Topological-metal to band-insulator transition in (Bi _1-xIn _x) ₂Se ₃ thin films

By combining transport and photoemission measurements on (Bi _1-xIn _x) ₂Se ₃ thin films, we report that this system transforms from a topologically nontrivial metal into a topologically trivial band insulator through three quantum phase transitions. At x≈3%-7%, there is a transition from a topologically nontrivial metal to a trivial metal. At x≈15%, the metal becomes a variable-range-hopping insulator. Finally, above x≈25%, the system becomes a true band insulator with its resistance immeasurably large even at room temperature. This material provides a new venue to investigate topologically tunable physics and devices with seamless gating or tunneling insulators.