Cynthia J. Olson

Nonequilibrium Dynamic Phase Diagram for Vortex Lattices

The new dynamic phase diagram for driven vortices with varying lattice softness we present here indicates that, at high driving currents, at least two distinct dynamic phases of flux flow appear depending on the vortex-vortex interaction strength. When the flux lattice is soft, the vortices flow in independently moving channels with smectic structure. For stiff flux lattices, adjacent channels become locked together, producing crystalline-like order in a coupled channel phase. At the crossover lattice softness between these phases, the system produces a maximum amount of voltage noise. Our results relate spatial order with transport and are in agreement with experiments.

Commensurate and incommensurate vortex states in superconductors with periodic pinning arrays

28th matching field! and for a wide range of pinning parameters and system sizes. Our results show that the vortex lattice ~VL! is highly ordered only at certain matching fields ~MF’s ! and can have various orientations with respect to the underlying pinning array. At some MF’s the VL is actually disordered. The enhancements of M(H) are most noticeable for fields less than the second matching field; however, we find some evidence of small enhancements of M(H) for higher fields. Square and triangular arrays produce different sequences of ordered matching fields at which the pinning is enhanced. At some MF’s, we find novel vortex arrangements with translational order only along certain directions. Our numerical results are in excellent agreement with recent low-field experiments on square pinning arrays. 7 Moreover, using geometrical arguments that take into account the constraints of the pinning array, we derive simple formulas for the ordered MF’s and for the orientation of the VL with respect to the square or triangular pinning array.

DYNAMIC PHASES OF VORTICES IN SUPERCONDUCTORS WITH PERIODIC PINNING

We present results from extensive simulations of driven vortex lattices interacting with periodic arrays of pinning sites. Changing an applied driving force produces a rich variety of novel dynamical plastic flow phases which are very distinct from those observed in systems with random pinning arrays. Signatures of the transition between these different dynamical phases include sudden jumps in the current-voltage curves as well as marked changes in the vortex trajectories and vortex lattice order. Several dynamical phase diagrams are obtained as a function of commensurability, pinning strength, and spatial order of the pinning sites. {copyright} {ital 1997} {ital The American Physical Society}

Spatiotemporal dynamics and plastic flow of vortices in superconductors with periodic arrays of pinning sites.

We present simulations of flux-gradient-driven superconducting rigid vortices interacting with square and triangular arrays of columnar pinning sites in an increasing external magnetic field. These simulations allow us to quantitatively relate spatiotemporal microscopic information of the vortex lattice with typically measured macroscopic quantities, such as the magnetization {ital M}({ital H}). The flux lattice does not become completely commensurate with the pinning sites throughout the sample at the magnetization matching peaks, but forms a commensurate lattice in a region close to the edge of the sample. Matching fields related to unstable vortex configurations do not produce peaks in {ital M}({ital H}). We observe a variety of evolving complex flux profiles, including flat terraces or plateaus separated by winding current-carrying strings and, near the peaks in {ital M}({ital H}), plateaus only in certain regions, which move through the sample as the field increases. Several short videos, illustrating several particular cases of the type of dynamics described here, are available at http://www-personal.engin.umich.edu/--nori. {copyright} {ital 1996 The American Physical Society.}

Fractal Networks, Braiding Channels, and Voltage Noise in Intermittently Flowing Rivers of Quantized Magnetic Flux

We analyze the microscopic dynamics of vortex motion through channels that form river-like fractal networks in a variety of superconducting samples, and relate it to macroscopic measurable quantities such as the power spectrum. As a function of pinning strength, we calculate the fractal dimension, tortuosity, and the corresponding voltage noise spectrum. Above a certain pinning strength, a remarkable universal drop in both tortuosity and noise power occurs when the vortex motion changes from shifting braiding channels to unbraided channels. We compare our results with experiments.

Vortex plastic flow, local flux density, magnetization hysteresis loops, and critical current, deep in the Bose-glass and Mott-insulator regimes.

We present simulations of flux-gradient-driven superconducting vortices interacting with strong columnar pinning defects as an external field

Moving Wigner glasses and smectics: dynamics of disordered Wigner crystals.

H(t)

Plastic flow, voltage noise and vortex avalanches in superconductors

is quasi-statically swept from zero through a matching field

Vortex Plastic Motion in Twinned Superconductors

B_{\phi}

Microscopic derivation of magnetic-flux-density profiles, magnetization hysteresis loops, and critical currents in strongly pinned superconductors

. We analyze several measurable quantities, including the local flux density