Topological edge states of Bi(110) islands on top of high-Tc superconductor

Recent Scanning Tunnelling Microscopy (STM) measurements showed that elemental bismuth hosts topological electronic states on both Bi(111) [1,2]and Bi(110) facets [3]. The question of higher-order topology (HOT) in bismuth is still a highly debatable matter [4]. Here we synthesized a Bi(110) thin film by molecular beam epitaxy on the cleaved extremely overdoped Bi₂Sr₂CaCu₂O_8+δ substrate and performed STM measurements on it. We observed Bi rectangular islands with (110) facet in which 1D edge state appears only on two or three out of four edges. Theoretically, this can be consistent with one of the phases with HOT, but it is also consistent with the geometrical properties of the edges [1]. Interestingly, we found an ‘L’ shaped island where two Bi(110) domains are merging together, and identified a 1D state propagating along the boundary at the same energy as the edge states. In this talk, we will discuss a possible topological nature of this edge state and its relation to the high-Tc superconducting proximity effect from the Bi₂Sr₂CaCu₂O_8+δ substrate.

1, Drozdov, I., Alexandradinata, A., Jeon, S. et al. One-dimensional topological edge states of bismuth bilayers. Nature Phys. 10, 664–669 (2014);

2, Schindler, F., Wang, Z., Vergniory, M.G. et al. Higher-order topology in bismuth. Nature Phys. 14, 918–924 (2018);

3, Aggarwal, L., Zhu, P., Hughes, T.L. et al. Evidence for higher order topology in Bi and Bi_0.92Sb_0.08. Nat Commun. 12, 4420 (2021);

4, Nayak, A. K., Reiner, J., Queiroz, R., et al. Resolving the topological classification of bismuth with topological defects. Sci. Adv. 5, eaax6996 (2019).