Two-dimensional (2D) van der Waals (vdW) magnetic semiconductors have attracted wide interest for their promising application in next-generation spintronic devices. We investigate the scaling behavior of the tunnel magnetoresistance (TMR) of the $\mathrm{Ag}/$n-layer ${\mathrm{Cr}\mathrm{I}}_3/\mathrm{Ag}$ and graphite/n-layer ${\mathrm{Cr}\mathrm{I}}_3$/graphite magnetic tunnel junctions (MTJs) by using ab initio quantum-transport simulations. The calculated monotonic increasing TMR of the graphite/n-layer ${\mathrm{Cr}\mathrm{I}}_3$/graphite MTJ with n = 2–4 at zero bias agrees with the experimental value. The TMR of the $\mathrm{Ag}/$n-layer ${\mathrm{Cr}\mathrm{I}}_3/\mathrm{Ag}$ MTJ generally increases with the tunnel-barrier layer number, n, that is, from 200% (2-layer ${\mathrm{Cr}\mathrm{I}}_3$) to a record ${10}^9$% value (12-layer ${\mathrm{Cr}\mathrm{I}}_3$) at zero bias but has an odd-even oscillation when n < 7. When we apply a bias voltage to the $\mathrm{Ag}/$2-layer ${\mathrm{Cr}\mathrm{I}}_3/\mathrm{Ag}$ MTJ, the TMR first decreases slightly and then increases, followed by a monotonic decrease. The noncollinear magnetization direction of the ${\mathrm{Cr}\mathrm{I}}_3$ layers also changes the TMR value of the graphite/n-layer ${\mathrm{Cr}\mathrm{I}}_3$/graphite MTJ relative to the collinear case, a result in agreement with experiments.

Dual-band equipment has unique advantages as regards ensuring the stability of wireless communication and improving efficiency. With the development of topological photonics and phononics, electromagnetic and mechanical wave transmission with simultaneous advantages, e.g., antireflection, broadband, and nondispersion characteristics, has been simultaneously realized. This outcome has greatly improved elastic wave manipulation performance in solids, which are important media for wireless communication. Here, using a plate phononic crystal (PnC), a dual-mode elastic topological insulator is theoretically designed and experimentally realized, and the quantum spin Hall effect is observed under a dual band. Using discrete Kekulé modulation to construct the PnC multidomain junction, dual-mode and dual-band Dirac vortexes, i.e., a type of topological corner state, are obtained in a single PnC. These transmitted and localized topological states have the same excellent properties as their antecedents, which are obtained with single-band materials. The implementation mechanisms are diverse and applicable to multiple modes and broad frequencies, offering antijamming, low-loss, high-efficiency, and high-capacity signal processing components. The findings of this study will aid development of solid-state topology PnCs, as well as future topological-phononic integrated circuits with high performance and multifunctionality.

The generation of terahertz (THz) spin current is highly desired for enhancing the speed and efficiency of information manipulation by ultrafast spintronics. We develop an analytical model to investigate the coherent and pure spin-current pulses generated by spin pumping in a canted insulating antiferromagnet (AFM) system with Dzyaloshinskii-Moriya interaction (DMI). As expected, the spin pumping signal is significant at resonance. However, we also predict efficient THz spin-current transient with a magnitude comparable with that of its resonant counterparts in the much higher off-resonance THz frequency regime. Its ultrafast temporal change compensates for the suppression of the dynamic magnetization amplitudes at off-resonance. In addition, a stronger DMI field enhances the amplitude of the spin-current transient. Our results represent an efficient approach to generate coherent THz spin-current pulses based on canted AFM heterostructures without requiring a static magnetic field.

Magnetodynamics of magnetic nanolayers is central to the emerging research field of magnonics. Here, we demonstrate an effective tuning of the dynamic properties of permalloy (Py, response layer) thin films, by capping with $\mathrm{Cu}/\mathrm{Fe}$-$\mathrm{Co}$-$\mathrm{Tb}$ (spin-sink layer) layers with adjustable interlayer coupling and magnetic configurations. The strategy enables a remarkably enhanced Gilbert damping of the response layer, by about 10 times; this enhancement is higher than most of the results reported so far. More importantly, dynamic damping is programmable between the two opposite configurations (parallel vs antiparallel) in Py and $\mathrm{Fe}$-$\mathrm{Co}$-$\mathrm{Tb}$ and remains intact even in the form of nano- and microdevices. The interlayer coupling between Py and $\mathrm{Fe}$-$\mathrm{Co}$-$\mathrm{Tb}$ is systematically studied by changing the thickness of the $\mathrm{Cu}$ spacer. It is demonstrated that the dynamic interlayer coupling between ferromagnetic layers plays the key role in increased damping. Our work provides a feasible route towards reconfigurable magnonic devices, especially for logic and high-speed computing.

Charge-spin interconversion via spin-orbit coupling (SOC) provides an effective way to generate spin currents for electrical control of nanomagnets for data storage and processing. Except for the widely studied giant spin Hall effect (SHE) and Rashba-Edelstein effect (REE) that can generate a spin current with in-plane transverse spin polarization, theoretically proposed spin swapping or spin-orbit precession effect (SOPE) also can substantially generate spin currents with different spin polarizations in magnetic multilayers. Here, we experimentally demonstrate that except the SHE-induced large effective SOT ${\theta }_y^{\mathrm{eff}}\sim 0.10-0.14$ comparable to the reported giant SHE β-phase $\mathrm{Ta}$, SOPE generated two considerable unconventional $\mathrm{SOTs}$ with in-plane longitudinal ${\theta }_x^{\mathrm{eff}}$ and out-of-plane spin polarizations ${\theta }_z^{\mathrm{eff}}$, which are also verified in a $\mathrm{Co}\text{−}\mathrm{Tb}/\mathrm{Cu}/\mathrm{Py}$ trilayer structure. The former ${\theta }_x^{\mathrm{eff}}$ changes its sign with the unit magnetization reversal of the perpendicularly magnetized $\mathrm{Co}\text{−}\mathrm{Tb}$ layer, while the latter ${\theta }_z^{\mathrm{eff}}$ does not change its sign, consistent with the theoretical model of the SOPE mechanism. Our results pave an alternative way to design current-induced high-efficient SOT-based devices using abundant ferrimagnetic alloys.

Quantum two-level systems (TLSs) are present in the materials of qubits and are considered defects because they limit qubit coherence. For superconducting qubits, the quintessential Josephson junction barrier is made of amorphous alumina, which hosts TLSs. However, TLSs are not generally understood, either structurally or in atomic composition. In this study, we greatly extend the quantitative data available on TLSs by reporting on the physical dipole moment in two alumina types: polycrystalline $\gamma$-${\mathrm{Al}}_2{\mathrm{O}}_3$ and amorphous a-$\mathrm{Al}{\mathrm{O}}_x$. To obtain the dipole moments $p_z$, rather than the less-structural coupling parameter $g$, we tune individual TLSs with a known external electric field in a cavity quantum electrodynamic system. We find a clear difference in the dipole moment distribution from the film types, indicating a difference in TLS structures. A large sample of approximately 400 individual TLSs are analyzed from the polycrystalline film type. Their dipoles along the growth direction $p_z$ have a mean value of $2.6\pm 0.3$ debye (D) ($0.54\pm 0.06e$ Å) and standard deviation $\sigma =1.6\pm 0.2\mathrm{D}$ ($0.33\pm 0.03e$ Å). The material distribution fits well to a single Gaussian function. Approximately 200 individual TLSs are analyzed from amorphous films. Both the mean $p_z=4.6\pm 0.5\mathrm{D}$ ($0.96\pm 0.1e$ Å) and $\sigma =2.5\pm 0.3\mathrm{D}$ ($0.52\pm 0.05e$ Å) are larger. Amorphous alumina also has very large $p_z$, greater than $8.6\mathrm{D}$ ($1.8e$ Å), in contrast to polycrystalline which has none of this moment. These large moments agree only with oxygen-based TLS models. Based on data and the candidate models (delocalized O and hydrogen-based TLSs), we find polycrystalline alumina has smaller ratio of O-based to H-based TLS than amorphous alumina.

Full-Heusler thermoelectric materials have intrinsically low lattice thermal conductivity. Our first-principles calculations show that ${\mathrm{Ba}}_2\mathrm{Ag}\mathrm{Sb}$ is a semiconductor with an indirect band gap of 0.49 eV. The electronic band degeneracy and pockets near the Fermi level facilitate electron transport. The short phonon relaxation time, small group velocity (1.89 km ${\mathrm{s}}^{-1}$), and large phonon scattering space reflect the intense phonon-phonon scattering. The large Grüneisen parameter (1.44) accounts for the strong phonon anharmonicity, thus the low lattice thermal conductivity of $0.5\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ at 800 K. The isotropic figure of merit with a maximum value of 4.7 at 750 K is comparable to that of reported materials. The distribution of phonon momentum uncovers the important role of $\mathrm{Ag}$ in resisting thermal transport. The analysis of symmetry-based phonon-phonon scattering routes reveals the significance of symmetry on phonon scattering. The crystal structure of ${\mathrm{Ba}}_2\mathrm{Ag}\mathrm{Sb}$ can be used to regulate chemical elements to build high-performance thermoelectric materials. Our calculations provide an effective way to design thermoelectric materials, stimulating the study of full-Heusler materials.

We observe a catalytic mechanism during the growth of III-$\mathrm{O}$ and IV-$\mathrm{O}$ materials by suboxide molecular-beam epitaxy ($S$-MBE). By supplying the molecular catalysts ${\mathrm{In}}_2\mathrm{O}$ and SnO  we increase the growth rates of ${\mathrm{Ga}}_2{\mathrm{O}}_3$ and ${\mathrm{In}}_2{\mathrm{O}}_3$. This catalytic action is explained by a metastable adlayer $A$, which increases the reaction probability of the reactants ${\mathrm{Ga}}_2\mathrm{O}$ and ${\mathrm{In}}_2\mathrm{O}$ with active atomic oxygen, leading to an increase of the growth rates of ${\mathrm{Ga}}_2{\mathrm{O}}_3$ and ${\mathrm{In}}_2{\mathrm{O}}_3$. We derive a model for the growth of binary III-$\mathrm{O}$ and IV-$\mathrm{O}$ materials by $S$-MBE and apply these findings to a generalized catalytic description for metal-oxide-catalyzed epitaxy (MOCATAXY), applicable to elemental and molecular catalysts. We introduce a mathematical description of $S$-MBE and MOCATAXY, providing a computational framework to set growth parameters in previously inaccessible kinetic and thermodynamic growth regimes when using the aforementioned catalysis. Our results indicate that MOCATAXY takes place with a suboxide catalyst rather than with an elemental catalyst. As a result of the growth regimes achieved, we demonstrate a ${\mathrm{Ga}}_2{\mathrm{O}}_3$/${\mathrm{Al}}_2{\mathrm{O}}_3$ heterostructure with an unrivaled crystalline quality, paving the way for the preparation of oxide device structures with unprecedented perfection.

Quantum control techniques applied at macroscopic scales provide us with opportunities in fundamental physics and practical applications. Among them, measurement-based feedback allows efficient control of optomechanical systems and quantum-enhanced sensing. In this paper, we propose a near-resonant narrow-band force sensor with extremely low optically added noise in a membrane in the middle optomechanical system subject to a feedback-controlled in-loop light. The membrane’s intrinsic motion consisting of zero-point motion and thermal motion is affected by the added noise of measurement due to the backaction noise and imprecision noise. We show that, in the optimal low-noise regime, the system is analogous to an optomechanical system containing a near quantum-limited optical parametric amplifier coupled to an engineered reservoir interacting with the cavity. Therefore, the feedback loop enhances the mechanical response of the system to the input while keeping the optically added noise of measurement below the standard quantum limit. Moreover, the system based on feedback offers a much larger amplification bandwidth than the same system with no feedback. Without the need to hybridize it with other quantum systems or introduce nonlinearities, our force sensor may have broad applications ranging from biology and medicine to gravitational wave detection and tests of fundamental physics.

Due to their limited number of units but outstanding ability to control rather complex wave-propagation phenomena, acoustic coding metasurfaces (ACMs) as two-dimensional metamaterials show a stronger competitiveness in metamaterial applications. However, hindered by their narrow-band modulation capability, the previously reported ACMs do not exhibit a broadband applicability. To address the frequency-based coding capability, in this paper we report broadband acoustic coding metasurfaces (BACMs) whose units are designed by the bottom-up topology optimization method. Subsequently, by utilizing our optimization strategy, we design the 1-bit coding units “0” and “1” with out-of-phase responses and the 2-bit coding units “00”, “01”, “10,” and “11” with four different phase shifts of 0°, 90°, 180°, and 270°. The topological features show constant phase differences, and in the following analysis, we attempt to explain this phenomenon by the related mechanisms of the internal resonances and the bianisotropy effect. The optimized BACMs are beneficial to improve the functions of a fixed coding metasurface in the frequency range. This idea provides an inspiration for fabricating fast-sector-scanning sound antenna. In combination with the convolution method, we also present the design strategy for the broadband fast-scanning multiple-beam antenna. The design of the acoustic antenna is a fixed coding sequence, and its scanning and echolocation mode does not depend on the reconfiguration of the coding units. Furthermore, we also demonstrate a pair of opposite functions, namely the broadband sound focusing and diffusion-scattering characteristics, which have potential applications in ultrasonic therapy, low-scattering target design and noise control, and so on.

As an alternative degree of freedom for wireless communications, orbital angular momentum (OAM) multiplexing and demultiplexing can be applied to achieve higher communication capacity. Metasurface has advanced ability to manipulate electromagnetic (EM) waves, and has gradually become an enabling EM technology for future wireless communications. It is meaningful and useful to combine the advantages of OAM and metasurfaces. Here we propose a multi-OAM-mode vortex wave multiplexing and demultiplexing scheme based on shared-aperture reflective metasurface. The specifically designed reflective metasurface can realize the corresponding OAM-mode modulations and demodulations of different incident carrier waves in the corresponding data channels. By modulating multiple data channels on multiple OAM modes, the multiplication of the communication capacity could be achieved. A prototype operating at microwave frequencies is designed, simulated, and fabricated for proof-of-concept illustration. To validate the OAM multiplexing and demultiplexing scheme, we conduct dual-channel OAM-mode transmission experiments, in which two shared-aperture reflective metasurfaces are adopted as the transmitter and receiver, respectively. This work paves the way for the metasurface-based OAM communication applications in future wireless communication technologies.

We present an eigenvalue-based approach for studying the magnetization dynamics in magnetic nanostructures driven by spintronic excitations, such as spin-transfer torque and spin-orbit torque. The approach represents the system dynamics in terms of normal oscillation modes (eigenstates) with corresponding complex eigenfrequencies. The dynamics is driven by a small number of active eigenstates and often considering just a single eigenstate is sufficient. We develop a perturbation theory that provides semianalytical dynamic solutions by using eigenstates for the case in the absence of damping and spintronic excitations as a basis. The approach provides useful insights into dynamics in such systems and allows solving several difficulties in their modeling, such as extracting the switching current in magnetic random-access memories and understanding switching mechanisms. We show that the presented approach directly predicts the critical switching current, i.e., switching current for an infinite time. The approach also provides solutions for the switching dynamics allowing the switching current to be obtained for a finite switching time, provided that the system symmetry is broken, e.g., by tilting the polarizer, so that switching by a finite pulse is possible.

Nonadiabatic holonomic quantum computation (NHQC) has attracted significant attention due to its fast evolution and the geometric nature-induced resilience to local noises. However, its long operation time and complex physical implementation make it hard to surpass the dynamical scheme, and thus hindering its wide application. Here, we present to implement NHQC with the shortest path under some conditions, through the inverse Hamiltonian engineering technique, which posseses higher fidelity and stronger robustness than previous NHQC schemes. Meanwhile, the gate performance in our scheme can be further improved by using the proposed composite dynamical decoupling pulses, which can efficiently improve both the gate fidelity and robustness, making our scheme outperform the optimal dynamical scheme in a certain parameter range. Remarkably, our scheme can be readily implemented with Rydberg atoms, and a simplified implementation of the controlled-not gate in the Rydberg blockade regime can be achieved. Therefore, our scheme represents a promising progress towards future fault-tolerant quantum computation in atomic systems.

The clinical utility of microfluidic techniques is often hampered by an unsatisfying sample throughput. Here, the effect of inertial forces on acoustofluidic particle sorting at high sample throughputs is investigated experimentally and theoretically. Polystyrene particles are acoustically prefocused to obtain precise trajectories. At increased flow rates it is observed that the particle stream is displaced towards the channel center, and above specific flow settings the particles spill over into the center outlet. This effect, coined the spillover effect, illustrates the complex interplay of viscous and inertial forces inside the microchannel. The effect is due to increased bending of the separatrices at the inlet and outlets and not due to the wall-lift force. The impact of the spillover effect on the separation of two different-sized particles is subsequently studied. Efficient sorting is done for subcritical splitting ratios and flow rates, but for close to critical settings or beyond, there is a breakdown of the acoustofluidic separation.

In two-dimensional van der Waals (vdW) materials, the relative twist angle between adjacent layers not only controls their electronic properties but also determines their stacking energy. This effect makes it difficult to stabilize the vdW materials with twist angles. Here, we demonstrate that we can controllably stabilize the system with custom-designed twist angles, for example, magic angle, which is realized by tailoring the adhesive-energy landscape of graphene nanostructures on graphene by using a one-dimensional tilt grain boundary (GB). Our result demonstrates that the flat band of the custom-built nanoscale magic-angle-twisted bilayer graphene is still robust, even when its size is comparable to a single moiré spot. Moreover, in our experiments, the area ratio with different stacking orders separated by the tilt GB can be continuously tuned by using the scanning-tunneling-microscope tip, and we can repeatedly fold and unfold the graphene nanostructure along the one-dimensional GB, demonstrating the ability to manipulate the graphene nanostructure at the atomic scale.

We show a concept of optical frequency tweezers for tweezing light in the optical frequency domain with a high resolution, which is the frequency version of optical tweezers for the spatial manipulation of microscopic objects. We report a proof-of-principle experiment via frequency conversion inside a cavity only for the converted light. Owing to the atypical configuration, the experiment successfully achieves the tweezing operation in the frequency domain, which picks light at a target frequency from the frequency-multiplexed input light and converts it to a different frequency, without touching any other light sitting in different frequency positions and shaking the frequency by the pump light.