Strong antiferromagnetic proximity coupling in the heterostructure superconductor Sr2VO3−δFeAs

We report the observation of strong magnetic proximity coupling in the heterostructure superconductor Sr2VO3-δFeAs, determined by upper critical field Hc2(T) measurements up to 65 T. Using the resistivity and the radio-frequency measurements for both H∥ab and H∥c, we found a strong upward curvature of Hc2c(T), together with a steep increase in Hc2ab(T) near Tc, yielding an anisotropic factor γH=Hc2ab/Hc2c up 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-δ layers. These findings provide evidence for strong antiferromagnetic proximity coupling that is comparable to the intralayer superexchange interaction of the SrVO3-δ layer and sufficient to induce magnetic frustration in Sr2VO3-δFeAs.