Spin-orbit torque (SOT) control of magnetization is being rapidly positioned for energy-efficient computing across various memory hierarchies. Concurrently, the study of intrinsic and extrinsic factors, such as doping, to enhance SOT is of considerable scientific interest. Here, we introduce 2% nominally doped oxygen via postdeposition oxygen flow in β-phase tungsten, one of the most promising SOT materials, to create laminated [$\mathrm{W}/\mathrm{O}$] structures. Incorporating them into annealed multilayer stacks compatible with industrial production, we find ∼50% enhancement in spin-Hall angle with minimal compromise in intrinsic spin-Hall conductivity. Furthermore, we integrate [$\mathrm{W}/\mathrm{O}$] into SOT magnetic tunnel junctions, achieving ∼30% reduction in critical switching current densities while maintaining a relatively large tunnel magnetoresistance (>135%). Our findings highlight that engineering nominal doping in established SOT materials offers an attractive alternative for accelerating materials development for SOT magnetic random-access memory (MRAM).

We present a first-principles investigation of the optoelectronic properties of vertically stacked bilayer heterostructures composed of 2D transition-metal dichalcogenides (TMDs). The calculations are performed with density-functional theory as well as many-body perturbation theory within the $G_0{W}_0$–Bethe-Salpeter-equation method. Our aim is to propose these TMD heterostructures for potential applications in solar cells. The TMD monolayers constituting the heterojunctions considered in this research are ${\mathrm{Mo}\mathrm{S}}_2$, ${\mathrm{WS}}_2$, ${\mathrm{Mo}\mathrm{Se}}_2$, and ${\mathrm{WS}\mathrm{e}}_2$ monolayers due to their favorable band gaps, high carrier mobility, robust absorption in the visible region, and excellent stability. These four TMD monolayers provide the basis for a total of six potential heterostructures (${\mathrm{WS}}_2$/${\mathrm{Mo}\mathrm{S}}_2$, ${\mathrm{Mo}\mathrm{Se}}_2$/${\mathrm{Mo}\mathrm{S}}_2$, ${\mathrm{Mo}\mathrm{Se}}_2$/${\mathrm{WS}}_2$, ${\mathrm{WS}\mathrm{e}}_2$/${\mathrm{Mo}\mathrm{S}}_2$, ${\mathrm{WS}\mathrm{e}}_2$/${\mathrm{Mo}\mathrm{Se}}_2$, and ${\mathrm{WS}\mathrm{e}}_2$/${\mathrm{WS}}_2$) whose structural, electronic, and optical properties have been studied in this work. At the density-functional-theory level, all six TMD heterostructures considered meet the essential criterion of type-II band alignment, a critical factor in extending carrier lifetime. However, according to $G_0{W}_0$ results, ${\mathrm{Mo}\mathrm{Se}}_2$/${\mathrm{WS}}_2$ does not exhibit type-II band alignment; instead it shows type-I band alignment. The significantly large quasiparticle band gaps obtained from the $G_0{W}_0$ approximation suggest the presence of strong electron-correlation effects. The heterostructures studied exhibit superior optoelectronic properties compared with their respective isolated monolayers. Quite-significant values of the intrinsic electric fields that arise due to the asymmetric geometry of the heterostructures are obtained. Additionally, the small and nearly equal electron and hole effective masses obtained indicate high mobility and efficient charge-carrier separation, resulting in low recombination losses. The quality of these heterojunction solar cells is estimated by computing their power-conversion efficiencies (PCEs). The PCEs are calculated at both the HSE06 level and the $G_0{W}_0$ level, and the maximum PCE predicted by HSE06 calculations on our designed solar cells is 19.25% for the ${\mathrm{WS}\mathrm{e}}_2$/${\mathrm{WS}}_2$ heterojunction. In addition, all six TMD heterostructures are examined for their potential applications in photocatalysis for the hydrogen-evolution reaction, and three of them—namely, ${\mathrm{WS}}_2$/${\mathrm{Mo}\mathrm{S}}_2$, ${\mathrm{Mo}\mathrm{Se}}_2$/${\mathrm{Mo}\mathrm{S}}_2$, and ${\mathrm{WS}\mathrm{e}}_2$/${\mathrm{Mo}\mathrm{S}}_2$ heterostructures—qualify as photocatalysts.

Dielectric elastomers have significant potential for new technologies, ranging from soft robots to biomedical devices, driven by their ability to display complex shape changes in response to electrical stimulus. However, an important shortcoming of current realizations is that large voltages are required for useful actuation strains. This work proposes, and demonstrates through theory and numerical simulations, a strategy to achieve large and controlled actuation by exploiting the electromechanical analogue of the Treloar-Kearsley (TK) instability. The key idea is to use the fact that the TK instability is a symmetry-breaking bifurcation, which implies the existence of a symmetry-driven constant-energy region in the energy landscape. This provides for nonlinear soft modes with large deformations that can be accessed with very small external stimulus, which is achieved here by applying a small in-plane electric field. First, the bifurcation and postbifurcation behavior of the electromechanical TK instability are established theoretically in the idealized setting of uniform deformation and electric field. Next, building on this, a finite-element analysis of a realistic geometry with patterned top and bottom electrodes is applied to demonstrate large and soft shape changes driven by small voltage differences across the electrodes.

Acoustic aggregation of particles in acoustic levitation is a well-known phenomenon. However, it is well described only in the dilute regime, i.e., when particles do not interact with each other. In this study, we first demonstrate that the acoustic focusing speed can be significantly increased when one is dealing with particle aggregates. This result suggests that acoustic aggregation can be more efficient when one is dealing with relatively dense suspensions. This principle is successfully applied to suspensions of microalgae. It is shown that harvesting of microalgae can be accelerated without power increase with acoustically induced flocculation if the initial concentration is sufficiently high. This demonstrates that a cost-effective industrial process for acoustic harvesting of microalgae is possible.

Carbon deposition in reversible solid-oxide cells (RSOCs) can block catalytic sites and may lead to delamination, resulting in performance degradation. In this study, we analyzed the thermodynamics at the fuel electrode of an RSOC during operation by modeling the oxygen chemical potential distribution across the RSOC to predict conditions for carbon deposition. It is found that carbon deposition is more likely to form under solid-oxide electrolysis (SOEC) mode than in solid-oxide fuel cell (SOFC) mode. We then investigated key parameters to suppress carbon deposition, including cell voltage, current density, electrolyte thickness, the electronic and ionic conductivity of electrolytes, and electronic and ionic area-specific resistances (ASRs) of the electrode-electrolyte interfaces. A thin electrolyte and a low ionic ASR of the fuel electrode-electrolyte interface suppress carbon deposition. A low electrolyte electronic conductivity ${\sigma }_e^{\mathrm{EL}}$, a high electrolyte ionic conductivity ${\sigma }_i^{\mathrm{EL}}$, and a low area-specific ionic resistance at the oxygen electrode-electrolyte interface $r_i^{\text{OE|EL}}$ result in a high Faradaic efficiency and enhanced electrolyzer performance, but they also accompany a high thermodynamic driving force for carbon deposition. In addition, maintaining a low cell voltage and a low $\mathrm{CO}$ composition in the fuel electrode helps suppress carbon deposition by avoiding and extremely reducing the atmosphere at the fuel electrode-electrolyte interface. A comparison between theoretical analysis and experimental observation is provided to validate our findings.

We present an experimental scheme for producing ultracold ytterbium atoms in a compact dual-chamber setup. A dispenser-loaded two-dimensional magneto-optical trap (MOT) using permanent magnets and operating on the broad ${}^1{S}_0\to {}^1{P}_1$ singlet transition delivers over ${10}^7$ atoms per second through a differential pumping stage into a three-dimensional MOT. The two-color three-dimensional MOT uses the broad singlet transition to accumulate $\sim 2\times {10}^7$ atoms of ${}^{174}\mathrm{Yb}$ within 2.5 s and subsequently the narrow ${}^1{S}_0\to {}^3{P}_1$ intercombination line to cool the atomic cloud to below 10 µK. We report optimized parameters for each stage of the atom collection sequence, achieving high transfer efficiency. We find that shelving into the triplet state during the broad-transition MOT almost doubles the number of trapped atoms.

Multiphoton hyperentangement is fundamental in optical quantum information processing. Existing theory and experiments usually focus on producing two-photon hyperentanglement and multiphoton entangled states encoded in a single degree of freedom. Multiphoton entangled states have until now relied on the outcome postselection, a procedure where only the measurement results corresponding to the desired state are considered. Such an approach severely limits the usefulness of the resulting entangled states. We present the protocols of direct production of three- and four-photon hyperentanglement and extend the approach to an arbitrary number of photons through a straightforward cascade of spontaneous parametric down-conversion (SPDC) sources. The generated multiphoton hyperentangled states are encoded in polarization-spatial modes and polarization-time bin degrees of freedom, respectively. Numerical calculation shows that if the average photon number $\mu$ is 1, the down-conversion efficiency is $7.6\times {10}^{-6}$ and the repetition frequency of the laser is ${10}^9$ Hz, the number of the generation of three-photon and four-photon hyperentanglement after cascading can reach about $5.78\times {10}^{-2}$ and $4.44\times {10}^{-7}$ pairs per second, respectively. By eliminating the constraints of outcome postselection, our protocols may represent progresses for multiphoton hyperentangement generation and provide a pivotal role in future multiparty and high-capacity communication networks.

Selective acoustic tweezers can focus the acoustic radiation force on a single particle to manipulate it without affecting its neighbors. Traditionally, this has required highly complex and specialized hardware, incompatible with high-throughput manipulation. In this two-dimensional numerical study, we demonstrate that two pairs of orthogonal transducers, known for manipulating arrays of particles, can also achieve selective particle manipulation. Specifically, we show that selectivity is possible by using sequences of acoustic pulses to iteratively construct a combined acoustic potential focused solely on the target particle.

Electromagnetic multipoles play an important role in the rapid development of micro-optics and nano-optics and offer unique degrees of freedom for tailoring the electromagnetic scattering at the subwavelength scale. The electromagnetic Kerker effect refers to a phenomenon of unidirectional light scattering, arising from the interaction between the induced electric dipole and magnetic dipole moments within a scatterer. Notably, both moments are typically constrained by the single-channel scattering limit. Therefore, the total scattering cross section at the Kerker condition is also limited, imposing a challenge to achieve superscattering and unidirectional scattering on resonance simultaneously. Herein, we introduce a concept of Kerker superscattering based on the interaction between super electric dipole scattering and super magnetic dipole scattering where both of their scattering cross sections exceed the single-channel scattering limit. This Kerker superscattering is achieved by the use of a dielectric resonator coated with a metasurface. Analytical conditions are derived for the Kerker superscattering, which agrees well with full-wave simulations. Microwave experiments in the frequency and temporal domains are conducted to further consolidate the theoretical results. It is anticipated that the proposed concept could facilitate the development of subwavelength antennas, unidirectional couplers, and Huygens metasurfaces.

The emergence of topological edge states is a key feature of various topological phases. This phenomenon, termed the bulk-edge correspondence, is regarded as the major experimental signature of topological materials. Recent theoretical studies reveal that topological defects, such as dislocations, can reveal more information about the topological properties of the hosting materials. Here, we observe such a phenomenon in experiments by engineering dislocations in topological photonic crystals. Instead of the topological edge states, we show that a fractional topological number and a local mode bound to the dislocation can emerge as the experimental manifestation of the underlying topology. The fractional topological number depends on both the photonic band topology in momentum space and the geometry of the dislocation in real space and, thus, it serves as a versatile probe of the band topology. We confirm with experiments that the photonic band topology can indeed be inferred from the fractional topological numbers at various dislocations, uncovering the underlying bulk-defect correspondence. Moreover, the geometry of the dislocation can be engineered, which in turn affects the fractional topological number, indicating the role of the real-space topology of the dislocation. Our work serves as a stepping stone toward probing topological phases with dislocations, especially for crystalline materials and metamaterials with time-reversal symmetry.

We studied the influence of defect states on the laser excitation process in silicon using time-dependent density functional theory. We assumed two types of point defects: interstitial oxygen and silicon vacancies. We found that the photoabsorption efficiency increased with defect density in both cases owing to the color center. These defects distorted the crystal structure, thereby relaxing the selection rules and changing the indirect gap to direct. At low laser intensities, the defect states dominated the absorption process. However, as the laser intensity increased, the excitation efficiency approached that of crystalline silicon. In addition, we observed that the excitation efficiency did not scale linearly with the pulse length. Notably, in the case of $\mathrm{Si}$ vacancies, saturable absorption reduced photoabsorption significantly. Our results suggest that the existence of a defect induces the even-order high-harmonics generation. The enhancement of even-order high-harmonics generation by the silicon vacancy is larger than the interstitial oxygen.

Ongoing advancements in geometric quantum computation, including the continuous refinement of evolution paths and the integration of optimal control techniques, have demonstrated their significant resilience against control errors resulting from imprecise operations. However, as the number of qubits increases with the scaling up of quantum systems, the emergence of residual crosstalk imposes demands on the error tolerance of geometric control. Here, we propose a crosstalk-resistant unconventional geometric quantum computation scheme in a superconducting circuit. This approach significantly broadens the error tolerance of geometric control by leveraging the additional parameter degrees of freedom available in the unconventional geometric process, along with further path optimization. Compared to conventional geometric gates and dynamical Rabi gates, our unconventional geometric gates can exhibit superior crosstalk resistance regardless of the gate type, and still maintain robustness against the main systematic error in superconducting systems. Additionally, our numerical simulations thoroughly evaluate the combined impacts of leakage errors and decoherence, validating the high-fidelity performance of our unconventional geometric gates.

Flexural-wave metalenses with a large numerical aperture (NA), high-efficiency focusing, and superresolution ability are desired in various applications, such as nondestructive testing and structure-health monitoring. Here, we propose a design paradigm of a hybrid metalens for the flexural wave, which is composed of a gradient metasurface in the central region and two metagratings in the surrounding region to achieve an ultrahigh focusing efficiency. With intelligently designed unit cells and deliberately matched transmissive phases, the metagrating’s high deflection efficiency at larger steering angles and the metasurface’s tunable phase shift and high efficiency at smaller steering angles are simultaneously and cooperatively utilized to realize an unprecedented focusing performance, where 240.9-times enhancement of wave intensity is attained at the focal spot. The ultrahigh-efficiency, large-NA (0.957), and superresolution (0.35λ) characteristics of the focusing performance, as well as the compact and planar configuration of the hybrid metalens, provide an alternative and promising solution to the sharp-focusing functionality of a flexural wave.

We develop a coherent perfect absorption (CPA) protocol for cases where scale invariance is violated due to the presence of nonlinear mechanisms. We demonstrate, using a microwave setting that lacks geometrical symmetries, that the nonlinearity offers new reconfigurable modalities: the destruction or formation of nonlinear CPAs (NL CPAs), and their frequency positioning and bandwidth management using the incident power as a control knob. The latter occurs via the formation of exceptional point degeneracies of the zeros of nonlinear scattering processes. Our results establish NL-CPA protocols as a versatile scheme for the creation of reconfigurable hot or cold spots in complicated enclosures (e.g., buildings or vessels) with applications to next-generation telecommunications, long-range wireless power transfer, and electromagnetic warfare.

Nonlinear quantum photonics serves as a cornerstone in photonic quantum technologies, such as universal quantum computing and quantum communications. The emergence of an integrated photonics platform not only offers the advantage of large-scale manufacturing but also provides a variety of engineering methods. Given the complexity of integrated photonics engineering, a comprehensive simulation framework is essential to fully harness the potential of the platform. In this context, we introduce a nonlinear quantum photonics simulation framework, which can accurately model a variety of features such as adiabatic waveguide, material anisotropy, linear optics components, photon losses, and detectors. Furthermore, utilizing the framework, we have developed a device scheme, chip-scale temporal walk-off compensation, that is useful for various quantum information-processing tasks. We further show that the proposed device scheme can enhance the squeezing parameter of photon-pair sources and the conversion efficiency of quantum frequency converters without relying on higher pump power.

The control of topological sound transport has attracted increasing attention from researchers. Topological interface states, which have pseudospin-momentum-locked dispersions, render sound transport backscattering immune against defects. Here we report on the experimental observation of topological energy transfer through distinct passages, whose existence and elimination are attributed to the coupling and decoupling between the topological interface states. The phenomenon of topological coupling is elucidated well using interference theory and the coupling wavelength, including the propagation constants of the two supermodes and coupling length as key parameters. As a potential application, we numerically and experimentally demonstrate a topological wavelength demultiplexer, where the incident sound can be split into different channels, immune to the structural disorder along the passages, by employing different coupling wavelengths of interface states at different coupled frequencies. Our work provides the prototype for controlling acoustic topological transport, and may facilitate practical applications in multichannel sound signal processing devices for separating sound at different wavelengths.

Topological materials, distinguished by symmetrically protected topological surface states (TSSs), have emerged as highly promising catalysts for hydrogen evolution reactions (HERs). In light of the promising potential of topological materials in catalytic processes, there is an urgent need to delve into the underlying mechanisms. In this work, our focus centers on ${\mathrm{Cu}}_3\mathrm{Pd}\mathrm{N}$, distinguished by its antiperovskite structure. Notably, this material exhibits a distinctive Weyl nodal chain featuring nodal loops in proximity to the Fermi level. We select ${\mathrm{Cu}}_3\mathrm{Pd}\mathrm{N}$ as a representative case study to explore and elucidate the intricate interplay between topological properties and catalytic performance. This work was carried out using first-principles calculations. The presence of topological nodal loops, characterized by drumhead surface states, significantly augments the surface density of states, resulting in an outstanding catalytic performance in the HER process. Remarkably, the catalytic efficiency demonstrated by this mechanism surpasses that of the benchmark catalyst $\mathrm{Pt}$. Notably, we uncover a linear correlation between the presence of TSSs and catalytic efficiency. This revelation establishes TSSs as a superior metric for characterizing the performance of topological catalysts compared to conventional descriptors such as the $d$-band center. Our study not only broadens the landscape of topological catalysis but also provides a tangible exemplar for elucidating the inherent topological mechanisms at play in these catalysts. The identification of ${\mathrm{Cu}}_3\mathrm{Pd}\mathrm{N}$ as a potent HER catalyst, guided by TSS properties, represents a significant advancement, offering other avenues for the design and understanding of topological materials in catalytic applications.

The observation of a substantial interfacial Dzyaloshinskii-Moriya interaction (IDMI) in two-dimensional (2D) transition-metal dichalcogenide (TMD)/ferromagnet (FM) interfaces has opened up the possibility of exploring chiral spin textures and spin dynamics in such systems. This makes the exploration of the additive IDMI in the 2D-TMD/FM/heavy-metal trilayer system an intriguing problem. Here, using the Brillouin light-scattering technique, we have demonstrated the significant contribution of the monolayer-${\mathrm{Mo}\mathrm{S}}_2/\mathrm{Co}$ interface to enhancing the IDMI strength of a widely investigated $\mathrm{Co}/\mathrm{Pt}$ interface by introducing an additive IDMI when combined to form the ${\mathrm{Mo}\mathrm{S}}_2/\mathrm{Co}/\mathrm{Pt}$ trilayer stack. Additionally, the FM-layer-thickness-dependent study serves the dual purpose of conducting a comparative analysis of the IDMI strength between $\mathrm{Co}(t)/\mathrm{Pt}(4)$ and ${\mathrm{Mo}\mathrm{S}}_2/\mathrm{Co}(t)/\mathrm{Pt}(4)$ systems (where t = 2, 4, and 8 nm), as well as confirming the pure interfacial origin of the DMI in these systems. Our study opens up the promising possibility of using hybrid multilayers to stabilize chiral spin textures, offering potential applications in future spintronic devices.

Dielectric nanophotonics enables almost-lossless resonant interaction between light and matter at the nanoscale. We show both theoretically and by electromagnetic simulations that the peculiar nature of Mie resonance–induced effective magnetic fields contrasts sharply with the optomagnetism of smooth bulk materials. Mie resonances produce strongly nonuniform effective magnetic fields generated by the inverse Faraday effect. Different orders of optical resonances are characterized by different types of the effective magnetic field patterns. The number of pointlike inverse-Faraday-effect sources can be controlled by adjustment of the pump wavelength, allowing the selective launch of spin waves with submicron wavelengths. A distinguishing feature of the Mie resonance–induced effective magnetic fields is the vortex structure that can be used for magnetic skyrmion generation. The proposed approach considerably broadens the scope of nanoscale optomagnetism.