5 research outputs found
Intrinsic Superconductivity at 25 K in Highly Oriented Pyrolytic Graphite
High resolution magnetoresistance data in highly oriented pyrolytic graphite
thin samples manifest non-homogenous superconductivity with critical
temperature K. These data exhibit: i) hysteretic loops of
resistance versus magnetic field similar to Josephson-coupled grains, ii)
quantum Andreev's resonances and iii) absence of the Schubnikov-de Haas
oscillations. The results indicate that graphite is a system with
non-percolative superconducting domains immersed in a semiconducting-like
matrix. As possible origin of the superconductivity in graphite we discuss
interior-gap superconductivity when two very different electronic masses are
present.Comment: 5 pages, 3 figure
Superconducting properties of [BaCuO_x]_2/[CaCuO_2]_n artificial structures with ultrathick CaCuO_2 blocks
The electrical transport properties of [BaCuO_x]_2/[CaCuO_2]_n
(CBCCO-2xn)underdoped high temperature superconducting superlattices grown by
Pulsed Laser Deposition have been investigated. Starting from the optimally
doped CBCCO-2x2 superlattice, having three CuO_2 planes and T_c around 80 K, we
have systematically increased the number n up to 15 moving toward the
underdoped region and hence decreasing T_c. For n>11 the artificial structures
are no longer superconducting, as expected, for a uniformly distributed charge
carriers density inside the conducting block layer. The sheet resistance of
such artificial structures (n nearly equal to 11) turns out to be quite
temperature independent and close to the 2D quantum resistance 26 kOhm. A
further increase of the number of CuO_2 planes results in an insulator-type
dependence of R(T) in the wide range of temperatures from room temperature to 1
K. The value of the sheet resistance separating the Superconducting and the
Insulating regimes supports the fermionic scenario of the
Superconductor-Insulator transition in these systems.Comment: 12 pages, 5 figures. Corresponding author: [email protected]
Activation energy in La 0.7 Ca 0.3 MnO 3/YBa 2Cu 3O 7-δ / La 0.7 Ca 0.3 MnO 3 superconducting trilayers
Resistivity vs. temperature measurements on La 0.7 Ca 0.3 MnO 3/YBa 2Cu 3O 7-δ /La 0.7 Ca 0.3 MnO 3 (LCMO/YBCO/LCMO) trilayers with different YBCO thickness, were performed in external magnetic field H up to 8 T. By evaluating the activation energy U from the slope of the resistivity Arrhenius plot, a strong depression of U has been observed when decreasing the YBCO layer thickness and the absolute U values appear to be reduced with respect to the values reported in literature in the case of YBCO thin films and YBCO/insulating multilayers. Moreover, a logarithmic U vs. H dependence is shown both in the case of thick and thin YBCO layers indicating the formation of a two dimensional vortex lattice. The experimental data are discussed considering the strong influence of the ferromagnetic LCMO on the superconducting YBCO properties which reduces the effective YBCO thickness more than predicted by the conventional theories. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 200674.25.Qt Vortex lattices, flux pinning, flux creep, 75.47.Lx Manganites, 74.78.Fk Multilayers, superlattices, heterostructures,