Magnetic-field penetration depth in TI2Ba2CuO6+δ in the overdoped regime

THE magnetic field penetration depth λ is a basic parameter of superconductivity, related to ns/m* (superconducting carrier density/effective mass) as λ-2 ∝ ns/m* in the limit where the coherence length ζ is much shorter than the mean free path l (the 'clean limit'). Muon spin relaxation (µSR) measurements1,2 of λ in high-transition-temperature (high-Tc ) copper oxide superconductors have revealed remarkable correlations between Tc and ns/m*: Tc increases linearly with ns/m* in the underdoped region, followed by a saturation with increasing carrier doping. Here we report µSR measurements of λ in ceramic specimens of of the superconductor TI-2Ba2CuO6+δ (TI-2201) in the 'overdoped' region where Tc decreases with increasing hole doping. Recent measurements of upper critical field and resistivity3confirm that overdoped TI-2201 lies well in the clean limit with a ζ<