Bismuth Films on EuO(111) as a Platform for Proximity-Induced Topological States

TL;DR

This study demonstrates the successful growth and characterization of epitaxial bismuth films on EuO(111), revealing properties consistent with a quantum spin Hall insulator and establishing a platform for topological phases.

Contribution

The paper reports the first experimental realization of bismuthene on EuO(111), showing atomically ordered films with topological insulating properties and edge states.

Findings

Atomically ordered bi-layer bismuth with a quasi-square lattice was observed.

A robust energy gap of about 400 meV indicates a quantum spin Hall phase.

Transport measurements show surface-dominated conduction and quantum confinement effects.

Abstract

Interfacing two-dimensional bismuth with a magnetic layer provides a promising route towards realizing higher-order topological phases. In particular, bismuthene on a ferromagnetic insulator substrate has been theoretically proposed by \citet{Chen2020} as a universal platform for magnetic second-order topological insulators. Here, we report the experimental realization of epitaxial bismuth films grown on the ferromagnetic insulator EuO(111). Using high-resolution scanning tunneling microscopy, we observe atomically ordered bi-layer bismuth with a (012)-oriented quasi-square lattice, corresponding to a stabilized $\alpha$-phase bismuthene. The resulting film is exceptionally flat compared to conventional metallic films, reflecting the intrinsic two-dimensional nature of the Bi(012) phase. Tunneling spectroscopy(STS) reveals a robust energy gap of about 400 meV in the local density of states, consistent with a quantum spin Hall insulating phase persisting up to room temperature. Spatially resolved STS further identifies enhanced edge-localised states at the island boundaries. Complementary low-temperature magnetotransport measurements on proximity-coupled ultrathin Bi films exhibit linear magnetoresistance and a Hall sign reversal, indicative of quantum-confinement-driven surface-dominated transport. Our results establish bismuthene-magnetic-insulator heterostructures as a viable experimental platform for realizing magnetically tunable topological phases, providing a critical step toward the observation of higher-order topology in two dimensions.