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

TL;DR

This study uses ARPES to investigate Dirac fermion states in antiferromagnetic SmBi, revealing complex behavior of Dirac cones, gap formation, and Fermi surface destruction across magnetic transition, highlighting the interplay between magnetism and topology.

Contribution

It provides the first detailed ARPES analysis of Dirac cones in SmBi, showing momentum-dependent gap formation and Fermi surface destruction related to magnetic ordering.

Findings

Dirac cones observed at $ar{ ext{Γ}}$ and $ar{ ext{M}}$ points.

Fermi surface destroyed across Neel temperature of 9 K.

Dirac cone at $ar{ ext{Γ}}$ becomes gapped at 15 K.

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.