Shapiro steps in a superconducting film with an antidot lattice

Shapiro voltage steps at voltages V_n=nV_0 (n integer) have been observed in the voltage-current characteristics of a superconducting film with a square lattice of perforating microholes (antidots)in the presence of radiofrequent radiation. These equidistant steps appear at the second matching field H_2 when the flow of the interstitial vortex lattice in the periodic potential created by the antidots and the vortices trapped by them, is in phase with the applied rf frequency. Therefore, the observation of Shapiro steps clearly reveals the presence of mobile intersitial vortices in superconducting films with regular pinning arrays. The interstitial vortices, moved by the driving current, coexist with immobile vortices strongly pinned at the antidots.Comment: 6 pages text, 3 EPS figures, RevTeX, accepted for publication in PRB Rapid Communication

Mode locking of vortex matter driven through mesoscopic channels

We investigated the driven dynamics of vortices confined to mesoscopic flow channels by means of a dc-rf interference technique. The observed mode-locking steps in the $IV$-curves provide detailed information on how the number of rows and lattice structure in the channel change with magnetic field. Minima in flow stress occur when an integer number of rows is moving coherently, while maxima appear when incoherent motion of mixed $n$ and $n\pm 1$ row configurations is predominant. Simulations show that the enhanced pinning at mismatch originates from quasi-static fault zones with misoriented edge dislocations induced by disorder in the channel edges.Comment: some minor changes were made, 4 pages, 4 figures, accepted for publication in Phys. Rev. Let

Anisotropic vortex pinning in superconductors with a square array of rectangular submicron holes

We investigate vortex pinning in thin superconducting films with a square array of rectangular submicron holes ("antidots"). Two types of antidots are considered: antidots fully perforating the superconducting film, and "blind antidots", holes that perforate the film only up to a certain depth. In both systems, we observe a distinct anisotropy in the pinning properties, reflected in the critical current Ic, depending on the direction of the applied electrical current: parallel to the long side of the antidots or perpendicular to it. Although the mechanism responsible for the effect is very different in the two systems, they both show a higher critical current and a sharper IV-transition when the current is applied along the long side of the rectangular antidots

Incommensuration Effects and Dynamics in Vortex Chains

We examine the motion of one-dimensional (1D) vortex matter embedded in a 2D vortex system with weak pinning using numerical simulations. We confirm the conjecture of Matsuda et al. [Science 294, 2136 (2001)] that the onset of the temperature induced motion of the chain is due to an incommensuration effect of the chain with the periodic potential created by the bulk vortices. In addition, under an applied driving force we find a two stage depinning transition, where the initial depinning of the vortex chain occurs through soliton like pulses. When an ac drive is added to the dc drive, we observe phase locking of the moving vortex chain.Comment: 4 pages, 4 postscript figure

Vortex Pinball Under Crossed AC Drives in Superconductors with Periodic Pinning Arrays

Vortices driven with both a transverse and a longitudinal AC drive which are out of phase are shown to exhibit a novel commensuration-incommensuration effect when interacting with periodic substrates. For different AC driving parameters, the motion of the vortices forms commensurate orbits with the periodicity of the pinning array. When the commensurate orbits are present, there is a finite DC critical depinning threshold, while for the incommensurate phases the vortices are delocalized and the DC depinning threshold is absent.Comment: 4 pages, 4 postscript figure

The Efficacy Of Rice As A Leaching

The concluding phase(s) of a rice rotation experiment presented the opportunity to assess the effect of consecutive crops of rice on the chemistry of the soil profile. An experiment which aimed to determine the potential to use high salinity groundwater for the irrigation of the non-rice phases of a wheat - sub.clover - rice rotation, and then use rice, irrigated with low salinity channel water (<0.1 dS/m), as a leaching crop was undertaken. The rotation included a single rice crop between each cycle of the application of saline groundwater. Although soil salinity of most horizons under saline treatments could be reduced by leaching in the rice phase (single crop), this was not true for sodicity. Average rootzone sodicity remained elevated above control values at the end of each cycle and increased following successive cycles. This project was implemented to further assess the effectiveness of rice as a leaching crop. As the blocks completed two cycles within the rice rotation the opportunity to grow successive crops of rice was undertaken. At the time of soil sampling (May, 2000) separate blocks had grown one, two, three or four consecutive rice crops. Soil samples were taken from each plot and processed for electrical conductivity and sodium (Na) content. Additional consecutive crops of rice resulted in more leaching of salt from the profile. After three crops sufficient salts had been leached to reduce ECe to below 0.6 dS/m to at least the depth sampled in this project (90 cm). Similar values were measured after a fourth crop. The levels of SARe measured after a second consecutive crop of rice were still higher than pre-treatment levels. Even after three and four crops of rice the SARe at profile depths below 60 cm, whilst reduced from the pre-treatment level, were still between 6 and 8