Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session A12: Vortices in Superconductors I |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Victor Gurarie, University of Colorado Room: LACC 402A |
Monday, March 21, 2005 8:00AM - 8:12AM |
A12.00001: Domain Regime in the 2D Disordered Vortex Matter Gergely Zimanyi, Mahesh Chandran, Richard Scalettar The 2D disordered vortex matter is simulated by large-scale molecular dynamics methods at T=0. Performing sweeps with the magnetic field and the disorder, we find a disordered Vortex Glass/Molasses Regime at high fields/disorder, and a Domain Regime at low fields/disorder. We do not find evidence for a region with a dilute gas of dislocations, assumed by some theoretical approaches. In the Domain Regime the dislocations are organized into domains walls, defining large dislocation-free domains. The boundary between these regimes exhibits reentrant behavior as a function of the magnetic field. This boundary is a crossover, characterized by the roughening of the domain walls. [Preview Abstract] |
Monday, March 21, 2005 8:12AM - 8:24AM |
A12.00002: Magnus Force in Discrete and Continuous Two-Dimensional Superfluids Zoltan Gecse, Sergei Khlebnikov Motion of vortices in two-dimensional superfluids is studied by solving the Gross-Pitaevsky equation numerically on a uniform grid. Simulations show that in the limit of small lattice spacing, corresponding to a nearly Galilean-invariant case, vortices move with the superflow, while on coarse grids their motion depends on the orientation of the superflow relative to the grid. In particular, when the superflow is parallel to one of the primitive vectors of the grid, vortices in the coarse limit move perpendicular to the superflow. Thus, in this case, we observe a crossover from the full Magnus force in a Galilean-invariant system to a sharply reduced effective Magnus force in a discrete system. The latter regime corresponds to existing experiments on vortex motion in Josephson junction arrays. [Preview Abstract] |
Monday, March 21, 2005 8:24AM - 8:36AM |
A12.00003: Density functional theory for freezing transition of interlayer Josephson vortex line liquid Xiao Hu, Mengbo Luo The freezing transition of interlayer Josephson vortex line liquid into lattice is studied in terms of the density functional theory for crystallization. The interplay between intervortex repulsion and layer pinning in presence of thermal fluctuations is analyzed. The enhancement of melting temperature by the layer pinning at high magnetic fields is revealed clearly where anisotropy scaling is broken. In certain regime of magnetic field a smectic phase is stabilized by strong layer pinning. The freezing of vortex liquid is then two-step, a second-order liquid-smectic transition and a first-order smectic-lattice transition. B-T phase diagrams for typical high-Tc cuprates will be presented. [Preview Abstract] |
Monday, March 21, 2005 8:36AM - 8:48AM |
A12.00004: Dissociation of vortex stacks into fractional-flux vortices Alvise De Col, Vadim Geshkenbein, Gianni Blatter We discuss the superconducting phase transition in a finite system of magnetically coupled superconducting layers. Transverse screening is modified by the presence of other layers resulting in topological excitations with fractional flux. The presence of additional layers leads to drastic modifivations in the potential between individual vortices in the same layer. Vortex stacks trapping a full flux and present at any finite temperature undergo a dissociation transition which corresponds to the depairing of fractional-flux vortices in individual layers. We propose an experiment with a bi-layer system allowing to identify the dissociation of bound vortex molecules. [Preview Abstract] |
Monday, March 21, 2005 8:48AM - 9:00AM |
A12.00005: Density oscillation of flux lines induced by a single twin plane with point pins Yoshihiko Nonomura, Xiao Hu, David R. Nelson In (1+1)-dimensional vortex matter with a single columnar defect [1], the density of flux lines parallel to a single columnar defect shows Friedel-like oscillations in a tilted field, with the correlation length of the amplitude of the oscillation diverging as the transverse field component vanishes. In this study, we show that similar behaviors are also observed in vortex states in three dimensions with a single twin plane and point pins. In a magnetic field along a twin plane at low enough temperatures, power-law decay of the density oscillation of flux lines is observed for sparse point pins, consistent with the existence of a Bragg glass phase. As the density of point pins increases, it changes to exponential decay in the strongly- pinned vortex glass regime. A similar density oscillation is observed in a slightly tilted field, and the range of the oscillation is enhanced in the limit of sparse point pins. [1] W. Hofstetter et al., Europhys. Lett. 66 (2004) 178; I. Affleck et al., J. Stat. Mech.: Theor. Exp. (2004) P10003. [Preview Abstract] |
Monday, March 21, 2005 9:00AM - 9:12AM |
A12.00006: Dynamics of half-quantized vortices in nanoscale superconducting composite structures (d-dot) Masaru Kato, Msayuki Ako, Masahiko Machida, Tomio Koyama, Takekazu Ishida Mesoscopic or nanoscopic superconductors shows sometime peculiar phenomena. When nanosize high-Tc d-wave superconductor is embedded in conventional s-wave superconductor matrix, it shows various spontaneous magnetic flux depending on the shape of the d-wave superconductor. The appearance of static magnetic field shows such state breaks the time reversal symmetry. So there another equally stable state, which has completely reversed magnetic fluxes. Therefore this d-wave superconducting dot in s-wave superconductor, which we call as ``d-dot,'' always has equally stable two states. For this system, we developed the numerical simulation method, which is based on the two component Ginzburg-Landau equation and the finite element method, and investigated the spontaneous magnetic field distribution. In this study we extended these previous study and we developed dynamical simulation method for d-dot's. Then we study the effect of external current to the spontaneous magnetic fluxes. We show external current causes the transition between two equally stable magnetic flux structures. This means the potential applications of these d-dot's. [Preview Abstract] |
Monday, March 21, 2005 9:12AM - 9:24AM |
A12.00007: Off-equilibrium dynamics and effective temperature of flux lines with random pinning and the vortex glass phase S. Bustingorry, L.F. Cugliandolo, D. Dominguez We investigate the low-temperature off-equilibrium dynamics of elastic lines embedded in three-dimensional disordered media using Langevin dynamics. The model describes interacting vortex lines in high-temperature superconductors with random pinning. We first study the case of isolated flux lines. At high temperatures the dynamics is stationary and the fluctuation dissipation theorem (FDT) holds. At low temperatures a simple multiplicative aging is found, as recently observed numerically in the directed polymer problem in (1+1) dimensions or analytically in the $2d$ XY model in the spin-wave approximation. Besides, the FDT is violated and we found a well defined effective temperature characterizing the slow modes of the system. This implies the existence of a dynamic crossover between a high-temperature equilibrium dynamic phase and a low-temperature glassy dynamic phase. We then discuss how the off-equilibrium dynamics and effective temperature are affected when the flux line interactions are taken into account and its relationship with the vortex glass phase. [Preview Abstract] |
Monday, March 21, 2005 9:24AM - 9:36AM |
A12.00008: Does the Vortex Glass Exist in Two Dimensions? Charles E. Creffield, Jose P. Rodriguez The nature of phase coherence in two-dimensional vortex lattices with random point pins is studied at the extreme type-II limit via the corresponding $XY$ model with uniform frustration. In particular, after taking the Villain approximation, we perform numerical Monte Carlo simulations of the resulting non-neutral Coulomb gas ensemble over the square lattice at low temperature [1]. Identical $\delta$-function pinning centers equal in number to the total number of vortices are also located at random throughout the model grid. A phase-coherent Bragg glass exists at the lowest levels of disorder pinning, with no unbound dislocations quenched in. Upon an increase in the strength of the pinning disorder, this phase becomes unstable to hexatic vortex glass states that show a diminished phase coherence, as well as to hexatic vortex liquid states that show no phase coherence at all. Yet stronger pinning disorder unbinds quenched-in pairs of disclinations, which results in a (pinned) vortex liquid phase that shows only short-range translational and orientational order.\\[4pt] [1] C.E. Creffield and J.P. Rodriguez, Phys. Rev. B {\bf 67}, 144510 (2003). [Preview Abstract] |
Monday, March 21, 2005 9:36AM - 9:48AM |
A12.00009: Slow dynamics of an elastic string in a random potential Alejandro Kolton, Alberto Rosso, Thierry Giamarchi We study the slow dynamics of an elastic string in a two dimensional pinning landscape by means of Langevin dynamics simulations. We find that the Velocity-Force characteristics are well described by the creep formula predicted from phenomenological scaling arguments. However, at strong disorder, the creep exponent $\mu$ and the roughness $\zeta$ of the string display a clear deviation from the values $\mu \approx 1/4$ and $\zeta \approx 2/3$ expected assuming a quasi-equilibrium-nucleation picture of the creep motion. We also analyzed the non-stationary relaxation of the string towards the steady state. We identify a slowly growing length $L(T,F,t)$ separating equilibrated and non-equilibrated length scales during the relaxation. For equilibrated lengths, $l < L$, we find a roughness $\zeta \approx 2/3$ at $F=0$ while for small $F > 0$ an ``excess'' of roughness $\zeta > 2/3$ is always observed. [Preview Abstract] |
Monday, March 21, 2005 9:48AM - 10:00AM |
A12.00010: Phase diagram of the vortex system in layered superconductors with random pinning Chandan Dasgupta, Oriol T. Valls Density functional theory based on a model free energy functional is used to study structural and thermodynamic properties of the vortex system in highly anisotropic layered superconductors with random pinning. For low concentrations of random columnar pins perpendicular to the layers, we find three distinct phases: a topologically ordered Bragg glass, a polycrystalline Bose glass and a vortex liquid. As the temperature is increased, the low-temperature Bragg glass transforms into the vortex liquid in two steps: these two phases are separated by a small region of the Bose glass phase. The Bragg glass phase disappears as the pin concentration is increased and the two-step first-order melting found at low pin concentrations is replaced by a single continuous transition from the Bose glass to the vortex liquid. This transition corresponds to the onset of percolation of liquid-like regions across the system. Results obtained from similar calculations for systems with random point pinning will also be presented. [Preview Abstract] |
Monday, March 21, 2005 10:00AM - 10:12AM |
A12.00011: Dynamic properties of vortex states as modeled by the disordered 3D uniformly frustrated XY model Peter Olsson Dynamic properties of the uniformly frustrated 3D XY model with point disorder are studied as a model of vortex flow in high temperature superconductors. Using both Monte Carlo and Resist Shunted Junctions dynamics, we compute the resistivity of the interacting vortex system both from equilibrium voltage fluctuations and from the response to a finite driving current. For a sufficiently strong disorder we find a non-trivial behavior: In the solid phase the resistance is very low, suggestive of a pinned vortex line lattice, but increases rapidly at the melting transition. In the simulations with a finite current we find that the same behavior is seen only for very small currents $I\approx 10^{-4}$. For larger currents the voltage instead decreases at the melting of the vortex lattice. This seems to be due to the increasing adjustment of the vortex lines to the pinning potential in the liquid phase. [Preview Abstract] |
|
A12.00012: Static and dynamic properties of pinned flux-line liquids A.M. Ettouhami We study the equilibrium statics and nonequilibrium driven dynamics of flux line liquids in presence of a random pinning potential. Under the assumption of replica symmetry, we find in the static case using a replica Gaussian variational method that the only effect of disorder is to increase the tilt modulus and the confining ``mass" of the internal modes of the flux lines, thus decreasing their thermal wandering. In the nonequilibrium, driven case, we derive the long scale, coarse-grained equation of motion of the vortices in presence of disorder, which apart from new Kardar-Parisi-Zhang nonlinearities, has the same form as the equation of motion for unpinned vortices, with renormalized coefficients. This implies, in particular, that the structure factor of a disordered vortex liquid has the same functional form as in the absence of pinning. The expression of the static structure factor derived within our approach is consistent both with experimental data and with the standard theory of elasticity of vortex lattices. [Preview Abstract] |
|
A12.00013: Interactions Effects and Effective Temperature in Driven Vortex Fluids with Random Pinning Alejandro Kolton, Daniel Dom\'{\i}nguez We study numerically the effects of vortex-vortex interactions on the fluctuation-dissipation relations of driven vortex fluids with random pinning. We show that the shaking temperature $T_{\tt sh}$ defined phenomenologically by Koshelev and Vinokur [1] corresponds to the effective transverse temperature $T_{\tt eff}$ defined from a generalized fluctuation-dissipation theorem [2,3] only in the limit of noninteracting vortices. $T_{\tt eff}$ is thus sensible to the short range anisotropic correlations in the driven fluid. In the noninteracting limit we use a simple model to derive an expression for $T_{\tt eff}$ which is valid for all finite velocities. [1] A.E. Koshelev and V.M. Vinokur, Phys. Rev. Lett. {\bf 73},3580 (1994). [2] L.F. Cugliandolo, J. Kurchan, and L. Peliti, Phys. Rev. E {\bf 55}, 3898 (1997) [3] A. B. Kolton {\it et al.}, Phys. Rev. Lett. {\bf 89}, 227001 (2002). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700