1Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 2Physical Science Laboratory, Huairou National Comprehensive Science Center, Huairou, Beijing 101400 3School of Physics, University of Chinese Academy of Sciences, Beijing 100190 4Laboratory for Topological Quantum Matter and Advanced Spectroscopy (B7), Department of Physics, Princeton University, Princeton, NJ, USA 5Songshan Lake Material Laboratory, Dongguan 523808 6Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467, USA 7CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190
Abstract：The topological edge states of two-dimensional topological insulators with large energy gaps furnish ideal conduction channels for dissipationless current transport. Transition metal tellurides $X$Te$_{5}$ ($X$=Zr, Hf) are theoretically predicted to be large-gap two-dimensional topological insulators, and the experimental observations of their bulk insulating gap and in-gap edge states have been reported, but the topological nature of these edge states still remains to be further elucidated. Here, we report our low-temperature scanning tunneling microscopy/spectroscopy study on single crystals of HfTe$_{5}$. We demonstrate a full energy gap of $\sim$80 meV near the Fermi level on the surface monolayer of HfTe$_{5}$ and that such an insulating energy gap gets filled with finite energy states when measured at the monolayer step edges. Remarkably, such states are absent at the edges of a narrow monolayer strip of one-unit-cell in width but persist at both step edges of a unit-cell wide monolayer groove. These experimental observations strongly indicate that the edge states of HfTe$_{5}$ monolayers are not trivially caused by translational symmetry breaking, instead they are topological in nature protected by the 2D nontrivial bulk properties.
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2019, Vol. 36 
