Upper critical field, pressure-dependent superconductivity and electronic anisotropy of Sm4Fe2As2Te1-xO4-yFy
We present a detailed study of the electrical transport properties of a recently discovered iron-based superconductor: Sm4Fe2As2Te0.72O2.8F1.2. We followed the temperature dependence of the upper critical field by resistivity measurement of single crystals in magnetic fields up to 16 T, oriented along the two main crystallographic directions. This material exhibits a zero-temperature upper critical field of 90 T and 65 T parallel and perpendicular to the Fe2As2 planes, respectively. An unprecedented superconducting magnetic anisotropy gamma(H) = H-c2(ab)/H-c2(c) similar to 14 is observed near T-c, and it decreases at lower temperatures as expected in multiband superconductors. Direct measurement of the electronic anisotropy was performed on microfabricated samples, showing a value of rho(c)/rho(ab) (300 K) similar to 5 that rises up to 19 near T-c. Finally, we have studied the pressure and temperature dependence of the in-plane resistivity. The critical temperature decreases linearly upon application of hydrostatic pressure (up to 2 GPa) similarly to overdoped cuprate superconductors. The resistivity shows saturation at high temperatures, suggesting that the material approaches the Mott-Ioffe-Regel limit for metallic conduction. Indeed, we have successfully modelled the resistivity in the normal state with a parallel resistor model that is widely accepted for this state. All the measured quantities suggest strong pressure dependence of the density of states.