Chemical Gating of a Weak Topological Insulator: Bi₁₄Rh₃I₉

The compound Bi₁₄Rh₃I₉ has recently been suggested as a weak three-dimensional topological insulator on the basis of angle-resolved photoemission and scanning-tunneling experiments in combination with density functional (DF) electronic structure calculations. These methods unanimously support the topological character of the headline compound, but a compelling confirmation could only be obtained by dedicated transport experiments. The latter, however, are biased by an intrinsic n-doping of the material's surface due to its polarity. Electronic reconstruction of the polar surface shifts the topological gap below the Fermi energy, which would also prevent any future device application. Here, we report the results of DF slab calculations for chemically gated and counter-doped surfaces of Bi₁₄Rh₃I₉. We demonstrate that both methods can be used to compensate the surface polarity without closing the electronic gap.