I-V characteristics of short superconducting nanowires with different bias and shunt: a dynamic approach

We derived the I-V characteristics of short nanowire in the circuit with and without resistive and inductive shunt. For that we used numerical calculations in the framework of time-dependent Ginzburg-Landau equations with different relaxation times for the amplitude and phase dynamics. We also derived dependence of the I-V characteristics on flux in superconducting quantum interference device (SQUID) made of such two weak links.Comment: 5.4 pages and 7 figure

Enhancement of critical current density in superconducting/magnetic multi-layers with slow magnetic relaxation dynamics and large magnetic susceptibility

We propose to use superconductor-magnet multi-layer structure to achieve high critical current density by invoking polaronic mechanism of pinning. The magnetic layers should have large magnetic susceptibility to enhance the coupling between vortices and magnetization in magnetic layers. The relaxation of the magnetization should be slow. When the velocity of vortices is low, they are dressed by nonuniform magnetization and move as polarons. In this case, the viscosity of vortices proportional to the magnetic relaxation time is enhanced significantly. As velocity increases, the polarons dissociate and the viscosity drops to the usual Bardeen-Stephen one, resulting in a jump in the I-V curve. Experimentally the jump shows up as a depinning transition and the corresponding current at the jump is the depinning current. For Nb and proper magnet multi-layer structure, we estimate the critical current density $J_c\sim 10^{9}\ \rm{A/m^2}$ at magnetic field $B\approx 1$ T.Comment: 4 pages, 2 figure

Quantum phase transition and engineering in two-component BEC in optical lattices

In this paper we review recent progress in studying quantum phase transitions in one- and two-component Bose-Einstein condensates (BEC) in optical lattices. These phase transitions involve the emergence and disappearance of quantum coherence over whole optical lattice and of linear superposition of macroscopic quantum states. The latter may provide new means to engineer and to manipulate novel macroscopic quantum states and novel coherent atomic beams for quantum information processing, quantum computing etc.Comment: Format: LaTex2e. 7 pages, no figure. Talk at the Yang Symposium (in honor of C.N. Yang's 80th birthday), Beijing, China, June 2002. To appear in the Proceeding

Surface-wave solitons on the interface between a linear medium and a nonlocal nonlinear medium

We address the properties of surface-wave solitons on the interface between a semi-infinite homogeneous linear medium and a semi-infinite homogeneous nonlinear nonlocal medium. The stability, energy flow and FWHM of the surface wave solitons can be affected by the degree of nonlocality of the nonlinear medium. We find that the refractive index difference affects the power distribution of the surface solitons in two media. We show that the different boundary values at the interface can lead to the different peak position of the surface solitons, but it can not influence the solitons stability with a certain degree of nonlocality.Comment: 8 pages, 14 figures, 15 references, and so o

Extended Schmidt law holds for faint dwarf irregular galaxies

The extended Schmidt law (ESL) is a variant of the Schmidt law which relates the surface densities of gas and star formation, with the surface density of stellar mass added as an extra parameter. We empirically investigate for the first time whether low metallicity faint dwarf irregular galaxies (dIrrs) follow the ESL. Here we consider the `global' law where surface densities are averaged over the galactic discs. dIrrs are unique not only because they are at the lowest end of mass and star formation scales for galaxies, but also because they are metal-poor compared to the general population of galaxies. Our sample is drawn from the Faint Irregular Galaxy GMRT Survey (FIGGS) which is the largest survey of atomic hydrogen in such galaxies. The gas surface densities are determined using their atomic hydrogen content. The star formation rates are calculated using GALEX far ultraviolet fluxes after correcting for dust extinction, whereas the stellar surface densities are calculated using Spitzer 3.6 $\mu$m fluxes. All surface densities are calculated over stellar discs defined by the 3.6 $\mu$m images. We find dIrrs indeed follow the extended Schmidt law. The mean deviation of the FIGGS galaxies from the relation is 0.01 dex, with a scatter around the relation of less than half that seen in the original relation. In comparison, we also show that the FIGGS galaxies are much more deviant when compared to the `canonical' Kennicutt-Schmidt relation. Our results help strengthen the universality of the extended Schmidt law, especially for galaxies with low metallicities. We suggest that models of star formation in which feedback from previous generations of stars set the pressure in the ISM, are promising candidates for explaining the ESL. We also confirm that ESL is an independent relation and not a form of a relation between star formation efficiency and metallicity.Comment: Accepted for publication in Astronomy & Astrophysics. Figure 2 on Page 5 shows the main resul

Properties of Mg-doped Nd-Ba-Cu-O generic seed crystals for the top seeded melt growth of (RE)-Ba-Cu-O bulk superconductors

We have recently developed a new generic seed crystal that has been used successfully to fabricate any oriented, single grain (RE)-Ba-Cu-O bulk superconductor by a cold seeding technique. In this paper we report the chemical, structural and microstructural properties of these seed crystals, including the variation of melting point, crystallographic parameters and volume fraction of Mg-rich inclusions in the Nd1 + xBa 2-x(Cu1-yMgy)3Oz matrix as a function of externally added MgO content. The influence of Mg-doping on the superconducting transition temperatures of YBCO grains fabricated using these seeds is investigated. Finally, an optimum MgO content of the generic seed that effectively controls the orientation of the seeded grain without compromising its superconducting properties is suggested from the many seed crystals fabricated with a wide range of Mg-rich addition