Epitaxial Growth of Quasi-One-Dimensional Bismuth-Halide Chains with Atomically Sharp Topological Non-Trivial Edge States

Abstract

Quantum spin Hall insulators have one-dimensional (1D) spin-momentum locked topological edge states (ES) inside the bulk band gap, which can serve as dissipationless channels for the practical applications in low consumption electronics and high performance spintronics. However, the clean and atomically sharp ES serving as ideal 1D conducting channels are still lack. Here, we report the formation of the quasi-1D Bi4I4 nanoribbons on the surface of Bi(111) with the support of the graphene-terminated 6H-SiC(0001) and the direct observations of the topological ES at the step edge by scanning tunneling microscopy and spectroscopic-imaging results. The ES reside surround the edge of Bi4I4 nanoribbons and exhibits remarkable robustness against non time reversal symmetry perturbations. The theoretical simulations verify the topological non-trivial character of 1D ES, which is retained after considering the presence of the underlying Bi(111). Our study supports the existence of topological ES in Bi4I4 nanoribbons, paving the way to engineer the novel topological features by using the nanoribbons as the 1D building block.

Large-Gap Quantum Spin Hall State and Temperature-Induced Lifshitz Transition in Bi4Br4

“…The calculated results in Figure B quantitatively resemble that of the freestanding monolayer Bi 4 Br 4 ribbon, indicating that the weak interlayer interaction engenders the neglectable effect on the topological nature of the edge state. The penetration depth of the topological edge state is 1.7 nm in Figure C,D, which is in accordance with the experimental findings in Figure H and comparable to other 2D topological insulators. − It should be noted that the linear dispersion of edge states is expected to result in a constant DOS inversely proportional to the Fermi velocity in the ideal single-particle scenario. In our work, the zero-bias dip at the Fermi energy leads to the deviation from constant DOS and the formation of the hump-like shape in d I /d V curve correlated to the edge states.…”

“…Figure H displays the spatially resolved d I /d V spectra as a function of energy and distance across the edge in Figure I, demonstrating that the conductive state is confined at the edge of Bi 4 Br 4 with a spatial extension close to the 1.7 nm, as labeled by the yellow and purple arrows. It should be noted that the penetration length of the conductive edge state is comparable to that of the topological 1D edge state observed in other systems. − Nevertheless, the conductive edge state could be evoked by the crystal-symmetry-broken factors, such as the dangling bonds at the edge and various defects. In view of the van der Waals force of intralayer ( ab plane) interaction, the contribution of the dangling bond on the formation of conductive edge state could be excluded.…”

Observation of Topological Edge States on α-Bi4Br4 Nanowires Grown on TiSe2 Substrates

“…As shown in the large-scale AFM images (Figure 1b), α-Bi 4 Br 4 nanowires are formed on the TiSe 2 substrates, distinct from the recent report of flat Bi 4 I 4 nanoislands grown on the Bi(111) surfaces. 39 The different morphologies of the two bismuth halides might originate from the distinct interfacial coupling between the bismuth halides and the substrates. The strong coupling between Bi 4 I 4 and the Bi(111) surface favors the formation of 2D nanoislands, while the vdW interaction between α-Bi 4 Br 4 and the TiSe 2 substrates leads to the three-dimensional growth of nanowires.…”

“…The α-Bi 4 Br 4 nanowires were grown on the TiSe 2 single crystals (Figure S1, Supporting Information) by molecular beam epitaxy (MBE) and characterized by atomic force microscopy (AFM). As shown in the large-scale AFM images (Figure b), α-Bi 4 Br 4 nanowires are formed on the TiSe 2 substrates, distinct from the recent report of flat Bi 4 I 4 nanoislands grown on the Bi(111) surfaces . The different morphologies of the two bismuth halides might originate from the distinct interfacial coupling between the bismuth halides and the substrates.…”

Phase Transformation-Induced Quantum Dot States on the Bi/Si(111) Surface

“…Here, we investigate a QD system synthesized on the √3 × √3-Bi/Si(111) surface reconstruction by phase transformation control. Bismuth is selected for investigation because of its strong Rashba splitting, which is attractive for quantum and spintronics applications. − There are two Bi phases on the Si(111) surface, known as the α and β phases. The atomic structure of both phases has been extensively studied in the past, with the α phase consisting of 1/3 of a monolayer (ML) of Bi adatoms on a bulk terminated Si(111) surface and the β phase having 1 ML of Bi atoms arranged in a trimer structure. − Both phases can be easily obtained by annealing the Bi/Si(111) surface at 470–800 K. The β-phase includes unique in-gap surface states, which are contributed from Bi in-plane p x , p y orbitals. − More importantly, those surface states provide a potential source for QDSs when arranging the α and β phases in desired configurations.…”