Doping dependence of the magnetic penetration depth in (Yb1−xCax)(Ba1.6Sr0.4)Cu3O7−δ studied by muon spin rotation

Abstract We report transverse-field muon spin rotation measurements on the 123 system (Yb 0.7 Ca 0.3 )(Ba 1.6 Sr 0.4 )Cu 3 O 7-δ for various oxygen and calcium contents. Ca substitution creates additional holes in the CuO 2 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 σ 0 and thus of the magnetic penetration depth from the under- to the heavily overdoped regime. In the heavily overdoped region σ 0 is reduced with T c despite an increased normal-state carrier concentration, as previously reported for Tl 2 Ba 2 CuO 6+ δ . Around optimal doping ( T c = T c,max ) we observe no “plateau” in σ 0 vs. T c like that reported for YBa 2 Cu 3 O 7−δ , 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.