Evidence of multiple pinning mechanisms in high-TC superconducting thin films by AC susceptibility measurements

Vortex pinning in high-TC superconductors is usually dominated by intersection of twin boundaries (Physica C, 372–376 (2002) 634). We have grown NdBa2Cu3O7−δ thin films by pulsed laser deposition on (1 0 0) SrTiO3 substrates, which present only one [1 1 0] twinning variant (the [1 1 0] being completely eliminated), thereby drastically reducing the density of twin boundary intersections. High-resolution AC susceptometry reveals several peaks in χ′′(T) curve, each one presumably associated with a specific pinning mechanism. For different samples, we correlate χ(T) data with microstructure to characterise vortex pinning sources.