Silicon ($\mathrm{Si}$) crystals are important materials for the modern microelectronics industry. While $\mathrm{Si}$ crystals are not piezoelectric materials due to their centrosymmetric structure, it is found in this work that $\mathrm{Si}$ crystals exhibit a large piezoelectric-like response under bending deformation. We show that this response is not intrinsic, but rather originates from the surfaces of crystals that are slightly oxidized upon their exposure to air. The weak piezoelectric response of the surface is amplified by high conductivity of the bulk and bending deformation of $\mathrm{Si}$ plates. In addition, the piezoelectric-like response is strongly dependent on the conduction type and the resistivity of the crystals and on the metal electrode used for piezoelectric measurements. A multilayer model is proposed to explain the piezoelectric-like response of the $\mathrm{Si}$ crystals. This finding may be exploited to design piezoelectric devices using $\mathrm{Si}$ only, without the integration of additional piezoelectric materials, and is important for understanding the $\mathrm{Si}$ crystal surfaces.

Applying strain to a Weyl semimetal (WSM) breaks its lattice symmetry and results in a valley-dependent strain gauge potential. Here, we investigate the application of the strain potential to modulate the valley and charge transport of a WSM-based $n$-$p$-$n$ junction system. The strain potential, in combination with insulating barriers, enables modulation of the current and the realization of valley-asymmetric transmission with a high on:off ratio. By considering the geometric optics of electron waves and the transverse displacement of Fermi surfaces due to the strain gauge, we derive the critical strains for switching the current, as well as for the onset of complete angular separation of the two valley currents. The analytical results are verified by numerical calculations of the tunneling transmission and conductance. We also derive the expression for the subthreshold swing of the device, which can achieve values below the thermionic limit by tuning the strain and barrier height.

High-sensitivity imaging of ultracold atoms is often challenging when interference patterns are imprinted on the imaging light. Such image noises result in low signal-to-noise ratio and limit the capability of extracting subtle physical quantities. Here we demonstrate an advanced fringe removal algorithm for absorption imaging of ultracold atoms, which efficiently suppresses unwanted fringe patterns using a small number of sample images without taking additional reference images. The protocol is based on an image decomposition and projection method with an extended image basis. We apply this scheme to raw absorption images of degenerate Fermi gases for the measurement of atomic density fluctuations and temperatures. A quantitative analysis shows that image noises can be efficiently removed with only tens of reference images, which manifests the efficiency of our protocol. Our algorithm would be of particular interest for quantum emulation experiments in which several physical parameters need to be scanned within a limited time duration.

Spin pumping in a ferromagnet-nonferromagnet heterostructure is directly imaged with spatial resolution as well as element selectivity. The time-resolved detection in scanning transmission x-ray microscopy allows us to directly probe the spatial extent of the ac spin polarization in Co-doped ZnO, which is generated by spin pumping from an adjacent permalloy microstrip. Comparing the relative phases of the dynamic magnetization component of the two constituents is possible and found to be close to antiphase. The correlation between the distribution of the magnetic excitation in the permalloy and the Co-doped ZnO reveals that laterally there is no one-to-one correlation. The observed distribution is rather complex, but integrating over larger areas demonstrates that the spin polarization in the nonferromagnet extends laterally beyond the region of the ferromagnetic microstrip. Therefore, the observations are better explained by a local spin pumping efficiency and a lateral propagation of the ac spin polarization in the nonferromagnet over the range of a few micrometers.

Janus particles are special types of nanoparticles or microparticles possessing at least two surfaces with distinct physical or chemical properties. The most-studied Janus particles are metal-dielectric particles, in which half the surface of the dielectric particles is coated with a very thin layer of a metal. The external electric field induces a dipole moment, and consequently the particles exhibit self-assembled dynamic structures in concentrated aqueous suspensions. Here we study metal-dielectric Janus particles in a nematic liquid crystal under an ac electric field and demonstrate a method for measuring the effective induced dipole moments of the particles through competition between elastic and electrostatic (Coulomb) forces of the two particles. The calculated polarizability of the particles based on a simple model agrees well with the effective polarizability measured in the experiments. Our findings have important bearing on functional materials based on metal-dielectric Janus particles dispersed in an anisotropic medium.

Non-Abelian geometric phases acquired in cyclic quantum evolution can be utilized as natural resources for constructing robust holonomic gates for quantum-information processing. Recently, an extensible holonomic quantum computation (HQC) was proposed and demonstrated in a recent superconducting experiment [Yan et al., Phys. Rev. Lett. 122, 080501 (2019)]. However, for the weakly anharmonic system, this HQC was given of low gate fidelity due to leakage to states outside of the computational subspace. Here, we propose a scheme to construct nonadiabatic holonomic gates via a dynamical invariant using resonant interaction of three-level superconducting quantum systems. Furthermore, the proposed scheme can be compatible with optimal control technology for maximizing the gate fidelity against leakage error. For benchmarking, we provide a thorough analysis on the performance of our scheme under experimental conditions, which shows that the gate error can be reduced by as much as 91.7% compared with the conventional HQC. Moreover, the leakage rates can be reduced to the ${10}^{-3}$ level by numerically choosing a suitable control parameter. Therefore, our scheme provides a promising way towards fault-tolerant quantum computation in a weakly anharmonic solid-state system.

Metasurfaces composed of anisotropic nanostructures possess the ability to manipulate the polarization and intensity of light simultaneously, which paves an emerging way to construct multiplexing metadevices capable of displaying gray images with high resolution and reliability. However, previous multiplexing metadevices for gray-image displaying are mostly based on nanostructures with varied geometries and/or supercell design strategies, which complicate both the metasurface design and manufacturing or decrease the information resolution. Here, benefiting from the orientation degeneracy implied in Malus’s law, we show that gray-image multiplexing can be implemented simply by a single-sized nanostructure-design approach. Specifically, by configuring the four-step orientations of silver nanobricks, two independent information channels can be established to store different gray images into a single metasurface. We experimentally demonstrate the Malus-assisted metasurface, which functions as a dual-channel gray-image display device to record two independent binary gray images without crosstalk. With the single-sized design strategy, each nanobrick can record information of two channels, and the proposed metasurface simultaneously owns an ultrahigh information density of 84 667 dots per inch for both of the two gray images. With advantages such as simplicity in nanostructure design, ultracompactness, high resolution, broadband working windows, and high security, the proposed metasurfaces empower advanced researches and applications in anticounterfeiting, information hiding, information multiplexing, ultracompact image displaying, high-density optical storage, integrated and multiplexed nanooptoelectronics, etc.

Recent research on nano-oscillators has shown the possibility of using a coupled-oscillator network as a core-computing primitive for non-Boolean computation. The spin-torque oscillator (STO) is an attractive candidate because it is CMOS compatible, highly integrable, scalable, and frequency and phase tunable. Based on these promising features, we propose an alternative coupled-oscillator-based architecture for hybrid spintronic and CMOS hardware that computes a multidimensional norm. The hybrid system, composed of an array of four injection-locked STOs and a CMOS detector, is experimentally demonstrated. The measured performance is then used as the input to simulations that demonstrate the hybrid system as both a distance metric and a convolution computational primitive for image-processing applications. Energy and scaling analysis shows that the STO-based coupled-oscillatory system has a higher efficiency than the CMOS-based system with an order of magnitude faster computation speed in distance computation for high-dimensional input vectors.

Realizing efficient spin-charge conversion is an important issue in spin-based electronics, especially for the development of low-power-consumption magnetization switching. A spin-charge conversion is generally induced in a nonmagnetic (NM) layer by the inverse spin Hall effect in the bulk or by the inverse Rashba-Edelstein effect at surfaces or interfaces. In the bulk, the spin-charge conversion efficiency is called the spin Hall angle, ${\theta }_{\mathrm{SHE}}$, and it is limited by the spin-orbit interaction of the bulk layer. Thus, artificially enhancing ${\theta }_{\mathrm{SHE}}$ to greater than its intrinsic value is difficult. Here, using spin-pumping measurements on a well-controlled interface between a ferromagnetic (FM) ${\mathrm{Co}}_2{\mathrm{Fe}\mathrm{Al}}_{0.5}{\mathrm{Si}}_{0.5}$ (CFAS) layer and a NM n-type $\mathrm{Ge}$ layer, we demonstrate that ${\theta }_{\mathrm{SHE}}$ can be strongly enhanced by annealing the sample and the resulting interdiffusion of atoms within only about 3.7 nm around the CFAS/n-$\mathrm{Ge}$ interface. Because of this annealing process, ${\theta }_{\mathrm{SHE}}$ is increased from 0.0058–0.0079 to 0.015–0.019, which is much larger than the intrinsic value of ${\theta }_{\mathrm{SHE}}$ reported for $\mathrm{Ge}$ (0.00096–0.002) and is comparable to ${\theta }_{\mathrm{SHE}}$ values reported for $\mathrm{Pt}$. This enhancement is attributed to strong scattering of the spin current in the intermixed layer formed at the interface by annealing. Our results indicate that ${\theta }_{\mathrm{SHE}}$ is strongly influenced by the atomic structure of the FM/NM interface, which suggests an efficient method to control spin-charge conversion by precise control of the FM/NM interface.

Exchange-bias effect is a widely investigated topic for spintronic applications in magnetic data storage read heads and spin-valve sensors. This effect is observed in bilayers of magnetic materials comprising of a soft ferromagnet (FM) and an antiferromagnet (AFM). In the last few years, unexpected observations of such an effect in ferromagnet-molecule heterostructures has raised curiosity in probing their underlying mechanism for potential technological applications. Here, we report our interface study between thin films of $\mathrm{Fe}$ and monolayer metal-phthalocyanine (MPc) molecules providing evidence of a robust exchange bias in zero-field cooled devices that is stable even after multiple training cycles. We ascribe the underlying mechanism to a combination of surface magnetic hardening and weakening of interlayer magnetic exchange that decouples the surface MPc-$\mathrm{Fe}$ hard magnetic layer from the soft switchable $\mathrm{Fe}$ layer underneath. We refer to this combined response to a molecular crane-pulley effect arising from the strong $\pi -d$ hybridization induced changes in the magnetization properties of surface $\mathrm{Fe}$ relative to the underlying film. Furthermore, analysis of our in-plane angle-dependent anisotropy magnetoresistance measurements reveal a surprisingly large biaxial anisotropy of the hard-surface layer with switching field exceeding 7 T. These studies provide us the opportunity to engineer the form of magnetic anisotropy at these spin interfaces.

Because of their record-low intrinsic magnetic damping properties, single-crystal yttrium-iron-garnet (YIG) films serve as an excellent model medium for studying magnon-induced spintronic phenomena such as spin pumping and the spin-orbit torque effect. For this purpose, YIG films are covered with sub-skin-depth layers of nonmagnetic heavy metals with strong spin-orbit coupling. In the present work, we show experimentally and theoretically that ohmic losses of spin-wave-induced microwave eddy currents in the heavy-metal layer deliver a strong contribution to spin-wave damping in these hybrid structures. We demonstrate that this adverse effect can be controlled and largely eliminated by placing a highly conducting metal plate near to the surface of the YIG/$\mathrm{Pt}$ structures. These findings are of value for a proper interpretation of experiments on the magnon spintronic effects and for the design of future magnon spintronic devices.

Monolithically integrated $\mathrm{Ga}\mathrm{As}$ $p$-$i$-$n$ diodes are demonstrated on 300-mm $\mathrm{Si}$ $(001)$ substrates using a nanoridge-engineering approach. Deep-level transient spectroscopy (DLTS) is used to perform defect analysis for nanoridge and planar $\mathrm{Ga}\mathrm{As}$ diodes. The point defect, EL2 with $N_T\simeq 3\times {10}^{14}{\mathrm{cm}}^{-3}$, is observed for nanoridge $p$-$i$-$n$ diodes. A methodology is developed to extract the surface-state density ($N_{\mathrm{SS}}$) directly from the DLTS spectrum. $\mathrm{Ga}\mathrm{As}$ nanoridge diodes show $N_{\mathrm{SS}}\simeq 2\times {10}^{13}{\mathrm{cm}}^{-2}$ compared to planar diode approximately $6.5\times {10}^{12}{\mathrm{cm}}^{-2}$. A clear correlation is observed between dark current and defect density. An investigation on the impact of an in situ and ex situ passivation layers on the leakage current reduction is performed for $\mathrm{Ga}\mathrm{As}$ $p$-$i$-$n$ diodes.

We introduce an open quantum-battery protocol using dark states to achieve both superextensive capacity and power density, with noninteracting spins coupled to a reservoir. Further, our power density actually scales with the number of spins $N$ in the battery. We show that the enhanced capacity and power are correlated with entanglement. While connected to the charger, the charged state of the battery is a steady state, stabilized through quantum interference in the open system.

Recently, the field of topological acoustics has rapidly developed, where the topological phase transition in phononic crystals is unveiled to occur through band inversion via the Dirac degeneracy in momentum space. Here, we focus on a class of low-symmetry acoustic valleylike topological insulators (VTIs), with honeycomb-lattice scatterers being chiral with $C_1$ symmetry. The valley Hall transition can be generated by simply rotating the chiral scatterers, where the topological phase transition is triggered by reopening the Dirac degeneracies beyond high-symmetry points and boundaries in the Brillouin zones. We numerically and experimentally demonstrate robust transport against different defects in chiral VTIs. For applications, we construct a topological beam splitter to verify the valley-selective one-way transport in chiral VTIs. Based on valleylike edge states, we design a topological acoustic switch with one input and two outputs, where the switching functionality at outputs with the on-off, off-off, and off-on states is confirmed by simulations and experimental tests. We also provide a more complex four-port acoustic switch based on chiral VTIs. The chiral VTI-based splitter and switches may have potential applications in constructing intelligent acoustic devices.

We propose a perfect photonic router based on a specially designed chiral bimetasurface membrane for spin-polarized point light sources. Due to the mirror symmetry breaking in the chiral metamembrane, the radiation power flux of the clockwise and counterclockwise spinning dipoles to the opposite sides of the slab becomes different. We show that spinning dipoles in the specially designed chiral $D_4$-symmetrical bimetasurface membrane can emit light either upward or downward depending on their rotation direction. We attribute this phenomenon to the Fano-resonance effect, which is a result of the guided modes coupling with the far field. We show the advantage of $D_4$-symmetrical structures for the achievement of 100% routing efficiency. This phenomenon can find applications in spintronics for spin-selective interchip coupling or as a measurement tool of spin polarization in memory cells.

By analogy with electromagnetic networks that connect multiple input-output ports, metasurfaces can be considered as multiport devices capable of providing different functionalities for waves of different polarizations illuminating the surface from different directions. The main challenge in the design of such multichannel metasurfaces is to realize independent and full control of the electromagnetic response for each channel incidence, ensuring the fulfilment of the boundary condition at the metasurface. In this work, we demonstrate that by properly engineering the evanescent fields excited at each port (that is, for all possible illumination directions), it is possible to independently control the reflection or transmission for all different illuminations. Using the mode-matching method, we analyze the scattering properties of generic space-modulated impedance metasurfaces. This method, combined with mathematical optimization, allows us to find a surface-impedance profile that simultaneously ensures the desired electromagnetic responses at each port. We validate the technique via the design of phase-controlled multichannel retroreflectors and multichannel perfect absorbers. In addition, we demonstrate that the method is rather powerful in the design of other functional metasurfaces, such as multifunctional reflectors.

Characterization of microstructures in living tissues is one of the keys to diagnosing early stages of pathology and understanding disease mechanisms. However, the extraction of reliable information on biomarkers based on microstructure details is still a challenge, as the size of features that can be resolved with noninvasive magnetic resonance imaging (MRI) is orders of magnitude larger than the relevant structures. Here we derive from quantum information theory the ultimate precision limits for obtaining such details by MRI probing of water-molecule diffusion. We show that currently available MRI pulse sequences can be optimized to attain the ultimate precision limits by choosing control parameters that are uniquely determined by the expected size, the diffusion coefficient, and the spin relaxation time $T_2$. By attaining the ultimate precision limit per measurement, the number of measurements and the total acquisition time may be drastically reduced compared to the present state of the art. These results are expected to open alternative avenues towards unraveling diagnostic information by quantitative MRI.

In this work, magnetization dynamics is studied in superconductor-ferromagnet-superconductor three-layered films in a wide frequency, field, and temperature ranges using the broad-band ferromagnetic resonance measurement technique. It is shown that in the presence of both superconducting layers and of superconducting proximity at both superconductor-ferromagnet interfaces a massive shift of the ferromagnetic resonance to higher frequencies emerges. The phenomenon is robust and essentially long-range: it has been observed for a set of samples with the thickness of ferromagnetic layer in the range from tens up to hundreds of nanometers. The resonance frequency shift is characterized by proximity-induced magnetic anisotropies: by the positive in-plane uniaxial anisotropy and by the drop of magnetization. The shift and the corresponding uniaxial anisotropy grow with the thickness of the ferromagnetic layer. For instance, the anisotropy reaches 0.27 T in experiment for a sample with a 350-nm-thick ferromagnetic layer, and about 0.4 T in predictions, which makes it a ferromagnetic film structure with the highest anisotropy and the highest natural resonance frequency ever reported. Various scenarios for the superconductivity-induced magnetic anisotropy are discussed. As a result, the origin of the phenomenon remains unclear. Application of the proximity-induced anisotropies in superconducting magnonics is proposed as a way for manipulations with a spin-wave spectrum.