Emergence of the Vortex State in Confined Ferroelectric Heterostructures
Abstract not provided
Hsu, Shang-Lin↗
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Observation of magnetic adatom-induced Majorana vortex and its hybridization with field-induced Majorana vortex in an iron-based superconductor
Braiding Majorana zero modes is essential for fault-tolerant topological quantum computing. Iron-based superconductors with nontrivial band topology have recently emerged as a surprisingly promising platform for creating distinct Majorana zero modes in magnetic vortices in a single material and at relatively high temperatures. The magnetic field-induced Abrikosov vortex lattice makes it difficult to braid a set of Majorana zero modes or to study the coupling of a Majorana doublet due to overlapping wave functions. Here we report the observation of the proposed quantum anomalous vortex with integer quantized vortex core states and the Majorana zero mode induced by magnetic Fe adatoms deposited on the surface. We observe its hybridization with a nearby field-induced Majorana vortex in iron-based superconductor FeTe 0.55 Se 0.45 . We also observe vortex-free Yu-Shiba-Rusinov bound states at the Fe adatoms with a weaker coupling to the substrate, and discover a reversible transition between Yu-Shiba-Rusinov states and Majorana zero mode by manipulating the exchange coupling strength. The dual origin of the Majorana zero modes, from magnetic adatoms and external magnetic field, provides a new single-material platform for studying their interactions and braiding in superconductors bearing topological band structures.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Influence of multiband sign-changing superconductivity on vortex cores and vortex pinning in stoichiometric high- T c CaKFe 4 As 4
We use a scanning tunneling microscope to study the superconducting density of states and vortex lattice of single crystals of CaKFe 4 As 4 . This material has a critical temperature of T c = 35 K, one of the highest among stoichiometric iron based superconductors (FeBSCs), and is comparable to T c found near optimal doping in other FeBSCs. We observe quasiparticle scattering from defects with a pattern related to interband scattering between zone centered hole sheets. We measure the tunneling conductance in vortex cores and find a peak due to Caroli–de Gennes–Matricon bound states. The peak is located above the Fermi level, showing that CaKFe 4 As 4 is a clean superconductor with vortex core bound states close to the so-called extreme quantum limit. We identify locations where the superconducting order parameter is strongly suppressed due to pair breaking. Vortices are pinned at these locations, and the length scale of the suppression of the order parameter is of order of the vortex core size. Finally, as a consequence, the vortex lattice is disordered up to 8 T.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Peak effect due to competing vortex ground states in superconductors with large inclusions
Not Available
Willa, Roland↗
Summary of some recent studies of subsonic vortex lift and parameters affecting the leading-edge vortex stability
Various subsonic configurations which develop vortex lift are examined herein. Comparisons are made with data and the combination of direct and indirect edge forces through use of the suction analogy. For most configurations, the use of the indirect or augmented vortex lift leads to improved agreement with data. The studies conducted showed that it is possible for the leading-edge vortex to exhibit bursting on a cropped wing and the wing aerodynamic characteristics not show the effect. It was further found that the distributions of leading-edge suction correlate well with the maintenance of vortex flow aerodynamic characteristics. Lastly, a method is presented for relating the initial value of circulation and axial velocity of the leading-edge shed vortex to the wing geometry.
Lamar, J. E.↗
VORCOR: A computer program for calculating characteristics of wings with edge vortex separation by using a vortex-filament and-core model
A computer code base on an improved vortex filament/vortex core method for predicting aerodynamic characteristics of slender wings with edge vortex separations is developed. The code is applicable to camber wings, straked wings or wings with leading edge vortex flaps at subsonic speeds. The prediction of lifting pressure distribution and the computer time are improved by using a pair of concentrated vortex cores above the wing surface. The main features of this computer program are: (1) arbitrary camber shape may be defined and an option for exactly defining leading edge flap geometry is also provided; (2) the side edge vortex system is incorporated.
Pao, J. L.↗
Vortex cloud model for body vortex shedding and tracking
The discrete vortex cloud approach models a missile airframe's vortex wake by means that are capable of treating a variety of configurations over a range of flow conditions. Attention is given to the sheets of vorticity formed on the lee side of a missile at moderate angles-of-attack. While three-dimensional attached flow models are used to represent the missile body, two-dimensional, incompressible, separated flow models are used to represent the separated vortex wake. The predicted pressure distribution of the body under the influence of the freestream and the separation vortex wake are used to calculate aerodynamic loads on the body. The separation vortex wake is represented by clouds of discrete vortices in cross flow planes normal to the body axis.
Mendenhall, Michael R.↗
Rotating hot-wire investigation of the vortex responsible for blade-vortex interaction noise
This distribution of the circumferential velocity of the vortex responsible for blade-vortex interaction noise was measured using a rotating hot-wire rake synchronously meshed with a model helicopter rotor at the blade passage frequency. Simultaneous far-field acoustic data and blade differential pressure measurements were obtained. Results show that the shape of the measured far-field acoustic blade-vortex interaction signature depends on the blade-vortex interaction geometry. The experimental results are compared with the Widnall-Wolf model for blade-vortex interaction noise.
Fontana, Richard Remo↗
Wingtip vortex turbine investigation for vortex energy recovery
A flight test investigation has been conducted to determine the performance of wingtip vortex turbines and their effect on aircraft performance. The turbines were designed to recover part of the large energy loss (induced drag) caused by the wingtip vortex. The turbine, driven by the vortex flow, reduces the strength of the vortex, resulting in an associated induced drag reduction. A four-blade turbine was mounted on each wingtip of a single-engine, T-tail, general aviation airplane. Two sets of turbine blades were tested, one with a 15' twist (washin) and one with no twist. Th power recovered by the turbine and the installed drag increment were measured. A trade-off between turbine power and induced drag reduction was found to be a function of turbine blade incidence angle. This test has demonstrated that the wingtip vortex turbine is an attractive alternate, as well as an emergency, power source.
Abeyounis, William K.↗
Coarse-grained discrete particle simulations of particle segregation in rotating fluidized beds in vortex chambers [Discrete particle simulations of particle segregation in rotating fluidized beds in vortex chambers]
Vortex chambers allow the generation of rotating fluidized beds, offering high-G intensified gas-solid contact, gas-solids separation and solids-solids segregation. Focusing on binary particle mixtures and fixing the density and diameter of the heavy/large particles, transient batch CFD-coarse-grained DPM simulations were carried out with varying densities or sizes of the light/small particles to evaluate to what extent combining these three functionalities is possible within a vortex chamber of given design. Both the rate and quality of segregation were analyzed. Within a relatively wide density and size range, fast and efficient segregation takes place, with an inner and slower rotating bed of the lighter/small particles forming within the outer and faster rotating bed of the heavier/large particles. Simulations show that the contamination of the outer bed with lighter particles occurs more easily than contamination of the inner bed with heavier particles and increases with decreasing difference in size or density of the particles. Bubbling in the inner bed is observed with an inner bed of very low density or small particles. Porosity plots show that vortex chambers with a sufficient number of gas inlet slots have to be used to guarantee a uniform gas distribution and particle bed. Lastly, the flexibility of particle segregation in vortex chambers with respect to the gas flow rate is demonstrated.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Vortex-antivortex coexistence in Nb-based superconductor/ferromagnet heterostructures
Low-temperature magnetic force microscopy was used to study the threshold of nucleation of spontaneous vortex-antivortex structures in superconductor/ferromagnet (S/F) hybrid systems. We investigated S/F heterostructures composed of Py as the magnetic material and Nb as the superconductor, with different thicknesses of Py and Nb. The condition for nucleation of spontaneous vortex-antivortex structures depends on fundamental parameters such as the superconducting penetration depth and the coherence length, as well as on the thickness of the superconducting film and the magnetic domain width. Here, we compare our experimental results with those of existing theoretical models and provide an estimate of the threshold of the local out-of-plane component of the magnetization for different Py film thicknesses.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Qualitative numerical study of simultaneous high-G-intensified gas–solids contact, separation and segregation in a bi-disperse rotating fluidized bed in a vortex chamber
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20 FOSSIL-FUELED POWER PLANTS↗
Ballistic rectification of vortex domain wall chirality at nanowire corners
The interactions of vortex domain walls with corners in planar magnetic nanowires are probed using magnetic soft X-ray transmission microscopy. Here,we show that when the domain walls are propagated into sharp corners using applied magnetic fields above a critical value, their chiralities are rectified to either clockwise or anticlockwise circulation depending on whether the corners turn left or right. Single-shot focused magneto-optic Kerr effect measurements are then used to demonstrate how, when combined with modes of domain propagation that conserve vortex chirality, this allows us to dramatically reduce the stochasticity of domain pinning at artificial defect sites. In conclusion, our results provide a tool for controlling domain wall chirality and pinning behavior both in further experimental studies and in future domain wall-based memory, logic and sensor technologies.
36 MATERIALS SCIENCE↗
Gyrotropic frequency control in ferromagnetic dots using a nanoscale vortex barrier
The vortex translational mode frequency is known to be only weakly dependent on the magnitude of an in-plane magnetic field (e.g. the vortex core position) for circular ferromagnetic dots. Here we demonstrated that the frequency-field dependence becomes discrete when a nanoscale vortex barrier is introduced in the dot structure. We found that the frequency is mostly defined by the outer diameter of the dot or the barrier size for the vortex core located outside or inside the barrier, correspondingly. The experimental results are in good agreement with the micromagnetic simulation.
Ding, Junjia↗
Josephson vortex lattice in layered superconductors
Many superconducting materials are composed of weakly coupled conducting layers. Such a layered structure has a very strong influence on the properties of vortex matter in a magnetic field. This review focuses on the properties of the Josephson vortex lattice generated by the magnetic field applied in the direction of the layers. The theoretical description is based on the Lawrence-Doniach model in the London limit, which takes only the phase degree of freedom of the superconducting order parameter into account. In spite of its simplicity, this model leads to an amazingly rich set of phenomena. We review in detail the structure of an isolated vortex line and various properties of the vortex lattice, in both dilute and dense limits. In particular, we extensively discuss the influence of the layered structure and thermal fluctuations on the selection of lattice configurations at different magnetic fields.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Method of stabilizing flueric vortex valves and vortex amplifiers
Inducing losses in the vortex chamber of vortex valves and vortex amplifiers resolves the problem of unstable operation caused by a sufficiently large positive feedback. Induced losses also reduce pressure gain and throttling range of vortex pressure amplifier.
Erwin, L. R.↗
Disrupted states of vortex flow and vortex breakdown
Flow visualization studies and laser Doppler anemometer measurements on swirling water flows reveal six distinct types of very large amplitude disturbance modes of the vortex core. Three, 'axisymmetric' and spiral vortex breakdowns, and the 'double helix,' have been described by others. A definite order of evolution in parameter space (Reynolds number and circulations) occurs, and is described. Puzzling responses of the axisymmetric and spiral vortex breakdowns to imposed flow transients reported previously are confirmed here, and are traced to the shedding of starting and stopping vortices from swirl vanes. Conclusions bearing upon the validity of some theories of vortex breakdown are possible from the data.
Faler, J. H.↗