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Using the nonlinear Ginzburg–Landau equations we study the vortex configurations in a superconducting square with a central square pillar in the presence of a uniform applied magnetic field. The presence of the pillar changes the vortex structure in the superconducting sample considerably. We calculate magnetization, magnetic induction, supercurrent and vorticity, which show different vortex configurations as a function of magnetic field. [ABSTRACT FROM AUTHOR]

In order to study site-selective NMR in chiral p -wave superconductors, we calculate local nuclear relaxation rate T 1 − 1 in the vortex lattice state by Eilenberger theory with and without non-magnetic impurity scattering in the Born limit and unitary limit. The local T 1 − 1 in the NMR resonance line shape is different between two chiral states p ± , depending on whether the chirality is parallel or anti-parallel to the vorticity. In the p − -wave, anomalous suppression of local T 1 − 1 occurs around the vortex core due to the negative coherence term coming from odd-frequency s -wave Cooper pair induced around the vortex. We especially examine the site dependence of the anomalous suppression of local T 1 − 1 , including the applied magnetic field dependence and the impurity effects. [ABSTRACT FROM AUTHOR]

The resistive state of a superconductor in magnetic field has been thoroughly investigated both by experiments and by theoretical simulations. However, a local study of vortex dynamics inducing dissipation was performed only recently by means of scanning Hall probe microscopy (SHPM). In this work we extend this idea and we visualize the oscillatory motion of vortices in NbSe2 using scanning tunneling microscopy (STM). In contrast to previous experiments, sensitive to magnetic fields, the STM probes the local density of states and the local topography. Its ability to resolve vortices is limited by the coherence length. In the case of type-II superconductors this is expected to resolve vortex motion beyond the detection limit of the SHPM. We experimentally verify the enhanced sensitivity by observing vortex motion in a very dense vortex lattice (H=600mT). [ABSTRACT FROM AUTHOR]

In this work we solved the time-dependent Ginzburg-Landau equations, TDGL, to simulate two superconducting systems with different lateral sizes and with an antidot inserted in the center. Then, by cycling the external magnetic field, the creation and annihilation dynamics of a vortex-antivortex pair was studied as well as the range of temperatures for which such processes could occur. We verified that in the annihilation process both vortex and antivortex acquire an elongated format while an accelerated motion takes place. [ABSTRACT FROM AUTHOR]

Highlights: [•] We study the switching phenomena in hybrid SC/FM coaxial cylinders. [•] The s-wave triplet Usadel equations are considered. [•] We investigate the T c behavior with different vorticities. [•] Numerical results exhibit the vortex states in favor of superconductivity in FM. [Copyright &y& Elsevier]

Abstract: RF responses of intrinsic Josephson junction stacks in the flux-flow state have been studied to explore vortex motion. We have reported various RF induced effects on flux-flow of Bi2Sr2CaCu2O8+ y intrinsic Josephson junctions. In a pinning free state, a remarkable zero-crossing step appears at a certain voltage on I–V curve, which is closed to the voltage V = NΦ 0 f, where N is the number of junction, Φ 0 is the flux quantum, f is the RF frequency, respectively. It is shown that vortex motion phase-locked to external microwaves play an important role in the responses. In this report, we have carried out numerical simulation by using the coupled sine-Gordon equations in order to compare with the experimental results. The numerical simulations reveal that the alternating magnetic field of microwaves drives vortices into the stack and generates the zero-crossing step. [Copyright &y& Elsevier]

Abstract: To explore vortex states and their dynamics in superconductors with large thermal fluctuation and artificial pinning potentials, we have studied the influence of periodic arrays of antidots in high-T c superconductor Bi2Sr2CaCu2O8+y (Bi2212). The diameter dependence of the matching effect in Bi2212 without a change of the thickness and oxygen doping level was investigated using one Bi2212 single-crystal film of homogeneous thickness in which several different-diameter antidot arrays were introduced. The matching effect observed by vortex-flow resistance measurements changed systematically depending on the diameter. The antidot-diameter dependence of the irreversibility lines was examined. [Copyright &y& Elsevier]

Abstract: We investigate the situation where a mesoscopic 1D ring or 2D cylinder is subject to a magnetic field by simulating the time dependant Ginzburg–Landau equations with periodic boundary conditions. We investigate the different possible evolutions for the 1D phase slip phenomenon. The case of the multiple phase slips is analyzed in details and we study the competition between simultaneous and consecutive multiple phase slips analytically and numerically. In 2D we study the creation of vortex–antivortex pairs. Following the theory of the Kibble–Zurek mechanism, we quenched the sample by applying a strong current and observe vortex–antivortex pairs dynamics. [ABSTRACT FROM AUTHOR]

Abstract: We reported dynamics of Josephson vortices interacting with electromagnetic waves in strongly coupled long Josephson junctions stack, such as an intrinsic Josephson junction (IJJ), by numerical simulations based on coupled sine-Gordon equations considering a periodic pinning potential of sinusoidal form. The numerical simulation results for the influence of the electromagnetic waves on flux-flow properties show that the periodic pinning potential induces an in-phase motion of Josephson vortices over the junction stacks, which achieve high performances of IJJ flux-flow oscillator. In order to prove it from another viewpoint, we calculate RF impedance of long Josephson junction stacks in flux-flow state. A remarkable negative real part region of RF impedance appears at 1st harmonic step, it means that the long Josephson junction stacks in flux-flow state acts as an oscillator at the negative real part region. In this study, we evaluate the optimum condition for RF radiation with the periodic pinning potential. [Copyright &y& Elsevier]

Abstract: We have fabricated finite-sized Pb superconducting networks with 10×10 square (each 6×6μm2) holes by using the electron beam lithography and vortex arrangements are visualized by using magneto-optical imaging. We find that the vortex penetration at low temperature is controlled by defects in the network. We also find nearly regular arrangements of vortices with defects close to 1/2 and1/3 of the matching field. [Copyright &y& Elsevier]

Abstract: We report various RF induced effects on Josephson vortex flow of Bi2Sr2CaCu2O8+ y intrinsic Josephson junctions in vortex states being different with existence of pancake vortices. For pancake free state, RF induced zero-crossing steps, which had been found in ordinary Josephson flux flow oscillators, were first observed at voltage V = NΦ 0 f for N-stacked intrinsic Josephson junctions. In contrast the RF irradiations to the junctions in mixed state with pancakes those step responses changed features similar to Shapiro steps at Vn = nNΦ 0 f with order n. The former evidently demonstrates that electromagnetic waves propagate in the intrinsic Josephson junctions interacting with moving vortices. The later indicates that Josephson vortices move at the same speed coherently. [Copyright &y& Elsevier]

Abstract: Vortex behavior of superconducting finite-sized networks with 2×2 and 10×10 hole arrays has been investigated in a weak magnetic field. Photoresist films spin-coated on silicon substrates were first processed to draw network patterns by using the electron beam lithography. Then, the Pb networks have been made up by a lift-off technique after depositing Pb film on the resist patterns. The thickness of deposited Pb films is 200–250nm. Photoresist film was coated to protect Pb networks fabricated on silicon substrates (4×4mm). We carried out magnetization measurements of the Pb networks by a SQUID magnetometer as well as vortex image observations by a SQUID microscope. Matching peaks appeared in magnetization curve when a magnetic field was scanned from −4.7G to +4.7G. The magnetic field in SQUID microscope measurements was chosen as the integral multiples of the matching field H ϕ , where the scanning area typically covers 128×128μm with 1- or 2-μm step. [Copyright &y& Elsevier]

The vortex patterns stabilized by the square array of artificial pinning sites with a tunable pinning strength are studied by using a phenomenological approach in the London limit. The transitions between pinned and deformed triangular lattices are analyzed as a function of the amplitude of vortex-pinning site interaction and the length-scale characteristic of this interaction. The critical current and different phases of vortex lattice are studied in presence of external transport current. [Copyright &y& Elsevier]

A single vortex in the charged Bose-gas (CBG) has a charged core and its profile different from the vortex in neutral and BCS superfluids. Lower and upper critical fields of CBG are discussed. The unusual resistive upper critical field, Hc2(T), of many cuprates and a few other unconventional superconductors is described as the Bose–Einstein condensation field of preformed bosons–bipolarons. Its nonlinear temperature dependence follows from the scaling arguments. Exceeding the Pauli paramagnetic limit is explained. Controversy in the determination of Hc2(T) of cuprates from kinetic and thermodynamic measurements is addressed in the framework of the bipolaron theory. [Copyright &y& Elsevier]

The superconducting state of mesoscopic square samples with two and four antidots is studied using the nonlinear Ginzburg–Landau (GL) theory. We found a qualitative difference in the nucleation of the superconducting state in samples with different number of antidots, which is related to the interplay of the different types of symmetry. The H–T phase diagram of these structures reveals an oscillatory behavior caused by the formation of different stable vortex configurations in these small clusters of pinning centers. A comparison with the experiment of H–T phase diagram is given. [Copyright &y& Elsevier]

Hollow YBaCuO superconducting cylinder has been placed in a d.c. magnetic field H⩽1200 Oe creating a mixed state in the sample and a.c. magnetic field h⩽1 Oe applied to its outer surface. An inductance coil was used inside to measure the response. Judgments are made on the elastic and viscous properties of vortices originated in the sample. Particularly, the character of the response signal (amplitude and phase) is explained by irreversible magnetization of the sample, due to vortices’ pinning and interaction with surface. Well-calibrated grains used in the ceramic (∼50 μm in average) allowed observation of the “commensurability” effect between the pinning centers’ and vortex–lattice periods, enhancing the volume force of pinning. [Copyright &y& Elsevier]

The 2D Josephson type media are supposed to be equivalently modelled by means of Chern–Simons–Higgs geometric Lagrangian functionals. It is shown that the corresponding Chern–Simons–Higgs model possesses of special structure singular geometric objects which can be interpreted as vortices of the Josephson medium. An N-vortex configuration studied in the frame of adiabatic approximation, revealed its particle-like Hamiltonian structure. The two-vortex configuration is investigated in detail, their motion is discussed making use of only analytical tools. Some special solutions are singled out as limiting cases. [Copyright &y& Elsevier]

The vortex dynamics at high velocities in niobium and niobium/gold thin films is studied by taking notice of the role of the metallic layer. The proximity effect and its influence on superconducting properties is first identified. We report then in a flux flow regime an abrupt transition to the normal state which has been predicted theoretically by Larkin and Ovchinnikov. The influence of the metallic layer on the parameters of this instability is studied. It demonstrates that the gold film decreases the critical force and the vortex velocity driving the transition. [Copyright &y& Elsevier]

Abstract: We have studied dynamics of Josephson vortices in strongly coupled long Josephson junctions stack, such as an intrinsic Josephson junction, by numerical simulations based on coupled sine–Gordon equations considering a periodic pinning potential. In this report, we investigate flux-flow oscillators induced two types of pinning potentials. One is magnetic periodic pinning potential, the other is periodic bias currents. Our results demonstrate that the periodic pinning potential can develop the generated power of flux-flow oscillator in certain condition. [ABSTRACT FROM AUTHOR]

Abstract: Significant enlargements of antidot diameter by Ar-ion milling were observed in Bi2Sr2CaCu2O8+y single-crystal films with antidot arrays as well as the thinning of the films. In an original sample with triangular array of antidots, whose diameter is about 200nm, a few dip structures by the matching effect were observed in the vortex-flow resistance as a function of magnetic field. With increasing the milling time, the number of the dips increases and the appearance of the flow resistance becomes periodic oscillations. These features can be explained mainly by the increase of the antidot diameter. [ABSTRACT FROM AUTHOR]

Abstract: To study the vortex behavior in 2D periodic pinning potentials, we measured field dependence of the vortex-flow resistance and the critical current in single-crystal (Bi2212) films with an equilateral triangular array of antidots. Fractional matching effect was observed in 1/4, 1/3, 1/2, 2/3, 3/4, and 6/7 of the first matching field , and even above . While the most of fractional numbers except 1/2 can be explained from commensurability between triangular lattices of antidots and vortices, the matching effect in 1/2 suggests the existence of the interstitial vortices in comparison with the results of a reported numerical simulation. The fractional matching effect above can be explained as a matching effect by multi-quanta vortices. [Copyright &y& Elsevier]

Abstract: We study the local density of states at the surface of a chiral p-wave superconductor in the presence of an Abrikosov vortex which is situated not too far from the surface. It is shown that the presence of the vortex leads to a zero-energy peak of the density of states at the surface if its chirality is the same as that of the superconductor, and to a gap structure for the opposite case. [ABSTRACT FROM AUTHOR]

Abstract: A Scanning SQUID Microscope (SSM), developed by using our own technology, is used to study the distribution of vortices in a superconducting thin film and their movements induced by applied current. The SQUID sensor is a first-order gradiometer with an overall equivalent flux noise of about . Using this SSM system, we obtain the vortex images before and after a pulse current with a variable amplitude and duration time is applied to the sample. The changes of a series of vortex images with increasing amplitude of the current pulse provide us with an estimate of the vortex pinning force at various pinning sites and their distribution. [ABSTRACT FROM AUTHOR]

Abstract: In order to study the influence of artificial pinning centers on vortex behavior in high- superconductors, we have measured vortex-flow resistance in single-crystal thin films with a square array of antidots. In addition to the integer matching effect, which is expected at integer multiples of the first matching field , fractional matching effects have been found as fine dip structures at fields (f: fractional number). The observed values of f are 1/6, 1/4, 1/3, 1/2, 2/3, and 3/4. While a square lattice of vortices (or unoccupied antidots) can fit on the antidot array for the cases of 1/4 and 1/2 (3/4), different vortex configurations are required to explain for the other fractions, viz., a stripe pattern at 1/3. [ABSTRACT FROM AUTHOR]

Abstract: We investigate numerically the transport of vortices in superconductors under a driving force by using Langevin dynamics. The velocity-driving force characteristic (V x –F L curve) of superconductors includes a region with series of stages. The impact of the initial states was investigated and there is a dramatic difference between the initial state produced by the current annealing process (CAP) and the well pinned state (WPS). [ABSTRACT FROM AUTHOR]

Abstract: We investigate microwave complex conductivity of La2−x Sr x CuO4 under finite magnetic fields by broadband technique, and analyze the result from the two alternative viewpoints; (1) superconductivity fluctuation, and (2) vortex motion. For higher fields, conventional scaling relation between conductivity and frequency does not hold. We propose a new “scaling” relation for these data. On the other hand, vortex picture works even in the vortex liquid state. However, a strange behavior of superfluid density indicates that the vortex picture alone cannot explain the whole behavior even just above the first order transition line. [ABSTRACT FROM AUTHOR]