Interlayer coupling in Pb-substituted Bi 2Sr 2CaCu 2O 8+δ single crystals

Abstract

We show that Pb-substitution for Bi in single crystals of highly anisotropic Bi 2Sr 2CaCu 2O 8+δ induces a decrease of the structural anisotropy. As a direct result, the out-of-plane resistivity ϱ c ( T) is reduced by four orders of magnitude and the temperature behavior changes from semiconductor-like (d ϱ c /d T < 0) to metallic (d ϱ c /d T > 0). The results can be explained by assuming that Pb-doping introduces an additional covalent type of bonding between the BiO-bilayers, which is not present in the undoped crystals. This additional bonding may be due to an enhanced overlap of atomic orbitals to such an extent that a metallic conductivity perpendicular to the CuO 2 planes becomes possible. By modeling the out-of-plane magnetoresistivity ϱ c ( T, H) with H ∥ c we show that also the strength of the interlayer Josephson coupling is significantlyl affected by the Pb-substitution.