Optically probing tunable band topology in atomic monolayers*

Experiments on Bi monolayers on a SiC substrate reveal an interplay between a huge topologically nontrivial gap ~0.8 eV and strong spin-orbit coupling (SOC), leading to striking transport properties such as a robust quantum spin Hall effect (QSHE) [1]. With a suitable choice of substrates it is also possible to remove valley degeneracy and realize multiple Hall effects in a single materials system [2]. In contrast to transport properties, much less is known about how an optical response could yield topological signatures in these group V monolayers. By combining first-principles calculations and a careful inclusion of strong SOC in effective models as well as the Coulomb interaction in these monolayers, we show that the changes in optical response reveal topological properties inherent to these systems [3]. We explain how these findings offer new opportunities for proximitized materials [4].
[1] F. Reis, et al., Science 357, 287 (2017); F. Dominguez, et al., Phys. Rev. B 98, 161407(R) (2018).
[2] T. Zhou, et al., npj Quant. Mater. 3, 39 (2018).
[3] G. Xu, et al., Phys. Rev. Lett. 125, 157402 (2020).
[4] I. Zutic, et al., Mater. Today 22, 85 (2019).