Intrinsic Josephson junctions in the iron-based multi-band superconductor (V sub(2)Sr sub(4)O sub(6)) Fe sub(2)As sub(2)

In layered superconductors, Josephson junctions may be formed within the unit cell as a result of sufficiently low inter-layer coupling. These intrinsic Josephson junction (iJJ) systems have attracted considerable interest for their application potential in quantum computing as well as efficient sources of THz radiation, closing the famous 'THz gap'. So far, iJJ have been demonstrated in single-band, copper-based high-T sub(c) superconductors, mainly in Bi-Sr-Ca-Cu-O (refs , , ). Here we report clear experimental evidence for iJJ behaviour in the iron-based superconductor (V sub(2)Sr sub(4)O sub(6)) Fe sub(2)As sub(2). The intrinsic junctions are identified by periodic oscillations of the flux-flow voltage on increasing a well-aligned in-plane magnetic field. The periodicity is 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. This finding adds the pnictide (V sub(2)Sr sub(4)O sub(6))Fe sub(2)As sub(2) to the copper-based iJJ materials of interest for Josephson junction applications. In particular, novel devices based on multi-band Josephson coupling may be realized.