23. M. H. Liu, C. Z. Chang, Z. C. Zhang, Y. Zhang, W. Ruan, K. He, L. L. Wang, X. Chen, J. F, Jia, S. C. Zhang, Q. K. Xue, X. C. Ma, Y. Y. Wang, Electron interaction-driven insulating ground state in Bi2Se3 topological insulators in the two-dimensional limit, PHYSICAL REVIEW B 83, 165440 (2011).