannel is embedded, the acoustic fields inside the microchannel, and the resulting acoustic radiation force and streaming-induced drag force acting on micro- and nanoparticles suspended in the microchannel. A specific device design is presented, for which numerical predictions of the acoustic resonances and the acoustophoretic response of suspended microparticles in three dimensions are successfully compared with experimental observations. The simulations provide a physical explanation of the observed qualitative difference between devices with acoustically soft and hard lids in terms of traveling and standing waves, respectively. The simulations also correctly predict the existence and position of the observed in-plane streaming-flow rolls. The simulation model presented may be useful in the development of SAW devices optimized for various acoustofluidic tasks.

We present techniques to model and design membrane phononic crystals with low-mass defects, optimized for force sensing. Further, we identify the importance of the phononic crystal mass contrast as it pertains to the size of acoustic band gaps and to the dissipation properties of defect modes. In particular, we quantify the tradeoff between high-mass-contrast phononic crystals, with their associated robust acoustic isolation, and a reduction of soft clamping of the defect mode. We fabricate a set of phononic crystals with a variety of defect geometries out of high-stress stoichimetric silicon-nitride membranes and measure at both room temperature and 4 K in order to characterize the dissipative pathways across a variety of geometries. Analysis of these devices highlights a number of design principles integral to the implementation of low-mass low-dissipation mechanical modes into optomechanical systems.

The semiconductor industry is continuously pushing the limits of photolithography, with feature sizes now smaller than 10 nm. To ensure quality, it has become necessary to look beyond the conventional metrological techniques. X-ray scattering has emerged as a possible contender to determine the average shape of a line grating with subnanometer precision. However, to fulfill its promise, faster algorithms must also be developed to interpret and extract metrics from reciprocal-space scattering data. In this paper, we present a fast and accurate x-ray technique and analysis algorithm: critical-dimension grazing-incidence small-angle x-ray scattering (CD GISAXS). The CD GISAXS technique is used in grazing-incidence configuration with a continuous azimuthal rotation of the sample, and thus does not require high-energy x-rays to penetrate the wafer and greatly reduces the data-acquisition times, permitting analysis within the framework of the distorted-wave Born approximation.

Electromagnetically induced transparency (EIT) and Autler-Townes splitting (ATS) share similar transparent windows in the transmission spectrum, which causes confusion and difficulty in discriminating between them. Essentially, EIT involves asymmetric profile interference, while ATS originates from a strong coupling effect. The conventional method uses the Akaike information criterion (AIC) to calculate the proportion of EIT and ATS, and then determines the dominant phenomenon by experimental data fitting without considering fundamental differences in physics. We present two kinds of acoustic structures by grafting two Helmholtz resonators to a cylindrical tube whose geometrical parameters are chosen by individual mechanisms of acoustically induced transparency (AIT) and ATS. Our results explicitly show AIT and ATS phenomena analytically, numerically, and experimentally, which are also supported by data-fitting and AIC methods. This study contributes to the design of AIT and ATS in their specific applications, avoiding any confusion.

The $\mathrm{Si}\mathrm{C}/{\mathrm{Si}\mathrm{O}}_2$ interface is a central component of many $\mathrm{Si}\mathrm{C}$ electronic devices. Defects intrinsic to this interface can have a profound effect on their operation and reliability. It is therefore crucial to both understand the nature of these defects and develop characterization methods to enable optimized $\mathrm{Si}\mathrm{C}$-based devices. Here we make use of confocal microscopy to address single $\mathrm{Si}\mathrm{C}/{\mathrm{Si}\mathrm{O}}_2$-related defects and show the technique to be a noncontact, nondestructive, spatially resolved and rapid means of assessing thequality of the $\mathrm{Si}\mathrm{C}/{\mathrm{Si}\mathrm{O}}_2$ interface. This is achieved by a systematic investigation of the defect density of the $\mathrm{Si}\mathrm{C}/{\mathrm{Si}\mathrm{O}}_2$ interface by varying the parameters of a nitric oxide passivation anneal after oxidation. Standard capacitance-based characterization techniques are used to benchmark optical emission rates and densities of the optically active $\mathrm{Si}\mathrm{C}/{\mathrm{Si}\mathrm{O}}_2$-related defects. Further insight into the nature of these defects is provided by low-temperature optical measurements on single defects.

Highly localized electromagnetic waves appearing in subwavelength structures, such as surface plasmons lying on a metal surface, are fundamental ingredients in nanophotonics since they offer novel routes for advanced subwavelength light control. Negative-magnetic-permeability metamaterials, already proposed for nuclear magnetic resonance imaging (MRI) applications, can also support magnetic-surface-plasmon excitations. Here we propose to exploit this phenomenon to increase MRI efficiency. We show that a negative-magnetic-permeability metamaterial slab, coupled to a standard radio-frequency surface coil, supports highly localized magnetic surface plasmons, allowing us to boost and to spatially manipulate the radio-frequency electromagnetic field. Our predictions indicate that the configuration considered holds great potential to enhance the MRI signal-to-noise ratio with respect to standard setups.

Experimental studies on spin valves with exfoliated 2D materials face the main technological issue of ferromagnetic electrode oxidation during the 2Ds integration process. As a twofold outcome, magnetoresistance (MR) signals are very difficult to obtain and, when they finally are, they are often far from expectations. We propose a fabrication method to circumvent this key issue for 2D-based spintronics devices. We report on the fabrication of $\mathrm{Ni}\mathrm{Fe}/{\mathrm{Mo}\mathrm{S}}_2/\mathrm{Co}$ spin valves with mechanically exfoliated multilayer ${\mathrm{Mo}\mathrm{S}}_2$ using an in situ fabrication protocol that allows high-quality nonoxidized interfaces to be maintained between the ferromagnetic electrodes and the 2D layer. Devices display a large MR of 5%. Beyond interfaces and material quality, we suggest that an overlooked more fundamental physics issue related to spin-current depolarization could explain the limited MR observed so far in ${\mathrm{Mo}\mathrm{S}}_2$-based magnetic tunnel junctions. This points to a path towards the observation of larger spin signals in line with theoretical predictions above 100%. We envision the impact of our work to be beyond ${\mathrm{Mo}\mathrm{S}}_2$ and its broader transition-metal dichalcogenides family by opening the way to an accelerated screening of other 2D materials that are yet to be explored for spintronics.

The photophysical properties of emitting charge-transfer states are often reported to be profoundly influenced by the dielectric environment that surrounds the emitter. This poses a technological challenge because chromophores based on thermally activated delayed fluorescence used in organic light-emitting diodes feature a strong charge-transfer character of the emitting state, and their photophysics can be greatly altered by the properties of the host material in the emitting layer. In this work, three isomers with different degrees of steric hindrance against the rotation around the donor-acceptor connection are investigated. Furthermore, a continuous variation of the dielectric constant is achieved by our mixing two solvents, and the time-resolved fluorescence is analyzed to understand how the ratio of the delayed fluorescence to the prompt fluorescence varies. The computation of the excitonic structure in media of different dielectric constants using an optimally tuned range-separated hybrid functional allows us to precisely interpret the experimental results and to pinpoint the participation of a higher triplet in the reverse intersystem crossing as the key factor causing the peculiar increase of delayed fluorescence at low dielectric constant for one of the model compounds.

Among various multipartite entangled states, Dicke states stand out because their entanglement is maximally persistent and robust under particle losses. Although they have attracted much attention for their potential applications in quantum information processing and foundational studies, the characterization of Dicke states remains as a challenging task in experiments. Here we propose efficient and practical protocols for verifying arbitrary $n$-qubit Dicke states in both adaptive and nonadaptive ways. Our protocols require only two distinct settings based on Pauli measurements besides permutations of the qubits. To achieve infidelity $ϵ$ and confidence level $1-\delta$, the total number of tests required is only $O(n{ϵ}^{-1}\ln {\delta }^{-1})$. This performance is exponentially more efficient than all previous protocols based on local measurements, including quantum state tomography and direct fidelity estimation, and is comparable to the best global strategy. Our protocols are readily applicable with current experimental techniques and are able to verify Dicke states of hundreds of qubits.

Recently, it has been shown that ferrimagnets made from $\mathrm{Gd}(\mathrm{Fe},\mathrm{Co})$ alloys exhibit ultrafast dynamics near the angular momentum compensation point. Owing to the small net magnetization in these alloys, stable magnetic vortices can be the ground state in a nanoscale disk, and gyrotropic motion can be driven by spin torque. It is shown that the Oersted field from the current can stabilize the vortex, and the critical current for gyrotropic motion and the current-dependent frequency are calculated in the Thiele model. This system can be used as a vortex-state spin-torque auto-oscillator working at frequencies of tens of gigahertz.

Among the various graphene-based structures, the graphene quantum well (QW) is a particularly intriguing example, as it exhibits unique electronic behavior and broad application prospects. An attractive way to achieve graphene QWs is the construction of a type-I band alignment based on an armchair graphene nanoribbon (AGNR) heterojunction, in which the electronic properties can be flexibly tuned by varying the detailed atomic structure. Intriguing characteristics of QW states have been observed in AGNR QWs, which are difficult to interpret merely by considering the band offset between the barrier and well regions. Therefore, a comprehensive understanding of the formation of QW states is required for the optimal design of AGNR QWs. An interesting phenomenon is demonstrated in that a state with a higher energy index exhibits stronger quantum confinement in the case of specific AGNR QW systems. This counterintuitive confinement originates from the wave-function symmetries of the electronic states in the constituent AGNR segments. Wave-function symmetry matching (even-even or odd-odd) leads to hybridization of corresponding states and consequently reduces the confinement, while wave-function symmetry mismatching (even-odd) suppresses the penetration of electronic states and consequently enhances the confinement. Moreover, a design method for AGNR QWs based on this wave-function symmetry mechanism through the modulation of geometric parameters and the displacement between the constituent AGNR segments is demonstrated. Finally, a demonstration of the application of this mechanism in an actual device is presented. Our perspective not only provides deep insight into the formation mechanism of QW states in AGNR QWs but also opens up a dimension for the design of AGNR QWs.

Manipulating microscale object plays a paramount role in a wide range of fundamental research efforts and applications. At the microscale, various methods have been developed in the past decades, including optical, electric, magnetic, aerodynamic, and acoustic methods. However, these noncontact forces are susceptible to external disturbance, and so finding a way to make microscale object manipulation immune to external perturbations is challenging and remains elusive. Here, we demonstrate a method based on a trapping mechanism to manipulate a microscale object in a gas flow at ambient conditions. We first show that the microdroplet is entrapped in a trapping ring constructed by a particular toroidal vortex. The vortex works as tweezers to control the position of the microdroplet. We then show that the microdroplet can be transported along the trapping ring. By virtue of the topological character of the gas flow, the transport path is able to bypass external strong perturbations automatically. We further demonstrate a topological transfer process of the microdroplet between two hydrodynamic tweezers. Our method provides an integrated toolbox to manipulate a microscale object, with an intrinsic mechanism that protects the target object from external disturbances.

Conventional axion haloscope detectors require high-Q cavities with tunable TM modes, the resonant electric fields of which occupy as much of the full volume of the cavity as possible. An analytical study of the effects of longitudinal symmetry breaking within microwave cavities is conducted to understand the mode structure. The study reveals that longitudinal symmetry breaking of the cavities is the mechanism for avoiding mode crossings in cylindrical microwave cavities. The results show the size of the gaps in the search frequency spectrum due to an avoided mode crossing is roughly proportional to the magnitude of the selective size of gaps between tuning mechanisms and cavity endcaps, or other deviations from perfect longitudinal uniformity of the cavity. The form factors of the modes in avoided mode crossings are equal when the frequencies of the modes are at the point of closest approach.

In this work, we investigate theoretically and demonstrate experimentally the existence of valley Hall edge states in the in-plane dynamics of honeycomb lattices with bivalued strut thickness. We exploit these states to achieve nontrivial waveguiding of optical modes that is immune to backscattering from sharp corners. We also present how different types of interfaces can be combined into multibranch junctions to form complex waveguide paths and realize a variety of structural logic designs with unconventional wave-transport capabilities. We illustrate this potential with two applications. The first is a direction-selective energy-splitting waveguide tree featuring a pronounced asymmetric wave-transport behavior. The second is an internal waveguide loop along which the energy can be temporarily trapped and periodically released, effectively working as a signal delayer. The modal complexity of in-plane elasticity has important consequences for the regime of manifestation of the edge states, as the availability of viable total band gaps is shifted to higher frequencies compared to the out-of-plane counterpart problem. It also poses additional experimental challenges, associated with proper acquisition and deciphering of the in-plane modes, the solution of which requires a systematic use of in-plane laser vibrometry.

A continuous guided atomic beam of ${}^{88}\mathrm{Sr}$ with a phase-space density exceeding ${10}^{-4}$ in the moving frame and a flux of $3\times {10}^7\mathrm{ at. }{\mathrm{s}}^{-1}$ is demonstrated. This phase-space density is around 3 orders of magnitude higher than previously reported for steady-state atomic beams. We detail the architecture necessary to produce this ultracold-atom source and characterize its output after propagation for approximately $4\mathrm{cm}$. With radial temperatures of less than $1\mu \mathrm{K}$ and a velocity of $8.4\mathrm{cm}{\mathrm{s}}^{-1}$, this source is ideal for a range of applications. For example, it could be used to replenish the gain medium of an active optical superradiant clock or be used to overcome the Dick effect, which can limit the performance of pulsed-mode atom interferometers, atomic clocks, and ultracold-atom-based sensors in general. Finally, this result represents a significant step toward the development of a steady-state atom laser.

Coherent superhigh-frequency (SHF) vibrations provide an excellent tool for the modulation and control of excitations in semiconductors. Here, we investigate the piezoelectric generation and propagation of longitudinal bulk acoustic waves (LBAWs) with frequencies up to 20 GHz in $\mathrm{Ga}\mathrm{As}$ crystals using bulk acoustic-wave resonators (BAWRs) based on piezoelectric thin $\mathrm{Zn}\mathrm{O}$ films. We show that the electroacoustic conversion efficiency of the BAWRs depends sensitively on the sputtering conditions of the $\mathrm{Zn}\mathrm{O}$ films. The BAWRs are then used for the study of the propagation properties of the LBAWs in $\mathrm{Ga}\mathrm{As}$ in the frequency and temperature ranges from 1 to 20 GHz and 10 and 300 K, respectively, which have so far not been experimentally accessed. We find that the acoustic absorption of $\mathrm{Ga}\mathrm{As}$ in the temperature range from 80 K to 300 K is dominated by scattering with thermal phonons. In contrast, at lower temperatures, the acoustic absorption saturates at a frequency-dependent value. Experiments carried out with different propagation lengths indicate that the saturation is associated with losses during reflections at the sample boundaries. We also demonstrate devices with a high quality factor fabricated on top of acoustic Bragg reflectors. The results presented here prove the feasibility of high-quality acoustic resonators embedding $\mathrm{Ga}\mathrm{As}$-based nanostructures, thus opening the way for the modulation and control of their properties by electrically excited SHF LBAWs.

A superconducting self-shielding three-solenoid system with an adjustable shielding factor is developed, implemented, and characterized using a single antiproton in a Penning trap. With the tuned system, we suppress external magnetic field disturbances by up to a factor of 225 ± 15, allowing antiproton-to-proton charge-to-mass ratio comparisons with fourfold reduced frequency fluctuations and antiproton magnetic moment determinations with tenfold reduced uncertainty.

Routing and guiding acoustic waves around sharp corners without backscattering losses is of great interest in the acoustics community. Sonic crystals are primarily utilized to design backscattering-immune waveguides. While conventional approaches use defects to guide waves, a considerably more sophisticated and robust approach was recently developed based on topological edge states. Here, we propose a radically different theoretical framework based on extremely anisotropic media for engineering backscattering-immune waveguides. We theoretically derive the exact condition for one-way wave propagation in zigzag paths. While the theoretical underpinning is universal and applicable to acoustic and electromagnetic waves, the experimental validation is conducted using spoof surface acoustic waves. The proposed metamaterial opens up possibilities for wave manipulation and leads to applications in on-chip devices and noise control.

The interplay between ferroelectricity and magnetism in multiferroic materials is of great scientific and technological interest, allowing magnetic control of ferroelectric properties and electric control of magnetic properties through the magnetoelectric coupling from interfacial strain, exchange bias, or charge-transfer process. We report the charge transfer at the $\mathrm{Co}/{\mathrm{Bi}\mathrm{Fe}\mathrm{O}}_3$ interface from which the interfacial exchange coupling is achieved with the formation of ${\mathrm{Fe}}^{2+}$. The x-ray linear dichroism and x-ray magnetic circular dichroism results reveal that the strain as well as the exchange coupling $J_{\mathrm{ex}}$ in ${\mathrm{Bi}\mathrm{Fe}\mathrm{O}}_3$ (BFO) with periodic 109° domains are stronger than that in BFO with 71° domains, resulting in the higher coercive field of $\mathrm{Co}/\mathrm{BFO}$ with 109° domain samples. The possible electric field control of the charge-transfer process at the $\mathrm{Co}/\mathrm{BFO}$ interface enables an alternative class of electrically controllable magnetization, exchange bias, and giant magnetoresistive response of spintronic devices.

Understanding and controlling chirality are important because of its ubiquity in nature. In recent years, we have witnessed the rapid development of chiral metamaterials with exceptional light-manipulating capabilities. Here, we present a design for photonic heterostructures in chiral photonics, demonstrating that photonic heterostructures stacked from achiral metasurfaces can create distinctive chiroptical functionalities. Analyses based on the symmetry group and microscopic dipolar interactions at two-dimensional boundaries reveal the implicit mechanism of the interlayer coupling in photonic heterostructures. By flip stacking, the photonic heterostructure gives rise to an asymmetric chiral phase from achiral composites, and hence, provides the full spin-flipped scattering of incident photons. Incident electromagnetic waves with arbitrary polarization orientations can be efficiently separated into two orthogonal circularly polarized ones with orthogonal trajectories, leading to an ideal circular beam splitter. This effect is experimentally demonstrated at microwave frequencies via the measurement of a scattering matrix. Due to its generality and scalability, we expect the methodology of photonic heterostructure might open up an alternative pathway for exploring intriguing and advanced metamaterials over a broad wavelength range.