Intrinsic Josephson Junctions in the iron-based multi-band superconductor (V$_2$Sr$_4$O$_6$)Fe$_2$As$_2$

We have observed clear experimental evidence for intrinsic Josephson junction (iJJ) behavior in the iron-based superconductor (V$_2$Sr$_4$O$_6$)Fe$_2$As$_2$ (T$_c \approx 20K$). The iJJs are identified by periodic oscillations of the flux flow voltage for out-of-plane (c-axis) currents upon increasing a well aligned in-plane magnetic field. Their periodicity is well explained by commensurability effects between the Josephson vortex lattice and the crystal structure, which is a hallmark signature of Josephson vortices confined into iJJ stacks. Essential for reliable c-axis transport measurements on the available microcrystals are Focused Ion Beam microstructuring and contacting techniques. The insulating temperature behavior of $\rho_c$ indicates S-I-S type junctions. This finding adds (V$_2$Sr$_4$O$_6$)Fe$_2$As$_2$ as the first iron-based, multi-band superconductor to the copper-based iJJ materials of interest for Josephson junction applications, and in particular novel devices based on multi-band Josephson coupling may be realized.