Fig. 1

Basic properties of Sr₂VO₃FeAs. a The crystal structure of Sr₂VO₃FeAs as a naturally assembled heterostructure of the [SrFeAs]⁺¹ and [SrVO₃]⁻¹ layers. V ions form a network of corner-sharing tetrahedra, while FeAs layers consist of edge-sharing FeAs₄ tetrahedra as in other iron-based superconductors. The local structure of an FeAs₄ tetrahedron and a VO₃ pyramid is highlighted at the bottom. FeAs₄ tetrahedra provide a moderate cubic crystal field splitting, much smaller than the band widths, while the VO₃ unit is missing one O entirely, and thus develops a strong Jahn–Teller splitting. The d _xy orbital is pushed up, and the two V d electrons occupy the d _xz and d _yz states, forming an S = 1 spin. The Fe and V planes are bridged by the As atoms, as indicated by the dashed line. b The resistivity ρ(T) in the αb plane (red) and along the c axis (blue) shows a weak anomaly at T ₀ ~ 155 K (blue highlighted region), which is more clear in their temperature derivatives (top panel). The large c-axis resistivity, which was scaled down by a factor of 100, is consistent with the quasi-2D nature of the material. c The magnetic susceptibility χ(T), taken at H = 1 T for H ⊥ c and H || c, shows clear anomalies at T ₀ and also at T _N ~ 45 K