Strong antiferromagnetic proximity coupling in the heterostructure superconductor Sr2VO3-delta FeAs

We report the observation of strong magnetic proximity coupling in the heterostructure superconductor Sr2VO3-delta FeAs, determined by upper critical field H-c2(T) measurements up to 65 T. Using the resistivity and the radio-frequency measurements for both H parallel to ab and H parallel to c, we found a strong upward curvature of H-c2(c)(T), together with a steep increase in H-c2(ab) (T) near T-c, yielding an anisotropic factor gamma H = H-c2(ab)/H-c2(c) up to similar to 20, much higher than those of other iron-based superconductors. These are attributed to the Jaccarino-Peter effect, rather than to the multiband effect, due to strong exchange interaction between itinerant Fe spins of the FeAs layers and localized V spins of Mott-insulating SrVO3-delta layers. These findings provide evidence for strong antiferromagnetic proximity coupling that is comparable to the intralayer superexchange interaction of the SrVO3-delta layer and sufficient to induce magnetic frustration in Sr2VO3-delta FeAs.