Zero-field superfluid density in d-wave superconductor evaluated from the results of muon-spin-rotation experiments in the mixed state

We report on measurements of the in-plane magnetic penetration lambda_{ab} in the optimally doped cuprate superconductor (BiPb)_2(SrLa)_2CuO_6+delta (OP Bi2201) by means of muon-spin rotation (muSR). We show that in unconventional $d-$wave superconductors (like OP Bi2201), muSR experiments conducted in various magnetic fields allow to evaluate the zero-field magnetic penetration depth lambda_0, which relates to the zero-field superfluid density in terms of rho_sproptolambda_0^-2.

Evidence for competition between the superconducting and the pseudogap state in (BiPb)_2(SrLa)_2CuO_{6+delta} from muon-spin rotation experiments

The in-plane magnetic penetration depth lambda_{ab} in optimally doped (BiPb)_2(SrLa)_2CuO_{6+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 {bf 98}, 267004 (2007)], where it was shown that the superconducting gap in OP Bi2201 exists only in segments of the Fermi surface near the nodes. We find that the remaining parts of the Fermi surface, which are strongly affected by the pseudogap state, do not contribute significantly to the superconducting condensate. Our data provide evidence that high temperature superconductivity and pseudogap behavior in cuprates are competing phenomena.

Universal observation of multiple order parameters in cuprate superconductors

The temperature dependence of the London penetration depth lambda was measured for an untwined single crystal of YBa_2Cu_3O_{7-delta} along the three principal crystallographic directions (a, b, and c). Both in-plane components (lambda_a and lambda_b) show an inflection point in their temperature dependence which is absent in the component along the c-direction (lambda_c). The data provide convincing evidence that the in-plane superconducting order parameter is a mixture of s+d-wave symmetry whereas it is exclusively s-wave along the c-direction. In conjunction with previous results it is concluded that coupled s+d-order parameters are universal and intrinsic to cuprate superconductors.