Friday, 2D-11, 4:50-5:00

Thermal Fluctuations and the Limits to Vortex Pinning in Coated Conductors

Leonardo Civale

Superconductivity Technology Center, Los Alamos National Laboratory, Los Alamos, NM

Based on present understanding, by engineering the appropriate vortex pinning landscape in a superconductor it should be possible to attain a critical current density J_c as large as the physical limit determined by the depairing current density J₀. However, after decades of large efforts and resources dedicated to pinning enhancement we are far below that limit. Presently, both the highest absolute values of J_c and the largest J_c/J₀ (~0.3) are obtained for thin epitaxial YBa₂Cu₃O₇ films. I will analyze what defects are effective vortex pinning centers in these films, and consider possible ways to increase J_c further. I will particularly focus on the influence of thermal fluctuations, which allow some vortex motion below J_c, resulting in a temporal decay of the supercurrents (flux creep) and consequently lower effective J_c. I will show that energy landscapes that combine several types of defects can reduce the detrimental flux creep effects.

Work performed in collaboration with B. Maiorov, S.A. Baily, H. Zhou, T.G. Holesinger, I.O. Usov, M. Feldmann, S.R. Foltyn, Q.X. Jia, and P. Dowden.

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