Topological Dirac Semimetallic Phase in Heusler-Type Li2YZ (Y = Zn or Cd and Z = Ge, Sn, or Pb) Compounds: A First-Principles Investigation.

Topological Dirac semimetals with robust surface states have drawn significant interest in condensed matter research, as they exhibit unique transport properties. Heusler compounds have emerged as an attractive platform offering a wide range of tunability in their electronic properties, ranging from semiconductors to semimetals, along with spin-orbit coupling-induced nontrivial topological states as well as crystalline symmetry-protected band crossings. These features position them as ideal candidates for investigating topological phases, including Dirac semimetallic behavior. In this study, we performed a first-principles investigation on Heusler-type Li2YZ (Y = Zn or Cd and Z = Ge, Sn, or Pb) compounds under two cubic space groups, F4̅3m (No. 216) and Fm3̅m (No. 225), to explore their electronic and topological properties, encompassing a total of 12 structures. Ground-state energy calculations identified the energetically preferred phase for each material. For brevity, Li2CdGe was selected as the representative compound, and its phonon dispersion spectra confirmed dynamic stability in both F4̅3m and Fm3̅m phases. Furthermore, the topological phase of Li2CdGe transitions from a triple-point phase to a fourfold Dirac node phase in both structures, F4̅3m and Fm3̅m, under spin-orbit coupling (SOC). The Dirac nature of Li2CdGe was validated by calculating its surface states on the (001) surface in both the F4̅3m and Fm3̅m phases. Notably, four of the studied compounds (Li2CdGe, Li2CdPb, Li2CdSn, and Li2ZnPb) exhibit nontrivial topological phases in two space groups. Our findings indicate that the Li2YZ family hosts promising nontrivial topological features to encourage further theoretical and experimental research in materials science and condensed matter.