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Md S. Hossain, F. Schindler, R. Islam, Z. Muhammad, Y.-X. Jiang, Z.-J. Cheng, Q. Zhang, T. Hou, H. Chen, M. Litskevich, B. Casas, J.-X. Yin, T. A. Cochran, M. Yahyavi, X. P. Yang, L. Balicas, G. Chang, W. Zhao,T. Neupert, M. Z. Hasan, A hybrid topological quantum state in an elemental solid, Nature 628, 527 (2024), arXiv:2401.04845 (2024)
Employing in-depth first-principles calculations, Magtop researcher Rajibul Islam in collaboration with experimental groups discovered a new quantum phase namely “Hybrid topological phase” in the elemental grey As materials. The authors demonstrated the hybridization between the gapped edge state and the gapless surface state. In the first column of the Figure, the free-standing monolayer exhibits a gapped edge state. The second column of the Figure demonstrates that the clean surface of gray arsenic (As) features a gapless Rashba surface state near the Fermi level. In the third column, with the introduction of monolayer step edges, the edge state undergoes hybridization with the gapless surface states, resulting in the emergence of gapless edge states at the step edges. The results presented here indicate that the experimentally observed step-edge states in α-As, unlike surface or hinge states, are not expected for either first or higher-order topological insulators separately but only for hybrid materials in which both kinds of band topology are present.