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Our study sample is a mesoscopic superconducting three-dimensional parallelepiped immersed in a magnetic field $$H_{z}$$ . The sample presents an anisotropy of the Ginzburg–Landau parameter $$\kappa (z)$$ in the z-axis. This dependence allows us to simulate a superconducting three layer system, where the top and bottom layers are made of a type-II superconducting material, and the middle layer is fabricated of a type-I material. We analyzed the superconducting electron density, free energy, and the magnetization curves as functions of H for different values of $$\kappa (z)$$ . Due to the effects of proximity and shielding on the borders of the layers, Abrikosov vortices are present in the type I regions, and a fractional vortex state is present in the type II superconducting region.

Tunneling in a many-body system appears as one of the novel implications of quantum physics, in which particles move in space under an otherwise classically-forbidden potential barrier. Here, we theoretically describe the quantum dynamics of the tunneling phenomenon of a few intricate bosonic clouds in a closed system of a two-dimensional symmetric double-well potential. We examine how the inclusion of the transverse direction, orthogonal to the junction of the double-well, can intervene in the tunneling dynamics of bosonic clouds. We use a well-known many-body numerical method, called the multiconfigurational time-dependent Hartree for bosons (MCTDHB) method. MCTDHB allows one to obtain accurately the time-dependent many-particle wavefunction of the bosons which in principle entails all the information of interest about the system under investigation. We analyze the tunneling dynamics by preparing the initial state of the bosonic clouds in the left well of the double-well either as the ground, longitudinally or transversely excited, or a vortex state. We unravel the detailed mechanism of the tunneling process by analyzing the evolution in time of the survival probability, depletion and fragmentation, and the many-particle position, momentum, and angular-momentum expectation values and their variances. As a general rule, all objects lose coherence while tunneling through the barrier and the states which include transverse excitations do so faster. Implications are briefly discussed., Comment: 20 Figures, 47 pages

CoNi/Ni multisegmented cylindrical nanowires were synthesized via an electrochemical route. The wires are 140 nm in diameter, with 1000 nm long Ni segments and CoNi segments between 600 and 1400 nm in length. The magnetic configuration was imaged by XMCD-PEEM in the demagnetized state and at remanence after magnetizing axially and perpendicularly. Ni segments, with cubic crystal symmetry, show an axial magnetic configuration with a small curling component at the surface. In turn, CoNi segments, with hexagonal crystal symmetry and a strong magnetocrystalline anisotropy perpendicular to the nanowires, show a single vortex state in the shorter segments and multivortex or multitransverse magnetic configurations in medium and long segments, respectively. A detailed study by micromagnetic simulations reveals that the magnetic configuration is determined mainly by the coupling between soft Ni and harder CoNi segments. For short CoNi segments, Ni segments are magnetostatically coupled and the chirality of the single vortex formed in CoNi remains the same as that of the curling in neighboring Ni segments. For longer CoNi segments, the remanent state is either the multivortex or multitransverse state depending on whether the previously applied field was parallel or perpendicular to the magnetocrystalline axis. The results point out the relevance of the cylindrical geometry to promote the occurrence of complex magneto-chiral effects and provide key information for the design of cylindrical magnetic nanowires for multiple applications.

Mixed-valance manganites with strong electron correlation exhibit strong potential for spintronics, where emergent magnetic behaviors, such as propagation of high-frequency spin waves and giant topological Hall Effects can be driven by their mesoscale spin textures. Here, we create magnetic vortex clusters with flux closure spin configurations in single-crystal La0.67Sr0.33MnO3 wire. A distinctive transformation from out-of-plane domains to a vortex state is directly visualized using magnetic force microscopy at 4 K in wires when the width is below 1.0 μm. The phase-field modeling indicates that the inhomogeneous strain, accompanying with shape anisotropy, plays a key role for stabilizing the flux-closure spin structure. This work offers a new perspective for understanding and manipulating the non-trivial spin textures in strongly correlated systems.

We investigate the superconducting critical current density (Jc), transition temperature (Tc), and flux pinning properties under hydrostatic pressure (P) for Cr0.0009NbSe2 single crystal. The application of P enhances Tc in both electrical resistivity (∼0.38 K GPa−1: 0 ≤ P ≤ 2.5 GPa) and magnetization (∼0.98 K GPa−1: 0 ≤ P ≤ 1 GPa) measurements, which leads to a monotonic increase in Jc and flux pinning properties. The field-dependent Jc at various temperatures under P is analyzed within the collecting pinning theory and it shows that δTc pinning is the crossover to δl pinning above the critical pressure (Pc ∼0.3 GPa). Our systematic analysis of the flux pinning mechanism indicates that both the density of pinning centers and pinning forces greatly increase with the application of P, which leads to an enhancement in the vortex state. Structural studies using synchrotron X-ray diffraction under pressure illustrate a stable hexagonal phase without any significant impurity phase and lattice parameter reduction with P shows highly anisotropic nature.

We report on the investigation of the magnetic superconductor EuFe$_{2}$(As$_{0.7}$P$_{0.3}$)$_{2}$ based on muon-spin spectroscopy and ac magnetic susceptibility ($\chi$) measurements. The dependence of the internal field at the muon site on temperature is indicative of a ferromagnetic ordering of Eu$^{2+}$ magnetic moments and only the conventional magnon scattering governs the longitudinal relaxation rate at low temperatures. At the same time, we observe a rich phenomenology for the imaginary component of the susceptibility $\chi^{\prime\prime}$ by means of both standard ac susceptibility and a novel technique based on a microwave coplanar waveguide resonator. In particular, we detect activated trends for several features in $\chi^{\prime\prime}$ over frequencies spanning ten orders of magnitude. We interpret our results in terms of the complex dynamics of vortices and antivortices influenced by the underlying structure of magnetic domains., Comment: 8 pages, 7 figures

We experimentally studied the effect of meter-range electromagnetic field (tens of MHz) on the current-voltage characteristic (I-V curve) of a wide superconducting film. The vortex resistivity region is shown to significantly extend under the effect of meter-range (MR) electromagnetic irradiation owing to rapid suppression of critical current with a slower change in the upper boundary of stability of the vortex state. We found that as the MR irradiation power increases, the I-V curve structure related to phase slip lines is smoothed out to eventually vanish. A model of the film I-V curve in the adiabatic regime is proposed that explains the effect of blurring of voltage steps and suppression of critical current.We experimentally studied the effect of meter-range electromagnetic field (tens of MHz) on the current-voltage characteristic (I-V curve) of a wide superconducting film. The vortex resistivity region is shown to significantly extend under the effect of meter-range (MR) electromagnetic irradiation owing to rapid suppression of critical current with a slower change in the upper boundary of stability of the vortex state. We found that as the MR irradiation power increases, the I-V curve structure related to phase slip lines is smoothed out to eventually vanish. A model of the film I-V curve in the adiabatic regime is proposed that explains the effect of blurring of voltage steps and suppression of critical current.

The stability of magnetism in reduced dimensions has become a major scientific agenda in the pursuit of implementing magnetic nanostructures as functional components in spintronic devices. Methods to probe and control magnetization states of such structures in a deterministic manner include use of spin polarized currents, photon absorption, and relatively recently, electric fields that tailor magnetoelectric coupling in multiferroic based structures. In theory, a short electric pulse is able to generate localized magnetic fields that can couple to the local magnetic dipoles electrodynamically. Here, using the Landau–Lifshitz–Gilbert formalism of magnetism dynamics combined with continuum Maxwell relations, the response of a ferromagnetic permalloy nanodisc to nanosecond electric field pulses is studied. The dynamics of the magnetic order of the nanodiscs during this process are examined and discussed. Ferromagnet nanodiscs, when below a critical size and in the absence of any external field, relax to a vortex phase as the ground state due to the demagnetizing field. Simulations demonstrate that the planar chirality of such a ferromagnet nanodisc can be switched via a time-wise asymmetric electric field pulse on the order of a few ns duration that generates radially varying tangential magnetic fields. These fields couple to the vortex state of the nanodisc ferromagnet electrodynamically, revealing an effective and robust method to control chirality.

Vortex dynamics in superconductors have received a great deal of attention from both fundamental and applied researchers over the past few decades. Because of its critical role in the energy relaxation process of type-II superconductors, vortex dynamics have been deemed a key contributor to the response rate of the emerging superconducting single photon detector (SSPD). With the support of electrical transport measurements under external magnetic fields, vortex dynamics in superconducting a-MoSi thin films are investigated in this work. It is ascertained that the vortex state changes from pinned to flux flow under the influence of the Lorentz force. The critical vortex velocity v* and quasi-particle inelastic scattering time {\tau}* under different magnetic fields are derived from the Larkin-Ovchinnikov model. Under high magnetic fields, the v* power law dependence (v*~B-1/2) collapses, i.e., v* tends to zero, which is attributed to the obstruction of flux flow by the intrinsic defects, while the {\tau}* increases with the increasing magnetic field strength. In addition, the degree of vortex rearrangement is found to be enhanced by photon-induced reduction in potential barrier, which mitigates the adverse effect of film inhomogeneity on superconductivity in the a-MoSi thin films. The thorough understanding of the vortex dynamics in a-MoSi thin films under the effect of external stimuli is of paramount importance for both further fundamental research in this area and optimization of SSPD design.

Néel theory (doi: 10.1080/0001873550010120 ) predicts that natural remanent magnetizations (NRMs) of thermal origin will be nearly linearly related to the magnetic field in which they are acquired for field strenghts as low as the Earth's. This makes it in principle possible to estimate the strength of ancient magnetic fields. In practice, however, recovering the ancient field strength is complicated. The simple theory only pertains to uniformly magnetized (single domain, SD particles). While SD theory predicts that a magnetization acquired at a temperature T should be demagnetized by zero-field reheating to T, yet failure of this “reciprocity” requirement has long been observed and the causes and consequences for grains with no domain walls are unknown. Recent experiments (Shaar and Tauxe, doi: 10.1073/pnas.1507986112 and Santos and Tauxe, doi:10.1029/2018GC007946) have demonstrated that, in contrast to the stability of SD remanences over time, the remanence in many paleomagnetic samples typically used in paleointensity experiments are unstable, exhibiting an "aging" effect in which the unblocking temperature spectrum changes over only a few years. This behavior is completely unexpected from theory. Solving these mysteries is key to cracking the problem of paleointensity estimation. In this presentation we will demonstrate that it is a shift in unblocking temperatures observed over even relatively short time intervals (two years) in certain samples that leads to the failure of reciprocity which in turn limits the ability to acquire accurate and precise estimates of the ancient magnetic field. From rock magnetic experiments (xFORCs) it seems likely that magnetic grains larger than the highly stable single vortex state are the source of the non-ideal behavior. This non-ideal behavior which leads to differences between known and estimated fields that can be rather large (up to 10 μT) for individual specimens, does appear to lead to a bias in field estimates. It is unclear how this behavior can be compensated for using the most common paleointensity estimation methods.

In many unconventional superconductors, the presence of a pseudogap - a suppression in the electronic density of states extending above the critical temperature - has been a long-standing mystery. Here, we employ combined in situ electrical transport and angle-resolved photoemission spectroscopy measurements to reveal an unprecedentedly large pseudogap regime in single-layer FeSe/SrTiO3, an interfacial superconductor where incoherent Cooper pairs are initially formed above TI��60 K but where a zero-resistance state is achieved only below T0

We investigate the superfluidity of a two-component Fermi gas with spin-orbital-angular-momentum coupling (SOAMC). Due to the intricate interplay of SOAMC, two-photon detuning and atom-atom interaction, a family of vortex ground states emerge in a broad parameter regime of the phase diagram, in contrast to the usual case where an external rotation or magnetic field is generally required. More strikingly, an unprecedented vortex state, which breaks the continuous rotational symmetry to a discrete one spontaneously, is predicted to occur. The underlying physics are elucidated and verified by numerical simulations. The unique density distributions of the predicted vortex states enable a direct observation in experiment., 5 pages, 4 figures, and 3 pages supplemental material

Magnetic nanodots are of high interest for basic research due to their broad spectrum of possible magnetic states and magnetization reversal processes. Besides, they are of technological interest since they can be applied in magnetic data storage, especially if vortex states occur in closed dots or open rings. While producing such nanorings and nanodots from diverse magnetic materials by lithographic techniques is quite common nowadays, these production technologies are naturally prone to small deviations of the borders of these nanoparticles. Here we investigate the influence of well-defined angular-dependent roughness of the edges, created by building the nanoparticles from small cubes, on the resulting hysteresis loops and magnetization reversal processes in five different round nanodots with varying open areas, from a thin ring to a closed nanodot. By varying the orientation of the external magnetic field, the impact of the angle-dependent roughness can be estimated. Especially for the thinnest ring, significant dependence of the transverse magnetization component on the field orientation can be found.

A magnetic nanoring model with surface anisotropy by bending a single-walled nanotube was proposed and was placed in an inhomogeneous magnetic field produced by an electric current passing through the center of the nanoring and perpendicular to the ring plane. The ground state with vortex spin structure was determined and the magnetization was calculated by using the spin Green’s function method. It is found that the strong surface anisotropy can ensure the spins vortex state of the system. With the increase of temperature, the total order parameter of the spins gradually decreases to zero from their classical values. As the radius of the nanoring increases, the transition temperature of the system decreases rapidly and then gradually tends to a finite value. Changing the direction of the current, the generated reverse toroidal magnetic field can switch the magnetic state of spins from a vortex state to a reversal vortex state. The value of the current required for magnetization switching shows monotonic relationship to the radius of nanoring, surface anisotropy and the temperature which is far below the transition temperature. When the temperature is greater than the transition temperature, system shows the paramagnetic behavior.

Stable fractional vortices are numerically generated in the two-dimensional rotating F = 2 spinor Bose-Einstein condensates. We demonstrate the existence of 1 4 -vortex state or 1 2 -vortex state in the biaxial nematic phase, and 1 3 -vortex state in the cyclic phase. At fast rotation a lattice of fractional vortex in the spin space emerges. Intriguingly, the integral spin-winding of the whole system does not increase with the rotation speed but equals to a simple fraction.

Stable and metastable vortex states in two-dimensional three-component Bose–Einstein condensates are studied in the presence of spin–orbit coupling. The ground states exhibit two skyrmion structures which respectively correspond to the d-skyrmion in antiferromagnetic or the F-skyrmion in ferromagnetic condensates. The half skyrmion and full skyrmion can be controlled by changing the strength of the spin–orbit coupling. We also find a stable composite vortex state which is associated to mixing of the ferromagnetic and antiferromagnetic manifolds.

Magnetic nanodots are of high technological importance in diverse storage and spintronics applications, especially in bit patterned media. Magnetization reversal in such nanodots typically occurs either by coherent rotation of the magnetization or along a vortex state. Other mechanisms of magnetization reversal are scarcely described in the literature. Understanding and predicting the magnetization reversal processes, however, is of utmost importance due to the varying stray fields in the different states under evolution, influencing neighboring nanodots in an array or matrix-like structure. Besides, the stability of vortex states against magnetic field changes – which corresponds to typically broad field ranges with reversible modifications of the magnetic state – influences the robustness of magnetically stored information as well as the necessary external fields for writing new information. Here we report on micromagnetic simulations on nanodots with 10 different, representative diameters and 10 dot thicknesses, respectively, giving rise to 8 possible magnetization reversal processes and suggesting the preconditions for the nucleation and propagation of one or two vortices in cylindrical iron disks. We show the impact of the dimensions and aspect ratios on all phases of magnetization reversal. This study results in a phase diagram of the different magnetization reversal processes.

Due to its potential application in magnetic memory, the vortex magnetization configuration has drawn much attention, which had been found in many magnetic nanostructure. In this paper, static and dynamic characteristics of magnetism in permalloy oval nanoring are investigated with varying thickness and arm width via micromagnetic simulation. Two magnetization configuration (vortex and onion states) were found in oval nanoring and the vortex state is a stable state. Although onion is a metastable state, it become more stable with the decrease of thickness. The magnetic hysteresis loop along long axis of oval nanoring is simulated and coercive forces are investigated as function of arm width and thickness. Coercive force increases firstly and then decrease with the increase of thickness. In meanwhile, the dynamic magnetic susceptibility of vortex state in oval nanoring is simulated for varying arm width and thickness. Uniform resonance mode and edge resonance mode can be found when thickness is above 25 nm. However, there is a single uniform resonance mode in oval nanoring with thickness less 20 nm. The resonance frequency can be significantly modulated in the region of 8.2–13.7 GHz when thickness changes from 4 to 100 nm.

We study the entanglement properties of a non-Gaussian two-mode vortex state that was theoretically proposed by Agarwal [New J Phys 13:073008 (2011)] by using the technique of photon subtraction from a two-mode squeezed state and detection of one photon by a single-photon detector. There are different conditions to quantify the entanglement of non-classical states. We compare the entanglement conditions for this state in terms of the Hillery–Zubairy (HZ) criterion, Hillery–Dung–Zhong (HDZ) criterion, Shchukin–Vogel (SV) criterion, and Duan–Giedke–Cirac–Zoller (DGCZ) criterion. We confirm that this non-Gaussian state shows strong entanglement under these different conditions, thus suggesting that this state may have potential applications in quantum information processing.

Finite element micromagnetics are used to simulate remanence, hysteresis and dynamic switching in crescent shaped permalloy caps, a geometry that corresponds to either normal or oblique deposition of films on nanosphere arrays. Oblique deposition breaks the symmetry and favours onion states rather than vortices. It introduces in-plane shape anisotropy analogous to that of an elongated island and increases the in-plane coercivity. In isolated caps, the critical diameter above which the vortex state is the minimum energy state, is D = 123 nm for angles below θ = 20 deg. It increases with θ up to a vlaue of D = 157 nm at θ = 45 deg. Even for sizes for which the onion state is the lowest energy state, vortex states can be stabilized in isolated caps but the interparticle magnetostatic interactions tend to destabilize them driving the system to its ground state. The switching field of onion states can be reduced by 36% using microwave resonance at frequencies approaching the resonant (Kittel mode) frequencies.

A cone phase appears as the ground state of uniaxial magnets with comparable second-order and fourth-order anisotropy constants. In such systems, specific vortex states can exist. The authors have studied magnetization oscillations in small cylindrical particles in a cone vortex state. The study has determined the frequencies of magnon excitations in the presence of a vortex in the cone phase of a ferromagnet. It has been established that there is a significant splitting of the doublets of modes with opposite values ​​of the azimuthal number m, including modes with |m| > 1.A cone phase appears as the ground state of uniaxial magnets with comparable second-order and fourth-order anisotropy constants. In such systems, specific vortex states can exist. The authors have studied magnetization oscillations in small cylindrical particles in a cone vortex state. The study has determined the frequencies of magnon excitations in the presence of a vortex in the cone phase of a ferromagnet. It has been established that there is a significant splitting of the doublets of modes with opposite values ​​of the azimuthal number m, including modes with |m| > 1.

We investigated the spin dynamics of a vortex state in a core-shell magnetic nanodisk driven by an oscillating field applied perpendicular to the disk plane by means of micromagnetic simulations. The nanodisk comprises a Py (Fe0.2Ni0.8) core of 100 nm in radius, surrounded by a 50 nm thick Fe shell. Fourier transform analyses show that the Py core and the Fe shell dominate spin-wave oscillation at the fundamental and higher order radial modes, respectively. For oscillating driving field tuned to the fundamental eigenfrequency, the Py/Fe interface effectively confines spin-wave excitation in the Py core region. This effect leads to significantly more rapid vortex core (VC) reversal in comparison to homogeneous disks. Our work demonstrates that the higher order modes can drive much faster VC reversal than the fundamental mode, in sharp contrast to the results obtained in homogeneous disks. With excitation levels up to 30 mT, we find strong nonlinear spin-wave dynamics in the system, which results in mode frequency redshifting, therefore the observation of the most rapid VC reversals below eigenfrequencies and VC switching in wide ranges of frequencies., 11 pages

The energy and spatial distributions of vortex bound state in superconductors carry important information about superconducting pairing and the electronic structure. Although discrete vortex states, and sometimes a zero energy mode, had been observed in several iron-based superconductors, their spatial properties are rarely explored. In this study, we used low-temperature scanning tunneling microscopy to measure the vortex state of (Li,Fe)OHFeSe with high spatial resolution. We found that the nonzero energy states display clear spatial oscillations with a period corresponding to bulk Fermi wavelength; while in contrast, the zero energy mode does not show such oscillation, which suggests its distinct electronic origin. Furthermore, the oscillations of positive and negative energy states near E_{F} are found to be clearly out of phase. Based on a two-band model calculation, we show that our observation is more consistent with an s_{++} wave pairing in the bulk of (Li, Fe)OHFeSe, and superconducting topological states on the surface.

The vector vortex light beam, which exhibits a space-variant polarization state and is coupled with orbital angular momentum of light, has been drawing much attention due to its fundamental interest and potential applications in a wide range. Here we reveal both theoretically and experimentally that a diffractive structure having cylindrical symmetry is shown to be transparent for the vector vortex state of light with arbitrary topology. We demonstrate such an intriguing phenomenon in the Fresnel diffraction condition, where the vector Helmholtz wave equation can be utilized in the paraxial regime. Our demonstration has implications in control and manipulation of vector vortex light beams in diffractive optics, and hence, it may find potential applications.