We present magneto optical studies of the critical state in YBa2Cu3O7-δ (YBCO) thick films prepared using BaF2 ex-situ post reaction process. A fractal-like propagation was observed as the magnetic flux entering the superconducting films, in striking contrast to the behavior expected of a uniform type II superconducting film in the critical state. However, by averaging the flux density over a c...

Ultrathin underdoped films of YBa2Cu3O7 d (YBCO) exhibit a prominent and abrupt downturn in ab-plane superfluid density nS(T) at a temperature consistent with a 2D vortex-pair unbinding transition. In this paper, we show that this characteristic feature of 2D superconductors diminishes with increasing film thickness consistent with theory, provided one uses the full film thickness rather than a...

We report on the degree of order of the vortex solid in YBa2Cu3O7 single crystals observed in ac susceptibility measurements. We show that when vortices are "shaken" by a temporarily symmetric ac field they are driven into an easy-to-move, ordered structure but, on the contrary, when the ac field is temporarily asymmetric, they are driven into a more pinned disordered state. This is characteris...

17O NMR is used to probe the local influence of nonmagnetic Zn and magnetic Ni impurities in the superconducting state of optimally doped high TC YBa2Cu3O7. Zn and Ni induce a staggered paramagnetic polarization, similar to that evidenced above TC, with a typical extension xi=3 cell units for Zn and xi>or=3 for Ni. In addition, Zn is observed to induce a local density of states near the Fermi e...

Forschungszentrum Karlsruhe, Institut für Festkörperphysik, Postfach 3640, D-76021 Karlsruhe, Germany Laboratoire Leon Brillouin, C.E.A./C.N.R.S., F-91191-Gif-sur-Yvette CEDEX, France Institute for Material Research, Tohoku University, Katahira, Aoba-ku, Sendai, 9808577, Japan Physics Department, Brookhaven National Laboratory, Upton, NY 11973 Superconductivity Research Laboratory, ISTEC, Shino...

The formation of superconducting YBa2Cu3O7−x (Y123) by in situ pulsed laser deposition from a stoichiometric Y123 target typically requires an oxygen-ambient environment (P ∼ 100–300-mtorr O2) and appropriate substrate temperature during deposition. We have found that pulsed laser deposition from a Y123 target in vacuo onto a (001) LaAlO3 substrate favors the formation of Y2O3. We observed that...

We report on measurements of YBa2Cu3O7 d nanowire based Superconducting QUantum Interference Devices (nanoSQUIDs) directly coupled to an in-plane pick-up loop. The pick-up loop, which is coupled predominantly via kinetic inductance to the SQUID loop, allows for a significant increase of the effective area of our devices. Its role is systematically investigated and the increase in the effective ...

We propose a phase diagram for the vortex structure of high temperature superconductors which incorporates the effects of anisotropy and disorder. It is based on numerical simulations using the three-dimensional Josephson junction array model. We support the results with an estimation of the internal energy and configurational entropy of the system. Our results give a unified picture of the beh...