Psuedo-isotropic upper critical field in cobalt-doped SrFe2As2 epitaxial films

Abstract

The temperature and angular dependence of the upper critical field (Hc2) is reported for cobalt-doped SrFe2As2 epitaxial films between Tc and 0.5 K in pulsed magnetic fields up to 50 T. For H parallel c, Hc2 is close to a linear function of temperature, while in the perpendicular direction there is significant downward curvature that results in an Hc2 ratio (gamma = Hc2(perpendicular)/Hc2(parallel) that decreases nearly linearly with temperature, approaching gamma = 1 at low temperature with Hc2(0) = 47 T. We measure the complete upper-critical field phase diagram including angular dependence and model the data using a two band theory allowing us to determine the anisotropy of both bands, their relative diffusivities, and the relationship between BCS coupling constant matrix elements. We find an unusual relationship between the diffusivities of the two bands, with two anisotropic and opposite bands. This relationship is supported by the observation of a local maximum for Hc2(parallel) at low temperature.

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• Multiband effects on beta-FeSe single crystals
• Calorimetric Evidence of Strong-Coupling Multiband Superconductivity in Fe(Te0.57Se0.43) Single Crystal
• Development of very high Jc in Ba(Fe1-xCox)2As2 thin films grown on CaF2
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• Effects of excess Fe on upper critical field and magnetotransport in Fe1+y(Te1-xSx)z
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• Inhomogeneous superconductivity induced by interstitial Fe deintercalation in oxidizing-agent-annealed and HNO3-treated Fe1+y(Te1-xSex)
• Superconductivity in 122-type antimonide BaPt${}_2$Sb${}_2$
• Large upper critical fields and dimensionality crossover of superconductivity in infinite-layer nickelate La${}_{0.8}$Sr${}_{0.2}$NiO${}_2$
• Superconducting Properties and Phase Diagram of Indirectly Electron-Doped (Sr1-xLax)Fe2As2 Epitaxial Films Grown by Pulsed Laser Deposition
• Fluctuations in two-band superconductors in a strong magnetic field
• Nearly isotropic upper critical fields in a SrFe${}_{1.85}$Co${}_{0.15}$As${}_2$ single crystal
• Upper critical field of the 122-type iron pnictide superconductors
• Temperature dependence and limiting mechanisms of the upper critical field of FeSe thin films
• Unconventional magnetization in the multiphase superconductor PdBi${}_2$