Kim, J., N. Haberkorn, K. Gofryk, M. J. Graf, F. Ronning, A. S. Sefat, R. Movshovich, and L. Civale. "Superconducting properties in heavily overdoped Ba(Fe0.86Co0.14)2As2 single crystals." Solid State Communications 201 (2015): 20–24.
Abstract: Abstract
We report the intrinsic superconducting parameters in a heavily overdoped Ba(Fe1−xCox)2As2 (x=0.14) single crystal and their influence in the resulting vortex dynamics. We find a bulk superconducting critical temperature of 9.8 K, magnetic penetration depth λab (0)=660±50 nm, coherence length ξab (0)=6.4±0.2 nm, and the upper critical field anisotropy γT→Tc≈3.7. The vortex phase diagram, in comparison with the optimally doped compound, presents a narrow collective creep regime. The intrinsic pinning energy plays an important role in the resulting vortex dynamics as compared with similar pinning landscape and comparable intrinsic thermal fluctuations.
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Kim, J., N. Haberkorn, E. Nazaretski, R. de Paula, T. Tan, X. X. Xi, T. Tajima, R. Movshovich, and L. Civale. "Strong magnetic field dependence of critical current densities and vortex activation energies in an anisotropic clean MgB2 thin film." Solid State Communications 204 (2015): 56–60.
Abstract: We report the influence of two-band superconductivity on the flux creep and the critical current densities of a MgB2 thin film. The small magnetic penetration depth of λ=50±10 nm at T=4 K is related to a clean π-band. We find a high self-field critical current density Jc, which is strongly reduced with applied magnetic field, and attribute this to suppression of the superconductivity in the π-band. The temperature dependence of the creep rate S (T) at low magnetic field can be explained by a simple Anderson–Kim mechanism. The system shows high pinning energies at low field that are strongly suppressed by high field.
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