Effect of Bi bilayers on the topological states ofBi2Se3: A first-principles study

Abstract

Bi 2 Se 3 is a three-dimensional topological insulator which has been extensively studied because it has a single Dirac cone on the surface, inside a relatively large bulk band gap. However, the effect of two-dimensional topological insulator Bi bilayers on the properties of Bi 2 Se 3 and vice versa, has not been explored much. Bi bilayers are often present between the quintuple layers of Bi 2 Se 3 , since (Bi 2 ) n (Bi 2 Se 3 ) m form stable ground-state structures. Moreover, Bi 2 Se 3 is a good substrate for growing ultrathin Bi bilayers. By first-principles techniques, we first show that there is no preferable surface termination by either Bi or Se. Next, we investigate the electronic structure of Bi bilayers on top of, or inside a Bi 2 Se 3 slab. If the Bi bilayers are on top, we observe a charge transfer to the quintuple layers that increases the binding energy of the surface Dirac cones. The extra states, originating from the Bi bilayers, were declared to form a topological Dirac cone, but here we show that these are ordinary Rashba-split states. This result, together with the appearance of a new Dirac cone that is localized slightly deeper, might necessitate the reinterpretation of several experimental results. When the Bi bilayers are located inside the Bi 2 Se 3 slab, they tend to split the slab into two topological insulators with clear surface states. Interface states can also be observed, but an energy gap persists because of strong coupling between the neighboring quintuple layers and the Bi bilayers.

Atomic and electronic structure of bismuth-bilayer-terminatedBi2Se3(0001) prepared by atomic hydrogen etching

“…It should be noted that our calculated dispersion curves are in disagreement with those published by Eich et al [39], who found a bismuth BL to be located 4.4Å above the substrate. However, our results are in good agreement with those of two other recent theoretical studies concerning the band dispersion, Dirac cone spin texture and its real-space localization [40,41]. In addition, we find excellent agreement of our dispersion curves with experimental ones collected in a photoemission study by Miao et al [41].…”

Band bending at the surface of Bi2Se3 studied from first principles

“…In this case the bands are shifted upward as shown in figures 4(c) and (d). In previous numerical studies the effective electric field responsible for the BB was controlled by a charge transfer originating from a sheet of adatoms located above the Bi2Se3 surface [23][24][25]32]. In these calculations additional SSs were identified in the band structure being attributed to the presence of the given adatoms.…”

“…Besides these comprehensive experimental studies, numerous theoretical works were also devoted to the description of the physical properties of the 2GTIs, including first principle calculations [1,[20][21][22][23][24][25], tight binding [23,26,27] or effective continuous [11] models. The structure of the 2GTIs can be described by a sequence of weakly bound quintuple layers (QLs), each consisting of five atomic layers.…”

The growth of bismuth on Bi2Se3 and the stability of the first bilayer

“…A periodic buckling of the lattice is found beginning from deposition of the 2 nd BL and lasting until the 5 th BL is deposited. The Bi BL lattice gradually relaxes to become bulk-like at a coverage of 24 BLs.…”

“…An interesting aspect of the Bi/Bi2Se3 system is the unique stability of a single deposited BL. Density functional theory (DFT) calculations show that the single BL-terminated structure has a lower surface energy than the bare Se-terminated surface [21,22] and there is a stronger bonding between a QL and a Bi BL than there is between QLs [23,24]. In support of this notion, Bi2Se3 surfaces terminated with a single Bi BL have been found to spontaneously form on in-situ [22] and ex-situ [25] cleaved samples.…”