Muon-spin rotation measurements of an unusual vortex-glass phase in the layered superconductor Bi2.15Sr1.85CaCu2O8+δ.

Muon-spin rotation measurements, performed on the mixed state of the classic anisotropic superconductor Bi(2.15)Sr(1.85)CaCu(2)O(8+δ), obtain quantities directly related to two- and three-body correlations of vortices in space. A novel phase diagram emerges from such local probe measurements of the bulk, revealing an unusual glassy state at intermediate fields which appears to freeze continuously from the equilibrium vortex liquid but differs both from the lattice and the conventional high-field vortex glass state in its structure.

Electrostatic and electrokinetic contributions to the elastic moduli of a driven membrane.

We discuss the electrostatic contribution to the elastic moduli of a cell or artificial membrane placed in an electrolyte and driven by a DC electric field. The field drives ion currents across the membrane, through specific channels, pumps or natural pores. In steady state, charges accumulate in the Debye layers close to the membrane, modifying the membrane elastic moduli. We first study a model of a membrane of zero thickness, later generalizing this treatment to allow for a finite thickness and finite dielectric constant. Our results clarify and extend the results presented by D. Lacoste, M. Cosentino Lagomarsino, and J.F. Joanny (EPL 77, 18006 (2007)), by providing a physical explanation for a destabilizing term proportional to [see formula in text] in the fluctuation spectrum, which we relate to a nonlinear (E(2)) electrokinetic effect called induced-charge electro-osmosis (ICEO). Recent studies of ICEO have focused on electrodes and polarizable particles, where an applied bulk field is perturbed by capacitive charging of the double layer and drives the flow along the field axis toward surface protrusions; in contrast, we predict "reverse" ICEO flows around driven membranes, due to curvature-induced tangential fields within a nonequilibrium double layer, which hydrodynamically enhance protrusions. We also consider the effect of incorporating the dynamics of a spatially dependent concentration field for the ion channels.

Microtubule dynamics regulated by stathmin.

Microtubules perform a variety of functions which lead to the complex regulation of intracellular transport and cell division. However, the regulation of microtubule growth is not clearly known. Based on a recent experimental finding, we explore the possibility of spatial regulation of microtubule growth by stathmin-tubulin interaction gradients. Computer simulation of the model with stathmin-tubulin interaction gradients gave regulated growth as seen in experiments. In future, the stathmin-tubulin interaction gradients can be made dynamic and its impact on the microtubule growth can be explored.

Persistence in one-dimensional Ising models with parallel dynamics.

We study persistence in one-dimensional ferromagnetic and antiferromagnetic nearest-neighbor Ising models with parallel dynamics. The probability P(t) that a given spin has not flipped up to time t, when the system evolves from an initial random configuration, decays as P(t) approximately 1/t(straight theta(p)) with straight theta(p) approximately 0.75 numerically. A mapping to the dynamics of two decoupled A+A-->0 models yields straight theta(p)=3/4 exactly. A finite size scaling analysis clarifies the nature of dynamical scaling in the distribution of persistent sites obtained under this dynamics.

Surface melting of the vortex lattice.

We discuss the effect of an (ab) surface on the melting transition of the pancake-vortex lattice in a layered superconductor within a density functional theory approach. Both discontinuous and continuous surface melting are predicted for this system, although the latter scenario occupies the major part of the low-field phase diagram. The formation of a quasiliquid layer below the bulk melting temperature inhibits the appearance of a superheated solid phase, yielding an asymmetric hysteretic behavior which has been seen in experiments.

Muons as local probes of three-body correlations in the mixed state of type-II superconductors.

The vortex glass state formed by magnetic flux lines in a type-II superconductor is shown to possess nontrivial three-body correlations. While such correlations are usually difficult to measure in glassy systems, the magnetic fields associated with the flux vortices allow us to probe these via muon-spin rotation measurements of the local field distribution. We show via numerical simulations and analytic calculations that these observations provide detailed microscopic insight into the local order of the vortex glass and more generally validate a theoretical framework for correlations in glassy systems.

Direct observation of the flux-line vortex glass phase in a type II superconductor.

The order of the vortex state in La1.9Sr0.1CuO4 is probed using muon-spin rotation and small-angle neutron scattering. A transition from a Bragg glass to a vortex glass is observed, where the latter is composed of disordered vortex lines. In the vicinity of the transition the microscopic behavior reflects a delicate interplay of thermally induced and pinning-induced disorder.