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 calc ium contents. Ca substitution creates additional holes in the CuO2 pla nes, with increasing Ca content the filling of the CuO chains therefor e occurs further in the overdoped regime. By varying the oxygen conten t in the system with a Ca content of x = 0.3 we investigated within a single system the doping dependence of the low-temperature depolarizat ion rate sigma0 and thus of the magnetic penetration depth from the un der- 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 opt imal doping (T(c) = T(c,max)) we observe no ''plateau'' in sigma0 vs. T(c) like that reported for YBa2Cu3O7-delta, where optimal doping near ly coincides with the filling of the CuO chains. A 'plateau' around op timum doping is however restored in a series of optimally doped sample s (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.