Quantum Size Effects, Multiple Dirac Cones, and Edge States in Ultrathin Bi(110) Films

Abstract

The presence of inherently strong spin-orbit coupling in bismuth, its unique layer-dependent band topology and high carrier mobility make it an interesting system for both fundamental studies and applications. Theoretically, it has been suggested that strong quantum size effects should be present in the Bi(110) films, with the possibility of Dirac fermion states in the odd-bilayer (BL) films, originating from dangling pz orbitals and quantum-spin hall (QSH) states in the even-bilayer films. However, the experimental verification of these claims has been lacking. Here, we study the electronic structure of Bi(110) films grown on a high-Tc superconductor, Bi2Sr2CaCu2O 8+δ (Bi2212) using angle-resolved photoemission spectroscopy (ARPES). We observe an oscillatory behavior of electronic structure with the film thickness and identify the Dirac-states in the odd-bilayer films, consistent with the theoretical predictions. In the even-bilayer films, we find another Dirac state that was predicted to play a crucial role in the QSH effect. In the low thickness limit, we observe several extremely one-dimensional states, probably originating from the edge-states of Bi(110) islands. Our results provide a much needed experimental insight into the electronic and structural properties of Bi(110) films.

Structures of α-BixSb1–x Alloys Formed on the TiSe2 Substrates

“…The surface structure of the as-grown α-Bi is characterized by high-resolution STM images, as depicted in Figure c. A rectangular unit cell with a = 4.76 ± 0.10 Å and b = 4.61 ± 0.10 Å is disclosed, in line with previous reports of α-Bi on Bi2212 . Deposition of 2.25 ML of Sb on the TiSe 2 substrates leads to the formation of α-Sb islands, as depicted in Figure e.…”

“…A rectangular unit cell with a = 4.76 ± 0.10 Å and b = 4.61 ± 0.10 Å is disclosed, in line with previous reports of α-Bi on Bi2212. 22 Deposition of 2.25 ML of Sb on the TiSe 2 substrates leads to the formation of α-Sb islands, as depicted in Figure 1e. The line profile (Figure 1g) of the as-grown α-Sb along the red line marked in Figure 1e reveals an interlayer spacing of 0.7 ± 0.01 nm, in accordance with the monolayer height of α-Sb on TiSe 2 .…”

van der Waals Epitaxy of Bi Nanowires and Bi2Se3 Thin Films on an Antiferromagnetic Substrate of CoNb3S6

“…As seen in Figure 3a, a rough polycrystalline Bi film is formed at a relatively low annealing temperature of 300 K. At an annealing temperature of 400 K, rod-like structures are formed with a longitudinal length of ∼150 nm, as shown in Figure 3b. Line profile analysis reveals an interlayer spacing of ∼11 Å, corresponding to a distorted black-phosphorus (BP)-like bilayer (BL) Bi(110) film grown on HOPG, 18 TiSe 2 , optimally doped Bi2212, 19 Cr 2 Ge 2 Te 6 , etc. 6 When the annealing temperature increases to 500 K, kinked Bi nanowires are observed.…”

Realization of unpinned two-dimensional dirac states in antimony atomic layers

“…The Dirac states with tunable properties and controllable couplings are useful for transport and optical applications 29 – 31 . All of group-Va elements including P, As, Sb and Bi can form phosphorene-like structures 9 , 10 , 13 – 19 . The conduction and valence bands of P and As monolayers are far apart in energy (1.2 eV for P and 0.4 eV for As).…”

“…The two phases are referred to as α and β -phases, respectively, in the literature. In the family of group-Va elements, P, As, Sb and Bi can form phosphorene-like structures 9 , 10 , 13 – 19 . Here we focus on the phosphorene-like α -antimonene ( α -Sb for short).…”