Figure 1: Evolution of tetradymite type TIs.
From: Sn-doped Bi1.1Sb0.9Te2S bulk crystal topological insulator with excellent properties
(a) Schematic representation of the evolution of Bi2Se3, (M2X3) type TIs, through the two approaches (Approach-1 and Approach-2). The arrows represent approaches and progresses made in achieving better materials. The solid lines represent the single atomic layers and zebra lines represent multi-element layers. The purple, green, red, dark orange and yellow colours are taken, respectively, for Bi, Sb, Se, Te and S atoms. (b) The schematic of a QL for Sn:Bi1.1Sb0.9Te2S and a QL obtained by structure refinement of a powdered specimen. The colour fraction for Bi/Sb atoms is according to the composition obtained by unit cell refinement.
