Upper Critical Field and Kondo Effects in Fe(Te{0.9} Se{0.1}) Thin Films by Pulsed Field Measurements
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Abstract
The transition temperatures of epitaxial films of Fe(Te{0.9} Se {0.1}) are remarkably insensitive to applied magnetic field, leading to predictions of upper critical fields B{c2}(T = 0) in excess of 100 T. Using pulsed magnetic fields, we find B{c2}(0) to be on the order of 45 T, similar to values in bulk material and still in excess of the paramagnetic limit. The same films show strong magnetoresistance in fields above B{c2}(T), consistent with the observed Kondo minimum seen above T{c}. Fits to the temperature dependence in the context of the WHH model, using the experimental value of the Maki parameter, require an effective spin-orbit relaxation parameter of order unity. We suggest that Kondo localization plays a similar role to spin-orbit pair breaking in making WHH fits to the data.