Strong antiferromagnetic proximity coupling in a heterostructured superconductor Sr$_2$VO$_3$FeAs

TL;DR

This study demonstrates strong antiferromagnetic proximity coupling in Sr$_2$VO$_3$FeAs, evidenced by high upper critical fields and magnetic interactions, revealing a significant magnetic influence on its superconducting properties.

Contribution

It provides the first evidence of strong antiferromagnetic proximity coupling in a heterostructured superconductor, highlighting the role of exchange interactions between Fe and V spins.

Findings

High anisotropic upper critical fields up to 20

Upward curvature of $H_{c2}^c(T)$ and steep increase of $H_{c2}^{ab}(T)$ near $T_c$

Magnetic proximity effect attributed to exchange interactions, not multiband effects

Abstract

We report observation of strong magnetic proximity coupling in a heterostructured superconductor Sr$_2$VO$_3$FeAs, determined by the upper critical fields $H_{c2}(T)$ measurements up to 65 T. Using the resistivity and the radio-frequency measurements for both $H \parallel ab$ and $H \parallel c$, we found a strong upward curvature of $H_{c2}^c(T)$, together with a steep increase of $H_{c2}^{ab}(T)$ near $T_c$, yielding the anisotropic factor $\gamma_H=H_{c2}^{ab}/H_{c2}^c$ up to $\sim$ 20, the largest value among 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 SrVO$_3$ layers. These findings provide evidence for strong antiferromagnetic proximity coupling, comparable with the intralayer superexchange interaction of SrVO$_3$ layer and sufficient to induce magnetic frustration in Sr$_2$VO$_3$FeAs.