Effect of varying material anisotropy on critical current anisotropy in vicinal YBa2Cu3O7-delta thin films

The high $T_{c}$ cuprate superconductors are noted for their anisotropic layered structure, certain of these materials indeed tend toward the limit of a Lawrence-Doniach superconductor. However, YBa$_2$Cu$_3$O$_{7-\delta}$ has a smaller anisotropy than would be expected from its interlayer spacing. This is due to the cuprate chains in the structure. To investigate the influence of the chain oxygen on transport properties critical current versus applied field angle measurements were performed on fully oxygenated and de-oxygenated YBa$_2$Cu$_3$O$_{7-\delta}$ thin films and optimally oxygenated Y$_{0.75}$Ca$_{0.2}$Ba$_2$Cu$_3$O$_{7-\delta}$ thin films. The films were grown on 10$^{\circ}$ mis-cut SrTiO$_3$ substrates to enable the intrinsic vortex channelling effect to be observed. The form of the vortex channelling minimum observed in field angle dependent critical current studies on the films was seen to depend on film oxygenation. The vortex channelling effect is dependent on a angular dependent cross-over to a string-pancake flux line lattice. The results obtained appear to be consistent with the prediction of Blatter et al. [Rev. Mod. Phys., 66 (4): 1125 (1994)] that increased superconducting anisotropy leads to the kinked string-pancake lattice existing over a smaller angular range.EPSR

Contrasting xylem vessel constraints on hydraulic conductivity between native and non-native woody understory species

We examined the hydraulic properties of 82 native and non-native woody species common to forests of Eastern North America, including several congeneric groups, representing a range of anatomical wood types. We observed smaller conduit diameters with greater frequency in non-native species, corresponding to lower calculated potential vulnerability to cavitation index. Non-native species exhibited higher vessel-grouping in metaxylem compared with native species, however, solitary vessels were more prevalent in secondary xylem. Higher frequency of solitary vessels in secondary xylem was related to a lower potential vulnerability index. We found no relationship between anatomical characteristics of xylem, origin of species and hydraulic conductivity, indicating that non-native species did not exhibit advantageous hydraulic efficiency over native species. Our results confer anatomical advantages for non-native species under the potential for cavitation due to freezing, perhaps permitting extended growing seasons

Investigation of superconducting interactions and amorphous semiconductors

Research papers on superconducting interactions and properties and on amorphous materials are presented. The search for new superconductors with improved properties was largely concentrated on the study of properties of thin films. An experimental investigation of interaction mechanisms revealed no new superconductivity mechanism. The properties of high transition temperature, type 2 materials prepared in thin film form were studied. A pulsed field solenoid capable of providing fields in excess of 300 k0e was developed. Preliminary X-ray measurements were made of V3Si to determine the behavior of cell constant deformation versus pressure up to 98 kilobars. The electrical properties of amorphous semiconducting materials and bulk and thin film devices, and of amorphous magnetic materials were investigated for developing radiation hard, inexpensive switches and memory elements

Evaporation of a packet of quantized vorticity

A recent experiment has confirmed the existence of quantized turbulence in superfluid He3-B and suggested that turbulence is inhomogenous and spreads away from the region around the vibrating wire where it is created. To interpret the experiment we study numerically the diffusion of a packet of quantized vortex lines which is initially confined inside a small region of space. We find that reconnections fragment the packet into a gas of small vortex loops which fly away. We determine the time scale of the process and find that it is in order of magnitude agreement with the experiment.Comment: figure 1a,b,c and d, figure2, figure

Dynamics of ripple formation on silicon surfaces by ultrashort laser pulses in sub-ablation conditions

An investigation of ultrashort pulsed laser induced surface modification due to conditions that result in a superheated melted liquid layer and material evaporation are considered. To describe the surface modification occurring after cooling and resolidification of the melted layer and understand the underlying physical fundamental mechanisms, a unified model is presented to account for crater and subwavelength ripple formation based on a synergy of electron excitation and capillary waves solidification. The proposed theoretical framework aims to address the laser-material interaction in sub-ablation conditions and thus minimal mass removal in combination with a hydrodynamics-based scenario of the crater creation and ripple formation following surface irradiation with single and multiple pulses, respectively. The development of the periodic structures is attributed to the interference of the incident wave with a surface plasmon wave. Details of the surface morphology attained are elaborated as a function of the imposed conditions and results are tested against experimental data

Optical interconnect with densely integrated plasmonic modulator and germanium photodetector arrays

We demonstrate the first chip-to-chip interconnect utilizing a densely integrated plasmonic Mach-Zehnder modulator array operating at 3 x 10 Gbit/s. A multicore fiber provides a compact optical interface, while the receiver consists of germanium photodetectors

Slow 4He^{4}He Quenches Produce Fuzzy, Transient Vortices

We examine the Zurek scenario for the production of vortices in quenches of liquid $^{4}He$ in the light of recent experiments. Extending our previous results to later times, we argue that short wavelength thermal fluctuations make vortices poorly defined until after the transition has occurred. Further, if and when vortices appear, it is plausible that that they will decay faster than anticipated from turbulence experiments, irrespective of quench rates.Comment: 4 pages, Revtex file, no figures Apart from a more appropriate title, this paper differs from its predecessor by including temperature, as well as pressure, quenche

Unraveling critical dynamics: The formation and evolution of topological textures

We study the formation of topological textures in a nonequilibrium phase transition of an overdamped classical O(3) model in 2+1 dimensions. The phase transition is triggered through an external, time-dependent effective mass, parameterized by quench timescale \tau. When measured near the end of the transition the texture separation and the texture width scale respectively as \tau^(0.39 \pm 0.02) and \tau^(0.46 \pm 0.04), significantly larger than \tau^(0.25) predicted from the Kibble-Zurek mechanism. We show that Kibble-Zurek scaling is recovered at very early times but that by the end of the transition the power-laws result instead from a competition between the length scale determined at freeze-out and the ordering dynamics of a textured system. In the context of phase ordering these results suggest that the multiple length scales characteristic of the late-time ordering of a textured system derive from the critical dynamics of a single nonequilibrium correlation length. In the context of defect formation these results imply that significant evolution of the defect network can occur before the end of the phase transition. Therefore a quantitative understanding of the defect network at the end of the phase transition generally requires an understanding of both critical dynamics and the interactions among topological defects.Comment: 12 pages, revtex, 9 figures in eps forma