ORAL SESSION 4B6: Vortex Dynamics

Thursday, Feb. 24, 3:45 p.m. – 6:15 p.m., General Assembly Hall A (GRB)

Chairs: T. Giamarchi (Lab de Physique des Solides)

4B6.1 Vortex Dynamics in Confined Geometries*

M. Cristina Marchetti, Syracuse University, Department of Physics, Syracuse NY 13244-1130

Presenting Author: M.C. Marchetti

Patterned irradiation of cuprate superconductors with columnar defects allows a new generation of experiments which can probe the properties of vortex liquids by forcing them to flow in confined geometries. Such experiments can be used to distinguish experimentally between continuous disorder-driven glass transitions of vortex matter, such as the vortex glass or the Bose glass transition, and nonequilibrium polymer-like glass transitions driven by interaction and entanglement. For continuous glass transitions, an analysis of such experiments that combines an inhomogeneous scaling theory with the hydrodynamic description of viscous flow of vortex liquids can be used to infer the critical behavior for all the transport coeffcients. I will focus on experiments in the Corbino disk geometry and discuss the response to both dc and ac probes.

*Work carried out in collaboration with David R. Nelson, Harvard University.

4B6.2 Driven Vortex Dynamics

G.W. Crabtree 1, W.K. Kwok 1, D. Lopez 1, H. Safar 2, A. Mazilu 1,2, R.J. Olsson 1,3, and L.M. Paulius 4. 1 Argonne National Laboratory, Argonne, IL 60439. 2 University of Illinois at Chicago, Chicago, IL 60680. 3 Michigan State University, East Lansing, MI 48824. 4 Western Michigan University, Kalamazoo, MI 49008.

Presenting Author: G.W. Crabtree

The dynamic behavior of vortex liquids and solids is distinguished by its shear response. Liquids respond to a shear force with a viscosity and flow hydrodynamically, while solids respond with an elastic shear modulus and flow plastically or elastically. We describe a transport experiment where a controlled gradient of the Lorentz driving force is introduced, allowing the shear response of the driven vortex motion to be measured. We directly observe hydrodynamic motion of the liquid, elastic motion of the lattice at low force gradients, and plastic motion of the lattice at high force gradients.

4B6.3 Dynamic Studies of Vortices, from Single Flux Lines to Lattices

Flavio Pardo 1, C. Bolle 1, V. Aksyuk 1, E. Zeldov 1, P.L. Gammel 1, D.J. Bishop 1, and F. de la Cruz 2. 1 Bell Labs Lucent Technologies, 700 Mountain Ave. Murray Hill, NJ 07974, USA. 2 Centro Atómico Bariloche, CNEA, S. C de Bariloche, Argentina.

Presenting Author: F. Pardo

We present different techniques to study the dynamics of the vortex lattice in NbSe₂ single crystal samples. In the first set of experiments, we applied a field parallel to c crystalline axis and extended the Bitter decoration technique to the study of dynamic structures by imaging the lattice during creep ("decoration during motion"). This method exposed a new smectic phase and an anisotropic "crystal" at higher fields. In the second set we used a micro-mechanical high Q oscillator to study the mesoscopic flux dynamics along the crystallographic ab plane. In this case we were able to observe single vortex penetration and interesting new telegraphic noise signatures.

4B6.4 Small Angle Neutron Scattering and Vortex Lattice Dynamical Phase Diagram

C. Goupil 1, A. Pautrat 1, Ch. Simon 1, P.G. Kealey 2, E.M. Forgan 2, S.L. Lee 3, G. Lazard 4, B. Placais 4, Y. Simon 4, P. Mathieu 4, S.T. Johnson 5, R. Cubitt 6, Ch. Dewhurst 6. 1 CRISMAT-ISMRA, CAEN, France. 2 University of Birmingham, Birmingham, United Kingdom. 3 University of St. Andrews, St. Andrews, United Kingdom. 4 Laboratoire de Physique de la Matiere Condensee ENS, Paris, France. 5 Laboratoire de Physique du Solide, Bat. 510 Université d'Orsay, Orsay, France. 6 Institut Laue Langevin, Grenoble, France.

Presenting Author: C. Goupil

We present a study of the influence of a current-induced driving force on flux lines in NbTa and PbIn samples using Small Angle Neutron Scattering (SANS). This study allowed us to explore some regions of the current versus magnetic field dynamic phase diagram. Increasing the applied current at fixed vortex density, or vortex density at fixed current, we observed a crossover from a mosaic of FLL domains (polycrystalline FLL) to a configuration with strongly coupled lines in an essentially single crystal FLL state, a "Moving Bragg Glass". The exact nature of the crossover from disordered configuration to FLL is discussed on the basis of different vortex pinning descriptions. In particular, bulk pinning and pinning by surface irregularities are discriminated by measuring the bending of the vortex lines extracted from the rocking curves. Our study of the dynamical phase diagram and the relative contributions of current density and magnetic field are discussed in terms of the theoretical predictions.

4B6.5 Vortex Dynamics in Superconductors

F. Nori, The University of Michigan, Ann Arbor, MI

Presenting Author: F. Nori

Driven vortices produce several dynamical phases with steady states of plastic and elastic motion. We characterize the dynamical instabilities (i.e., flux avalanches or cascades producing voltage bursts), as well as the evolution of the topological order and vortex flow paths ("vortex streets" surrounded by regions of pinned flux).

Our analysis of the microscopic spatio-temporal dynamics of individual flux-lines in superconductors lends insight to commonly measured bulk macroscopic quantities, such as magnetization and critical currents. We have performed extensive simulations [1] of current- and flux-gradient-driven flux lines. We explore a wide variety of relevant parameters which are difficult to continuously tune experimentally, such as the density, strength, radius, and location of the pinning sites.

Our predictions (e.g., magnetization hysteresis loops) can be directly compared with commonly-measured experimental quantities. We analyze both global (e.g., M(H), J_c(H)) and local (e.g., B(x,y,H(t)), M(x,y,H(t)), J_c(x,y,B)) measurable quantities. Our results elucidate the topological order dynamics of a driven plastic lattice interacting with a rigid disordered substrate, a problem that has recently attracted considerable attention [2].

We will also consider periodic arrays of pinning sites, including novel applications: quantum logic gates, quantum computers, and also fluxon optics: concave/covex flux lenses, and fluxon pumps.

[1] C. Reichhardt et al, Phys. Rev. Lett. 78, 2648 (1997); Olson et al, Phys. Rev. B 56, 6175 (1997); Phys. Rev. Lett. 80, 2197 (1998); 81, 3757 (1998); C. Reichhardt and F. Nori, Phys. Rev. Lett, 82, 414 (1999); 82, 3641 (1999); preprints.

[2] F. Nori, Science 271, 1373 (1996).

Video clips can be found at http://www-personal.engin.umich.edu/~nori

4B6.6 Vortex Instability and the Normal State at Low Temperatures

Milind N. Kunchur 1, B.I. Ivlev 2, D.K. Christen 3, and J.M. Phillips 4. 1 University of South Carolina, Dept. of Physics and Astronomy, Columbia, SC 29208. 2 Universidad Autonoma de San Luis Potosi, Mexico. 3 Oak Ridge National Lab. 4 Sandia National Lab.

Presenting Author: M.N. Kunchur

The motion of flux vortices in YBCO has been studied in the low temperature limit (T ~ 2% of T_c) at extreme current and dissipation densities (~ 10⁹ W/cm³). As the flux motion is driven into free flow and vortex velocities approach the speed of sound, a novel instability is observed signalled by a discontinuous drop in vortex viscosity. In contrast to the Larkin-Ovchinnikov instability commonly observed near T_c, this low-temperature instability has unusual features and appears to arise from a suppression of the order parameter. The critical resistivity at the point of vortex instability is roughly twice the free-flux-flow value r */r _n ~ 2 r _f ~ 2 B/H_c2, allowing an estimation of the illusive normal-state resistivity, r _n, in the zero-temperature limit. Contrary to some speculation, r _n saturates to a residual value, much like an ordinary metal, and the vortex dissipation continues to be finite as T ® 0.

1. "Vortex instability and the normal state of YBa₂Cu₃O_7-d at low temperatures", M.N. Kunchur, B.I. Ivlev, D.K. Christen, and J.M. Phillips, submitted to Phys. Rev. Lett. (MS# LE7138).

2. "Cherenkov resonances in vortex dissipation in superconductors", B.I. Ivlev, S. Mejia Rosales, and M.N. Kunchur, Phys. Rev. B., vol. 60 (1999) in press.

3. "Novel transport behavior found in the dissipative regime of superconductors", M.N. Kunchur, Mod. Phys. Lett. B. 9, 399 (1995).

4. "Observation of free flux flow at high dissipation levels in YBa₂Cu₃O₇", M.N. Kunchur, D.K. Christen, and J.M. Phillips, Phys. Rev. Lett.70, 998(1993).

5. "Pair-breaking effect of high current densities on the superconducting transition on YBa₂Cu₃O₇", M.N. Kunchur, D.K. Christen, C.E. Klabunde, and J.M. Phillips, Phys. Rev. Lett. 72, 752 (1994).

6. "Hall effect in YBa₂Cu₃O₇ in the limit of free flux flow", M.N. Kunchur, D.K. Christen, C.E. Klabunde, and J.M. Phillips,Phys. Rev. Lett.72, 2259(1994).

4B6.7 Dynamical transition in the c-axis correlation in 3D driven vortex lattices

Alejandro B. Kolton 1, Daniel Dominguez 1, and Niels Gronbech-Jensen 2. 1 Centro Atómico Bariloche, 8400 S. C. de Bariloche, Rio Negro, Argentina. 2 Department of Applied Science, University of California, Davis, CA 95616, USA.

Presenting Author: D. Dominguez

We present molecular dynamics simulations of driven vortices in layered superconductors in the presence of an external homogeneous force and point disorder. We use a model introduced by J.R. Clem for describing 3D vortex lines as stacks of 2D pancake vortices where only magnetic interactions are considered and the Josephson interlayer coupling is neglected. We numerically evaluate the long-range magnetic interaction between pancake vortices exactly. We analyze the vortex correlation along the field direction (c-axis). We find that above the critical current, in the "plastic flow" regime, pancakes are completely uncorrelated in the c-direction. When increasing the current, there is an onset of correlation along the c-axis at the transition from plastic flow to a moving smectic. This transition coincides with the peak in the differential resistance.

4B6.8 Pattern formation due to non-linear vortex diffusion

R.J. Wijngaarden 1, R. Surdeanu 1, J.M. Huijbregtse 1, J.H. Rector 1, B. Dam 1, R. Woerdenweber 2, and R. Griessen 1. 1 Division of Physics and Astronomy, Faculty of Sciences, Vrije Universiteit, De Boelelaan 1081, NL-1081 HV Amsterdam, The Netherlands. 2 Institut fuer Schicht- und Ionentechnik (ISI), Forschungszentrum Jülich, Germany.

Presenting Author: R.J. Wijngaarden

Penetration of magnetic flux in YBa₂Cu₃O₇ superconducting thin films in an external magnetic field is visualized using a magneto-optic technique. A variety of flux patterns due to non-linear vortex behavior is observed:

1. Roughening of the flux front [1] with scaling exponents identical to those observed in burning paper including the observation of two distinct regimes where respectively spatial disorder and temporal disorder dominate. In the latter regime Kardar-Parisi-Zhang behavior is found.

2. Fractal penetration [2] of flux with Hausdorff dimension depending on the critical current anisotropy.

3. Penetration as 'flux-rivers'.

4. The occurrence of commensurate and incommensurate channels in films with anti-dots as predicted in numerical simulations by Reichhardt, Olson and Nori [3].

It is shown that most of the observed behavior can be explained in terms of non-linear diffusion of vortices by comparison with various simulations of the non-linear diffusion equation appropiate for vortices.

[1] R. Surdeanu, R.J. Wijngaarden, E. Visser, J.M. Huijbregtse, J.H. Rector, B. Dam and R. Griessen, Phys.Rev. Lett. 83 (1999) 2054.

[2] R. Surdeanu, R.J. Wijngaarden, B. Dam, J. Rector, R. Griessen, C. Rossel, Z.F. Ren and J.H. Wang, Phys Rev B 58 (1998) 12467.

[3] C. Reichhardt, C.J. Olson and F. Nori, Phys. Rev. B 58, 6534 (1998).