Magnetic penetration depths of (BiPb)-2212 and (TlPb)-1212 — Universal correlations revisited

A systematic study of the dependence of the critical temperature on the superconducting carrier density, as measured byμ+SR, was carried out for a variety of cuprate oxides. We have shown that substitution of Pb for Bi and La for Sr result in well pinned vortex lattices in Bi2Sr2CaCu2Ox, and studied (BiPb)-2212 from the underdoped to the slightly overdoped regime. We also found that Tl-1212 samples, which have optimal maximumTc=108 K, trace a separate line with parameters comparable to overdoped Tl-2223 at the maximum. These data, together with data on Y-124/247, Tl-2201 and other cuprates result in an larger set of “universal correlations” between Tc andσ(0) ∞ns/m* for the high temperature superconductors.