Strong antiferromagnetic proximity coupling in the heterostructure superconductor <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Sr</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>VO</mml:mi><mml:mrow><mml:mn>3</mml:mn><mml:mo>−</mml:mo><mml:mi>δ</mml:mi></mml:mrow></mml:msub><mml:mi>FeAs</mml:mi></mml:mrow></mml:math>

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. © 2022 American Physical Society.11Nsciescopu