Hole-doping dependence of the magnetic penetration depth and vortex core size in YBa2Cu3Oy:: Evidence for stripe correlations near 1/8 hole doping

We report on muon spin rotation measurements of the internal magnetic field distribution n(B) in the vortex solid phase of YBa2Cu3Oy (YBCO) single crystals, from which we have simultaneously determined the hole-doping dependences of the in-plane Ginzburg-Landau (GL) length scales in the underdoped regime. We find that T-c has a sublinear dependence on 1/lambda(2)(ab), where lambda(ab) is the in-plane magnetic penetration depth in the extrapolated limits T -> 0 and H -> 0. The power coefficient of the sublinear dependence is close to that determined in severely underdoped YBCO thin films, indicating that the same relationship between T-c and the superfluid density is maintained throughout the underdoped regime. The GL coherence length xi(ab) (vortex core size) is found to increase with decreasing hole-doping concentration and to exhibit a field dependence that is explained by proximity-induced superconductivity on the CuO chains. Both lambda(ab) and xi(ab) are enhanced near 1/8 hole doping, supporting the belief by some that stripe correlations are a universal property of high-T-c cuprates.