Electronic anisotropy from magneto-transport near T$_{c}$ in SmFeAs(O$_{0.7}$F$_{0.25})$ and (Ba,Rb)Fe$_{2}$As$_{2}$ single crystals

We derived thermally activated flux flow (TAFF) activation energies E$_{a}$(H) and the upper critical fields \textbf{Hc}$_{2}$(T) parallel to the c-axis and in the Lorentz-force free configuration (\textbf{H} $\vert \vert $ \textbf{ab} $\vert \vert $ \textbf{j}) of SmFeAs(O$_{0.7}$F$_{0.25})$ and (Ba,Rb)Fe$_{2}$As$_{2}$ single crystals from resistance measurements and compare them to the ones reported for other REFeAs(OF). A perfectly rectangular rod (67x11x4 $\mu $m), aligned with the crystal axes, was cut from a larger SmFeAs(O$_{0.7}$F$_{0.25})$ single crystal ($\sim $ 200 $\mu $m) by a Focused Ion Beam (FIB) which allowed us to precisely control its geometry factor L/A = 0.89 1/$\mu $m. The FIB was also used to deposit 4 Pt contacts. We found a slope of \textbf{H}$_{c2, 50\% }$ (T), parallel to the c-axis, of 1.9 T/K for SmFeAs(O$_{0.7}$F$_{0.25})$ and 3.7 T/K for (Ba,Rb)Fe$_{2}$As$_{2}$ near T$_{c}$. The electronic anisotropy, derived from magneto-transport, is significantly larger in the REFeAs(OF) crystals than in (Ba,Rb)Fe$_{2}$As$_{2}$.