Robust superzone gap opening in incommensurate antiferromagnetic semimetal EuAg$_4$Sb$_2$ under in-plane magnetic field

TL;DR

This study demonstrates that in EuAg$_4$Sb$_2$, an incommensurate antiferromagnetic semimetal, the superzone gap remains robust under in-plane magnetic fields, revealing new magnetic phases and potential for tunable electronic properties.

Contribution

The paper uncovers the in-plane magnetic-field tunability of spin moiré superlattice in EuAg$_4$Sb$_2$ and shows the persistent superzone gap despite spin reorientations.

Findings

Identification of incommensurate noncollinear cycloidal magnetic ground state.

Multiple spin-reoriented phases induced by in-plane magnetic fields.

Persistence of the superzone gap despite spin reorientation.

Abstract

The interplay between magnetism and charge transport in semimetals has emerged as a fertile ground for discovering novel electronic phenomena. A notable example is the recent discovery of electronic commensuration arising from a spin moir\'e superlattice (SMS), realized as double-q spin modulation in the antiferromagnetic semimetal EuAg$_4$Sb$_2$. Here, we investigate the in-plane magnetic-field tunability of the SMS using neutron scattering, magnetic and transport measurements. We reveal an incommensurate noncollinear cycloidal magnetic ground state. Temperature-field phase diagrams constructed with field tilting uncover multiple spin-reoriented phases, suggesting the critical role of in-plane field components in driving magnetic transitions. Despite substantial spin reorientation of the double-q phase, we observe a persistent gap opening, evidenced by strong suppression in both Hall and longitudinal conductivities. Model calculations attribute this robustness to the stability of SMS under tilting fields. Our results establish EuAg$_4$Sb$_2$ as a tunable platform for exploring spin-texture-driven superzone gap opening in electronic states.