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Abstract

In layered superconductors, Josephson junctions may be formed within the unit cell^1,2,3 as a result of sufficiently low inter-layer coupling. These intrinsic Josephson junction (iJJ) systems⁴ have attracted considerable interest for their application potential in quantum computing as well as efficient sources of THz radiation, closing the famous ‘THz gap’⁵. So far, iJJ have been demonstrated in single-band, copper-based high-Tc superconductors, mainly in Bi–Sr–Ca–Cu–O (refs 6, 7, 8). Here we report clear experimental evidence for iJJ behaviour in the iron-based superconductor (V₂Sr₄O₆)Fe₂As₂. The intrinsic junctions are identified by periodic oscillations of the flux-flow voltage on increasing a well-aligned in-plane magnetic field⁹. 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^10,11. This finding adds the pnictide (V₂Sr₄O₆)Fe₂As₂ 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.