The theoretical discovery and experimental realisation of topological insulators, a new state of matter, has brought enormous research interest in the field of condensed matter physics. The novel and fascinating phenomenon in topological insulators (TIs) is the existence of gapless surface states (or edge states) while the bulk interior has an energy gap. These states are intriguing because they enable the transport of charges with no backscattering, which means less heat generation than ordinary conductors. The unique transport in TIs arises because of the spin-momentum locking of the surface...