Quantum fluctuation in thermopower at the topological phase transition in CaSrX (X: Si, Ge, Sn, Pb) studied from first principles theory.

The present density functional calculations propose the compounds CaSrX (X: Si, Ge, Sn, Pb) as strong topological insulators, with appreciable thermoelectric properties. Emergence of Dirac semi-metallic states has been observed in CaSrX (X: Si, Ge, Sn, Pb), which is induced by uni-axial strain along 'b' axis. CaSrSi and CaSrGe evolved as normal semiconductors with uni-axial strain. The trivial and non-trivial topological phases are evaluated by band inversion and Z topological invariants. A comprehensive analysis of thermopower, electrical conductivity scaled by relaxation time at these Dirac semi-metallic states exposes the highly oscillating behaviour, which gives insight to quantum oscillations driven by uni-axial strain. Further the thermoelectric properties at strong topological insulating states and normal insulating states have been summarized, which reveals the potential thermoelectric properties of these materials.