We report measurements of the ab-plane superfluid density ns (magnetic penetration depth, λ) of severely underdoped films of YBa2Cu3O6+x, with TCs from 6 to 50 K. TC is not proportional to ns(0); instead, we find TC ∝ n 1/2.3±0.4 s . At the lowest dopings, TC is as much as 5 times larger than the upper limit set by the KTB transition temperature of individual CuO2 bilayers.
Magnetic lens effect using Gd-Ba-Cu-O bulk superconductor in very high magnetic field J. Appl. Phys. 111, 07E728 (2012) Considerable asymmetry of the critical current in a niobium thin strip of plano-convex section J. Appl. Phys. 111, 053912 (2012) Lateral imaging of the superconducting vortex lattice using Doppler-modulated scanning tunneling microscopy Appl. Phys. Lett. 99, 192505 (2011) Infinite series models of flux relaxation and vortex penetration constructed at critical points and their unification
Ba2RENbO6 (RE = rare earth elements including Y) compounds are considered new additives for superior flux-pinning in YBa2Cu3O7-δ (YBCO) films due to their excellent chemical inertness to and large lattice mismatches with YBCO. Simultaneous laser ablation of a YBCO target and a Nb metal foil attached to the surface of the target resulted in epitaxial growth of YBCO films having columnar defects comprised of self-aligned Ba2YNbO6 (BYNO) nanorods parallel to the c-axis of the film. Compared to pure YBCO, YBCO+BYNO films exhibited no Tc reduction as well as superior Jc performance with higher self- and in-field Jc by a factor of 1.5–7 and also exhibited a strong Jc peak for H∥c indicative of strong c-axis correlated flux-pinning.
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