DOPING DEPENDENCE OF THE MAGNETIC PENETRATION DEPTH IN (YB1-XCAX) (BA1.6SR0.4)CU3O7-DELTA STUDIED BY MUON SPIN ROTATION

We report transverse-field muon spin rotation measurements on the 123 system (Yb0.7Ca0.3)(Ba1.6Sr0,4)Cu3O7-delta for various oxygen and calcium contents. Ca substitution creates additional holes in the CuO2 planes, with increasing Ca content the filling of the CuO chains therefore occurs further in the overdoped regime. By varying the oxygen content in the system with a Ca content of x = 0.3 we investigated within a single system the doping dependence of the low-temperature depolarization rate sigma0 and thus of the magnetic penetration depth from the under- to the heavily overdoped regime. In the heavily overdoped region sigma0 is reduced with T(c) despite an increased normal-state carrier concentration, as previously reported for Tl2Ba2CuO6+delta. Around optimal doping (T(c) = T(c,max)) we observe no ''plateau'' in sigma0 vs. T(c) like that reported for YBa2Cu3O7-delta, where optimal doping nearly coincides with the filling of the CuO chains. A 'plateau' around optimum doping is however restored in a series of optimally doped samples (T(c) = T(c,max)) with progressively lower Ca content. These results are discussed in terms of induced superconductivity on well-ordered, nearly oxygen-filled CuO chains.