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A two-dimensional topological insulator features (only) one bulk gap with nontrivial topology, which protects one-dimensional boundary states at the Fermi level. We find a quantum phase of matter beyond this category: a multiple topological insulator. It possesses a ladder of topological gaps; each gap protects a robust edge state. We prove a monolayer of van der Waals material PtBi2 as a two-dimensional multiple topological insulator. By means of scanning tunneling spectroscopy, we directly visualize the one-dimensional hot electron (and hole) channels with nanometer size on the samples. Furthermore, we confirm the topological protection of these channels by directly demonstrating their robustness to variations of crystal orientation, edge geometry, and sample temperature. The discovered topological hot electron materials may be applied as efficient photocatalysts in the future.

We prepare orthorhombic CoSb monolayer films on SrTiO3(001) substrate by molecular beam epitaxy and observe symmetric gap around the Fermi level with coherence peaks at ± (6–7) meV by in situ scann...

A two-dimensional topological insulator features (only) one bulk gap with nontrivial topology, which protects one-dimensional boundary states at the Fermi level. We find a quantum phase of matter beyond this category: a multiple topological insulator. It possesses a ladder of topological gaps; each gap protects a robust edge state. We prove a monolayer of van der Waals material PtBi

We prepare orthorhombic CoSb monolayer films on SrTiO

The freestanding PbSe monolayer has been predicted as a candidate of the two-dimensional topological crystalline insulator, which possesses the Dirac-cone-like edge states resided at the edge. Up to now, however, direct experimental evidence of topological PbSe monolayer has not yet been reported. Here, we report the epitaxial growth and scanning tunneling microscopy study of few-layers PbSe islands grown on SrTiO3 substrate. From the investigation of different thickness, we discover the release of compressive strain and the reduction of bandgap as the thickness becomes thick. Following detailed spectroscopic measurements, a signature of Dirac-like edge states is observed at the edge of seventh-layer PbSe. In conjunction with first-principle calculations, we find that compressive-strain-induced buckling adjusts the topological band inversion and eventually leads to a phase transition from nontrivial two-dimensional topological crystalline insulator to trivial insulator, which match well with our experimen...

The freestanding PbSe monolayer has been predicted as a candidate of the two-dimensional topological crystalline insulator, which possesses the Dirac-cone-like edge states resided at the edge. Up to now, however, direct experimental evidence of topological PbSe monolayer has not yet been reported. Here, we report the epitaxial growth and scanning tunneling microscopy study of few-layers PbSe islands grown on SrTiO