Breakdown of bulk-projected isotropy in surface electronic states of topological Kondo insulator SmB$_6$(001)

TL;DR

This study reveals that the topological surface states of SmB$_6$ break bulk-related isotropy, showing anisotropy and symmetry loss due to surface atomic structure, which could enable tailored electronic properties.

Contribution

It demonstrates the breakdown of bulk-related isotropy in the surface states of SmB$_6$ through ARPES, highlighting surface atomic structure's role in topological insulators.

Findings

Surface states are anisotropic and lack fourfold symmetry.

Surface atomic structure influences topological surface states.

Potential to engineer surface properties via atomic structure control.

Abstract

The topology and spin-orbital polarization of two-dimensional (2D) surface electronic states have been extensively studied in this decade. One major interest in them is their close relationship with the parities of the bulk (3D) electronic states. In this context, the surface is often regarded as a simple truncation of the bulk crystal. Here we show breakdown of the bulk-related in-plane rotation symmetry in the topological surface states (TSSs) of the Kondo insulator SmB$_6$. Angle-resolved photoelectron spectroscopy (ARPES) performed on the vicinal SmB$_6$(001)-$p$(2$\times$2) surface showed that TSSs are anisotropic and that the Fermi contour lacks the fourfold rotation symmetry maintained in the bulk. This result emphasizes the important role of the surface atomic structure even in TSSs. Moreover, it suggests that the engineering of surface atomic structure could provide a new pathway to tailor various properties among TSSs, such as anisotropic surface conductivity, nesting of surface Fermi contours, or the number and position of van Hove singularities in 2D reciprocal space.