Spin-orbit coupling tuned crossover of gapped and gapless topological phases in the chalcopyrite HgSnX2 (X = N, P): An ab initio investigation

The coupling between electron orbital momentum and spin momentum, known as spin -orbit coupling (SOC), is a fundamental origin of a multitude of fascinating physical phenomena, especially it holds paramount significance in the realm of topological materials. In our paper, we have predicted the topological phase in Hg -based chalcopyrite compounds using the first -principles density functional theory. The initial focus was on HgSnN2, revealing it to be a nonmagnetic Weyl semimetal, while HgSnP2 displayed characteristics of a strong topological insulator. What makes our study truly unique is that despite both compounds having the same SOC strength, arising from Hg, they exhibit distinct topological phases due to the distinct hybridization effect of the Hg -5d and X -p bands. This finding can address a significant factor, i.e., the effect of the band hybridization in deriving distinct topological phases, keeping the symmetry aspect intact. Our results indicate that due to the presence of band hybridization between the dominant X-np orbitals n = 2 and 3 for X = N and P respectively and a minor contribution from Hg -5d, we can tune the topological phase by manipulating SOC strength, which equivalently achievable by chemical substitutions. This investigation stands as a remarkable illustration of the unique roles that hybridization plays in sculpting the topological properties of these compounds while simultaneously preserving their underlying symmetries.