Abstract
The transition temperatures of epitaxial films of Fe(Te0:9Se0:1) are remarkably insensitive to applied magnetic field, leading to predictions of upper critical fields Bc2(T = 0) in excess of 100 T. Using pulsed magnetic fields, we find Bc2(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 Bc2(T), consistent with the observed Kondo minimum seen above Tc. 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.
Highlights
In National High Magnetic this work, we report the actual upper critical Field Laboratory
The SrTiO3 crystalline substrates were cleaved to appropriate size for 4-terminal resistivity measurements in a Quantum Design Physical Properties Measurement system, for R (H, T) measurements to 2 K and in dc fields up to 7 T
Samples in the pulsed-field experiment were immersed in liquid helium below 4 K; some problems with sample heating were encountered when the sample is in exchange gas at temperatures between 4 K and the transition temperature T c 12 K, a challenging temperature range due to small sample heat capacity and poor thermal conductivity of the exchange gas
Summary
Effects in Fe(Te0.9Se0.1) Thin Films by Pulsed Field Measurements received: 08 October 2015 accepted: 22 January 2016 Published: 10 February 2016. 3. do not expect the Maki parameter α is defined ηλ, which takes into account the competing effects as of electron-phonon mass enhancement and Stoner increase in susceptibility, to differ strongly from unity In either case, these values of α, when included in the WHH expression, lead, absent spin-orbit effects, to re-entrant behavior[7]. For the purposes of this work, to regard the spin-orbit parameter as a sample-dependent parameter, possibly correlated with the excess Fe concentration, which could be monitored via the magnitude of the Kondo resistance RK This would require measurements on high-field, low temperature measurements samples on such with a variety samples
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