arXiv subjects

V. M. Vinokur

Publications and source records attributed to V. M. Vinokur.

158 records · Page 9Linked to original sources

arXiv2000

Transient Dynamics of Pinning

We study the evolution of an elastic string into the pinned state at driving forces slightly below the depinning threshold force $F_c$. We quantify the temporal evolution of the string by an {\it activity function} $A(t)$ representing the fraction of active nodes at time $t$ and find three distinct dynamic regimes. There is an initial stage of fast decay of the activity; in the second, intermediate, regime, an exponential decay of activity is observed; and, eventually, the fast collapse of the string towards its final pinned state results in an decay in the activity with $\Am \sim (t_p-t)^ψ$, where $t_p$ is the pinning time in the finite system involved.

cond-mat.dis-nn↗

arXiv2000

Continuum field description of crack propagation

We develop continuum field model for crack propagation in brittle amorphous solids. The model is represented by equations for elastic displacements combined with the order parameter equation which accounts for the dynamics of defects. This model captures all important phenomenology of crack propagation: crack initiation, propagation, dynamic fracture instability, sound emission, crack branching and fragmentation.

cond-mat.mtrl-sci↗

arXiv1999

Plasma resonance at low magnetic fields as a probe of vortex line meandering in layered superconductors

We consider the magnetic field dependence of the plasma resonance frequency in pristine and in irradiated Bi$_2$Sr$_2$CaCu$_2$O$_8$ crystals near $T_c$. At low magnetic fields we relate linear in field corrections to the plasma frequency to the average distance between the pancake vortices in the neighboring layers (wandering length). We calculate the wandering length in the case of thermal wiggling of vortex lines, taking into account both Josephson and magnetic interlayer coupling of pancakes. Analyzing experimental data, we found that (i) the wandering length becomes comparable with the London penetration depth near T$_{c}$ and (ii) at small melting fields ($< 20$ G) the wandering length does not change much at the melting transition. This shows existence of the line liquid phase in this field range. We also found that pinning by columnar defects affects weakly the field dependence of the plasma resonance frequency near $T_c$.

cond-mat.supr-con↗

arXiv1999

Electrostatically-Driven Granular Media: Phase Transitions and Coarsening

We report the experimental and theoretical study of electrostatically driven granular material. We show that the charged granular medium undergoes a hysteretic first order phase transition from the immobile condensed state (granular solid) to a fluidized dilated state (granular gas) with a changing applied electric field. In addition we observe a spontaneous precipitation of dense clusters from the gas phase and subsequent coarsening - coagulation of these clusters. Molecular dynamics simulations shows qualitative agreement with experimental results.

cond-mat.soft↗

arXiv1999

Nucleation of vortices by rapid thermal quench

We show that vortex nucleation in superfluid $^3$He by rapid thermal quench in the presence of superflow is dominated by a transverse instability of the moving normal-superfluid interface. Exact expressions for the instability threshold as a function of supercurrent density and the front velocity are found. The results are verified by numerical solution of the Ginzburg-Landau equation.

cond-mat.supr-con↗

arXiv1998

Controlled Dynamics of Interfaces in a Vibrated Granular Layer

We present experimental study of a topological excitation, {\it interface}, in a vertically vibrated layer of granular material. We show that these interfaces, separating regions of granular material oscillation with opposite phases, can be shifted and controlled by a very small amount of an additional subharmonic signal, mixed with the harmonic driving signal. The speed and the direction of interface motion depends sensitively on the phase and the amplitude of the subharmonic driving.

patt-sol↗

arXiv1998

Dynamic vortex mass in clean Fermi superfluids and superconductors

We calculate the dynamic vortex mass for clean Fermi superfluids including both s- and d-wave superconductors as a response to a vortex acceleration. Assuming a finite quasiparticle mean free time, the vortex mass appears to be a tensor. The diagonal component dominates in the limit of long mean free time while the off-diagonal mass takes over in the moderately clean regime.

cond-mat.supr-con↗

arXiv1998

Driven Vortex States and Relaxation in Single Crystal $YBa_2Cu_4O_8$

The vortex response to various ac-drives has been studied in high quality $YBa_2Cu_4O_8$ single crystals. Well within the vortex solid phase a re-entrant resistive state has been observed that is characterized by long relaxation times. Pulse current response and IV characteristics reveal that in this state the driven vortex system relaxes in a way to increase t he effective pinning force. A phenomenological model accounts for the observed features, in particular the clock-wise hysteresis of the IV-curves and the increase of the apparent critical current with applied current amplitude.

cond-mat.supr-con↗

arXiv1998

Hexagons and Interfaces in a Vibrated Granular Layer

The order parameter model based on parametric Ginzburg-Landau equation is used to describe high acceleration patterns in vibrated layer of granular material. At large amplitude of driving both hexagons and interfaces emerge. Transverse instability leading to formation of ``decorated'' interfaces and labyrinthine patterns, is found. Additional sub-harmonic forcing leads to controlled interface motion.

patt-sol↗

arXiv1998

Pinning-induced transition to disordered vortex phase in layered superconductors

Destruction of the vortex lattice by random point pinning is considered as a mechanism of the ``second peak'' transition observed experimentally in weakly coupled layered high temperature superconductors. The transition field separating the topologically ordered quasilattice from the amorphous vortex configuration is strongly influenced by the layered structure and by the nonlocal nature of the vortex tilt energy due to the magnetic interlayer coupling. We found three different regimes of transition depending on the relative strength of the Josephson and magnetic couplings. The regimes can be distinguished by the dependence of the transition field

cond-mat.supr-con↗

arXiv1996

Plastic vortex-creep in YBa$_2$Cu$_3$O$_{7-x}$ crystals

Local magnetic relaxation measurements in YBa$_2$Cu$_3$O$_{7-x}$ crystals show evidence for plastic vortex-creep associated with the motion of dislocations in the vortex lattice. This creep mechanism governs the vortex dynamics in a wide range of temperatures and fields below the melting line and above the field corresponding to the peak in the ''fishtail'' magnetization. In this range the activation energy $U_{pl}$, which decreases with field, drops below the elastic (collective) creep activation energy, $U_{el}$, which increases with field. A crossover in flux dynamics from elastic to plastic creep is shown to be the origin of the fishtail in YBa$_2$Cu$_3$O$_{7-x}$.

supr-con↗

arXiv1995

Peak effect in twinned superconductors

A sharp maximum in the critical current $J_c$ as a function of temperature just below the melting point of the Abrikosov flux lattice has recently been observed in both low and high temperature superconductors. This peak effect is strongest in twinned crystals for fields aligned with the twin planes. We propose that this peak signals the breakdown of the collective pinning regime and the crossover to strong pinning of single vortices on the twin boundaries. This crossover is very sharp and can account for the steep drop of the differential resistivity observed in experiments.

cond-mat↗

arXiv1995

Sign Change of the Flux Flow Hall Effect in HTSC

A novel mechanism for the sign change of the Hall effect in the flux flow region is proposed. The difference $δn $ between the electron density at the center of the vortex core and that far outside the vortex causes the additional contribution to the Hall conductivity $δσ_{xy}=-δn ec/B$. This contribution can be larger than the conventional one in the dirty case $Δ(T)τ<1$. If the carrier density inside the core exceeds that far outside, a double sign change may occur as a function of temperature.

cond-mat↗

arXiv1994

Twin-Boundary Pinning of Superconducting Vortex Arrays

We discuss the low-temperature dynamics of magnetic flux lines in high-temperature superconductors in the presence of a family of parallel twin planes that contain the $c$ axis. A current applied along the twin planes drives flux motion in the direction transverse to the planes and acts like an electric field applied to {\it one-dimensional} carriers in disordered semiconductors. As in flux arrays with columnar pins, there is a regime where the dynamics is dominated by superkink excitations that correspond to Mott variable range hopping (VRH) of carriers. In one dimension, however, rare events, such as large regions void of twin planes, can impede VRH and dominate transport in samples that are sufficiently long in the direction of flux motion. In short samples rare regions can be responsible for mesoscospic effects. The phase boundaries separating various transport regimes are discussed. The effect of tilting the applied field out of the twin planes is also considered. In this case the resistivity from flux motion is found to depend strongly on the tilt angle.

cond-mat↗