Topological Insulators

“zero-gap” Semiconductors

Theoretical predictions in novel material, like topological insulators, are also investigated by HAXPES. The comparison between HAXPES valence band spectra and ab initio calculations shows clear evidence of zero band gap states in C1b Heuslers: LuPdBi, PtYSb and PtLaBi.  The zero band gap is resulted from the cubic symmetry and is a signature of  band inversion, which is an essential feature for a topological insulator state [1][2].

Figure 1: Valence band of LuPdBi. (a) and (b) HAXPES spectra. (c) and (d)  Ab inition density of states, and the density localized at the Pd atoms is marked by the shaded area.

 

 

 

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