Hydrostatic strain-induced topological phase of KNa2Sb

Topological insulators are novel state of quantum matter that have a bulk band gap like an ordinary insulator, but have protected conducting states by time reversal symmetry on their edge or surface. The spin-orbit coupling can play an important role in these materials, resulting in a band inversion at time reversal invariant momenta (TRIM) points. The topological phase and the effect of the hydrostatic pressure on the electronic structure and topological phase of the KNa2Sb compound are investigated by using both first-principles calculations and ab-initio based tight-binding computations. Under hydrostatic lattice strain until 5.6%, the KNa2Sb compound is semimetal with zero energy band gap and has an inverted band order. In this pressure, the Z2 invariants of this compound are calculated using the parity analysis at TRIM points and evolution of wannier charge centers at the six TRIM plane. The calculated surface states at (0 0 1) surface show a single Dirac cone exists on the X¯Γ¯W¯ line at the surface Brillouin zone. To investigate the stability of KNa2Sb compound the phonon dispersions and elastic tensors of this compound in the cubic structure are calculated.