Nano-X users Prof. Shaochun Li of Nanjing University and Prof. Ping Cui of University of Science and Technology of China have successfully grown a monolayer of ZrTe₅ on a bilayer graphene/SiC substrate, which is supported by the MBE-STM and the X-ray Photoelectron Spectrometer XPS from Nano-X.

Topological insulators (TIs) hold an insulating band gap in the bulk and a time-reversal symmetry-protected gapless state on the boundary. The two-dimensional (2D) version of a TI, namely, 2D TI, features the one-dimensional (1D) helical edge states as the conductive channels.Due to spin−momentum locking, the backscattering on nonmagnetic impurities is strictly prohibited in the 1D edge states, thus leading to a dissipationless spin current, as characterized by the quantized spin Hall conductance. To realize the high-temperature QSH effect (up to room temperature), substantial efforts have been made to search for alternative QSH materials with wide band gaps. However, most of the discovered QSH monolayers thus far exhibit either narrow or even negative SOC gaps.

In this work, via elegant control of van der Waals epitaxy, successfully grown monolayer ZrTe₅ on a bilayer graphene/SiC substrate. Different from its bulk counterpart, the epitaxial ZrTe₅ monolayer exhibits two allotrope isomers with distinct intralayer alignments of trigonal ZrTe₃ prisms. By combining scanning tunneling microscopy/spectroscopy (STM/STS) measurements with first-principles calculations, this work determined the atomic structures of the two ZrTe₅ isomers and revealed an intrinsic SOC gap as large as ~ 254 meV in the ZrTe₅ monolayers. Discovered the 1D gapless edge states localized along the periphery of the ZrTe₅ monolayer, as verified to be topologically nontrivial by calculations. These findings render the ZrTe₅ monolayer a promising material for demonstrating the high-temperature QSH effect. These findings thus provide a highly desirable material platform for the exploration of the high-temperature quantum spin Hall effect.

The research result was recently published in Nature Communications of "Realization of monolayer ZrTe₅ topological insulators with wide band gaps", the first author is Yong-Jie Xu from Nanjing University and Guohua Cao from University of Science and Technology of China. Prof. Shaochun Li of Nanjing University and Prof. Ping Cui of University of Science and Technology of China, respectively, were the first authors of this paper. Prof. Fangsen Li, Lianlian Ji and Wei Li of Nano-X Vacuum Interconnected Nanotech WorkStation  were participated in this work.

Fig. 1 Epitaxial ZrTe₅ monolayers grown on the BLG/SiC(0001) substrate.

Fig. 2 Crystal structures of the ZrTe₅ monolayers.

Link to article: 

https://doi.org/10.1038/s41467-024-49197-x