Surface resonances of topological origin in bcc iron

Chiral band degeneracies are ubiquitous in the band structures of systems wtih broken inversion or time-reversal symmetries. While in Weyl semimetals such degeneracies are isolated near the Fermi level, the broadly defined notion of topological metal implies the presence of disconnected Fermi surface sheets characterized by non-zero Chern numbers. Bcc iron is an archetypal example of ferromagnetic metal with two non-trivial Fermi surface electron pockets along the direction parallel to the magnetization [1]. In this work, we investigate the surface-state signatures of the topological nature of these Fermi surface pockets. We find that the (110) surface presents arc-like resonances attached to the non-trivial electron pockets. These Fermi arc resonances are due to two chiral degeneracies, a type-I elementary Weyl point and a type-II composite (Chern number ±2) Weyl point, located at slightly different energies. We further show that such surface resonances can be controlled by the orientation of magnetization, and can eventually be eliminated following a topological phase transition.
[1] D. Gosálbez-Martínez, I. Souza, and D. Vanderbilt, Phys. Rev. B 92, 085138 (2015).