Response of the C4 magnetic phase in iron-based superconductors to electronic structure tuning via doping/uniaxial strain

Elucidating how magnetic interactions are established in high-temperature superconductors is crucial for resolving the long-standing puzzle of the superconducting pairing mechanism. However, for iron-based superconductors, due to the diversity of their magnetic and electronic structures, the mechanism of magnetic interactions remains controversial. Here, we employed in-situ alkali-metal deposition and uniaxial strain to tune the four-fold (C4) magnetic phase in Sr_0.64Na_0.36Fe₂As₂ and utilized angle-resolved photoemission spectroscopy (ARPES) to probe the response of its electronic structure. We found that the alkali-metal deposition suppresses the C4 magnetic phase effectively, driving the system into a stripe spin density wave phase with two-fold rotational (C2) symmetry. Counterintuitively, the uniaxial strain that naturally breaks the C4 rotational symmetry of the lattice exerts only a limited suppressive effect on the C4 magnetic phase. While the sensitivity of C4 magnetic phase to electron doping implies that the orbital selectivity of Fermi surface nesting plays a critical role in determining the magnetic configuration, validating the contribution of itinerant electrons in mediating the magnetic fluctuations, the insensitivity of the C4 magnetic phase to uniaxial strain suggests that the nematic order exhibits no intermediate correlation with the magnetism in iron-based superconductors. Our results provide crucial clues for a comprehensive understanding of the complex phase diagram of iron-based superconductors.