Magnetic Penetration Depth and Flux Pinning Effects in High T sub c Superconductor La sub 1.85 Sr sob 0.15 CuO sub 4

We have performed muon spin relaxation (uSR) measurements on La sub 1.85 Sr sub 0.15 CuO sub 4 above and below its superconducting transition temperature, T sub c = 37K. From transverse field uSR at 6K, the magnetic penetration depth is lambda = 2500 angstroms, which, together with previous thermodynamic data and the London formula, implies a carrier density of 0.3 x 10 sup 22 cm sup -3.