Mapping thermal fluctuations in YBa2Cu3O7 films with strong mixed pinning landscape

L. CIVALE; S.A. BAILY; H. ZHOU; B. MAIOROV; T.G. HOLESINGER; P. DOWDEN; J. KENNISON; N. HABERKORN; M. MIURA

Santa Fe, NM, USA

Conferencia; Strongly Correlated Electron Systems - SCES 2010; 2010

Vortex thermal fluctuations are very large in the oxide HTS due to a combination of high Tc, small coherence length and large anisotropy, which combine to produce a Ginzburg number (Gi) orders of magnitude higher than in conventional SC. This produces a rich vortex dynamics with proliferation of glassy and nonglassy flux creep regimes in the solid phases, but the large creep rates (S) are detrimental for applications, because they reduce the effective critical current density (Jc). We mapped the creep effects over a large T-H range in YBa2Cu3O7 films with BaZrO3 inclusions, which produce very high Jc by creating a mixed pinning landscape, composed of random nanoparticles and self-assembled splayed nanorods. This strong pinning is in part due to vortex entanglement by splay and nanoparticles, which arrest low energy double-kink creep excitations typical of columnar defects. We identified a new glassy regime at low H, characterized by low S and high glassy exponent m, and observed a decrease of S(T,H) as the film thickness increases.