Scanning Hall-Probe Microscopy of a Vortex and Field Fluctuations in La _1.85 Sr _0.15 CuO ₄ Films

A high-resolution scanning Hall-probe microscope is used to spatially resolve vortices in high-temperature superconducting La1.85Sr0.15CuO4 films. At low magnetic fields, a disordered vortex arrangement is observed. A fit to the surface field of an individual vortex is consistent with one flux quantum, and is used to determine the local penetration depth and its temperature dependence. At higher fields, magnetic fluctuations are observed and...