Topological surface states in epitaxial (SnBi2Te4)n(Bi2Te3)m natural van der Waals superlattices

Abstract

Topological insulators are good candidates for charge to spin conversion with high efficiency due to their spin-polarized topological surface states (TSSs). In this work, we provide experimental evidence for two-dimensional (2D) TSSs in ${(\mathrm{Sn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4})}_{n} {({\mathrm{Bi}}_{2}{\mathrm{Te}}_{3})}_{m}$ natural van der Waals superlattices grown by molecular beam epitaxy using angle resolved photoelectron spectroscopy and magnetotransport. While the TSSs overlap with bulk conduction band (BCB) states at the Fermi energy, it is shown that by increasing the Sn composition, the influence of BCB states is reduced and becomes minimum for $\mathrm{Sn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$. The latter compound, found to be in the form of septuplet layers, shows weak antilocalization effect with a prefactor $\ensuremath{\alpha}\ensuremath{\sim}--0.41$, indicating that the TSSs and the bulk behave as one 2D channel in which magnetotransport properties are influenced by large spin-orbit coupling.