Prediction of topological insulators in supercubane-like materials based on first-principles calculations

The lattice structures and topological properties of X8 (X  =  C, Si, Ge, Sn, Pb) under hydrostatic strain have been investigated based on first-principle calculations. Among the materials, 8, Si8, Ge8 and Sn8 are dynamically stable with negative formation energy and no imaginary phonon frequency. We find that the hydrostatic strain cannot induce a quantum phase transition between topological trivial and nontrivial state for both C8 and Si8, while for Ge8 and Sn8 the tensile strain can play a unique role in tuning the band topology, which will lead to a topological nontrivial state with Z2 invariants (1;111). Although the topological transition occurs above the Fermi level, the Fermi level can be tuned by applying electrostatic gating voltage.