Topological Phase Transition and Texture Inversion in a Tunable Topological Insulator

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Science  31 Mar 2011:
DOI: 10.1126/science.1201607


The recently discovered three-dimensional or bulk topological insulators are expected to exhibit exotic quantum phenomena. It is believed that a trivial insulator can be twisted into a topological state by modulating the spin-orbit interaction or the crystal lattice, driving the system through a topological quantum phase transition. We report the observation of a phase transition in a tunable spin-orbit system BiTl(S1–δSeδ)2 where the topological state formation is visualized. In the topological state, vortex-like polarization states are observed to exhibit 3D vectorial textures, which collectively feature a chirality transition as the spin-momentum locked electrons on the surface go through the zero carrier density point. Such phase transition and texture inversion can be the physical basis for observing fractional charge (±e/2) and other fractional topological phenomena.