ac currents in a vortex state of layered superconductors (original) (raw)
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Vortex Core Structure and Dynamics in Layered Superconductors
Vortices in Unconventional Superconductors and Superfluids, 2002
We investigate the equilibrium and nonequilibrium properties of the core region of vortices in layered superconductors. We discuss the electronic structure of singly and doubly quantized vortices for both s-wave and d-wave pairing symmetry. We consider the intermediate clean regime, where the vortex-core bound states are broadened into resonances with a width comparable to or larger than the quantized energy level spacing, and calculate the response of a vortex core to an a.c. electromagnetic field for vortices that are pinned to a metallic defect. We concentrate on the case where the vortex motion is nonstationary and can be treated by linear response theory. The response of the order parameter, impurity self energy, induced fields and currents are obtained by a self-consistent calculation of the distribution functions and the excitation spectrum. We then obtain the dynamical conductivity, spatially resolved in the region of the core, for external frequencies in the range, 0.1∆ < ω < ∼ 3∆. We also calculate the dynamically induced charge distribution in the vicinity of the core. This charge density is related to the nonequilibrium response of the bound states and collective mode, and dominates the electromagnetic response of the vortex core.
On the possibility of a first-order phase transition to the vortex state in layered superconductors
Physica C-superconductivity and Its Applications, 1990
Layered superconductors with a second-order phase transition in a magnetic field parallel to the layers and a first-order phase transition in a perpendicular field are considered. In the case of an inclined field a first-order phase transition to the vortex state is predicted. A new type of intermediate state with the coexistence of normal and vortex regions is shown to exist.
Transport properties and structures of vortex matter in layered superconductors
Physical Review B, 2000
In this paper we analyze the structure, phase transitions and some transport properties of the vortex system when the external magnetic field lies parallel to the planes in layered superconductors. We show that experimental results for resistivity are qualitatively consistent with numerical simulations that describe the melting of a commensurate rotated lattice. However for some magnetic fields, the structure factor indicates the occurrence of smectic peaks at an intermediate temperature regime.
Vortex pumps in the crossing lattices regime of highly anisotropic layered superconductors
It is now well established that vortex dynamics in samples with a spatially asymmetric pinning potential can lead to rectifying vortex 'diode' behaviour. Spatial asymmetry is not a fundamental requirement for the control of vortex motion, however, and we demonstrate that vortex 'lensing' is possible in highly anisotropic layered superconductors simply under the action of non time-reversible trains of inplane magnetic field pulses. Our devices depend crucially on the existence of 'crossing' pancake vortex (PV) and Josephson vortex (JV) lattices in Bi 2 Sr 2 CaCu 2 O 8+d (BSCCO) single crystals under tilted magnetic fields. An attractive interaction between these two sub-lattices makes it possible to indirectly manipulate the PV distribution by modifying the JV lattice, and a number of functional devices based on this principle have been proposed. In our experiments a BSCCO single crystal is placed on a Hall probe array, and cooled below T c in a small out-of-plane magnetic field. Trains of sawtooth in-plane field pulses are then applied to the system and different elements of the Hall array used to demonstrate PV lensing or antilensing behaviour, depending on the pulse shape. The mechanism leading to lensing will be discussed and results compared with molecular dynamics simulations.
Physical Review B
We report numerical simulations of the nonlinear dynamics of Josephson vortices driven by strong dc currents in layered superconductors. Dynamic equations for interlayer phase differences in a stack of coupled superconducting layers were solved to calculate a drag coefficient η(J) of the vortex as a function of the perpendicular dc current density J. It is shown that Cherenkov radiation produced by a moving vortex causes significant radiation drag increasing η(v) at high vortex velocities v and striking instabilities of driven Josephson vortices moving faster than a terminal velocity vc. The steady-state flux flow breaks down at v > vc as the vortex starts producing a cascade of expanding vortex-antivortex pairs evolving into either planar macrovortex structures or branching flux patterns propagating both along and across the layers. This vortex-antivortex pair production triggered by a rapidly moving vortex is most pronounced in a stack of underdamped planar junctions where it can occur at J > Js well below the interlayer Josephson critical current density. Both vc and Js were calculated as functions of the quasiparticle damping parameter, and the dc magnetic field applied parallel to the layers. The effects of vortex interaction on the Cherenkov instability of moving vortex chains and lattices in annular stacks of Josephson junctions were considered. It is shown that a vortex driven by a current density J > Js in a multilayer of finite length excites selfsustained large-amplitude standing waves of magnetic flux, resulting in temporal oscillations of the total magnetic moment. We evaluated a contribution of this effect to the power W radiated by the sample and showed that W increases strongly as the number of layers increases. These mechanisms can result in nonlinearity of the c-axis electromagnetic response and contribute to THz radiation from the layered cuprates at high dc current densities flowing perpendicular to the ab planes.
Physica C: Superconductivity, 2007
We show that in both high anisotropy superconductors Bi2212 (T c = 90 K), and Bi2223 (T c = 110 K), an AC magnetic field applied collinear to the DC field and parallel to the Cu layers induces strong microwave dissipation. It is theoretically predicted that the Josephson solitons are responsible for this absorption. Good qualitative agreement of experimental data with theoretical predictions is found. Differences observed in the experimental results between these two compounds are discussed.
Vortex chains in anisotropic superconductors
Journal of Physics: Condensed Matter, 2005
T superconductors in small magnetic fields directed away from the crystal symmetry axes have been found to exhibit inhomogeneous chains of flux lines (vortices), in contrast to the usual regular triangular flux-line lattice. We review the experimental observations of these chains, and summarize the theoretical background that explains their appearance. We treat separately two classes of chains: those that appear in superconductors with moderate anisotropy due to an attractive part of the interaction between tilted flux lines, and those with high anisotropy where the tilted magnetic flux is created by two independent and perpendicular crossing lattices. In the second case it is the indirect attraction between a flux line along the layers (Josephson vortex) and a flux line perpendicular to the layers (pancake vortex stack) that leads to the formation of chains of the pancake vortex stacks. This complex system contains a rich variety of phenomena, with several different equilibrium phases, and an extraordinary dynamic interplay between the two sets of crossing vortices. We compare the theoretical predictions of these phenomena with the experimental observations made to date. We also contrast the different techniques used to make these observations. While it is clear that this system forms a wonderful playground for probing the formation of structures with competing interactions, we conclude that there are important practical implications of the vortex chains that appear in highly anisotropic superconductors.
Surface instabilities and vortex transport in current-carrying superconductors
Physical Review B, 1998
We investigate the stability of the vortex configuration in thin superconducting films and layered Josephsoncoupled superconductors under an applied current analytically and by numerical simulations of the timedependent Ginzburg-Landau equation. We show that the stationary vortex lattice becomes unstable with respect to long-wavelength perturbations above some critical current I c. We find that at currents slightly exceeding I c the vortex phase develops plastic flow, where large coherent pieces of the lattice are separated by lines of defects and slide with respect to each other. At elevated currents a transition to elastic flow is observed. We obtained the effective one-dimensional Ginzburg-Landau equation for a description of the vortex penetration from the edges. We discuss this transition in terms of a one-dimensional phase-slip phenomenon in superconducting wires with a periodically modulated temperature. We found several distinct dynamic vortex phases in the layered current-carrying superconductors. We show that for some intermediate range of the current, depending on the coupling between the layers, the coherent motion of the pancake vortices in different layers becomes unstable leading to dynamic decoupling. ͓S0163-1829͑98͒07205-1͔
Spectroscopy of Magnetic Excitations in Magnetic Superconductors Using Vortex Motion
Physical Review Letters, 2005
In magnetic superconductors a moving vortex lattice is accompanied by an ac magnetic field which leads to the generation of spin waves. At resonance conditions the dynamics of vortices in magnetic superconductors changes drastically, resulting in strong peaks in the dc I-V characteristics at voltages at which the washboard frequency of vortex lattice matches the spin wave frequency ωs(g), where g are the reciprocal vortex lattice vectors. We show that if washboard frequency lies above the magnetic gap, peaks in the I-V characteristics in borocarbides and cuprate layered magnetic superconductors are strong enough to be observed over the background determined by the quasiparticles.
Magnetic field of an in-plane vortex outside a layered superconductor
Physical Review B, 1999
We present the solution to London's equations for the magnetic fields of a vortex oriented parallel to the planes, and normal to a crystal face, of a layered superconductor. These expressions account for flux spreading at the superconducting surface, which can change the apparent size of the vortex along the planes by as much as 30%. We compare these expressions with experimental results.