Prof. J. Carlos Egues
Instituto de Física de São Carlos – Universidade de São Paulo

Common wisdom has it that edge states appear only in topological systems, e.g., topological insulators and topological superconductors hosting Majorana fermions. In this work I will discuss edge states in topological and nontopological InAsBi quantum dots described by a confined Bernevig-Hughes-Zhang (BHZ) model – the paradigmatic two-band 2D insulator displaying a topological quantum phase transition.

Surprisingly we find that these BHZ dots exhibit protected helical edges states in both the topological and non-topological regimes [1]. This clearly contrasts the bulk-edge correspondence. Our calculated transport properties, e.g., two-terminal conductance, are essentially identical in both regimes. Hence our findings blur the boundaries between topological and non-topological phenomena in small systems.

I should also touch upon Chern insulators and nodal semimetals, which display trivial edge states not arising from band topology [2], skyrmionic textures, resulting from the excitation of crossed persistent spin helices in ordinary GaAs wells [3] and the concept of stretchable helices [4] in these wells. This work has been supported by FAPESP, CNPq and Capes.

[1] D. R. Candido, M. E. Flatté and J. C. Egues, Phys. Rev. Lett. 121, 256804 (2018).

[2] D. R. Candido, M. Kharitonov, J. C. Egues, and E. Hankiewicz, Phys. Rev. B 98, 161111(R) (2018), (Editors’ Suggestion).

[3] J. Fu. P. H. Penteado, M. O. Hachiya, D. Loss, and J. C. Egues, Phys. Rev. Lett. 17, 226401 (2016).

[4] F. Dettwiler, J. Fu, S. Mack, Pirmin J. Weigele, J. C. Egues, D. D. Awschalom, and D. M. Zumbühl, Phys. Rev. X 7, 031010 (2017).