No abstract

The interaction between surface acoustic waves (SAWs) and spin waves (SWs) in a piezoelectric/magnetic thin film heterostructure yields potential for the realization of novel microwave devices and applications in magnonics. In the present work, we investigate the SAW-SW interaction in a Pt/Co(2 nm)/Ru(0.85 nm)/Co(4 nm)/Pt synthetic antiferromagnet (SAF) composed of two ferromagnetic layers with different thicknesses separated by a thin nonmagnetic Ru spacer layer. Because of the combined presence of interfacial Dzyaloshinskii-Moriya interaction (iDMI) and interlayer dipolar coupling fields, the optical SW mode shows a large nondegenerate dispersion relation for oppositely propagating SWs. Due to SAW-SW interaction, we observe nonreciprocal SAW transmission in the piezoelectric/SAF hybrid device. The equilibrium magnetization directions of both Co layers are manipulated by an external magnetic field to set a ferromagnetic, canted, or antiferromagnetic configuration. This has a strong impact on the SW dispersion, its nonreciprocity, and SAW-SW interaction. The experimental results are in agreement with a phenomenological SAW-SW interaction model, which considers the interlayer exchange coupling, iDMI, and interlayer dipolar coupling fields of the SWs.

We study the interaction of surface acoustic waves (SAWs) with spin waves (SWs) in a Co 40 Fe 40 B 20 /Au/Ni 81 Fe 19 system composed of two ferromagnetic layers separated by a nonmagnetic Au spacer layer. Because of interlayer magnetic dipolar coupling between the two ferromagnetic layers, a symmetric and an antisymmetric SW mode form, which both show a highly nondegenerate dispersion relation for oppositely propagating SWs. Due to magnetoacoustic SAW-SW interaction, we observe highly nonreciprocal SAW transmission in the piezoelectric-ferromagnetic hybrid device. We experimentally and theoretically characterize the magnetoacoustic wave propagation as a function of frequency, wave vector, and external magnetic field magnitude and orientation. Additionally, we demonstrate that the nonreciprocal SW dispersion of a coupled magnetic bilayer is highly tuneable and not limited to ultrathin magnetic films, in contrast to the nonreciprocity induced by the interfacial Dzyaloshinskii-Moriya interaction. Therefore, magnetoacoustic coupling in ferromagnetic multilayers provides a promising route towards building efficient acoustic isolators.

Wide passband interdigital transducers are employed to establish a stable phase-lock between a train of laser pulses emitted by a mode-locked laser and a surface acoustic wave generated electrically by the transducer. The transducer design is based on a multi-harmonic split-finger architecture for the excitation of a fundamental surface acoustic wave and a discrete number of its overtones. Simply by introducing a variation of the transducer's periodicity a frequency chirp is added. This combination results in wide frequency bands for each harmonic. The transducer's conversion efficiency from the electrical to the acoustic domain was characterized optomechanically using single quantum dots acting as nanoscale pressure sensors. The ability to generate surface acoustic waves over a wide band of frequencies enables advanced acousto-optic spectroscopy using mode-locked lasers with fixed repetition rate. Stable phase-locking between the electrically generated acoustic wave and the train of laser pulses was confirmed by performing stroboscopic spectroscopy on a single quantum dot at a frequency of 320 MHz. Finally, the dynamic spectral modulation of the quantum dot was directly monitored in the time domain combining stable phase-locked optical excitation and time-correlated single photon counting. The demonstrated scheme will be particularly useful for the experimental implementation of surface acoustic wave-driven quantum gates of optically addressable qubits or collective quantum states or for multicomponent Fourier synthesis of tailored nanomechanical waveforms.{|}~\ and rate \] were incommensurate ( \] ≠ • {|}~\ , being integer) to average the dynamic modulation of the QD over a full rf cycle in a single time-integrated spectrum [71].Phase-locked excitation with tunable laser of fixed repetition rate

A surface acoustic wave (SAW) delay line is used to study the metal-to-insulator (MI) transition of V2O3 thin films deposited on a piezoelectric LiNbO3 substrate. Effects contributing to the sound velocity shift of the SAW which are caused by elastic properties of the lattice of the V2O3 films when changing the temperature are separated from those originating from the electrical conductivity. For this purpose the electric field accompanying the elastic wave of the SAW has been shielded by growing the V2O3 film on a thin metallic Cr interlayer (coated with Cr2O3), covering the piezoelectric substrate. Thus, the recently discovered lattice precursor of the MI transition can be directly observed in the experiments, and its fine structure can be investigated.

We have measured both the current-voltage (I SD -V GS ) and capacitance-voltage (C-V GS ) characteristics of a MoS 2 − LiNbO 3 field effect transistor. From the measured capacitance we calculate the electron surface density and show that its gate voltage dependence follows the theoretical prediction resulting from the twodimensional free electron model. This model allows us to fit the measured I SD -V GS characteristics over the entire range of V GS . Combining this experimental result with the measured current-voltage characteristics, we determine the field effect mobility as a function of gate voltage. We show that for our device this improved combined approach yields significantly smaller values (more than a factor of 4) of the electron mobility than the conventional analysis of the current-voltage characteristics only.After the rise of graphene 1-3 , a wide range of twodimensional (2D) materials 4 shifted into focus of fundamental and applied research 5 . One particularly important class of 2D materials are transition metal dichalcogenides (TMDs) 6 . One important representative TMD is molybdenum disulfide, MoS 2 , whose indirect band gap changes to a direct one when its thickness is reduced to one single monolayer 7,8 . The resulting high optical activity and sizable bandgap of ∼ 1.9 eV make this material ideally suited for optoelectronic applications 9 and, thus the optical and electronic properties of MoS 2 and related materials have been investigated intensively in the last years 10 . In particular, field effect transistors (FETs) and logical circuit prototypes have been devised and realized [11][12][13] . In such devices, source and drain contacts are patterned onto the TMD film, and the charge carrier density is controlled by gate contacts. For FET devices, the transport mobility of the charge carriers in the conducting channel is of paramount importance. Here, different approaches exist to derive this key figure for FET devices. The most commonly applied method is to measure the source-drain current I SD as a function of the gate voltage V GS . Then, the field effect mobility µ FE is determined from a tangent to the linear region of the I SD (V GS )-dependence using the following formula known from FET theory:Here, C(V GS )/A is the capacitance per unit area, V SD the source-drain voltage, ∂ISD ∂VGS the slope of the linear a) Electronic region, L the length and w the width of the conducting channel. The intersection of the tangent with the abscissa represents the threshold voltage, V Th . However, this simple FET formula (1) assumes that the mobility is independent of the gate voltage. Moreover, the underlying parallel-plate capacitor model used to quantify the capacitance 11,14 assumes perfectly conducting, infinitely large plates. These assumptions may represent an oversimplification for 2D semiconductors 15,16 . To quantify the capacitance more precisely, Radisavljevic and coworkers 17 followed an indirect approach: the capacitance was determined from the carrier density obtained from Hall effect me...

Automated mixing of fluids with control over mixing parameters is of highest importance for reproducible production and chemical synthesis processes. We here introduce Surface Acoustic Waves (SAW) induced mixing of µL droplets for tailorable nanoparticle (NP) formation. Nucleic acid therapeutics represent extremely potent and innovative approaches to a variety of medical challenges, such as the treatment of cancer and genetic diseases. In this study, we apply this method to produce nucleic acid polymer complexes. Fusing two droplets containing either pDNA or cationic polymers leads to the formation of well-defined polyplexes. We show that droplet size and incubation time do not influence the desired particle characteristics significantly. However, the resulting nanoparticle diameter strongly depends on the SAW power level and educt concentrations, which indicates a kinetically controlled assembly process, while the particle shape is largely unaffected. Applying our novel technique to the formation of three-component-NP, we find that the choice of the mixing order can be used to decrease NP size even further. To address the kinetic interplay between mixing and particle growth, we apply our technique to homogenous mixing at high salt concentrations followed by a subsequent dilution step. Finally, by comparing various hand-and SAW-mixed polyplexes, we demonstrate significant differences in size while the cytotoxicity and in vitro efficacy remain roughly the same.

We study the interaction of Rayleigh and shear horizontal surface acoustic waves (SAWs) with spin waves in thin Ni films on a piezoelectric LiTaO 3 substrate, which supports both SAW modes simultaneously. Because Rayleigh and shear horizontal modes induce different strain components in the Ni thin films, the symmetries of the magnetoelastic driving fields, of the magnetoelastic response, and of the transmission nonreciprocity differ for both SAW modes. Our experimental findings are well explained by a theoretical model based on a modified Landau-Lifshitz-Gilbert approach. We show that the symmetries of the magnetoelastic response driven by Rayleigh and shear horizontal SAWs complement each other, which makes it possible to excite spin waves for any relative orientation of magnetization and SAW propagation direction and, moreover, can be utilized to characterize surface strain components of unknown acoustic wave modes.