Design and realization of topological Dirac fermions on a triangular lattice

TL;DR

This paper reports the design and experimental realization of a triangular indium monolayer on SiC that exhibits topological Dirac fermions and quantum spin Hall phase, driven by strong spin-orbit coupling and valley physics.

Contribution

It introduces 'indenene', a novel triangular monolayer with non-trivial topological properties, demonstrating a new route to engineer quantum spin Hall insulators.

Findings

Identification of quantum spin Hall phase in indenene

Observation of hidden honeycomb connectivity from interference patterns

Valley physics driven by local spin-orbit coupling

Abstract

Large-gap quantum spin Hall insulators are promising materials for room-temperature applications based on Dirac fermions. Key to engineer the topologically non-trivial band ordering and sizable band gaps is strong spin-orbit interaction. Following Kane and Mele's original suggestion, one approach is to synthesize monolayers of heavy atoms with honeycomb coordination accommodated on templates with hexagonal symmetry. Yet, in the majority of cases, this recipe leads to triangular lattices, typically hosting metals or trivial insulators. Here, we conceive and realize "indenene", a triangular monolayer of indium on SiC exhibiting non-trivial valley physics driven by local spin-orbit coupling, which prevails over inversion-symmetry breaking terms. By means of tunneling microscopy of the 2D bulk we identify the quantum spin Hall phase of this triangular lattice and unveil how a hidden honeycomb connectivity emerges from interference patterns in Bloch $p_x \pm ip_y$-derived wave functions.