报告题目：Enhance topological gaps of 2D materials to the energy scale of atomic spin-orbit coupling

报 告 人：Congjun Wu, University of California, San Diego

报告时间：2:00pm, Thursday, August 16, 2018

报告地点：理科楼C302报告厅

报告摘要：The 2D topological (quantum spin Hall) insulators are particularly important for their potential of being integrated for future device applications. However, the gap values of the current experimental systems (e.g. HgTe/CdTe and InAs/GaInSb) are too small at the order of a few Kelvins as constrained by the band inversion mechanism. Their energy scale is in fact determined by the small s-p hybridization rather than directly by spin-orbit coupling. We propose a new mechanism based on the 2D orbital-active (px and py) honeycomb lattice materials. Due to the orbital-active Dirac physics, their topological gap values equal the full scale of the atomic spin-orbit coupling, hence, can reach the order of 1eV. This mechanism was motivated by the study of the orbital-active honeycomb optical lattices with ultra-cold atoms, and can be directly applied to a large class of 2D materials including the Bismuthene on the SiC substrate and Stanene. The recent experiments of Bismuthene on SiC have shown the evidence of the gap up to 0.8eV. Possibility towards the quantum anomalous Hall insulator and mechanism for unconventional superconductivity assisted by the orbital structure in this class of materials will also be studied. The flat band structure can arise in other 2D orbital-active honeycomb materials, such as organic metal frameworks and transition metal oxide films, in which strong correlation phenomena including Wigner crystallization and ferromagnetism appear.

Selected References

1. 1. G. Li, W. Hanke, E. M. Hankiewicz, F. Reis, J. Schaefer, R. Claessen, Congjun Wu , Ronny Thomale, “A new paradigm for the quantum spin Hall effect at high temperatures” , arXiv:1807.09552

2. 2. Gu-Feng Zhang, Yi Li, Congjun Wu, “The honeycomb lattice with multi-orbital structure: topological and quantum anomalous Hall insulators with large gaps, Phys. Rev. B 90, 075114 (2014)”.

3. 3. Congjun Wu, “Orbital analogue of quantum anomalous Hall effect in $p$-band systems”, Phys. Rev. Lett. 101, 186807 (2008).

4. 4. Congjun Wu, Doron Bergman, Leon Balents, and S. Das Sarma, "Flat bands and Wigner crystallization in the honeycomb optical lattice", Phys. Rev. Lett. 99, 70401 (2007) ,