Controlling topologically protected states by external fields and doping

Topological materials often display topologically protected surface states with Dirac-like dispersions. Controlling their properties is desirable for their foreseen applications and a number of proposals have been put forward to this respect (e.g. [1,2,3,4]). In this contribution, the system I will consider is a topological boundary. I will discuss how applying uniform electric and magnetic fields that preserve the symmetries lead to an anisotropic reduction of the Fermi velocity as the fields are increased. [5,6]. I will also show how a δ-layer of donor atoms at the boundary can lead to a coexistence of a two-dimensional electron gas with the topological surface states. Moreover, the linear optical response is markedly reshaped by the presence of the topological state [7].

[1] Li, G. et al., Nat. Phys. 6, 109 (2010)
[2] Trambly de Laissardière et al., Nano Lett. 10, 804 (2010)
[3] P. D. C. King et al., Phys. Rev. Lett. 107, 096802 (2011)
[4] M. Bahramy et al., Nat. Commun. 3, 1159 (2012)
[5] A. Díaz-Fernández et al., Sci. Rep. 7, 8058 (2017)
[6] A. Díaz-Fernández et al., Beilstein J. Nanotechnol. 9, 1405 (2018)
[7] A. Díaz-Fernández et al., Phys. Rev. B 9