Coupled Magnetic and Superconducting Transitions in Sr${}_2$VO${}_3$FeAs Under Pressure

We report muon spin rotation ($\mu$SR) and magnetization measurements on superconducting Sr${}_2$VO${}_3$FeAs under pressure. At ambient pressure, Sr${}_2$VO${}_3$FeAs undergoes an antiferromagnetic transition of the V moments at $T_N$ and becomes superconducting at $T_c<T_N$. As a function of pressure, $T_N$ initially decreases while $T_c$ increases. Surprisingly, once $T_N\approx T_c$ at 0.6~GPa, $T_N$ reverses its trend and increases together with $T_c$ suggesting that the static V magnetism is a prerequisite for superconductivity. We explain this cooperative coupling by a possible localization of the V 3$d$ states below the magnetic transition which enables the nesting of the Fermi surface necessary for superconductivity.