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.
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The authors thank Y. K. Bang for fruitful discussions. We also thank H. G. Kim at Pohang Accelerator Laboratory (PAL) for the technical support. This work was supported by the Institute for Basic Science (IBS) through the Center for Artificial Low Dimensional Electronic Systems (Gran No. IBS-R014-D1) and by the National Research Foundation of Korea (NRF) through SRC (Grant No. 2018R1A5A6075964) and the Max Planck-POSTECH Center for Complex Phase Materials (Grant No. 2016K1A4A4A01922028). W.K. acknowledges the support from NRF (Grants No. 2018R1D1A1B07050087 and 2018R1A6A1A03025340), and Y.J.J. was supported by NRF (Grant No. NRF-2019R1A2C1089017). J.M.O. acknowledges support from the Korea Basic Science Institute (National research Facilities and Equipment Center) grant funded by the Ministry of Education (Grant No. 2021R1A6C101A429) and the National Research Foundation of Korea (NRF) (Grant No. 2021R1F1A1056934). C.K. acknowledges support from IBS-CCES (Grant No. IBS-R009-G2). E.G.M. acknowledges the support from NRF (Grants No. NRF-2019M3E4A1080411, No. NRF-2020R1A4A3079707, and No. NRF-2021R1A2C4001847). A portion of this work was performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative Agreement No. DMR-1644779 and the state of Florida.
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