The Weak 3D Topological Insulator Bi₁₂Rh₃Sn₃I₉

Topological insulators (TIs) gained high interest due to their protected electronic surface states that allow dissipation-free electron and information transport. In consequence, TIs are recommended as materials for spintronics and quantum computing. Yet, the number of well-characterized TIs is rather limited. To contribute to this field of research, we focused on new bismuth-based subiodides and recently succeeded in synthesizing a new compound Bi12Rh3Sn3I9, which is structurally closely related to Bi14Rh3I9- a stable, layered material. In fact, Bi(14)Rh(3)I(9)is the first experimentally supported weak 3D TI. Both structures are composed of well-defined intermetallic layers of(infinity)(2)[(Bi4Rh)(3)I](2+)with topologically protected electronic edge-states. The fundamental difference between Bi(14)Rh(3)I(9)and Bi(12)Rh(3)Sn(3)I(9)lies in the composition and the arrangement of the anionic spacer. While the intermetallic 2D TI layers in Bi(14)Rh(3)I(9)are isolated by(infinity)(1)[Bi2I8](2-)chains, the isoelectronic substitution of bismuth(III) with tin(II) leads to(infinity)(2)[Sn3I8](2-)layers as anionic spacers. First transport experiments support the 2D character of this material class and revealed metallic conductivity