Magnetic-field penetration depth in Tl2Ba2CuO(6 + delta) in the overdoped regime

The study reports muon spin relaxation (muSR) measurements of the magnetic field penetration depth, lambda, in ceramic specimens of the superconductor Tl2Ba2CuO(6 + delta) (Tl-2201) in the 'overdoped' region where Tc decreases with increasing hole doping. It is inferred that either n(s) no longer scales with the normal-state carrier density, and/or m* for a superconducting pair becomes much larger than the value expected from the normal-state effective mass. This behavior of overdoped Tl-2201 is in marked contrast to conventional metallic superconductors having a retarded interaction, in which the normal-state properties directly represent the corresponding values in the superconducting state.