Magnetic penetration depth and flux-pinning effects in high-Tc superconductor La1.85Sr0.15CuO

We have performed muon-spin-relaxation (μSR) measurements on La1.85Sr0.15CuO4 above and below its superconducting transition temperature, Tc=37 K. From transverse-field μSR at 6 K, the magnetic penetration depth is λ≊2500 Å, which, together with previous thermodynamic data and the London formula, implies a carrier density of 0.3×1022 cm-3. The temperature dependence of λ in our sintered powder sample differs from that for an ordinary homogeneous superconductor. We also show that the longitudinal- and transverse-field μSR techniques are sensitive probes of Hc1 and flux-pinning effects.