Collective and plastic vortex motion in superconductors at high flux densities

Abstract

A separate fit for R h Ͻ 2 AU (Q CO ¼ ð2:07 ϫ 10 30 ÞR Ϫ 1:66Ϯ0:22 h ) shows the same heliocentric dependence, and is displaced above the 'native' fit by a factor of ϳ2. Thus the present analysis suggests approximately equal contributions from native and distributed sources to the total CO production in comet Hale-Bopp within R h ϳ1:5 AU (Table 1).Could the onset of a distributed source for CO be related to a change in dust production or destruction? Our measurements of dust (at 4.7 m wavelength) sample particles with sizes of a few micrometres, and follow a heliocentric dependence (Q dust ϰ R Ϫ 2:73Ϯ0:12 h ) which is steeper than our findings for Q CO and Q H 2 O (see note added in proof, below). This implies a rapid increase in dust fragmentation, and hence a decrease in mean particle size, with decreasing heliocentric distance. (In our analysis, we have assumed the same heliocentric dependence of outflow velocity (R −0.5 h ) for dust and gas.) Detailed modelling of dust properties (outflow, composition, destruction) convolved with geometrical effects, will be reported elsewhere.If the onset of distributed CO emission was related to increased dust release as the comet approached perihelion, a sharp increase (that is, a 'jump') in Q dust similar to that observed for Q CO between 2.02 and 1.48 AU would be expected. Whereas Q CO follows two distinct distributions-one for R h Ͻ 2 AU and another for R h Ͼ 2 AU -Q dust appears to fit a single distribution, with no such jump near (or inside)The lack of a jump in Q dust near R h ¼ 2:0-1.5 AU demonstrates that the onset of distributed CO emission cannot be explained by increased dust production alone. Rather, it is plausible that a threshold (most likely thermal) is reached for release of additional CO in the coma. The similar power-law dependence exhibited by Q CO for both R h Ͻ 2 AU and R h Ͼ 2 AU, and by Q H 2 O (ref. 17), suggests that release of the 'parent' giving rise to distributed CO is controlled by sublimation of the same nuclear ice as seen for other native volatiles (water, native CO). We thus infer that the distributed parent has a constant mixing ratio in the nucleus relative to native H 2 O and CO ices.The difference between the Q-curves for CO and (scaled) dust approximates the Q-curve for the distributed component alone. This reaches its terminal value at a projected distance rϷ 6:5 ϫ 10 3 km from the nucleus for R h ¼ 1:48 AU, and at ϳ5:1 ϫ 10 3 km for R h ¼ 1:06 AU. The distance r approximates the scale for release of distributed CO, and can be compared with model predictions to better constrain the scale length of the distributed parent. Future refinements 21-24 to our analytical approach include accounting for axisymmetric outflow and for gas acceleration in the coma. We expect such modelling to have relatively little effect on our retrieved amount of native CO, but it should provide significant improvements to our understanding of the distributed source.We have characterized the release of carbon monoxide in comet Hale-Bopp, and compared it with w...

Location-sensitive measurement of the local fluctuation of driven vortex density inBi2Sr2CaCuMaeda1, Tsuboi2, Abiru3 et al. 2002Phys. Rev. B243140View full textAdd to dashboardCite

“…To elucidate this issue, several experimental efforts have been made [17,[19][20][21][22]. In particular, various imaging techniques [17,21,22] have established the existence of various states of driven vortices in conventional superconductors.…”

“…In particular, various imaging techniques [17,21,22] have established the existence of various states of driven vortices in conventional superconductors. However, for high-T c superconductors, almost nothing has been clarified, since these probes are applicable only over a limited parameter range (temperature, magnetic field, and driving force) [23][24][25].…”

“…This was based on the experimental fact that the washboard noise had not been observed in the vortices of superconductors before, except in a system with artificially introduced strong periodic pinning centers [16] and in the thermally-excited motion of a limited number of vortices [17].…”

Flow and Tilt-Induced Orientation of the Moving Vortex Lattice in Amorphous NbGe Superconducting Thin Films

“…1) Within the London approximation for isotropic superconductors all the possible orientations of the vortex lattice are degenerate in energy, 2,3) while this is lifted not simply by tilting an applied magnetic field, 4,5) but also when driven by applying a transport current. In experiments various imaging techniques such as Bitter decoration, 6) small angled neutron scattering 7,8) and scanning tunneling microscopy [9][10][11] have provided structural evidence for the hexagonal order in moving VLs, and some of them have shown that the lattice orientation (one of close-packed directions of the hexagonal VL) is aligned to be either parallel or perpendicular to the flow direction. These flow-induced orientations, including a reorientation between them, have been observed on both crystalline 6,10) and non-crystalline weak pinning superconductors, [12][13][14] and thus underlying crystallographic orientations are not at play.…”

Anisotropic response of the moving vortex lattice in superconducting Mo(1−x)Gex amorphous films

“…More recently Kokubo and coworkers [8] have proven this dynamical ordering from mode locking experiments. Snapshots of moving vortex structures have been obtained in decoration experiments [9,10] that have shown evidence for these smectic and moving glass phases of vortices. However one of the most striking properties of these quasi-ordered driven phases is the existence of barriers to a small force transverse to the direction of motion.…”