Electronic commensuration of a spin moiré superlattice in a layered magnetic semimetal.

Spin moiré superlattices (SMSs) have been proposed as a magnetic analog of crystallographic moiré systems and a source of electron minibands offering vector-field moiré tunability and Berry curvature effects. However, it has proven challenging to realize an SMS in which a large exchange coupling J is transmitted between conduction electrons and localized spins. Furthermore, most systems have carrier mean free paths l(mfp) shorter than their spin moiré lattice constant a(spin), inhibiting miniband formation. Here, we discover that the layered magnetic semimetal EuAg(4)Sb(2) overcomes these challenges by forming an interface with J ~ 100 milli-electron volts transferred between a Eu triangular lattice and anionic Ag(2)Sb bilayers hosting a two-dimensional electron band in the ballistic regime (l(mfp) >> a(spin)). The system realizes an SMS with a(spin) commensurate with the Fermi momentum, leading to a marked quenching of the transport response from miniband formation. Our findings demonstrate an approach to magnetically engineering moiré superlattices and a potential route to an emergent spin-driven quantum Hall state.