We investigate magnetization-reversal processes in half-metallic epitaxial films of ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{Mn}\mathrm{O}}_3$ on ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_3$ (110) substrates. At 150 K, major-loop magnetization reversal (MLMR) occurs beyond minor-loop switching fields, implying that MLMR is limited by domain nucleation. At 280 K, MLMR overlaps with minor-loop switching fields if there are deliberately introduced precipitates, implying that the precipitates limit MLMR by pinning domain walls. To confirm that the precipitates pin domain walls at 280 K, we use a two-dimensional analogue of the Gaunt pinning model to show that pinning-limited switching occurs at fields consistent with the observed precipitate density of 0.3–2.0 μm${}^{-2}$. Our work demonstrates that comparing major and minor loops at any temperature of interest represents a simple way to check whether spintronic electrode materials show nucleation-limited MLMR, as circumstantially required for single-domain switching in micron-scale elements of ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{Mn}\mathrm{O}}_3$ that represent spintronic electrodes [L. C. Phillips et al., Phys. Rev. Appl. 4, 064004 (2015)].

Strong Coulomb repulsion and spin-orbit coupling are known to give rise to exotic physical phenomena in transition metal oxides. Here, we report magnetic characteristics of a ${\mathrm{Sr}\mathrm{Mn}}_{0.3}{\mathrm{Ir}}_{0.7}{\mathrm{O}}_3$ perovskite thin film, having both 3d and 5d elements on the $B$ sites, with a strong perpendicular magnetic anisotropy (PMA), which is rare in perovskite oxide thin films. The ${\mathrm{Sr}\mathrm{Mn}}_{0.3}{\mathrm{Ir}}_{0.7}{\mathrm{O}}_3$ films have been epitaxially deposited on (001)-oriented ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_3$ single-crystal substrates by pulsed-laser deposition, exhibiting a para-to-ferromagnetic transition at about 110 K. The average valence of $\mathrm{Mn}$ and $\mathrm{Ir}$ cations are estimated as +3.61 and +4.17, respectively, by x-ray photoelectron spectroscopy. X-ray absorption spectroscopy reveals that $\mathrm{Mn}$ $e_g$ electrons occupy preferentially the $d_{3z^2-r^2}$ orbital, which produces the observed PMA in the framework of spin-orbital coupling. The ${\mathrm{Sr}\mathrm{Mn}}_{0.3}{\mathrm{Ir}}_{0.7}{\mathrm{O}}_3$ thin film shows a large effective anisotropy constant of about 1.2 × ${10}^6$ erg ${\mathrm{cm}}^{-3}$ at 10 K, which is found to decrease with decreasing tetragonality c/a of the film. First-principles calculations reveal that $\mathrm{Mn}$ and $\mathrm{Ir}$ cations provide opposite magnetizations in ${\mathrm{Sr}\mathrm{Mn}}_{0.3}{\mathrm{Ir}}_{0.7}{\mathrm{O}}_3$ and the $\mathrm{Mn}$ $e_g$ orbital polarization comes from both lattice distortion and oxygen octahedron rotation. The ${\mathrm{Sr}\mathrm{Mn}}_{0.3}{\mathrm{Ir}}_{0.7}{\mathrm{O}}_3$ thin film with strong PMA may have applications in future low-power-consumption oxide spintronic devices.

Physical parameters, such as decay rates and photoluminescence (PL) quantum efficiencies, associated with thermally activated delayed fluorescence (TADF) emitters play a critical role in determining the performance of organic light-emitting diodes (OLEDs). Herein, we investigate the impact of TADF decay rates and PL quantum efficiencies on external quantum efficiency (EQE) roll-off. Our analysis reveals that a high EQE with suppressed efficiency roll-off in TADF OLEDs can be achieved by shortening the delayed lifetime with an increasing delayed contribution or by shortening the prompt lifetime with increasing prompt contribution simultaneously. We further show that TADF compounds with long delayed and/or prompt lifetimes can give rise to multiple spin cycling and subsequently result in significant exciton quenching and efficiency roll-off in OLEDs. These results provide universal selection criteria for TADF emitters in OLEDs to concurrently achieve a high maximum EQE and low-efficiency roll-off.

We study experimentally the propagation of spin waves in waveguide structures consisting of two submicrometer-width yttrium iron garnet waveguides intersecting at a right angle. We show that, despite the significant spatial variations of the internal static magnet field and the in-plane anisotropy of the dispersion characteristics, the incident spin wave can efficiently pass through the microscopic cross-shaped structure and be transmitted into all its arms. This process depends strongly on the frequency of the wave and the orientation of the static magnetic field. By varying these parameters, one can achieve a controllable uniform or preferential transmission of the wave into different arms of the cross. Our results create the basis for the implementation of nanoscale magnonic networks to be used for the realization of complex non-Boolean data-processing schemes, including neuromorphic computing.

Full-space metasurfaces exhibit considerable capacities in the fields of electromagnetic wave-front tailoring due to their functional and spatial integration, and extensive applications in modern communication systems. However, almost all metasurfaces for wave-front tailoring are implemented by multilayer dielectric cascade structures, which not only present imperfections in the cost and manufacturing process, but are also detrimental to integration. As such, it is highly desirable to actualize a high-performance metasurface that merely relies on elaborated designs and simple manufacturing process. This study combines frequency multiplexing, spatial channel multiplexing, and polarization multiplexing to propose a full-space metahologram with four different information channels based on a thin double-face copper-cladded metasurface. Exploiting the propagation phase, linear-polarized incident waves can be independently manipulated for the reflection semispace. Integrating the Pancharatnam-Berry (PB) phase, circular-polarized incident waves are tailored for the transmission semispace. To validate the concept, a metahologram sample is fabricated and tested. The experimental results are fully consistent with theoretical calculations and numerical simulation results. The metasurface has a useful role in multifunctional metadevices, and paves the way for potential applications in the fields of antennas and communication systems.

We report on a spin-orbit-torque study of the spin-current generation in ${\mathrm{Cr}}_{1-x}{\mathrm{Pt}}_x$ alloy, using the light 3d ferromagnetic Co as the spin-current detector. We find that the dampinglike spin-orbit torque of ${\mathrm{Cr}}_{1-x}{\mathrm{Pt}}_x/\mathrm{Co}$ bilayers can be enhanced by tuning the $\mathrm{Cr}$ concentration in the ${\mathrm{Cr}}_{1-x}{\mathrm{Pt}}_x$ layer, with a maximal value of 0.31 at the optimal composition of ${\mathrm{Cr}}_{0.2}{\mathrm{Pt}}_{0.8}$. The mechanism and the efficiency of spin-current generation in the ${\mathrm{Cr}}_{1-x}{\mathrm{Pt}}_x$ alloy can be fully understood by the characteristic trade-off between the intrinsic spin Hall conductivity of $\mathrm{Pt}$ and the spin carrier lifetime in the dirty limit. This suggests that $\mathrm{Cr}$ is simply as effective as other metals, oxides, and nitrides (e.g., $\mathrm{Hf}$, $\mathrm{Au}$, $\mathrm{Pd}$, $\mathrm{Cu}$, $\mathrm{Ti}$, $\mathrm{Mg}\mathrm{O}$, and ${\mathrm{Si}}_3{\mathrm{N}}_4$) in enhancing the dampinglike spin-orbit torque generated by the spin Hall effect of a $\mathrm{Pt}$ host via strengthening the spin carrier scattering and that alloying $\mathrm{Pt}$ with $\mathrm{Cr}$ does not employ observable spin-current generation via additional spin Hall effect, orbital Hall effect, or interfacial spin-orbit coupling effects. This work also establishes the low-resistivity ${\mathrm{Cr}}_{0.2}{\mathrm{Pt}}_{0.8}$ as an energy-efficient spin-orbit-torque provider for magnetic memory and computing technologies.

Surface-acoustic-wave (SAW) devices have a wide range of applications in microwave signal processing. Microwave SAW components benefit from higher quality factors and much smaller crosstalk when compared to their electromagnetic counterparts. Efficient routing and modulation of SAWs are essential for building large-scale and versatile acoustic wave circuits. Here, we demonstrate integrated thermoacoustic modulators using two SAW platforms: bulk lithium niobate and thin-film lithium niobate on sapphire. In both approaches, the gigahertz-frequency SAWs are routed by integrated acoustic waveguides, while on-chip microheaters are used to locally change the temperature, and thus, control the phase of the SAW. Using this approach, we achieve phase changes of over 720° with the responsibility of 2.6°/mW for bulk lithium niobate and 0.52°/mW for lithium niobate on sapphire. Furthermore, we demonstrate amplitude modulation of SAWs using acoustic Mach-Zehnder interferometers. Our thermoacoustic modulators can enable reconfigurable acoustic signal processing for next-generation wireless communications and microwave systems.

The effectiveness and accuracy of parameter estimation are guarantees for the high-performance and high-safety operation of practical continuous-variable quantum key distribution systems. A scheme based on Bayesian estimation is proposed to tackle the fluctuations of channels. In free-space channel, the Bayesian random-effects model is employed to construct complete prior information, and the channel state information extracted through pilot signals is applied to rectify the prior information. Compressed sensing technology is applied due to the sparsity of the free-space channel to reduce the cost of the system. Experimental results show that the proposed scheme has higher estimation accuracy under the free space, and the system performance is also enhanced. Moreover, the results under fiber show higher estimation accuracy and better stability than that of traditional methods. In conclusion, the scheme can create practical conditions for the construction of future global quantum networks.

Single-crystal growth, magnetic properties, and magnetocaloric effect of the $S=3/2$ kagome ferromagnet ${\mathrm{Li}}_9{\mathrm{Cr}}_3({\mathrm{P}}_2{\mathrm{O}}_7{)}_3({\mathrm{PO}}_4{)}_2$ (trigonal, space group: $P\overline{3}c1$) are reported. Magnetization data suggest dominant ferromagnetic intraplane coupling with a weak anisotropy and the onset of ferromagnetic ordering at $T_C\simeq 2.6$ K. Microscopic analysis reveals a very small ratio of interlayer to intralayer ferromagnetic couplings ($J_{\perp }/J\simeq 0.02$). Electron spin-resonance data suggest the presence of short-range correlations above $T_C$ and confirms the quasi-two-dimensional character of the spin system. A large magnetocaloric effect characterized by isothermal entropy change of $-\mathrm{\Delta }{S}_m\simeq 31\mathrm{J}{\mathrm{kg}}^{-1}{\mathrm{K}}^{-1}$ and adiabatic temperature change of $-\mathrm{\Delta }{T}_{\mathrm{ad}}\simeq 9\mathrm{K}$ upon a field sweep of 7 T is observed around $T_C$. This leads to a large relative cooling power of $\mathrm{RCP}\simeq 284\mathrm{J}{\mathrm{kg}}^{-1}$. The large magnetocaloric effect, together with negligible hysteresis render ${\mathrm{Li}}_9{\mathrm{Cr}}_3({\mathrm{P}}_2{\mathrm{O}}_7{)}_3({\mathrm{PO}}_4{)}_2$ a promising material for magnetic refrigeration at low temperatures. The magnetocrystalline anisotropy constant $K\simeq -7.42\times {10}^4\mathrm{erg}{\mathrm{cm}}^{-3}$ implies that the compound is an easy-plane-type ferromagnet with the hard axis normal to the $a$$b$ plane, consistent with the magnetization data.

High-fidelity control of quantum systems is crucial for quantum information processing, but is often limited by perturbations from the environment and imperfections in the applied control fields. Here, we investigate the combination of dynamical decoupling (DD) and robust optimal control (ROC) to address this problem. In this combination, ROC is employed to find robust shaped pulses, wherein the directional derivatives of the controlled dynamics with respect to control errors are reduced to a desired order. Then, we incorporate ROC pulses into DD sequences, achieving a remarkable improvement of robustness against multiple error channels. We demonstrate this method in the example of manipulating nuclear spin bath via an electron spin in the nitrogen-vacancy center system. Simulation results indicate that ROC-based DD sequences outperform the state-of-the-art robust DD sequences. Our work has implications for robust quantum control on near-term noisy quantum devices.

Thermal noise in amorphous coatings is a limitation for a wide range of precision experiments such as gravitational-wave detectors (GWDs). Mirrors for GWDs are composed of multiple thin layers of dielectric materials deposited on a substrate: the stack is made of layers with a high-refractive index interleaved with layers of a low-refractive index. The goal is to obtain high reflectivity and low thermal noise. In this paper we report on the optical and mechanical properties of ion-beam-sputtered aluminium fluoride (${\mathrm{Al}\mathrm{F}}_3$) thin films that have one of the lowest refractive indexes among the known coating materials and we discuss their application in current and future GWDs.

The transport behaviors of topological guiding modes for classical waves in heterostructures with width degree of freedom have attracted much attention recently. With the width degree of freedom, topological waveguides are endowed with increased capacity in energy transport and improved flexibility in interfacing existing devices. However, to date, such topological waveguides are only realized in hexagonal lattices, by virtue of the known valleys existing at the Brillouin zone corners. Here, we report on the implementation of topological waveguides in heterostructures of a square lattice, consisting of three domains of acoustic crystals: the middle domain has Dirac points and the two side domains have valleys of opposite valley Chern numbers. A pair of counterpropagating topological waveguide modes, with amplitudes that are uniform in the central domain and attenuated sidewards in the two side domains, are supported in the heterostructure. We experimentally verify that the topological waveguide modes are valley locked and backscattering immune, and they have a high capacity for energy transport. We also demonstrate experimentally the conversion between the valley waveguide states and the usual valley edge states. More interestingly, when the central domain of the Dirac points is applied with a transverse structural gradient mirror symmetrically, a different kind of topological waveguide mode emerges. We verify that the waveguide modes possess the same topological properties.

Disorder in ultrathin magnetic films can significantly hinder domain-wall motion. One of the main issues on the path toward efficient domain-wall-based devices remains the characterization of the pinning landscape at the nanoscale. In this paper, we study domain-wall motion in $\mathrm{W}$/$\mathrm{Co}$-$\mathrm{Fe}$-$\mathrm{B}$/$\mathrm{MgO}$ thin films with perpendicular magnetic anisotropy crystallized by annealing at $400{}^{\circ }\mathrm{C}$ and a process based on $\mathrm{He}$${}^{+}$ irradiation combined with moderated temperatures. The magnetic properties are similar for the whole series of samples, while the magnetic domain-wall mobility is critically improved in the irradiated samples. By using an analytical model to extract the nanoscale pinning parameters, we reveal important variations in the disorder of the crystallized samples. This work offers an opportunity to selectively analyze the effects of disorder on the domain-wall dynamics, without the contribution of changes in the magnetic properties. Our results highlight the importance of evaluating the nanoscale pinning parameters of the material when designing devices based on domain-wall motion, which in return can be a powerful tool to probe the disorder in ultrathin magnetic films.

Topological insulators, protected by nontrivial band topology, exhibit backscattering-immune edge states, conducive to robust waveguiding with high efficiency. However, routing such robust edge states has been restricted by the isotropy in conventional unit cells respecting crystalline symmetries, such as $C_{4v}$ symmetry in a square lattice or $C_3$ symmetry in a hexagonal lattice. We effectively tackle this issue by introducing anisotropic coupling into a square lattice. With theoretical prediction from the discrete mechanical model, we experimentally demonstrate that such anisotropy can enable distinctive topological phases along different directions, giving rise to directional edge states. In addition, when the bands along the two directions are topologically identical and untrivial, the coexisting edge states have distinctive frequency ranges, giving rise to the frequency-routed properties. Our work offers an effective strategy for the robust steering, filtering, detection, and transmission of elastic waves through tactical edge state routing.

Size-dependent continuous microparticle separation is important for various applications in sensing and drug delivery to particle manufacturing. Several invasive, noninvasive, active, and passive methods have been developed, spanning operation across a wide range of system scales, from bulk-macroscale devices to precise-microscale systems. However, devices in these wide system scales have contradictory benefits. Bulk methods have limitations with the size of particles that can be manipulated, while microscale methods have limitations with processing volumes. Here, we present a method to continuously separate micron- and submicron-sized particles using low-frequency vibrations (of the order of 10 Hz). We generate capillary waves in an open channel with a continuous particle-laden flow perpendicular to the vibration direction. The size-based response of the ensuing flow field aligns particles above a critical size along the center of the channel, while the remaining particles remain in the bulk and undergo downstream separation. A key feature of this mechanism is that the separated particle sizes can be controlled by changing the vibration amplitude. The proposed mechanism and design provides a semibulk method to distinguish submicron-sized particles with robust in situ control using a simple millimeter-scale setup and operation.

Voltage-induced dynamic switching in magnetic tunnel junctions (MTJs) is a writing technique for voltage-controlled magnetoresistive random access memory (VCMRAM), which is expected to be an ultimate nonvolatile memory with ultralow power consumption. In conventional dynamic switching, the width of subnanosecond write voltage pulses must be precisely controlled to achieve a sufficiently low write-error rate (WER). This very narrow tolerance of pulse width is the biggest technical difficulty in developing VCMRAM. Heavily damped precessional switching is a writing scheme for VCMRAM with a substantially high tolerance of pulse width, although the minimum WER has been much higher than that of conventional dynamic switching with an optimum pulse width. In this study, we theoretically investigate the effect of MTJ shape and the direction of the applied magnetic field on the WER of heavily damped precessional switching. The results show that the WER in elliptical-cylinder MTJs can be several orders of magnitude smaller than that in usual circular-cylinder MTJs when the external magnetic field is applied parallel to the minor axis of the ellipse. The reduction in the WER is due to the fact that the demagnetization field narrows the component of the magnetization distribution perpendicular to the plane direction immediately before the voltage is applied.

Binding, magnetic, and electron transport properties of $3d$ transition-metal (TM) adatoms ($\mathrm{Cr}$-$\mathrm{Cu}$) on an antiferromagnetic armchair graphene nanoribbon heterojunction are studied by means of density-functional-theory (DFT) calculations and nonequilibrium Green function (NEGF) formalism. The heterojunction emulates a system of two symmetric potential barriers and one well with resonances (quasibound states). Binding energies show a strong interaction between $3d$ TM adatoms and heterojunction hollow sites, where $3d$ TM adatoms prefer the edges rather than the middle of the graphene heterojunction. As for magnetic properties, heterojunctions with Cr, $\mathrm{Mn}$, and $\mathrm{Fe}$ have a ferromagnetic behavior with a total magnetic moment $\ge 4{\mu }_B$, while $\mathrm{Co}$, $\mathrm{Ni}$, and $\mathrm{Cu}$ adatoms induce antiferromagnetism in the full system with total magnetizations $<3{\mu }_B$. Transmission curves show that electronic resonances undergo a spin-splitting effect induced by $3d$ TM adatoms, and current versus bias-voltage curves show spin currents from which spin-polarized ratios (SPRs) $>75\mathrm{\%}$ for $\mathrm{Co}$ and approximately $100\mathrm{\%}$ for $\mathrm{Ni}$ adatoms are calculated. Finally, an oscillatory behavior is observed in SPR curves at low bias due to a combined effect of resonant tunneling and spin filtering. Therefore, these results suggest that the present antiferromagnetic graphene heterojunction with $\mathrm{Co}$ and $\mathrm{Ni}$ adatoms is suitable for future spin and low-power nanoelectronics as a spin-dependent resonant tunneling device.

We report a switchable time-varying mirror, composed of an indium-tin-oxide–gold bilayer, displaying a tenfold modulation of reflectivity ($\mathrm{\Delta }R\approx 0.6$), which saturates for a driving-pump intensity $I_{\mathrm{pump}}\approx 100\mathrm{GW}/{\mathrm{cm}}^2$. Upon interacting with the saturated time-varying mirror, the frequency content of a reflected pulse is extended up to 31 THz, well beyond the pump spectral content (2.8 THz). We interpret the spectral broadening as a progressive shortening of the mirror rise time from 110 fs to below 30 fs with increasing pump power, which is confirmed by four-wave-mixing experiments and partially captured by a linear time-varying model of the mirror. A temporal response unbounded by the pump bandwidth enables applications for spectral manipulation from time-varying systems with impact for communication networks, optical switching, and computing.

The discovery of very large piezo- and pyroelectric effects in ${\mathrm{Zr}\mathrm{O}}_2$ and ${\mathrm{Hf}\mathrm{O}}_2$-based thin films opens up opportunities to develop silicon-compatible sensor and actor devices. The effects are amplified close to the polar-orthorhombic to tetragonal phase-transition temperature. Molecular dynamics is the preferred technique to simulate such effects, though its application has to solve the dilemma between sufficient accuracy and sufficient efficiency of the interatomic force field. Here we present a deep neural-network-based interatomic force field of ${\mathrm{Zr}\mathrm{O}}_2$ learned from ab initio data using a systematic learning procedure in the deep potential framework. The model potential is verified to predict a variety of structural and dynamic properties with an accuracy comparable to density-functional-theory calculations. Then the deep potential model is used to reproduce the different thermal expansion and piezo- and pyroelectric phenomena in ${\mathrm{Zr}\mathrm{O}}_2$ with molecular dynamics calculations. At low temperature simulating the direct effect we find negative values for the piezo- and pyroelectric coefficients matching the ab initio calculations. Approaching the phase-transition temperature these values remain negative and become large. Simulating the field-induced effect above the phase-transition temperature we find positive, giant piezoelectric coefficients matching the observations. The model is able to explain the large values and the sign of the experimental observations in relation to the polar-orthorhombic to tetragonal phase transition. The model furthermore explains the recently observed giant dielectric constant in a similar system.