Centrosymmetric Li2NaN: a superior topological electronic material with critical-type triply degenerate nodal points

Abstract

It has been, for the first time, reported that centrosymmetric Li₂NaN is a realistic triply degenerate nodal point (TDNP) material with three superior characteristics. In the band structure of the centrosymmetric Li₂NaN material, there is only a single pair of TDNPs at the Fermi level and not coexisting with other extraneous bands, which indicates that the unique physical properties of the topological semimetal can be clearly detected via experiments and the Li₂NaN material is an ideal TDNP semimetal. More importantly, the TDNPs identified in the Li₂NaN material show an unusual critical-type band crossing, which is different from previously reported ones. Under lattice strain, we show that the positions of the TDNPs can be tuned, and the TDNPs can even be annihilated. Upon increasing the spin–orbit coupling, the centrosymmetry in the material makes the TDNPs transform into a pair of critical-type Dirac points, which are different from those in noncentrosymmetric systems. So, the centrosymmetric Li₂NaN material is considered to be a superior topological semimetal with an ideal band structure, clear topological signs of physical properties, the novel pair of Dirac points and TDNPs.