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

Abstract: We studied the behavior of nontrivial Dirac fermion states in an antiferromagnetic metal SmBi using angle-resolved photoemission spectroscopy (ARPES). The experimental results exhibit multiple Fermi pockets around $\overline{\Gamma}$ and $\overline{M}$ points along with a band inversion in the spectrum along the $\overline{\Gamma}$-$\overline{M}$ line consistent with the density functional theory results. In addition, ARPES data reveal Dirac cones at $\overline{\Gamma}$ and $\overline{M}$ points within the energy gap of the bulk bands. The Dirac cone at $\overline{M}$ exhibit a distinct Dirac point and is intense in the high photon energy data while the Dirac cone at $\overline{\Gamma}$ is intense at low photon energies. Employing ultra-high-resolution ARPES, we discover destruction of a Fermi surface constituted by the surface states across the Ne\'{e}l temperature of 9 K. Interestingly, the Dirac cone at $\overline{\Gamma}$ 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 magnetic transition in an exotic correlated topological material; the interplay between magnetism and topology in this system calls for ideas beyond existing theoretical models.