High-temperature ferromagnetic resonance (FMR) in $\mathrm{FePt}$-based media materials is studied for the first time. The FMR linewidth (ΔH) as a function of temperature (T), field angle (${\theta }_H$), and the volume fraction (x) of carbon in the material is determined, and the effective Gilbert damping constant and the Bloch−Bloembergen relaxation time are estimated. The data suggest that at temperatures 10–45 K below the Curie temperature, two-magnon scattering and spin-flip magnon-electron scattering make comparable contributions to ΔH. With a decrease in T, ΔH increases due to enhancement of the two-magnon scattering. ΔH can be tuned via varying x and shows a maximum at ${\theta }_H\approx {45}^{\circ }$ when varying ${\theta }_H$.

We demonstrate the complete filling of both deionized water (DI water) and liquid metal (eutectic gallium-indium, $\mathrm{E}\mathrm{Ga}\mathrm{In}$) into closed-end microchannels driven by a constant pressure at the inlet. A mathematical model based on gas diffusion through a porous polydimethylsiloxane (PDMS) wall is developed to unveil the physical mechanism in the filling process. The proposed theoretical analysis based on our model agrees well with the experimental observations. We also successfully generate traveling surface acoustic waves by actuating interdigitated microchannels filled with $\mathrm{E}\mathrm{Ga}\mathrm{In}$. Our work provides significant insights into the fabrication of liquid electrodes that can be used for various acustofluidics applications.

We provide a transmission-line representation for channels exhibiting spin-momentum locking (SML) that can be used for both time-dependent and steady-state transport analysis on a wide variety of materials with spin-orbit coupling such as topological insulators, Kondo insulators, transition metals, semimetals, oxide interfaces, and narrow band-gap semiconductors. This model is based on a time-dependent four-component diffusion equation obtained from the Boltzmann transport equation assuming linear response and elastic scattering in the channel. We classify all electronic states in the channel into four groups ($U^{+}$, $D^{+}$, $U^{-}$, and $D^{-}$) depending on the spin index [up ($U$), down ($D$)] and the sign of the $x$ component of the group velocity ($+,-$) and assign an average electrochemical potential to each of the four groups to obtain the four-component diffusion equation. For normal metal channels, the model decouples into the well-known transmission-line model for charge and a time-dependent version of the Valet-Fert equation for spin. We first show that, in the steady-state limit, our model leads to simple expressions for charge-spin interconversion in SML channels in good agreement with existing experimental data on diverse materials. We then use the full time-dependent model to study spin-charge separation in the presence of SML, a subject that has been controversial in the past. Our model shows that the charge and spin signals travel with two distinct velocities, resulting in well-known spin-charge separation, which is expected to persist even in the presence of SML. However, our model predicts that the lower velocity signal is purely spin, while the higher velocity signal is largely charge with an additional spin component proportional to the degree of SML, which has not been noted before. Finally, we note that our model can be used within standard circuit simulators such as SPICE to obtain numerical results for complex geometries.

The magnetic properties of graphene have attracted much attention for more than a decade. Recent studies have shown that adatoms or atomic vacancies in graphene could exhibit localized magnetic moments. However, a macroscopic spin-polarized semiconducting band structure has never been experimentally realized in graphene. Here, we demonstrate that a graphene monolayer, hybridized with an underlying $\mathrm{Ni}(111)$ substrate, exhibits a spin-polarized semiconducting state even at room temperature. Our spin-polarized scanning tunneling microscopy (STM) experiments, complemented by first-principles calculations, explicitly demonstrate that the interaction between graphene and the $\mathrm{Ni}$ substrate generates a large gap in graphene and simultaneously leads to a relative shift between majority- and minority-spin bands. Consequently, the graphene sheet on the $\mathrm{Ni}$ substrate exhibits a spin-polarized gap with an energy of several tens of meV even at room temperature.

The formation of instabilities linked with plasma flares of several centimeters (ionization zone) and driven by low to moderate current in three-dimensionally confined magnetron plasma is experimentally observed in a side-on view near the vicinity of the substrate. The flare velocity on account of cross-field drift is found to be 20.5 km/s with an estimated local tangential field $E_t\sim 205\mathrm{V}/\mathrm{m}$. The optical and Langmuir-probe measurements unambiguously demonstrate that an approximately 5.3-cm-wavelength wave of plasma particles propagating along the approximately $E_t\times B_0$ drift is accountable for the excitation and ionization of atoms. The observed instability is associated with a characteristic double layer with a potential drop of approximately 6.1 V.

We demonstrate spectroscopic microtomography in the visible wavelength range (450–700 nm) using digital holographic tomography, a wavelength-scanning source, and a variable-optical-path-length strategy. This multidimensional imaging system can directly measure the absorption-coefficient and refractive-index spectra of a three-dimensional specimen. We apply the system developed to characterize three types of polystyrene beads (undyed, blue dyed, and red dyed) as well as oxygenated and deoxygenated single red blood cells.

In this paper, we present and study the dynamics of an active microwave cloaking technique that alleviates the trade-offs between loss, bandwidth, and size inherent in passive approaches. The presented cloak consists of a finite number of satellite antennas loaded with parity-time-symmetric lumped admittances, which, without external control, can track in real time the amplitude, frequency, and phase variations of the impinging signals and generate the required current distributions at the antennas to totally suppress the scattered waves, including reflections and shadows. We analytically derive the optimal density and frequency dispersion of the antenna satellites surrounding the object in order to achieve substantial reduction in the scattering crosssection over a wide bandwidth. We also investigate the conditions necessary to maintain the cloak stability and study its transient response for excitation with pulsed signals.

Based on micromagnetic simulations, magnetization switching in a triangle magnetic element by voltage control of the magnetic anisotropy and Dzyaloshinskii-Moriya interaction under an in-plane magnetic field is proposed. The proposed switching scheme is not toggle switching but deterministic switching, in which the magnetic state is determined by the polarity of the applied voltage pulse. The mechanism and conditions for the switching are clarified. The results provide a fast and low-power writing method for magnetoresistive random-access memories.

We introduce a multiscale framework that combines a time-dependent nonequilibrium Green-function (TDNEGF) algorithm, scaling linearly in the number of time steps and describing quantum-mechanically the conduction electrons in the presence of time-dependent fields of arbitrary strength or frequency, with classical time evolution of localized magnetic moments described by the Landau-Lifshitz-Gilbert (LLG) equation. The TDNEGF+LLG framework can be applied to a variety of problems where current-driven spin torque induces the dynamics of magnetic moments as the key resource for next-generation spintronics. Previous approaches to such nonequilibrium many-body systems (like the steady-state-NEGF+LLG framework) neglect noncommutativity of a quantum Hamiltonian of conduction electrons at different times and, therefore, the impact of time-dependent magnetic moments on electrons leading to the pumping of spin and charge currents. The pumped currents can, in turn, self-consistently affect the dynamics of magnetic moments themselves. Using the magnetic domain wall (DW) as an example, we predict that its motion will pump time-dependent spin and charge currents (on top of the unpolarized dc charge current injected through normal-metal leads to drive the DW motion), where the latter can be viewed as a realization of quantum charge pumping due to the time dependence of the Hamiltonian and the left-right symmetry breaking of the two-terminal device structure. The conversion of ac components of spin current, whose amplitude increases (decreases) as the DW approaches (recedes from) the normal-metal lead, into ac voltage via the inverse spin Hall effect offers a tool to precisely track the DW position along magnetic nanowire. We also quantify the DW transient inertial displacement due to its acceleration and deceleration by pulse current and the entailed spin and charge pumping. Finally, TDNEGF+LLG as a nonperturbative (i.e., numerically exact) framework allows us to establish the limits of validity of the so-called spin-motive force (SMF) theory for pumped charge current by time-dependent magnetic textures—the perturbative analytical formula of SMF theory becomes inapplicable for large frequencies (but unrealistic in a magnetic system) and, more importantly, for increasing noncollinearity when the angles between neighboring magnetic moments exceed approximately ${10}^{\circ }$.

Laser-induced modulation of the magnetization dynamics occurring over various timescales are unified here for a ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ thin film excited by amplified femtosecond laser pulses. The weak correlation between demagnetization time and pump fluence with substantial enhancement in remagnetization time is demonstrated using a three-temperature model considering the temperatures of electron, spin, and lattice. The picosecond magnetization dynamics is modeled using the Landau-Lifshitz-Gilbert equation. With increasing pump fluence the Gilbert damping parameter shows significant enhancement from its intrinsic value due to an increment in the ratio of electronic temperature to Curie temperature within a very short timescale. The precessional frequency experiences a noticeable redshift with increasing pump fluence. The changes in the local magnetic properties due to accumulation and dissipation of thermal energy within the probed volume are described by the evolution of the temporal chirp parameter in a comprehensive manner. A unification of ultrafast magnetic processes and its control over a broad timescale will enable the integration of various magnetic processes in a single device and use one effect to control another.

Active research on mesoscopic quantum systems has increased our understanding of and ability to control quantum objects, allowing the construction of a universal form for quantum networks that consist of more than one physical system. This kind of quantum network is anticipated to enable the building of quantum infrastructure, such as long-distance quantum communication and distributed quantum computers, and motivates the establishment of photonic quantum interfaces that are compatible with physical systems. Here, a universal photonic quantum interface is experimentally developed with the benefit of a unique, specially designed entangled photon source. The detailed experimental results show that this configuration can satisfy all the urgent demands for a photonic quantum interface, including the accurate matching of the working wavelength and bandwidth and specifically, the entanglement ability ($F=89.6\mathrm{\%}$, $S=2.36\pm 0.03$). The realization of this universal photonic quantum interface is expected to expedite the construction of much more complex quantum networks and to be a major step in the area of optical engineering and control.

Oxygen ion exchanges at the surface of transition metal oxides have been extensively studied for understanding their nanoscale ionic behavior as well as for realizing multifunctionalities such as exotic magnetism, insulator-to-metal transition, band gap tuning, etc. To activate this exchange behavior, in many cases extreme conditions such as high temperature, high electric fields, and high vacuum are often required. These conditions have blocked the promising materials from being applied on real devices such as solid-oxide fuel cells and other electrochemical devices. In this article, we show that redox-driven reversible topotactic transformation in epitaxial $\mathrm{Sr}{\mathrm{Fe}}_{0.8}{\mathrm{Co}}_{0.2}{\mathrm{O}}_{3\text{−}x}$ thin films can be achieved at low temperature and at atmospheric pressure. This transformation triggers changes in electronic structures as well. These reversible redox reactions and/or associated changes at low temperature and under atomospheric pressure are particularly needed to develop a cathode for low solid-oxide fuel cells.

Conventional impurity doping of ultrasmall nanoscale silicon ($\mathrm{Si}$) currently used in very-large-scale integration faces serious miniaturization challenges below the 14-nm technology node such as dopant out-diffusion and inactivation by clustering in $\mathrm{Si}$-based field-effect transistors (FETs). For $\mathrm{Si}$ nanocrystals showing quantum confinement, self-purification and massively increased ionization energies cause doping to fail. Modulation doping is widely used in group III–group V materials in particular for optoelectronic applications, where high carrier densities at low scattering and nonradiative recombination rates are crucial. Setting out from our recent success to introduce modulation acceptors into ${\mathrm{Si}\mathrm{O}}_2$ with aluminum to provide holes to $\mathrm{Si}$ [König et al., Sci. Rep. 7, 46703 (2017)], we follow our atomistic concept to investigate other possible modulation acceptors in ${\mathrm{Si}\mathrm{O}}_2$. Using density functional theory and experimental verification of key candidates by capacitance-voltage and deep-level-transient-spectroscopy measurements, we elucidate the role of atomistic parameters that determine the ability of the dopant species to provide modulation-acceptor states to ${\mathrm{Si}\mathrm{O}}_2$ and thus holes to $\mathrm{Si}$. Modulation-doped ${\mathrm{Si}\mathrm{O}}_2$ can replace conventional doping of ultrasmall nanoscale $\mathrm{Si}$ from the ${\mathrm{Si}\mathrm{O}}_2$ coating or trench of a FET and have a high potential for carrier-selective tunneling contacts in $\mathrm{Si}$-based heterojunction solar cells and tunnel FETs.

Nanocatalysts with their unique properties play an increasingly crucial role in areas ranging from energy and the environment to medical sciences. Despite numerous experimental studies on the utilization of nanocatalysts, there is a lack of theoretical understanding about the effectiveness of nanocatalyst application in porous media. In this study, we conduct both linear stability analysis (based on Quasi-Steady-State approximation) and nonlinear numerical simulations (based on a pseudospectral technique) to investigate mixing and in situ conversion of a reactant in the presence of nanocatalysts. Using the linear stability analysis, we parameterize the role of the in situ conversion on the stability of the system. Characterization of the nanocatalyst efficiency in terms of the degree of mixing and in situ conversion rate of the reactant is also performed through nonlinear numerical simulations. Our results show that while the increase of the nanocatalyst log mobility ratio attenuates the instabilities at the displacement front, the progress of the nanocatalytic reaction demonstrates a destabilizing effect. It is also seen that the nanocatalyst deposition leads to the rise of two competing mechanisms, the interplay of which controls the dynamics of miscible nanocatalytic reactive flows in porous media. Moreover, we introduce the effective penetration depth of nanocatalysts in porous media. Results reveal the crucial role of viscous fingering for increasing the reaction rate and indicate how the injected nanocatalysts lose their effectiveness due to their deposition in porous media. This study provides new insight into the application of nanocatalysts in porous media.

Optical and thermal metamaterials-based devices have been extensively explored under the guidance of transformation optics/thermotics theories to tune light and heat propagation to realize unprecedented functions, such as cloaking, concentrating, camouflaging, etc. Other than these functions, what else can they do? In this paper, we demonstrate another interesting and potential application, thermal encoding, based on the thermal energy shielding and harvesting units. The proposed thermal encoding protocol takes advantage of the binary (contrary) states of heat flux through two units, which can be encoded as binary digits of 1 and 0, respectively. Steady and transient simulations and experiments validate the feasibility of thermal encoding, which can be further effectively encrypted depending on the encoding or decoding protocol. Such thermal encoding supplements the existing implementations of thermal memory or computing. The proposed encoding protocol may open an alternative avenue for triggering counterpart developments by utilizing the binary states of electromagnetic and optical metamaterials for information encoding, decoding, and storage.

We present a rigorous analytical model for understanding the multipole emission enhancement of sound using acoustic metamaterials. A two-dimensional cylindrical hyperlens-like structure is utilized as a demonstration structure. An analytical expression for the enhanced efficiency is obtained via radiation impedance theory. The analytical results show that enhanced multipole radiation can be achieved by using only one monopole source encircled by the structure. The good agreement between the analytical and the simulation results and the experimental results verifies the applicability of our analytical model. Consequently, our analytical model provides an efficient and intuitive tool for synthesis and analysis of enhanced emission systems.

Magnetoelectric interfaces provide efficient pathways for manipulating the magnetic order with low-power-consuming electric fields. A prime example of this is the voltage-controlled domain-pattern transfer from a multiferroic ${\mathrm{Bi}\mathrm{Fe}\mathrm{O}}_3$ film into an amorphous ${\mathrm{Co}}_{0.9}{\mathrm{Fe}}_{0.1}$ ferromagnetic layer. Here we use a combination of optical second-harmonic generation and magnetic force microscopy to scrutinize the evolution of this transfer under voltage application. The nondestructive nature of our analysis permits the in operando examination of the magnetoelectric poling. We trigger ferroelectric switching events in ${\mathrm{Bi}\mathrm{Fe}\mathrm{O}}_3$ and track the evolution of their magnetoelectric transfer to the ferromagnetic domains of ${\mathrm{Co}}_{0.9}{\mathrm{Fe}}_{0.1}$ with spatial resolution. This reveals a wake-up effect in the magnetoelectric coupling across the interface. It is followed by simultaneous 90° rotations of the in-plane net polarization and net magnetization that progress with the increase of the voltage applied to the device.

Based on standard silicon-on-insulator platforms, we propose an interferometer structure operating at telecom wavelengths that is driven by pump-induced nonlinear Kerr-effect. Special attention is given to the waveguide design in achieving the smallest full-vectorial effective mode area corresponding to the largest nonlinear phase shift. We present that this work is so far, in theory, the most promising approach for high-speed optical-driven quantum interference, whose realizability is reflected in two advantages: (1) the proposed strategy mitigates the pump-induced noise from the sideband, spontaneous four-wave mixing, and spontaneous Raman scattering and (2) the pulsed pump at $2.2\mu \mathrm{m}$ facilitates a relatively higher nonlinear response and negligible free-carrier absorption.

Through recent advances, the relevance of magnetic tunnel junctions (MTJs) to the microelectronics industry continues to rise. However, their reversal speed still suffers from incubation delay, a consequence of the collinear magnetization equilibrium states in perpendicularly magnetized MTJs (p-MTJs). We propose to tune the free layer in a $\mathrm{Co}\text{−}\mathrm{Fe}\text{−}\mathrm{B}$/$\mathrm{Mg}\mathrm{O}$/$\mathrm{Co}\text{−}\mathrm{Fe}\text{−}\mathrm{B}$ stack close to the reorientation transition, aiming to inducing a noncollinearity between the free layer and the reference layer to improve the magnetization reversal speed. Upon varying the layer thickness, the introduction of an in-plane magnetic component is observed in the free layer. Through time-resolved step-response measurements of the conductance, the dynamics are observed to consist of a stochastic delay followed by a repeatable magnetization-reversal pathway. We explore the separation of the measured response into these components and find the power requirements and switching speed to improve over the p-MTJ reference. This is a direct demonstration of the noncollinear improvement pathway, which is appealing for applications where the switching speed and a low energy cost of operation prevail over long-term stability.

Photophoretic force due to the optically-induced thermal effect provides an effective way to manipulate the light-absorbing particles suspended in ambient gases. However, how this force temporally responds to the intensity modulation of the illumination light is unclear. Here, by vertically trapping a micron-sized absorbing particle with a negative photophoretic force generated by a focused Gaussian beam, we demonstrate that the temporal change in the photophoretic force in response to the intensity modulation is remarkably slow (with a time constant up to approximately 1 s) due to the slow change in the particle’s temperature. When the trapping beam is turned off for a few tens or hundreds of milliseconds, the trapped particle is pulled up toward the light source by the remaining photophoretic force, whereas when the intensity of the trapping beam is increased for a short duration, the particle is pushed off by the radiation pressure. The instantaneous position of the trapped particles following the intensity modulation of the trapping laser is tracked and theoretically modelled. The understanding of the temporal behavior of the photophoretic force will be useful for the control of photophoretic-based optical pulling, transportation, and manipulation of atmospheric particles.