Magnetic penetration depth of Tl[sub 2]Ba[sub 2]CuO[sub 6+[delta]]. Tc [approximately] [sigma][sub 0] in the overdoped region

We report transverse-field muon-spin-rotation experiments carried out on Tl[sub 2]Ba[sub 2]CuO[sub 6+[delta]]. This system spans the whole overdoped regime, and Tc is reduced by excess oxygen doping, which increases the normal-state carrier concentration. In the heavily overdoped regime [sigma](0) is found to scale linearly with the superconducting critical temperature Tc, similar to the behavior previously observed for other cuprates in the underdoped regime. However, for the overdoped region one has to explain the reduction of [sigma][sub 0], thus the increase of the magnetic penetration depth [lambda], in spite of an increasing normal-state carrier concentration. We discuss some possible explanations for this behavior. 19 refs., 2 figs.