In-plane Components Research Articles

Vectorization of magneto-optical images of a in plane component of inhomogeneous magnetic fields

A method based on the magneto-optical Kerr effect is demonstrated, which makes it possible to quantitatively determine spatial dependences of the directions of an in-plane component of inhomogeneous magnetic field visualized by soft nanocrystalline films. The method consists in obtaining magneto-optical images of micromagnetic structures that are formed under the influence of an inhomogeneous field. Images in the longitudinal and transverse sensitivity of the Kerr effect are used to calculate the angular dependence of the directions of the unit vectors of this field under the assumption that the components of the field are proportional to the brightness of magneto-optical images. The field direction maps obtained in this way agree with model calculations for our magnets.

Seismic responses of near-fault building clusters including in-plane rotational component in investigated lump model of earth medium

An algorithm is proposed for modeling wave propagation with in-plane rotational component in earth medium. The proposed algorithm can not only carry out in-plane rotational wave propagation in half-space medium but also correctly undertake in-plane dynamic moment loading. Connecting ground and structure dynamically, a numerical method is given for implementing translational and rotational wave propagation in building clusters and earth medium caused by fault rupture. Three verification examples’ results show correctness of the proposed algorithm in calculating ground responses due to a single vertical force, dynamic moment loading and finite-fault seismic sources, respectively. The seismic responses of near-fault building clusters are simulated during an Mw6.0 hypothetical earthquake. It is shown that in-plane rotational wave propagation in earth medium may increase significantly structural seismic responses. In all the three building clusters, the structural seismic response most affected by in-plane rotational wave propagation in earth medium is median bending moment (maximal increasing rate up to 163.0%), the second is inter-storey shear force (maximal increasing rate up to 37.5%) and the third is inter-storey drift (maximal increasing rate up to 24.2%). The existence of structural in-plane rotation can increase the horizontal displacements on the roof of buildings on the hanging wall and rupture forward of fault and decrease those on the footwall of fault. Altogether, the each-storey peak earthquake responses of one structure on hanging wall are larger than those of another identical structure on footwall at the same distance from fault-ground intersecting line. The contribution of rotational wave field in earth media and structures to structural responses should be considered in analyzing seismic responses of a city.

A Homogeneous Anisotropic Hardening Model in Plane Stress State for Sheet Metal under Nonlinear Loading Paths.

In sheet metal forming, the material is usually subjected to a complex nonlinear loading process, and the anisotropic hardening behavior of the material must be considered in order to accurately predict the deformation of the sheet. In recent years, the homogeneous anisotropic hardening (HAH) model has been applied in the simulation of sheet metal forming. However, the existing HAH model is established in the second-order stress deviator space, which makes the calculation complicated and costly, especially for a plane stress problem such as sheet metal forming. In an attempt to reduce the computational cost, an HAH model in plane stress state is proposed, and called the HAH-2d model in this paper. In the HAH-2d model, both the stress vector and microstructure vector contain only three in-plane components, so the calculation is significantly simplified. The characteristics of the model under typical nonlinear loading paths are analyzed. Additionally, the feasibility of the model is verified by the stress-strain responses of DP780 and EDDQ steel sheets under different two-step uniaxial tension tests. The results show that the HAH-2d model can reasonably reflect the Bauschinger effect and the permanent softening effect in reverse loading, and the latent hardening effect in cross loading, while the predictive accuracy for cross-loading softening remains to be improved. In the future, the HAH-2d model can be further modified to describe more anisotropic hardening behaviors and applied to numerical simulations.

Strain-induced giant enhancement of anisotropic dielectric constant in layered nitrides SrHfN2 and SrZrN2.

The development of information technology puts forward huge demand for electronic materials with high dielectric constants; first-principles calculations and simulations have been demonstrated as an efficient technique for screening and exploring novel dielectric materials. In the present study, first-principles calculations combined with density functional perturbation theory are employed to study the dielectric properties of two newly discovered layered nitrides SrHfN2 and SrZrN2 under strain. By analyzing the evolution of lattice distortion, dielectric constant, Born effective charge, and phonon modes along with the applied strain, we find that the biaxial strain and isotropic strain can effectively modulate the dielectric constant. The two nitrides SrHfN2 and SrZrN2 are dynamically stable up to biaxial tensile strains of 2.1% and 1.8%, and the dielectric constants have been enlarged to about 500 and 2000. Furthermore, the dielectric constant is dramatically enhanced by 15 (9) times to a maximum value of ∼2600 (2700) under an isotropic tensile strain of 1.2% (0.7%) for SrHfN2 (SrZrN2), which is mainly due to the softening of the lowest-frequency infrared-active phonon mode and the increasing octahedral distortion degree. Particularly, the ionic contribution of the dielectric constant shows very remarkable anisotropy and plays a dominant role in the change of the dielectric constant, whose in-plane components exhibit giant enhancement by 18 (10) times for SrHfN2 (SrZrN2). This work not only sheds light on the experimentally observed high dielectric constants of SrHfN2 and SrZrN2, but also provides an effective route to regulate the anisotropic dielectric constants by applied strain, which indicates promising applications in optical and electronic devices.

Majorana zero modes in a magnetic and superconducting hybrid vortex

We propose and investigate a new platform for the realization of Majorana zero modes in a thin-film heterostructure composed of an easy-plane ferromagnet and a superconductor with spin-orbit coupling. The system can support an energetically favorable bound state comprising a magnetic vortex and a superconducting vortex. We show that a hybrid vortex thus created can host a robust zero-energy Majorana bound state at its core over a wide range of parameters, with its partner zero mode located at the boundary of a disk-shaped topological region. We identify a novel mechanism underlying the formation of the topological phase that, remarkably, relies on the orbital effect of the magnetization field and not on the usual Zeeman effect. The in-plane components of magnetization couple to electrons as a gauge potential with nonzero curl, thus creating an emergent magnetic field responsible for the gapped topologically nontrivial region surrounding the vortex core. Our construction allows the mobility of magnetic vortices to be imposed on the Majorana zero mode at the core of the superconducting vortex. In addition, the system shows a rich interplay between magnetism and superconductivity which might aid in developing future devices and technologies.

Angle-resolved resistivity method for precise measurements of electronic nematicity

Electronic nematicity is an intriguing phenomenon found in unconventional superconductors and its mechanism invokes intense studies. The precise measurement of the director and amplitude of electronic nematicity by electric transport demands a full mapping of the longitudinal and transverse resistivity, $\ensuremath{\rho}$ and ${\ensuremath{\rho}}_{T}$, along different directions. Fabricating Hall bars along every possible in-plane direction would be so labor intensive and vulnerable to sample to sample variations that it becomes impractical. Instead, here we make the local current density $\mathbit{J}$ continuously rotate in plane by independently controlling its in-plane components along two orthogonal axes and measure $\ensuremath{\rho}$ and ${\ensuremath{\rho}}_{T}$ as a function of the azimuth angle $\ensuremath{\phi}$ between $\mathbit{J}$ and the crystallographic $[100]$ direction. Clear substantial angular oscillations in $\ensuremath{\rho}(\ensuremath{\phi})$ and ${\ensuremath{\rho}}_{T}(\ensuremath{\phi})$ were observed from the optimally doped ${\mathrm{La}}_{1.84}{\mathrm{Sr}}_{0.16}\mathrm{Cu}{\mathrm{O}}_{4}$ film, in stark contrast to those of the control gold film. This angle-resolved resistivity method demonstrates unprecedented precision in determining the director and amplitude of electronic nematicity and is applicable to anisotropic transport due to mechanisms other than electronic nematicity as well. This method paves the way for the studies of the nematic domains and fluctuations of the nematic order in films and bulk crystals.

Effect of electron–electron interaction on magnitude of quantum oscillations of dissipative resistance in magnetic fields

Magneto-intersubband resistance oscillations (MISOs) of highly mobile 2D electrons in symmetric GaAs quantum wells with two populated subbands are studied in magnetic fields B=(B⊥,B∥) tilted from the normal to the 2D electron layer at different temperatures T. The in-plane component (B∥) of the field B induces magnetic entanglement between subbands, leading to beating in oscillating density of states (DOS) and to MISO suppression. Model of the MISO suppression is proposed. Within the model, a comparison of MISO amplitude in the entangled and disentangled (B∥=0) 2D systems yields both difference frequency of DOS oscillations, df, and strength of the electron–electron interaction, described by parameter εF∗, in the 2D system. These properties are analyzed using two methods, yielding consistent but not identical results for both df and εF∗. The analysis reveals an additional angular dependent factor of MISO suppression. The factor is related to spin splitting of quantum levels in magnetic fields.

Mechanics of vibrotactile sensors for applications in skin-interfaced haptic systems

Recent advances in haptic interfaces support a range of options in adding sensations of touch to virtual and augmented reality experiences. A fundamental understanding of the mechanics associated with coupling between vibro-tactile actuators and the skin is important in considering device designs and interpreting sensory perceptions. Here, we investigate vibrational dynamics induced by the three main classes of such actuators in bilayer elastomer structures that capture essential mechanical properties of human skin. The measurements rely on three dimensional digital image correlation methods, with corresponding simulations based on finite element analysis techniques. Studies examine the effects of key parameters relevant to the mechanics and resulting sensations, such as those related to contact area, actuation amplitude and spatio-temporal distributions of displacements in terms of both surface and body waves. Results reveal that tactor type actuators operate in a power efficient mode to produce deformations largely oriented out of the plane of the skin, for robust sensations that can, however, depend strongly on mounting strategy. Actuators based on eccentric rotating motors yield deformations with similar magnitudes but with substantial in-plane components and reduced sensations. Key attractive features of these actuators are in small, lightweight designs that facilitate mounting on the skin and deployment into large arrays. A third type of device, linear resonant actuators, produce the weakest sensations and the lowest power efficiencies, with limited potential for practical applications.

Unidirectional Rashba spin splitting in single layer WS2(1−x)Se2x alloy

Atomically thin two-dimensional (2D) layered semiconductors such as transition metal dichalcogenides have attracted considerable attention due to their tunable band gap, intriguing spin-valley physics, piezoelectric effects and potential device applications. Here we study the electronic properties of a single layer WS1.4Se0.6 alloys. The electronic structure of this alloy, explored using angle resolved photoemission spectroscopy, shows a clear valence band structure anisotropy characterized by two paraboloids shifted in one direction of the k-space by a constant in-plane vector. This band splitting is a signature of a unidirectional Rashba spin splitting with a related giant Rashba parameter of 2.8 ± 0.7 eV Å. The combination of angle resolved photoemission spectroscopy with piezo force microscopy highlights the link between this giant unidirectional Rashba spin splitting and an in-plane polarization present in the alloy. These peculiar anisotropic properties of the WS1.4Se0.6 alloy can be related to local atomic orders induced during the growth process due the different size and electronegativity between S and Se atoms. This distorted crystal structure combined to the observed macroscopic tensile strain, as evidenced by photoluminescence, displays electric dipoles with a strong in-plane component, as shown by piezoelectric microscopy. The interplay between semiconducting properties, in-plane spontaneous polarization and giant out-of-plane Rashba spin-splitting in this 2D material has potential for a wide range of applications in next-generation electronics, piezotronics and spintronics devices.

Anisotropic Vortex Squeezing in Synthetic Rashba Superconductors: A Manifestation of Lifshitz Invariants

Most of 2D superconductors are of type II, i.e., they are penetrated by quantized vortices when exposed to out-of-plane magnetic fields. In presence of a supercurrent, a Lorentz-like force acts on the vortices, leading to drift and dissipation. The current-induced vortex motion is impeded by pinning at defects, enabling the use of superconductors to generate high magnetic fields without dissipation. Usually, the pinning strength decreases upon any type of pair-breaking. Here we show that in Rashba superconductors the application of an in-plane field leads, instead, to an unexpected enhancement of pinning. When rotating the in-plane component of the field with respect to the current direction, the vortex inductance turns out to be highly anisotropic. We explain this phenomenon as a manifestation of Lifshitz invariant terms in the Ginzburg-Landau free energy, which are enabled by inversion and time-reversal symmetry breaking and lead to an elliptic squeezing of vortex cores. Our experiment provides access to a fundamental property of Rashba superconductors and offers an entirely new approach to vortex manipulation.

Superposing plane strain on anti-plane shear deformations in a special class of fiber-reinforced incompressible hyperelastic materials

The purpose of the present research is to investigate how the nonlinearity and the boundary conditions have the power to influence the coupling of the various modes of deformation when a plane strain deformation is superimposed on anti-plane shear deformation for a class of fiber-reinforced incompressible hyperelastic materials described by a strain energy density W. Attention is confined when W depends only on the first invariant of the strain tensor and on the square of the stretch in the direction of the fibers.We are able to write down the governing equations of equilibrium as a coupled system of three nonlinear partial differential equations for three displacement fields. Two displacements are the in-plane components and one displacement is the anti-plane state. The system that we are able to deduce in a compact form is always compatible at variance with the case in which the anti-plane shear problem is analyzed. As explicit example of our findings we study the problem of the helical shear and we investigate into details the coupling of its axial and azimuthal components.

In vivo quantification of 3D displacement in sacral soft tissues under compression: Relevance of 2D US-based measurements for pressure ulcer risk assessment

Objective2D Ultrasound (US) imaging has been recently investigated as a more accessible alternative to 3D Magnetic Resonance Imaging (MRI) for the estimation of soft issue motion under external mechanical loading. In the context of pressure ulcer prevention, the aim of this pilot MRI study was to design an experiment to characterize the sacral soft tissue motion under a controlled mechanical loading. Such an experiment targeted the estimation of the discrepancy between tissue motion assessed using a 2D imaging modality (echography) versus tissue motion assessed using a (reference) 3D imaging modality (MRI). MethodsOne healthy male volunteer participated in the study. An MRI-compatible custom-made setup was designed and used to load the top region of the sacrum with a 3D-printed copy of the US transducer. Five MR images were collected, one in the unloaded and four in the different loaded configurations (400–1200 [g]). Then, a 3D displacement field for each loading configuration was extracted based on the results of digital volume correlation. Tissue motion was separated into the X, Y, Z directions of the MRI coordinate system and the ratios between the out-of-plane and in-plane components were assessed for each voxel of the selected region of interest. ResultsRatios between the out-of-plane and in-plane displacement components were higher than 0.6 for more than half of the voxels in the region of interest for all load cases and higher than 1 for at least quarter of the voxels when loads of 400–800 [g] were used. ConclusionThe out-of-ultrasound-plane tissue displacement was not negligible, therefore 2D US imaging should be used with caution for the evaluation of the tissue motion in the sacrum region. The 3D US modality should be further investigated for this application.

Spin angular momentum and nonreciprocity of ghost surface polariton in antiferromagnets.

We investigated the spin angular momentum (SAM) and nonreciprocity of ghost surface polariton (GSP) at the surface of an antiferromagnet (AF) in the normal geometry, where the AF easy axis and external field (H0) both are normal to the AF surface. We found that the dispersion equation is invariant when the inversions of wavevector and external magnetic field, k→-k and H0→-H0, are taken. However, its polarization and SAM are nonreciprocal. The SAM is vertical to the propagation direction of GSP, and consists of two components. We analytically found that the in-plane component is locked to H0, or it is changed in sign due to the inversion of H0. The out-plane one is locked to k since it is changed in sign as the inversion of k is taken. Either component contains an electric part and a magnetic part. Above the AF surface, the two electric parts form the left-handed triplet with the wavevector k, but the two magnetic parts form the right-handed triplet with k. In the AF, the chirality of the SAM changes with the distance from the surface. The SAM is very large on or near the surface and it may be very interesting for the manipulation of micron and nano particles on the AF surface. These are obviously different from the relevant features of conventional surface polaritons. The SAM also is field-tunable.

Crossed Andreev reflection in spin-polarized chiral edge states due to the Meissner effect

We consider a hybrid quantum Hall-superconductor system, where a superconducting finger with oblique profile is wedged into a two-dimensional electron gas in the presence of a perpendicular magnetic field, as considered by Lee et al., Nat. Phys. 13, 693 (2017). The electron gas is in the quantum Hall regime at filling factor $\ensuremath{\nu}=1$. Due to the Meissner effect, the perpendicular magnetic field close to the quantum Hall-superconductor boundary is distorted and gives rise to an in-plane component of the magnetic field. This component enables nonlocal crossed Andreev reflection between the spin-polarized chiral edge states running on opposite sides of the superconducting finger, thus opening a gap in the spectrum of the edge states without the need of spin-orbit interaction or nontrivial magnetic textures. We compute numerically the transport properties of this setup and show that a negative resistance exists as a consequence of nonlocal Andreev processes. We also obtain numerically the zero-energy local density of states, which systematically shows peaks stable to disorder. The latter result is compatible with the emergence of Majorana bound states.

Supercurrent diode effect and magnetochiral anisotropy in few-layer NbSe2

Nonreciprocal transport refers to charge transfer processes that are sensitive to the bias polarity. Until recently, nonreciprocal transport was studied only in dissipative systems, where the nonreciprocal quantity is the resistance. Recent experiments have, however, demonstrated nonreciprocal supercurrent leading to the observation of a supercurrent diode effect in Rashba superconductors. Here we report on a supercurrent diode effect in NbSe2 constrictions obtained by patterning NbSe2 flakes with both even and odd layer number. The observed rectification is a consequence of the valley-Zeeman spin-orbit interaction. We demonstrate a rectification efficiency as large as 60%, considerably larger than the efficiency of devices based on Rashba superconductors. In agreement with recent theory for superconducting transition metal dichalcogenides, we show that the effect is driven by the out-of-plane component of the magnetic field. Remarkably, we find that the effect becomes field-asymmetric in the presence of an additional in-plane field component transverse to the current direction. Supercurrent diodes offer a further degree of freedom in designing superconducting quantum electronics with the high degree of integrability offered by van der Waals materials.

Probing Magnetism in Exfoliated VI3 Layers with Magnetotransport.

We perform magnetotransport experiments on VI3 multilayers to investigate the relation between ferromagnetism in bulk and in exfoliated layers. The magnetoconductance measured on field-effect transistors and tunnel barriers shows that the Curie temperature of exfoliated multilayers is TC = 57 K, larger than in bulk (TC,bulk = 50 K). Below T ≈ 40 K, we observe an unusual evolution of the tunneling magnetoconductance, analogous to the phenomenology observed in bulk. Comparing the magnetoconductance measured for fields applied in- or out-of-plane corroborates the analogy, allows us to determine that the orientation of the easy-axis in multilayers is similar to that in bulk, and suggests that the in-plane component of the magnetization points in different directions in different layers. Besides establishing that the magnetic state of bulk and multilayers are similar, our experiments illustrate the complementarity of magnetotransport and magneto-optical measurements to probe magnetism in 2D materials.

On the Identification of Orthotropic Elastic Stiffness Using 3D Guided Wavefield Data.

Scanning laser Doppler vibrometry is a widely adopted method to measure the full-field out-of-plane vibrational response of materials in view of detecting defects or estimating stiffness parameters. Recent technological developments have led to performant 3D scanning laser Doppler vibrometers, which give access to both out-of-plane and in-plane vibrational velocity components. In the present study, the effect of using (i) the in-plane component; (ii) the out-of-plane component; and (iii) both the in-plane and out-of-plane components of the recorded vibration velocity on the inverse determination of the stiffness parameters is studied. Input data were gathered from a series of numerical simulations using a finite element model (COMSOL), as well as from broadband experimental measurements by means of a 3D infrared scanning laser Doppler vibrometer. Various materials were studied, including carbon epoxy composite and wood materials. The full-field vibrational velocity response is converted to the frequency-wavenumber domain by means of Fourier transform, from which complex wavenumbers are extracted using the matrix pencil decomposition method. To infer the orthotropic elastic stiffness tensor, an inversion procedure is developed by coupling the semi-analytical finite element (SAFE) as a forward method to the particle swarm optimizer. It is shown that accounting for the in-plane velocity component leads to a more accurate and robust determination of the orthotropic elastic stiffness parameters.

Numerical analysis of self-propulsion flow characteristics in model scale

In this paper, a detailed numerical analysis of global, and local flow characteristics of a self-propelled KCS model is presented. Global flow characteristics are integral values such as thrust and torque, while the local flow characteristics are represented by the velocity components. Three different numerical propeller representations are considered: fully discretized propeller, actuator disc model which models the thrust effect on the fluid flow only, and actuator disc model that models both thrust and torque effects. Verification is performed using method based on Richardson extrapolation, and the approach is validated with publicly available experimental data, both for global and local flow characteristics. A procedure for accurate prediction of global and local self-propulsion characteristics using a combination of actuator disc and discretized propeller methods is presented. The hybrid procedure was proved to provide a good agreement of global flow characteristics with experimental data. The fully discretized propeller model using overset grid showed good accuracy of predicting local flow characteristics, observed by comparing axial and in-plane velocity components behind the working propeller.

LEGO Calibration Targets For Large-FOV Particle Image Velocimetry

Particle-image or particle-tracking velocimetry (PIV/PTV) nonintrusively provides velocity field information, and consequently, the proposition of measurements in a large plane is highly attractive from an experimental standpoint, particularly for experiments conducted in large atmospheric and flight-scale wind tunnels. Physical limits to the size of the useful field-of-view (FOV) that can be achieved with a single camera depend on striking a balance between the physical capabilities of the cameras and the physics of interest in the flow. A typical solution is to stitch together multiple smaller FOVs to achieve the large FOV of interest, presenting a number of challenges, some of which are rooted in the calibration process. For SPIV calibrations, the use of a multi-level target simplifies the calibration process. However, this is problematic for large-FOV measurements, as standardised multi-level targets are typically relatively small and expensive due to the precision-engineering required. As an alternative, LEGO bricks are extremely well-suited to the construction of large, customised multi-level targets due to their high dimensional tolerance and their stackability with high precision. In order to create a prototype two-sided multi-level SPIV target and evaluate whether the LEGO bricks can be used successfully to calibrate a large FOV, the LaVision Type 31 target was chosen as a model. In order to further augment the flexibility offered by the LEGO-based targets, the backing used to mount the baseplates was designed to be modularly reconfigurable. The resultant two-sided multi-level target has an area of approximately 380 x 1150 mm. To evaluate the target, SPIV measurements of the inflow conditions of the Atmospheric Wind Tunnel Munich (AWM) were performed; calibrations were also performed using the Type 31 target for comparison. Analysis of the datasets with both calibration targets shows good agreement in the measurement of the streamwise, out-of-plane component u. However, there is some uncertainty regarding the accuracy of the computation of in-plane components. Due to the high level of agreement in calibration parameters, out-of-plane component, and the qualitative location of flow features, this disagreement is believed to be a fixable issue. These early results indicate that with some refinement, the LEGO-based calibration target can be developed further and used for large-FOV measurements in the future.

Revealing local structural properties of an atomically thin MoSe2 surface using optical microscopy

Using a triangular molybdenum diselenide (MoSe2) flake as surface-enhanced Raman spectroscopy (SERS) platform, we demonstrate the dependency of the Raman enhancement on laser beam polarization and local structure using copper phthalocyanine (CuPc) as probe. Second harmonic generation (SHG) and photoluminescence spectroscopy and microscopy are used to reveal the structural irregularities of the MoSe2 flake. The Raman enhancement in the focus of an azimuthally polarized beam, which possesses exclusively an in-plane electric field component is stronger than the enhancement by a focused radially polarized beam, where the out-of-plane electric field component dominates. This phenomenon indicates that the face-on oriented CuPc molecules strongly interact with the MoSe2 flake via charge transfer and dipole–dipole interaction. Furthermore, the Raman scattering maps on the irregular MoSe2 surface show a distinct correlation with the SHG and photoluminescence optical images, indicating the relationship between local structure and optical properties of the MoSe2 flake. These results contribute to understand the impacts of local structural properties on the Raman enhancement at the surface of the 2D transition-metal dichalcogenide.