The in-plane magnetic penetration depth lambda ab in optimally doped (BiPb)2(SrLa)2CuO6+delta (OP Bi2201) was studied by means of muon-spin rotation. The measurements of lambda ab(-2)(T) are inconsistent with a simple model of a d-wave order parameter and a uniform quasiparticle weight around the Fermi surface. The data are well described assuming the angular gap symmetry obtained in ARPES experiments [Phys. Rev. Lett. 98, 267004 (2007)], which suggest that the superconducting gap in OP Bi2201 exists only in segments of the Fermi surface near the nodes. The remaining parts of the Fermi surface, which are strongly affected by the pseudogap state, do not contribute significantly to the superconducting condensate.

We report on measurements of the in-plane magnetic penetration λ ab in the optimally doped cuprate superconductor (BiPb)2(SrLa)2CuO 6+δ (OP Bi2201) by means of muon-spin rotation (µSR). We show that in unconventional d−wave superconductors (like OP Bi2201), µSR experiments conducted in various magnetic fields allow to evaluate the zero-field magnetic penetration depth λ0, which relates to the zero-field superfluid density in terms of ρs ∝ λ Muon-spin-rotation (µSR) measurements in the mixed state of type-II superconductors provide valuable information on the superconducting properties. An important advantage of this method is that the muons probe the bulk of the material, and the results are not complicated by surface imperfections. The quantitative parameters extracted from µSR experiments depend, however, on the details of the model applied to reconstruct the internal magnetic field distribution in the superconductor in the mixed state. So far, field distributions measured by means of µSR were analyzed within the framework of analytical models based on London and GinzburgLandau (GL) theories, which can be applied, in general, to conventional superconductors with a single isotropic energy gap.

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Muon-spin rotation measurements, performed on the mixed state of the classic anisotropic superconductor Bi 2:15 Sr 1:85 CaCu 2 O 8þ , obtain quantities directly related to two-and three-body correlations of vortices in space. A novel phase diagram emerges from such local probe measurements of the bulk, revealing an unusual glassy state at intermediate fields which appears to freeze continuously from the equilibrium vortex liquid but differs both from the lattice and the conventional high-field vortex glass state in its structure.

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