Behavior of gapped and ungapped Dirac cones in the antiferromagnetic topological metal SmBi

We studied the behavior of nontrivial Dirac fermion states in the antiferromagnetic metal SmBi using angle-resolved photoemission spectroscopy (ARPES). The experimental results exhibit multiple Fermi pockets around the (gamma) over the bar and (M) over the bar points along with a band inversion in the spectrum along the (gamma) over the bar -(M) over the bar line consistent with the density functional theory results. In addition, ARPES data reveal Dirac cones at the (gamma) over the bar and (M) over the bar points within the energy gap of the bulk bands. The Dirac cone at (M) over the bar exhibits a distinct Dirac point and is intense in the high-photon-energy data, while the Dirac cone at (gamma) over the bar is intense at low photon energies. Employing ultrahigh-resolution ARPES, we discover destruction of a Fermi surface constituted by the surface states across the Neel temperature of 9 K. Interestingly, the Dirac cone at (gamma) over the bar is found to be gapped at 15 K, and the behavior remains similar across the magnetic transition. These results reveal complex momentum-dependent gap formation and Fermi surface destruction across the magnetic transition in an exotic correlated topological material; the interplay between magnetism and topology in this system calls for ideas beyond the existing theoretical models.