Spin-orbit band gaps and destruction of Dirac cones

The relativistic band structures of the IV group honeycomb monolayers, from graphene to plumbene (C-Si-Ge-Sn-Pb), have been calculated within DFT in Local Density Approximation (LDA). Basing on the obtained results, we suggest that the spin-orbit coupling leads to opening of the band gaps and therefore will unavoidably cause the destruction of the perfect shape of Dirac cones which is responsible for the existence of the massless Fermions. The applicability of ordinary non-relativistic DFT calculations of bands for graphene-like layered structures is discussed in this regard. Forming spin-orbit gaps in Ge and Sn monolayers. The shape of Dirac cone (shown in the insert) is distorted due to spin-orbit splitting. [Display omitted] •Spin-orbit coupling in honeycomb monolayers causes the opening of the band gap thus destroying Dirac cone.•Electrons acquire some mass and hence are not massless Fermions.•Relativistic effects in graphene are minimal, and Dirac theory becomes unnecessary to explain the band structure.