Maxwell’s fish-eye lens (MFEL) with positive refraction has been shown to achieve perfect imaging, but with the cost of drain assistance. This has led to ongoing heated debates about the rigor of the physics of super-resolution phenomena in MFEL. In this work, we report that a MFEL embedded in an exterior coating, inspired by the solid immersion concept, can realize super-resolution imaging without a drain. Such a solution mitigates and bypasses the corresponding criticisms and debates of the past decades. We find that the total reflection at the outer solid-immersion interface and the native perfect focusing of MFEL synthetically contribute to a super-resolution image formed in the air. Moreover, this intuitive yet simple recipe can be robustly applied to other absolute instruments, such as the general Luneburg lens and more versatile superimaging systems are anticipated. We demonstrate the imaging performance in a solid immersion general Luneburg lens both numerically and experimentally, which indirectly verifies the imaging validity of the solid immersion MFEL without a drain.

The presence of a partially reflecting screen on top of a grounded dielectric slab strongly perturbs its modal spectrum. The modes supported by such structures have been investigated in the literature for some specific, yet relevant cases. Here, a comprehensive modal analysis is presented, which emphasizes the inductive or capacitive nature of the partially reflecting sheet. The results of this analysis not only provide a clear overview of a wide class of structures of relevance in applied electromagnetics, but also unveil the presence of some useful propagating regimes so far barely explored.

We theoretically and numerically study the terahertz auto-oscillations, or self-oscillations, in thin-film metallic noncollinear coplanar antiferromagnets (AFMs), such as ${\mathrm{Mn}}_3\mathrm{Sn}$ and ${\mathrm{Mn}}_3\mathrm{Ir}$, under the effect of antidamping spin torque with spin polarization perpendicular to the plane of the film. To obtain the order parameter dynamics in these AFMs, we solve three Landau-Lifshitz-Gilbert equations coupled by exchange interactions assuming both single- and multidomain (micromagnetics) dynamical processes. In the limit of a strong exchange interaction, the oscillatory dynamics of the order parameter in these AFMs, which have opposite chiralities, could be mapped to that of two damped-driven pendulums with significant differences in the magnitude of the threshold currents and the range of frequency of operation. The theoretical framework allows us to identify the input current requirements as a function of the material and geometry parameters for exciting an oscillatory response. We also obtain a closed-form approximate solution of the oscillation frequency for large input currents in the case of both ${\mathrm{Mn}}_3\mathrm{Ir}$ and ${\mathrm{Mn}}_3\mathrm{Sn}$. Our analytical predictions of threshold current and oscillation frequency agree well with the numerical results and thus can be used as compact models to design and optimize the auto-oscillator. Employing a circuit model, based on the principle of tunnel anisotropy magnetoresistance, we present detailed models of the output power and efficiency versus oscillation frequency of the auto-oscillator. Finally, we explore the spiking dynamics of two unidirectional as well as bidirectional coupled AFM oscillators using nonlinear damped-driven pendulum equations. Our results could be a starting point for building experimental setups to demonstrate auto-oscillations in metallic AFMs, which have potential applications in terahertz sensing, imaging, and neuromorphic computing based on oscillatory or spiking neurons.

Realistic modeling of qubit systems including noise and constraints imposed by control hardware is required for performance prediction and control optimization of quantum processors. We introduce qopt, a software framework for simulating qubit dynamics and robust quantum optimal control considering common experimental situations. To this end, we model open and closed qubit systems with a focus on the simulation of realistic noise characteristics and experimental constraints. Specifically, the influence of noise can be calculated using Monte Carlo methods, effective master equations or with the efficient filter function formalism, which enables the investigation and mitigation of autocorrelated noise. In addition, limitations of control electronics, including finite bandwidth effects as well as nonlinear transfer functions and drive-dependent noise, can be considered. The calculation of gradients based on analytic results is implemented to facilitate the efficient optimization of control pulses. The software easily interfaces with QuTiP, is published under an open-source license, is well tested, and features a detailed documentation.

The hydrogen-evolution reaction is an essential step in the electrochemical production of hydrogen without the emission of greenhouse gases. For this reaction, alternative catalyst materials that can replace the platinum of current catalysts are needed. Recent alternatives include two-dimensional materials such as transition metal dichalcogenides. Here, we show the electronic and electrochemical properties of the two-dimensional material palladium disulfide (${\mathrm{Pd}\mathrm{S}}_2$) with two crystal structures (phases) and the formation of native point defects. We analyze the differences between the pentagonal ($P$-${\mathrm{Pd}\mathrm{S}}_2$) phase and the octahedral ($1T$-${\mathrm{Pd}\mathrm{S}}_2$) phase, point defects and the Gibbs free energies for hydrogen adsorption from first-principles calculations. Our results show that the $1T$-${\mathrm{Pd}\mathrm{S}}_2$ phase has better catalytic activity than the $P$-${\mathrm{Pd}\mathrm{S}}_2$ phase in the pristine basal plane. In addition, the point defects of lower formation energy in the $1T$-${\mathrm{Pd}\mathrm{S}}_2$ phase, the $S$ vacancies, further improve the catalytic activity for hydrogen production.

Capillary adhesion is commonly present in ambient conditions. It can be measured in single-asperity contacts through atomic force microscopy using a sharp probe that is pulled off a smooth substrate. However, for macroscopic multiasperity interfaces, the measured adhesive force is always close to zero because of the elastic energy stored into the deformation of surface roughness; this is known as the adhesion paradox. Here, we experimentally show how capillary adhesion influences friction between macroscopic $\mathrm{Si}$-on-$\mathrm{Si}$ interfaces, covered with native oxide, in two vapor environments: humid air and isopropyl alcohol (IPA) vapor. To quantify the adhesion contribution to friction, we present a boundary element method that successfully models the interplay between capillary adhesion, surface topography, and friction without adjustable parameters and show that the evolution of the surface topography during sliding dramatically increases capillary adhesion and thus friction. Replacing the water vapor with an organic (IPA) vapor, we find a lower adhesion due to the smaller surface tension.

Static and dynamic magnetic properties of $\mathrm{Co}$-$\mathrm{Fe}$(10 nm)/$\mathrm{Ru}$$(t_{\mathrm{Ru}}=0-3\mathrm{nm})$/$\mathrm{Co}$-$\mathrm{Fe}$(5 nm) asymmetric trilayers are systematically investigated. The interlayer exchange coupling (IEC) strengths of bilinear $(J_1)$, biquadratic $(J_2)$, and their equivalent $(J_{\mathrm{eff}})$ terms are determined; they show a weak nonmonotonic behavior with $t_{\mathrm{Ru}}$. Interestingly, the magnetic remanence ratio η of hard axis to easy axis has two distinct peaks; this can reasonably be interpreted by taking the strong $J_2$ term into account. Various pump-laser fluences are utilized to modulate the static IEC during the time-resolved magneto-optical Kerr effect measurements, by which individual magnetization precessions of the two $\mathrm{Co}$-$\mathrm{Fe}$ layers are achieved and the effects of dynamic IEC through mutual spin currents are highlighted. With the increase in $t_{\mathrm{Ru}}$, the magnetic damping factors of both layers display the same nonmonotonic behavior, which has been mainly ascribed to the spin pumping damping ${\alpha }_{\mathrm{SP}}$ associated with the dynamic IEC. Moreover, it is found that the variation trend of damping difference $\mathrm{\Delta }{\alpha }_{\mathrm{SP}}$ between the two $\mathrm{Co}$-$\mathrm{Fe}$ layers is similar to that of $J_{\mathrm{eff}}$, revealing that the dynamic IEC effect is actually dominated by the static IEC and thereupon a theoretical formula is proposed to describe the correlation between $\mathrm{\Delta }{\alpha }_{\mathrm{SP}}$ and $J_{\mathrm{eff}}$. These results suggest the feasibility of efficient control of spin pumping damping through controlled IEC, which has great significance for microwave spintronic devices based on asymmetric trilayer structures.

Magnetic-field-resilient superconducting circuits enable sensing applications and hybrid quantum computing architectures involving spin or topological qubits and electromechanical elements, as well as studying flux noise and quasiparticle loss. We investigate the effect of in-plane magnetic fields up to 1 T on the spectrum and coherence times of thin-film three-dimensional aluminum transmons. Using a copper cavity, unaffected by strong magnetic fields, we can probe solely the effect of magnetic fields on the transmons. We present data on a single-junction and a superconducting-quantum-interference-device (SQUID) transmon that are cooled down in the same cavity. As expected, the transmon frequencies decrease with increasing field, due to suppression of the superconducting gap and a geometric Fraunhofer-like contribution. Nevertheless, the thin-film transmons show strong magnetic field resilience: both transmons display microsecond coherence up to at least 0.65 T, and $T_1$ remains above $1\mu \text{s}$ over the entire measurable range. SQUID spectroscopy is feasible up to 1 T, the limit of our magnet. We conclude that thin-film aluminum Josephson junctions are suitable hardware for superconducting circuits in the high-magnetic-field regime.

The magneto-optical trap (MOT) is an essential tool for collecting and preparing cold atoms with a wide range of applications. We demonstrate a planar-integrated MOT by combining an optical grating chip with a magnetic coil chip. The flat grating chip simplifies the conventional six-beam configuration down to a single laser beam, and the flat coil chip replaces the conventional anti-Helmholtz coils of cylindrical geometry. Up to ${10}^6$ cold ${}^{87}\mathrm{Rb}$ atoms are trapped by the planar-integrated MOT, with the atom cloud being approximately $6\mathrm{mm}$ above the chip surface. This configuration effectively reduces the volume, weight, and complexity of the MOT, bringing benefits to applications including gravimeter, clock, and quantum memory devices.

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.