Evidence for Higher order topology in Bi and Bi${}_{0.92}$Sb${}_{0.08}$

Abstract

Higher order topological insulators (HOTIs) are a new class of topological materials which host protected states at the corners or hinges of a crystal. HOTIs provide an intriguing alternative platform for helical and chiral edge states and Majorana modes, but there are very few known materials in this class. Recent studies have proposed Bi as a potential HOTI, however, its topological classification is not yet well accepted. In this work, we show that the (110) facets of Bi and BiSb alloys can be used to unequivocally establish the topology of these systems. Bi and Bi${}_{0.92}$Sb${}_{0.08}$ (110) films were grown on silicon substrates using molecular beam epitaxy and studied by scanning tunneling spectroscopy. The surfaces manifest rectangular islands which show localized hinge states on three out of the four edges, consistent with the theory for the HOTI phase. This establishes Bi and Bi${}_{0.92}$Sb${}_{0.08}$ as HOTIs, and raises questions about the topological classification of the full family of Bi${}_x$Sb${}_{1-x}$ alloys.

References in corpus (5)

• Electric Multipole Moments, Topological Multipole Moment Pumping, and Chiral Hinge States in Crystalline Insulators
• $(d-2)$-dimensional edge states of rotation symmetry protected topological states
• Surface States of the Topological Insulator Bi_{1-x}Sb_x
• One-dimensional Topological Edge States of Bismuth Bilayers
• One-Dimensional Edge States with Giant Spin Splitting in a Bismuth Thin Film

Cited by in corpus (3)

• Dirac cones and higher-order topology in quasi-continuous media
• Bulk-boundary-transport correspondence of the second-order topological insulators
• Spin separation and filtering assisted by topological corner states in the Kekulé lattice