The surfaces of three-dimensional topological insulators (TIs) characterized by a spin-helical Dirac fermion provide a fertile ground for realizing exotic phenomena as well as having potential for wide-ranging applications. To realize most of their s
pecial properties, the Dirac point (DP) is required to be located near the Fermi energy with a bulk insulating property while it is hardly achieved in most of the discovered TIs. It has been recently found that TlBiSe2 features an in-gap DP, where upper and lower parts of surface Dirac cone are both utilized. Nevertheless, investigations of the surface transport properties of this material are limited due to the lack of bulk insulating characteristics. Here, we present the first realization of bulk insulating property by tuning the composition of Tl1-xBi1+xSe2-d without introducing guest atoms that can bring the novel properties into the reality. This result promises to shed light on new exotic topological phenomena on the surface.
The surface termination of the promising topological insulator TlBiSe$_{2}$ has been studied by surface and bulk sensitive probes. Our scanning tunneling microscopy has unmasked for the first time the unusual surface morphology of TlBiSe$_{2}$ obtain
ed by cleaving, where islands are formed by residual atoms on the cleaved plane. The chemical condition of these islands was identified using core-level spectroscopy. We observed thallium core-level spectra that are strongly deformed by a surface component in sharp contrast to the other elements. We propose a simple explanation for this behavior by assuming that the sample cleaving breaks the bonding between thallium and selenium atoms, leaving the thallium layer partially covering the selenium layer. These findings will assist the interpretation of future experimental and theoretical studies on this surface.
