FeAs

The interplay of spin and orbital degrees of freedom induces various magnetic or nematic phases, coexisting with the superconductivity, and leads to rich phase diagrams in iron-based superconductors (FeSCs). Among various iron-based superconductors, Sr₂VO₃FeAs holds a unique position as a naturally-assembled heterostructure of a FeSC and a Mott-insulating vanadium oxide, in which the unusual C₄ symmetric phases are recently identified and found to be highly distinct from those found in other FeSCs. In this talk, I will present our experimental explorations on these unusual phase transitions in the FeAs layers of Sr₂VO₃FeAs, and discuss the possible role of the magnetic proximity coupling and the resulting frustration of the otherwise dominant Fe stripe and V Neel fluctuations for stabilizing hidden orders in FeSCs.