38 research outputs found
Correlation between superfluid density and Tc of underdoped YBa2Cu3O6+x near the superconductor-insulator transition
We report measurements of the ab-plane superfluid density Ns (magnetic
penetration depth, \lambda) of severely underdoped films of YBa2Cu3O6+x, with
Tc's from 6 to 50 K. Tc is not proportional to Ns(0); instead, we find Tc ~
Ns^{1/2.3 +/- 0.4}. 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.Comment: 4 pages, 2 figures, Submitted to Phys. Rev. Let
Superfluid density of superconductor-ferromagnet bilayers
We report the first measurements of the effective superfluid density n_S(T)
\propto \lambda^{-2}(T) of Superconductor-Ferromagnet (SC/FM) bilayers, where
\lambda is the effective magnetic field penetration depth. Thin Nb/Ni bilayers
were sputtered in ultrahigh vacuum in quick succession onto oxidized Si
substrates. Nb layers are 102 A thick for all samples, while Ni thicknesses
vary from 0 to 100 A. T_C determined from \lambda^{-2}(T) decreases rapidly as
Ni thickness d_Ni increases from zero to 15 A, then it has a shallow minimum at
d_Ni \approx 25 A. \lambda^{-2}(0) behaves similarly, but has a minimum several
times deeper. In fact, \lambda^{-2}(0) continues to increase with increasing Ni
thickness long after T_C has stopped changing. We argue that this indicates a
substantial superfluid density inside the ferromagnetic Ni films.Comment: 13 pages, 2 figures, MMM 2007 proceeding
Magnetic Penetration Depth Measurements of PrCeCuO Films on Buffered Substrates: Evidence for a Nodeless Gap
We report measurements of the inverse squared magnetic penetration depth,
, in PrCeCuO () superconducting films grown on SrTiO (001) substrates coated with a
buffer layer of insulating PrCuO. , and
normal-state resistivities of these films indicate that they are clean and
homogeneous. Over a wide range of Ce doping, ,
at low is flat: it changes by less than 0.15% over a
factor of 3 change in , indicating a gap in the superconducting density of
states. Fits to the first 5% decrease in produce values of
the minimum superconducting gap in the range of .Comment: 4 pages 5 figure