An optical investigation of the strong spin-orbital coupled magnetic semimetal YbMnBi2

Abstract

Strong spin-orbit coupling can result in ground states with non-trivial topological properties. The situation is even richer in magnetic systems where the magnetic ordering can potentially have strong influence over the electronic band structure. The class of AMnBi2 (A = Sr, Ca) compounds are important in this context as they are known to host massive Dirac fermions with strongly anisotropic dispersion, which is believed to be due to the interplay between strong SOC and magnetic degrees of freedom. We report the optical conductivity of YbMnBi2, a newly discovered member of this family and a proposed Weyl semi-metal candidate with broken time reversal symmetry. Comparing experimental and theoretical optical spectra we show that the complex conductivity can be interpreted as the sum of an intra-band Drude response and inter-band transitions. We find signatures of a gapped Dirac dispersion, common in other members of AMnBi2 family or compounds with similar 2D network of Bi atoms.