Topological insulator in a Bi-Bi$_2$Se$_3$ infinitely adaptive superlattice phase

TL;DR

This study investigates a new topological insulator material, Bi$_4$Se$_{2.6}$S$_{0.4}$, formed by a natural superlattice of Bi and Bi$_2$Se$_3$, revealing its surface states and topological properties through advanced photoemission techniques.

Contribution

It reports the discovery and characterization of a topological insulator in a Bi-Bi$_2$Se$_3$ superlattice phase, demonstrating its surface states and spin structure.

Findings

Existence of a large, hexagonally shaped Fermi surface around the $b3$ point.

Surface state exhibits spin-momentum locking characteristic of topological insulators.

Crystals cleave along interfaces, creating terraces for one-dimensional topological studies.

Abstract

We report spin- and angle-resolved photoemission studies of a topological insulator from the infinitely adaptive series between elemental Bi and Bi$_2$Se$_3$. The compound, based on Bi$_4$Se$_3$, is a 1:1 natural superlattice of alternating Bi$_2$ layers and Bi$_2$Se$_3$ layers; the inclusion of S allows the growth of large crystals, with the formula Bi$_4$Se$_{2.6}$S$_{0.4}$. The crystals cleave along the interfaces between the Bi$_2$ and Bi$_2$Se$_3$ layers, with the surfaces obtained having alternating Bi or Se termination. The resulting terraces, observed by photoemission electron microscopy, create avenues suitable for the study of one-dimensional topological physics. The electronic structure, determined by spin- and angle- resolved photoemission spectroscopy, shows the existence of a surface state that forms a large, hexagonally shaped Fermi surface around the $\Gamma$ point of the surface Brillouin zone, with the spin structure indicating that this material is a topological insulator.