Abstract
We performed angle-resolved photoelectron spectroscopy of the Bi(111) surface to demonstrate that this surface supports edge states of non-trivial topology. Along the -direction of the surface Brillouin zone, a surface-state band disperses from the projected bulk valence bands at to the conduction bands at continuously, indicating the non-trivial topological order of three-dimensional Bi bands. We ascribe this finding to the absence of band inversion at the L point of the bulk Bi Brillouin zone. According to our analysis, a modification of tight-binding parameters can account for the non-trivial band structure of Bi without any other significant change in other physical properties.
Highlights
Ever since the experimental realization of a two-dimensional (2D) topological insulator (TI) in 2007 [1], topological order (TO) has attracted a tremendous interest in the band-structure characterization of condensed-matter systems [2, 3, 4]
The dispersion of SS calculated at one surface time-reversal-invariant momenta (TRIM) on Bi(111) is in qualitative disagreement with the one observed by angle-resolved photoelectron spectroscopy (ARPES) experiments, both in 3D bulk samples [16] and in thin films [13, 17, 18]: a SS was observed to be connected to bulk conduction bands (BCB) in contrast to the abovementioned theoretical calculations
Our result demonstrates the non-trivial topology of the SS bands on Bi(111) around M : a SS branch is connected to both bulk valence bands (BVB) and BCB continuously along the line connecting the surface Brillouin zone (SBZ) points Γand M
Summary
Ever since the experimental realization of a two-dimensional (2D) topological insulator (TI) in 2007 [1], topological order (TO) has attracted a tremendous interest in the band-structure characterization of condensed-matter systems [2, 3, 4]. The most popular models [9, 10] indicate that pure Bi possesses trivial TO [2, 3, 11] and various first-principles calculations [12, 13, 14, 15] show a SS dispersion consistent with this absence of TO According to these works, no spinsplit SS connects the projected bulk valence bands (BVB) and bulk conduction bands (BCB) between surface time-reversal-invariant momenta (TRIM) on surface Brillouin zone (SBZ). Our result demonstrates the non-trivial topology of the SS bands on Bi(111) around M : a SS branch is connected to both BVB and BCB continuously along the line connecting the SBZ points Γand M This discrepancy between the theory and experiment can be solved by assuming the non-trivial TO of the bulk bands of Bi. We propose a modification of the common tight-bonding (TB) model [10], which can explain the non-triviality of bulk Bi without contradiction against previous experimental results.
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