Strong antiferromagnetic proximity coupling in the heterostructure superconductor Sr2VO3−δFeAs

Abstract

We report the observation of strong magnetic proximity coupling in the heterostructure superconductor ${\mathrm{Sr}}_{2}{\mathrm{VO}}_{3\ensuremath{-}\ensuremath{\delta}}\mathrm{FeAs}$, determined by upper critical field ${H}_{c2}(T)$ measurements up to 65 T. Using the resistivity and the radio-frequency measurements for both $H\ensuremath{\parallel}ab$ and $H\ensuremath{\parallel}c$, 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 ${\ensuremath{\gamma}}_{H}={H}_{c2}^{ab}/{H}_{c2}^{c}$ up to $\ensuremath{\sim}20$, 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 ${\mathrm{SrVO}}_{3\ensuremath{-}\ensuremath{\delta}}$ layers. These findings provide evidence for strong antiferromagnetic proximity coupling that is comparable to the intralayer superexchange interaction of the ${\mathrm{SrVO}}_{3\ensuremath{-}\ensuremath{\delta}}$ layer and sufficient to induce magnetic frustration in ${\mathrm{Sr}}_{2}{\mathrm{VO}}_{3\ensuremath{-}\ensuremath{\delta}}\mathrm{FeAs}$.