Identification of massive and topological surface states in the 3D topological insulator tensile strained HgTe

Topological surface states (TSS) with their linear dispersion and spin momentum locking constitute an interesting playground for basic research and future applications and have been identified in the topological insulator tensilely strained HgTe by magnetotransport measurements [1]. While the TSS are created due to the inversion of the bulk bands, additional surface states of different origin have been reported in gated devices of the topological insulator and the Dirac semi-metal phase of HgTe [2, 3]. These additional surface states are formed due to the shape of the electrochemical potential introduced by the electric field of the gate and are of general interest, since they can also be present in other topological materials. They are called massive Volkov-Pankratov states (VPS) after their first report in Ref. [4].
Here we present the unambiguous identification and manipulation of the different surface states, namely the TSS and the massive VPS, in the topological insulator HgTe by means of magnetotransport using top- and backgated devices as well as modulation doping.

[1] C. Brüne, et al. PRL 106, 126803 (2011)
[2] A. Inhofer, et al. PRB 96, 195104 (2017)
[3] D. M. Mahler, et al. Phys. Rev. X 9, 031034 (2019)
[4] B. A. Volkov and O. A. Pankratov, JETP Lett. 42, 4 (1985)