Robust Spin-Moiré-Superlattice-Driven Gap Opening in EuAg₄Sb₂ under in-Plane Magnetic Field

Moiré superlattices introduce new length and energy scales, enabling discoveries, such as unconventional superconductivity, in 2D systems. This concept has recently been extended to bulk materials with multiple-q spin textures, opening exciting opportunities for spin moiré physics. A notable example is EuAg₄Sb₂, where a spin moiré superlattice (SMS), manifested as a double-q spin modulation, induces a superzone gap opening. 

In this talk, we will present results on the tunability of this gap under an in-plane magnetic field in EuAg₄Sb₂, using neutron scattering, magnetization, and transport measurements.  We identify a cycloidal magnetic ground state and observe multiple spin-reoriented phases induced by the in-plane field, highlighting the critical role of in-plane spin components in driving magnetic transitions. Moreover, we demonstrate that a robust gap opening persists in the double-q phase, regardless of in-plane field orientation. Model calculations attribute this robustness to the stability of the SMS under tilted magnetic fields. These results establish EuAg₄Sb₂ as a tunable platform for exploring spin-texture–driven electronic reconstruction and advancing the emerging field of spin-moiré physics in bulk correlated systems.