On the origin of high smectic fluidity of the vortex lattice in a 2D superconductor (original) (raw)
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Structure and orientation of the moving vortex lattice in clean type-II superconductors
Physical Review B, 2004
The dynamics of moving vortex lattice is considered in the framework of the time dependent Ginzburg - Landau equation neglecting effects of pinning. At high flux velocities the pinning dominated dynamics is expected to cross over into the interactions dominated dynamics for very clean materials recently studied experimentally. The stationary lattice structure and orientation depend on the flux flow velocity. The vortex lattice will have a different orientation for V>V_c. The two orientations can be desribed as motion "in channels" and motion of "lines of vortices perpendicular to the direction of motion. Although we start from the lowest Landau level approximation, corrections to conductivity and the vortex lattice energy dissipation from higher Landau levels are systematically calculated and compared to a recent experiment.
Effect of dimensionality on the vortex dynamics in a type-II superconductor
Physical Review B, 2019
We explore the effects of sample dimensionality on vortex pinning in a type-II, low-T C , s-wave superconductor, NbN, in the presence of a perpendicular magnetic field, H. We find significant differences in the phase diagrams in the magnetic field-temperature plane between three-dimensional (3D) and 2D NbN films. The differences are most striking close to the normal-superconductor phase transition. We establish that these variances have their origin in the differing pinning properties in two different dimensions. We obtain the pinning strength quantitatively in both the dimensions from two independent transport measurements performed in two different regimes of vortex motion: (i) thermally assisted flux-flow regime and (ii) flux flow regime. Both the measurements consistently show that both the pinning potential and the zero-field free-energy barrier to depinning in the 3D superconductor are at least an order of magnitude stronger than that in the 2D superconductor. Further, we probed the dynamics of pinning in both 2D and 3D superconductor through voltage fluctuation spectroscopy. We find that the mechanism of vortex pinning-depinning is qualitatively similar for the 3D and 2D superconductors. The voltage-fluctuations arising from vortex motion are found to be correlated only in the 2D superconductor. We establish this to be due to the presence of long-range phase fluctuations near the Berezinskii-Kosterlitz-Thouless-type superconducting transition in 2D superconductors.
Driven motion of vortices in superconductors
Lecture Notes in Physics
The driven motion of vortices in the solid vortex state is analyzed with the time-dependent Ginzburg-Landau equations. In large-scale numerical simulations, carried out on the IBM Scalable POWERparallel (SP) system at Argonne National Laboratory, many hundreds of vortices are followed as they move under the influence of a Lorentz force induced by a transport current in the presence of a planar defect (similar to a twin boundary in YBa2Cu3O7). Correlations in the positions and velocities of the vortices in plastic and elastic motion are identified and compared. Two types of plastic motion are observed. Organized plastic motion displaying long-range orientational correlation and shorter-range velocity correlation occurs when the driving forces are small compared to the pinning forces in the twin boundary. Disorganized plastic motion displaying no significant correlation in either the velocities or orientation of the vortex system occurs when the driving and pinning forces are of the s...
Physical Review B, 2003
The effect of a periodic pinning array on the vortex state in a 2D superconductor at low temperatures is studied within the framework of the Ginzburg-Landau approach. It is shown that attractive interaction of vortex cores to a commensurate pin lattice stabilizes vortex solid phases with long range positional order against violent shear fluctuations. Exploiting a simple analytical method, based on the Landau orbitals description, we derive a rather detailed picture of the low temperatures vortex state phase diagram. It is predicted that for sufficiently clean samples application of an artificial periodic pinning array would enable one to directly detect the intrinsic shear stiffness anisotropy characterizing the ideal vortex lattice.
Dynamic vortex phases and pinning in superconductors with twin boundaries
Phys Rev B, 2000
We investigate the pinning and driven dynamics of vortices interacting with twin boundaries using large scale molecular-dynamics simulations on samples with near one million pinning sites. For low applied driving forces, the vortex lattice orients itself parallel to the twin boundary and we observe the creation of a flux gradient and vortex-free region near the edges of the twin boundary. For increasing drive, we find evidence for several distinct dynamical flow phases which we characterize by the density of defects in the vortex lattice, the microscopic vortex flow patterns, and orientation of the vortex lattice. We show that these different dynamical phases can be directly related to microscopically measurable voltage-current V(I) curves and voltage noise. By conducting a series of simulations for various twin boundary parameters we derive several vortex dynamic phase diagrams.
Influence of artificial pinning on vortex lattice instability in superconducting films
New Journal of Physics, 2012
In superconducting films under an applied dc current, we analyze experimentally and theoretically the influence of engineered pinning on the vortex velocity at which the flux-flow dissipation undergoes an abrupt transition from low to high resistance. We argue, based on a nonuniform distribution of vortex velocity in the sample, that in strongly disordered systems the mean critical vortex velocity for flux-flow instability (i) has a nonmonotonic dependence on magnetic field and (ii) decreases as the pinning strength is increased. These findings challenge the generally accepted microscopic model of Larkin and Ovchinnikov (1979 J. Low. Temp. Phys. 34 409) and all subsequent refinements of this model which ignore the presence of pinning centers.
Numerical Simulation of Vortex Dynamics in Type-II Superconductors
Journal of Computational Physics, 1996
This article describes the results of several numerical simulations of vortex dynamics in type-II superconductors. The underlying mathematical model is the time-dependent Ginzburg-Landau model. The simulations concern vortex penetration in the presence of twin boundaries, interface patterns between regions of opposite vortex orientation, and magnetic-ux entry patterns in superconducting samples. r r A = ? 4 c 1 c @A @t + r + 4 c J s :
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
Superconducting film with weak pinning centers: Incommensurate vortex lattices
Physical Review B, 2007
Vortex configurations in a superconducting film with a square array of small antidots are studied within the Ginzburg-Landau ͑GL͒ theory. We find that in addition to the conventional vortex structures at the matching fields, a variety of vortex states can be stabilized by decreasing the pinning strength of the antidots, including ͑i͒ the triangular vortex lattice where some vortices are pinned by the antidots and others are located between them, ͑ii͒ vortex line structures, and ͑iii͒ a lattice of vortex cluster structures around the empty pinning centers. Although these partially pinned vortex structures are obtained more frequently in field cooled experiments than the square pinned vortex lattice, they are not the lowest energy states, i.e., the ground state, contrary to the results from a London approach. This result can be understood as due to the presence of a broad local minimum in the GL free energy which keeps the vortices away from the pinning centers. Our results can also be related to recent experiments on macroscopic metallic particles that move in a plane in the presence of a weak electrostatic pinning potential.
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.