Electronic structure of ${\mathrm{Bi}}_2{X}_3$ $(X=\mathrm{S},\mathrm{Se},\mathrm{T})$ compounds:  Comparison of theoretical calculations with photoemission studies

In recent years electronic structures of ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ and related materials have been studied theoretically through ab initio band-structure calculations and experimentally through photoemission experiments, but to the best of our knowledge, a detailed comparison between experiment and theory has not been attempted so far. In this paper we discuss the density of states (DOS) of the narrow-gap semiconductors ${\mathrm{Bi}}_2{X}_3$ $(X=\mathrm{S},\mathrm{Se},\mathrm{Te})$ obtained within density-functional theory. While several electronic structure calculations for ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ and ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ have been reported in the literature, there have been no published calculations for ${\mathrm{Bi}}_2{\mathrm{S}}_3$ or ${\mathrm{Bi}}_2{\mathrm{Te}}_2\mathrm{Se}.$ Recent photoemission and inverse-photoemission measurements in these systems, performed by four separate groups (including our photoemission measurements of ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ and ${\mathrm{Bi}}_2{\mathrm{Se}}_3),$ allows for a comparison of the general features of the calculated DOS for both valence- and conduction-band states with photoemission and inverse-photoemission spectra. The agreement between the positions of the prominent peaks in the calculated DOS and photoemission spectra continues to improve with better energy resolution in the experiment.