Superfluid Density and Angular Dependence of the Energy Gap in Optimally Doped (BiPb)2(SrLa)2CuO6+ δ .

We present a muon-spin rotation study of the optimally doped cuprate superconductor (BiPb)₂(SrLa)₂ CuO_{6+ δ} . The measured magnetic field dependence of the in-plane magnetic penetration λ _ab suggests superconductivity with a dominant d-wave order parameter. The comparison of the temperature dependence of λ _ab with calculations, assuming the angular gap symmetry as obtained from photoemission measurements, is consistent with a partial suppression of the quasi-particle weight towards the anti-nodal region of the Fermi surface. This suggests that the superconducting and the pseudogap state are dominated by different parts of the Fermi surface. [ABSTRACT FROM AUTHOR]