Dirac fermions in solids have been of current interest for their unique transport properties. The interplay of Dirac fermion with magnetism in magnetic Dirac materials is recently of particular interest. Among them, EuMnBi₂ is a rare compound that exhibits quantum transport of Dirac fermions coupled with the field-tunable magnetic order. However, it remains elusive how and to what extent the Dirac-like band dispersion is affected.
In this study, we report spin-split Landau levels of quasi-two-dimensional Dirac fermions in EuMnBi₂, as revealed by interlayer resistivity measurements in a tilted magnetic field up to ~35 T. The amplitude of Shubnikov–de Haas (SdH) oscillation in interlayer resistivity is strongly modulated by changing the tilt angle of the field, i.e., the Zeeman-to-cyclotron energy ratio. The effective g factor estimated from the tilt angle, where the SdH oscillation exhibits a phase inversion, differs by approximately 50% between two antiferromagnetic phases. This observation signifies a marked impact of the magnetic order of Eu sublattice on the Dirac-like band structure. The origin may be sought in strong exchange coupling with the local Eu moments, as verified by the first-principles calculation. [H. Masuda, H. Sakai et al., Phys. Rev. B 98, 161108(R) (2018)]