Magnetic droplets are strongly nonlinear and localized spin-wave solitons that can be formed in current-driven nanocontacts. Here, we propose a simple way to launch droplets in an inhomogeneous nanoscopic waveguide. We use the drift motion of a droplet and show that in a system with broken translational symmetry, the droplet acquires a linear momentum and propagates. We find that the droplet velocity can be tuned via the strength of the break in symmetry and the size of the nanocontact. In addition, we demonstrate that the launched droplet can propagate up to several micrometers in a realistic system with reasonable damping. Finally, we demonstrate how an annihilating droplet delivers its momentum to a highly nonreciprocal spin-wave burst with a tunable wave vector with nanometer wavelengths. Such a propagating droplet can be used as a moveable spin-wave source in nanoscale magnonic networks. The presented method enables full control of the spin-wave emission direction, which can largely extend the freedom to design integrated magnonic circuits with a single spin-wave source.

Stochastic behavior fundamentally limits the performance and reliability of nanomagnetic devices. Typically, stochastic behavior is assumed to be the result of simple thermal activation, but it may also be “dynamically induced,” i.e., a direct result of the spatial and temporal complexity of magnetization dynamics. Here, we show how materials engineering can be used to comprehensively suppress dynamically induced stochasticity. Using the dynamics of magnetic domain walls in ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ nanowires as a case study, we show how manipulation of the Gilbert damping constant via doping with the rare-earth-element terbium dramatically simplifies domain-wall dynamics. This allows us to obtain quasi-deterministic behaviors from systems that nominally exhibit exceptionally high levels of stochasticity.

Thermoelectric (TE) materials can convert temperature difffferences into electricity directly and reversibly without air pollution, which provides a viable route for alleviating global warming and the energy crisis. Here, we use first-principles calculations combined with semiclassical Boltzmann transport theory to assess the potential of layered $\mathrm{La}\mathrm{Cu}\mathrm{O}\mathrm{Se}$ for TE applications. Originating from the layered crystal structure, the electronic and thermal transport properties (i.e., Seebeck coefficient, electrical conductivity, and thermal conductivity) are highly anisotropic between the in-plane and out-of-plane directions. The optimal figure of merit of 2.71 is achieved along the out-of-plane direction for electron doping at 900 K. Such excellent TE properties can be attributed to desired $\mathrm{La}$-$\mathrm{Se}$ interlayer interaction between adjacent layers and relatively strong coupling between acoustic phonons and optical phonons, resulting in simultaneous enhancement of the electrical conductivity and suppression of the lattice thermal conductivity. This study provides an effective route to improve the TE performance of layered $\mathrm{La}\mathrm{Cu}\mathrm{O}\mathrm{Se}$ by utilizing the anisotropic character of transport properties and offers implications in promoting related experimental investigations.

Quantum phase-estimation protocols can provide a measuring method of phase shift with precision superior to the standard quantum limit (SQL) due to the application of a nonclassical state of light. A squeezed vacuum state, whose variance in one quadrature is lower than the corresponding SQL, has been pointed out as a sensitive resource for quantum phase estimation and the estimation accuracy is directly influenced by the properties of the squeezed state. Here we analyze in detail the influence of the purity and squeezing level of the squeezed state on the accuracy of quantum phase estimation. The maximum precision that can be achieved for a squeezed thermal state is evaluated, and the experimental results are in agreement with the theoretical analyses. It is also found that the width of the phase-estimation interval $\mathrm{\Delta }\theta$ beyond SQL is correlated with the purity of the squeezed state.

Flux avalanche is commonly found in type II superconductors, and this event is always featured as being unpredictable and having ultrafast development with time. It is difficult to capture dynamically by any experimental method available today. Here, we propose a hypervelocity magnetic-optical system with two optical branches; one branch can trigger a dendritic flux avalanche in a superconducting film, and the other is capable of producing continuous multiexposure to record the lightning avalanche process. In contrast with some traditional trigger models, the present method realizes control of the position where the flux avalanche takes place. Second, we study the sensitive dependence on initial conditions of the present flux avalanche and find a series of positive Lyapunov exponents between two adjacent trajectories, which can be considered direct evidence for the chaotic dynamics in this kind of avalanche. Moreover, we reveal that, whether the laser spot is in the Meissner state or the mixed state, avalanches always penetrate from the edge of the superconducting film to the Meissner region, instead of occurring around the laser spot. This behavior clearly demonstrates that the presented avalanche is driven by the magnetic pressure force, which suggests that the optically triggered vortex avalanche possesses a different mechanism from that of the thermomagnetic avalanches commonly found in superconducting films.

We experimentally study the morphology of a radially expanding sheet of liquid tin, formed by nanosecond-pulse Nd:YAG laser impact on a spherical microdroplet. Specifically, the sheet thickness profile and its time evolution are captured in detail over a range of laser-pulse energies and for two droplet sizes. Two complementary methods to determine this thickness are employed and shown to be in excellent agreement. All obtained thickness profiles collapse onto a single self-similar curve. Spatial integration of the thickness profiles allows us to determine the volume of the sheet. Remarkably, less than half of the initial amount of tin remains in the sheet under conditions relevant for industrial sources of extreme ultraviolet light, where these thin tin sheets serve as target material. Further analysis shows that the dominant fraction of the mass lost from the sheet during its expansion ends up as fine fragments. We propose that such mass loss can be minimized by producing the sheet targets on the shortest possible time scale. These findings may be particularly valuable for ongoing developments in state-of-the-art nanolithography.

We experimentally demonstrate an alternative type of spin Hall nano-oscillator based on a vertical nanocontact fabricated on a $\mathrm{Pt}$/($\mathrm{Co}$/$\mathrm{Ni}$) multilayer. We analyze the spectral characteristics of the nano-oscillator as a function of current, magnetic field, and temperature. At sufficiently large currents, the oscillator exhibits dynamics at a frequency far below the ferromagnetic resonance, which at large fields exhibits a redshift with increasing current. At smaller fields and low temperatures, the frequency becomes nearly independent of current, with a well-defined threshold current. These distinct spectral characteristics of the demonstrated nano-oscillator can be explained by the formation of the magnetic droplet—a dissipative magnetic soliton stabilized by the local injection of spin current produced by the spin Hall effect in $\mathrm{Pt}$. The minimum linewidth exhibits a linear temperature dependence, suggesting single-mode dynamics, and enabling coherent magnetization auto-oscillation at room temperature. The demonstrated nano-oscillator geometry provides alternative opportunities for the development of active nanomagnetic devices and for optimization of their spectral characteristics for applications in microwave technology and spin-wave logic.

As opposed to metasurfaces, which can produce a single output waveform in response to a single input waveform, volumetric metamaterials have the ability to perform independent functions on many distinct input waveforms. Here, we present an experimental demonstration of this multiplexing capability using a volumetric metamaterial designed using the symphotic method, which realizes highly efficient multiplexing structures in the strong scattering limit. In contrast to perturbative design methods such as volume holography that are only applicable in weakly scattering media, we provide a comprehensive approach that takes into consideration design and fabrication constraints and that can be verified in simulations. We then demonstrate an experimental realization of a symphotic device operating at a frequency of 10 GHz, which has been optimized for three distinct input waveforms corresponding to three distinct output waveforms. The device is realized using a low-loss three-dimensionally printed material. The symphotic device consists of a lattice of dielectric cylindrical elements with varying radii, excited in a parallel-plate waveguide to enforce two-dimensional field symmetry. The experimental results show excellent agreement with analytical coupled-dipole-method simulations and finite-element simulations. The experiments further demonstrate the scalability of symphotic metamaterials and their viability for advanced rf and optical devices.

Despite rapid progress in the power-conversion efficiency of $\mathrm{Pb}$-based perovskite solar cells, both the long-term instability and $\mathrm{Pb}$ toxicity are still the main challenges for their commercial applications. Here, by first-principles $GW$ calculations, we find three kinds of two-dimensional (2D) 111-type $\mathrm{Pb}$-free $\mathrm{In}$-based halide perovskites of the form ${\mathrm{Cs}}_3{\mathrm{In}}_2{X}_9(X=\mathrm{Cl},\mathrm{Br},\mathrm{I})$ as promising alternatives to the star material ${{\mathrm{CH}}_3{\mathrm{NH}}_3\mathrm{Pb}\mathrm{I}}_3$ (${\mathrm{MA}\mathrm{Pb}\mathrm{I}}_3$) because of the following excellent electronic, optical, and transport properties: (i) The 2D $\mathrm{In}$-based halide perovskites are environmentally friendly lead-free materials. (ii) Compared with $\mathrm{MA}\mathrm{Pb}{X}_3$, they have greater structural stability. (iii) As energetic photovoltaic materials, 2D ${\mathrm{Cs}}_3{\mathrm{In}}_2{\mathrm{I}}_9$ perovskites are direct-band-gap semiconductors with optimal band gaps from 1.25 eV (trilayer) to 1.47 eV (monolayer). (iv) The 2D ${\mathrm{Cs}}_3{\mathrm{In}}_2{X}_9$ perovskites have ideal band structures for solid-state lighting with a wide direct-optical-band-gap range (approximately 0.94–3.54 eV), covering the whole visible-light region, and light electron (heavy hole) effective mass, which will directly enhance the defect-insensitive emission efficiency due to the localization of holes. Particularly, ${\mathrm{Cs}}_3{\mathrm{In}}_2{\mathrm{Br}}_x{\mathrm{Cl}}_{9-x}$ has a suitable direct optical band gap for highly desired blue emission. (v) The absorption coefficient of ${\mathrm{Cs}}_3{\mathrm{In}}_2{X}_9$ is up to $7\times {10}^4{\mathrm{cm}}^{-1}$, which is between that of $\mathrm{Ga}\mathrm{As}$ (${10}^4{\mathrm{cm}}^{-1}$) and that of ${\mathrm{MA}\mathrm{Pb}\mathrm{I}}_3$ (${10}^5{\mathrm{cm}}^{-1}$). (vi) The estimated power-conversion efficiency in ${\mathrm{Cs}}_3{\mathrm{In}}_2{\mathrm{I}}_9$ reaches 28%, which is close to that of ${\mathrm{MA}\mathrm{Pb}\mathrm{I}}_3$ (30%). These findings pave a way for designing nontoxic, stable, and high-performance photovoltaic and light-emitting devices.

By dissolving sodium chloride ($\mathrm{Na}\mathrm{Cl}$) in liquid water, we realize an obvious enhancement of stimulated Raman scattering (SRS). Compared with pure water, the performance improvements include spectrum purification, an increased Raman gain, a decreased pump threshold, and an increased conversion efficiency. In the best SRS results, the pump threshold decreases by 45% and the maximum conversion efficiency increases by 10.4%. Then, water becomes a typical Raman-scattering medium that generates narrowband light. Moreover, we find that the bulk structure of water and $\mathrm{Na}\mathrm{Cl}$ solutions can be analyzed in detail by combining the principles of SRS and analysis of the SRS spectra. In water, the $\mathrm{O}—\mathrm{H}$ stretching band is proved to be a superposition of stretching modes of different water clusters. For the solution, the $\mathrm{O}—\mathrm{H}$ stretching vibration of water molecules in hydration shells around ${\mathrm{Cl}}^{-}$ ions can be obtained directly, and its variation with respect to solute concentration is investigated using SRS spectra. The superior SRS properties of solutions originate from the hydration shell around the ${\mathrm{Cl}}^{-}$ ions. This work suggests that SRS is a promising approach to identifying structures in water and $\mathrm{Na}\mathrm{Cl}$ solutions, and that it can easily be extended to other liquids and solutions.

${\mathrm{He}}^{+}$-ion irradiation enables controlled postdeposition modification of layered magnetic thin-film systems. The degree of modification and its depth profile can be tuned by the irradiation dose and energy. Here, we use magnetometry and magnetic force microscopy to explore the impact of gentle ${\mathrm{He}}^{+}$-ion irradiation on synthetic antiferromagnets, consisting of ferromagnetic $\mathrm{Co}/\mathrm{Pt}$ multilayers with perpendicular magnetic anisotropy, which are antiferromagnetically (AF) coupled via $\mathrm{Ru}$ interlayers. This system shows a rich variety of magnetic domain patterns due to the strong competition between different magnetic energies. We show that AF interlayer exchange and perpendicular interface anisotropy energy are gradually reduced by the ion irradiation while the demagnetization energy is mainly preserved, which thus results in multiple successive magnetic-phase transitions.

We investigate theoretically the possibility of using the cold-electron bolometer (CEB) as a counter for 1-cm-wavelength (30-GHz) photons. To reduce the flux of photons from the environment that interact with the detector, the bath temperature is assumed to be below 50 mK. At such temperatures, the time interval between two subsequent photons of 30 GHz that hit the detector is more than 100 h, on average, for a frequency window of 1 MHz. Such temperatures allow the observation of the physically significant photons produced in rare events, such as axion conversion (or Primakoff conversion) in a magnetic field. We present the general formalism for the detector’s response and noise, together with numerical calculations for proper experimental setups. We observe that the current-biased regime is favorable due to lower noise and allows for photon counting at least below 50 mK. For the experimental setups investigated here, the voltage-biased CEBs may also work as photon counters but with less accuracy and, eventually, may require smaller volumes of the normal-metal island.

Spintronic materials with two-dimensional (2D) transition-metal dichalcogenide (TMD)/ferromagnet (FM) interfaces have received a great deal of interest recently due to strong modulation of the magnetic properties, which provide attractive opportunities for magnetic information storage. Here, we demonstrate the strong spin-orbit coupling (SOC) effect and great interfacial tuning of magnetization dynamics in $M{X}_2$/$\mathrm{Co}\text{−}\mathrm{Fe}\text{−}\mathrm{B}$ thin films by means of a time-resolved magneto-optical Kerr approach, where M is chosen as $\mathrm{Mo}$ or $\mathrm{W}$ and X is $\mathrm{S}$ or $\mathrm{Se}$. The significant drop of demagnetization time, ${\tau }_m$, and increase of magnetic damping factor, ${\alpha }_s$, clearly highlight the presence of high interfacial SOC strength in just one monolayer of ${\mathrm{Mo}\mathrm{S}}_2$. Compared with the single $\mathrm{Co}\text{−}\mathrm{Fe}\text{−}\mathrm{B}$ film, the precession frequency, f, is lowered after inserting a $M{X}_2$ layer, suggesting a reduction of the effective magnetization, $4\pi M_{\mathrm{eff}}$, originating from the interfacial d-d hybridization effect. The role of SOC strength on ${\tau }_m$, $M_{\mathrm{eff}}$, and ${\alpha }_s$ is confirmed by using different TMD materials, and thus, demonstrates that the element M plays a dominant role. The samples with ${\mathrm{WS}}_2$ or ${\mathrm{W}\mathrm{Se}}_2$ have much shorter ${\tau }_m$, smaller $M_{\mathrm{eff}}$, and larger ${\alpha }_s$ values due to the strong SOC interaction of heavier atoms. The observed efficient control of dynamic magnetic behavior will further promote the development of TMD/FM materials for practical spintronic applications with ultrafast manipulation speed and low energy consumption.

The magnetoelectric (ME) effect in composites, a strain-mediated coupling phenomenon between piezoelectric and magnetostrictive phases, has a wide range of technological applications. Here, ME coupling phenomena are explored in $\mathrm{Pb}$-free piezoelectric, $0.5\mathrm{Ba}({\mathrm{Zr}}_{0.2}{\mathrm{Ti}}_{0.8}){\mathrm{O}}_3\text{−}0.5({\mathrm{Ba}}_{0.7}{\mathrm{Ca}}_{0.3}){\mathrm{Ti}\mathrm{O}}_3$ and piezomagnetic ${\mathrm{Ni}\mathrm{Fe}}_2{\mathrm{O}}_4$ bilayer laminate composites. The direct and converse ME coupling strengths are found to be enhanced at the electromechanical resonance modes, rather than at the off-resonance frequencies. Here, it is proposed to further enhance the ME coupling strength at electromechanical resonance modes by the in-phase superimposition of the radial and second bending modes via varying the bilayer thickness, which, in turn, varies the volume fraction of the bilayer. The proposed enhanced ME coupling is experimentally demonstrated at a theoretically envisaged bilayer thickness of about 1.8 mm. This results in a large direct ME coupling coefficient of $22.5\mathrm{V}\mathrm{c}{\mathrm{m}}^{-1}\mathrm{O}{\mathrm{e}}^{-1}$, which is around 100% more than the values observed at individual resonance modes. The results are further validated by calculations from theoretical models. The method adopted in this work gives a roadmap to the significant enhancement of the ME effect in laminate composites.

Temporal variations of $\mathrm{Cu}(\mathrm{In},\mathrm{Ga}){\mathrm{Se}}_2$ photovoltaic device properties during light exposure at various temperatures and voltage biases for times up to 100 h are analyzed using the kinetic theory of large lattice relaxations. Open-circuit voltage and $p$-type doping increased with charge injection and decreased with temperature at low injection conditions. Lattice relaxation can account for both trends and activation energies extracted from the data are approximately 0.9 and 1.2 eV for devices with lower and higher sodium content, respectively. In these devices, increased sodium content resulted in higher initial $p$-type doping with greater stability. First-principles calculations providing revised activation energies for the $(V_{\mathrm{Se}}-V_{\mathrm{Cu}})$ complex suggest that this defect does not account for the metastability observed here.

Highly directional and lossless surface waves have significant potential applications in two-dimensional photonic circuits and devices. Here, we experimentally demonstrate a selective Dyakonov surface wave coupling at the interface between a transparent polycarbonate material and a nematic liquid crystal 5CB. By controlling the anisotropy of the nematic liquid crystal with an applied magnetic field, a single ray at a certain incident angle from a diverged incident beam can be selectively coupled into a surface wave. The implementation of this property may lead to a new generation of on-chip integrated optics and two-dimensional photonic devices.