Nicole Bontemps

Kinetic energy change with doping upon superfluid condensation in high-temperature superconductors

In conventional BCS superconductors, the electronic kinetic energy increases upon superfluid condensation (the change DEkin is positive). Here we show that in the high critical temperature superconductor Bi-2212, DEkin crosses over from a fully compatible conventional BCS behavior (DEkin>0) to an unconventional behavior (DEkin<0) as the free carrier density decreases. If a single mechanism is responsible for superconductivity across the whole phase diagram of high critical temperature superconductors, this mechanism should allow for a smooth transition between such two regimes around optimal doping.

The vortex state

An introduction to superfluidity, vortices in superfluid 4 Helium W.F. Vinen. Anisotropic superconductors: fundamentals of vortices in layered superconductors J.R. Clem. Pinning, fluctuations and melting of superconducting vortex arrays D.R. Nelson. Two-dimensional superfluids A.P. Young. Short coherence length superconductors G. Deutscher. Magnetic decoration studies of flux line lattices in the cuprate superconductors D.J. Bishop, P.L. Gammel, C.A. Murray. Flux and AC measurements in superconductors E.H. Brandt. Pinning and dynamics of magnetic vortices P.H. Kes. Pinning and correlations in the vortex phase J.P. Bouchaud. Vortex dynamics in superfluids and superconductors E.B. Sonin, M. Krusius. Experimental observation of the Kosterlitz-Thouless transition J.E. Mooij. Fermi liquid theory of non-S-wave superconductivity P. Muzikar, D. Rainer, J.A. Sauls. Flux motion by quantum tunnelling A.C. Mota. Layered superconductors: do vortices interact with the crystal lattice? D. Feinberg. Vortex state and dimensionality V.V. Moshchalkov, Y. Bruynseraede, V.V. Metlushko, G. Guntherodt, I.N. Goncharov, A.Y. Didyk, P. Wagner, H. Adrian, H. Thomas, K. Winzer. Enhancement of superconductivity by photoexcitation Y. Bruynseraede, E. Osquiguil, M. Maenhoudt, B. Wuyts, G. Nieva, J. Guimpel, D. Lederman, I.K. Schuller. Surface ESR probing of superconductors N. Bontemps, P.Y. Bertin, P. Monod.

Anisotropic specific heat behavior of textured YBa2Cu3O7 under a magnetic field

Abstract Measurements of specific heat as a function of temperature, under various magnetic fields parallel or normal to the ( a, b ) plane, have been carried out on highly textured YBa 2 Cu 3 O 7 samples. The samples have been prepared by creep-sintering and characterized by X-ray diffraction, magnetisation and resistivity. We observe that the effect of a magnetic field on the specific heat anomaly at T c is strongly anisotropic: namely when the field is normal to the ( a, b ) plane the specific heat peak almost vanishes at 6 T whereas the same field hardly affects the specific heat when parallel to the ( a, b ) plane.

Flux‐creep‐limited critical currents in YBa2Cu3O7−δ ceramics

Critical currents of YBa2Cu3O7−δ bulk‐sintered samples were measured at and above 77 K in the presence of magnetic fields. In moderate magnetic fields a H−n dependence with n<1 was observed. Transport measurements give n≂0.5, indicating that critical currents are limited by flux creep rather than by field quenching of Josephson junctions.

Flux creep limited current in YBa2Cu3O7-† ceramics under applied fields

Abstract We present measurements of the field dependence of critical currents in YBa 2 Cu 2 O 7-† ceramics prepared by the sintering and by the sol-gel reaction methods. For high quality samples we find a region in magnetic fields where the transport critical current decreases like H −n with n=0.52±0.06. This behavior is qualitatively similar to that observed in single grains, interpreted as indicative of flux creep rather than Josephson limited critical current.