R. Wu, J.-Z. Ma, S.-M. Nie, L.-X. Zhao, X. Huang, J.-X. Yin, B.-B. Fu, P. Richard, G.-F. Chen, Z. Fang, X. Dai, H.-M. Weng, T. Qian, H. Ding, and S. H. Pan. Evidence for Topological Edge States in a Large Energy Gap near the Step Edges on the Surface of ZrTe5. Phys. Rev. X 6, 021017(2016)
https://journals.aps.org/prx/abstract/10.1103/PhysRevX.6.021017