First principles predictions of structural, electronic and topological properties of two-dimensional Janus TiNXI (X = Br, Cl) structures

Motivated by the report of the giant Rashba effect in ternary layered compounds BiTeX, we consider two Janus structured compounds Ti 2 N 2 XI (X = Br, Cl) of the same ternary family exhibiting a 1 : 1 : 1 stoichiometric ratio. Broken inversion symmetry in the Janus structure, together with its unique electronic structure exhibiting anti-crossing states formed between Ti-d states and strong spin-orbit coupled I-p states, generates large Rashba cofficients of 2-3 eV Å for these compounds, classifying them as strong Rashba compounds. The anti-crossing features of the first-principles calculated electronic structure also result in non-trivial topology, combining two quantum phenomena - Rashba effect and non-trivial topology - in the same materials. This makes Janus TiNI compounds candidate materials for two-dimensional composite quantum materials. The situation becomes further promising by the fact that the properties are found to exhibit extreme sensitivity and tunability upon application of uniaxial strain. Large Rashba effect and nontrivial topological properties of the Janus mono layers, resulting from inversion symmetry breaking, band-inversion and band anticrossing effects.