Anisotropic shear melting and recrystallization of a two-dimensional complex (dusty) plasma

A two-dimensional plasma crystal was melted by suddenly applying localized shear stress. A stripe of particles in the crystal was pushed by the radiation pressure force of a laser beam. We found that the response of the plasma crystal to stress and the eventual shear melting depended strongly on the crystal's angular orientation relative to the laser beam. Shear stress and strain rate were measured, from which the spatially resolved shear viscosity was calculated. The latter was shown to have minima in the regions with high velocity shear, thus demonstrating shear thinning. Shear-induced reordering was observed in the steady-state flow, where particles formed strings aligned in the flow direction.Comment: 7 pages, 8 figures, submitted to Physical Review

The bifurcation phenomena in the resistive state of the narrow superconducting channels

We have investigated the properties of the resistive state of the narrow superconducting channel of the length L/\xi=10.88 on the basis of the time-dependent Ginzburg-Landau model. We have demonstrated that the bifurcation points of the time-dependent Ginzburg-Landau equations cause a number of singularities of the current-voltage characteristic of the channel. We have analytically estimated the averaged voltage and the period of the oscillating solution for the relatively small currents. We have also found the range of currents where the system possesses the chaotic behavior

Microstructure of a liquid complex (dusty) plasma under shear

The microstructure of a strongly coupled liquid undergoing a shear flow was studied experimentally. The liquid was a shear melted two-dimensional plasma crystal, i.e., a single-layer suspension of micrometer-size particles in a rf discharge plasma. Trajectories of particles were measured using video microscopy. The resulting microstructure was anisotropic, with compressional and extensional axes at around $\pm 45^{\circ}$ to the flow direction. Corresponding ellipticity of the pair correlation function $g({\bf r})$ or static structure factor $S(\bf{k})$ gives the (normalized) shear rate of the flow.Comment: 5 pages, 6 figure

Current-voltage characteristic of narrow superconducting wires: bifurcation phenomena

The current-voltage characteristics of long and narrow superconducting channels are investigated using the time-dependent Ginzburg-Landau equations for complex order parameter. We found out that the steps in the current voltage characteristic can be associated with bifurcations of either steady or oscillatory solution. We revealed typical instabilities which induced the singularities in current-voltage characteristics, and analytically estimated period of oscillations and average voltage in the vicinity of the critical currents. Our results show that these bifurcations can substantially complicate dynamics of the order parameter and eventually lead to appearance of such phenomena as multistability and chaos. The discussed bifurcation phenomena sheds a light on some recent experimental findings

Onset of cavity deformation upon subsonic motion of a projectile in a fluid complex plasma

We study deformation of a cavity around a large projectile moving with subsonic velocity in the cloud of small dust particles. To solve this problem, we employ the Navier--Stokes equation for a compressible fluid with due regard for friction between dust particles and atoms of neutral gas. The solutions shows that due to friction, the pressure of dust cloud at the boundary of the cavity behind the projectile can become negative, which entails formation of a microscopic void free from dust particles -- the cavity deformation. Corresponding threshold velocity is calculated, which is found to decrease with increasing cavity size. Measurement of such velocity makes it possible to estimate the static pressure inside the dust cloud.Comment: 7 pages, 3 figure

Spontaneous superconducting islands and Hall voltage in clean superconductors

We study a clean superconductor in the Hall configuration, in the framework of a purely dissipative time-dependent Ginzburg--Landau theory. We find situations in which the order parameter differs significantly from zero in a set of islands that appear to form a periodic structure. When the pattern of islands becomes irregular, it moves in or against the direction of the current and a Hall voltage is found. Tiny differences in the initial state may reverse the sign of the Hall voltage. When the average Hall voltage vanishes, the local Hall voltage does not necessarily vanish. We examine the influence that several boundary conditions at the electrodes have on these effects.Comment: 6 pages, Includes additional cases and more detailed result

Wave mode coupling due to plasma wakes in two-dimensional plasma crystals: In-depth view

Experiments with two-dimensional (2D) plasma crystals are usually carried out in rf plasma sheaths, where the interparticle interactions are modified due to the presence of plasma wakes. The wake-mediated interactions result in the coupling between wave modes in 2D crystals, which can trigger the mode-coupling instability and cause melting. The theory predicts a number of distinct fingerprints to be observed upon the instability onset, such as the emergence of a new hybrid mode, a critical angular dependence, a mixed polarization, and distinct thresholds. In this paper we summarize these key features and provide their detailed discussion, analyze the critical dependence on experimental parameters, and highlight the outstanding issues