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

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.