  Magneto-transport measurements on gated high mobility heterostructures
containing a 60 nm layer of tensile strained HgTe, a three-dimensional
topological insulator, show well-developed Hall quantization from surface
states both in the n- as well as in the p-type regime. While the n-type
behavior is due to transport in the topological surface state of the material,
we find from 8-orbital k.p calculations that the p-type transport results from
massive Volkov-Pankratov states. Their formation prevents the Dirac point and
thus the p-conducting topological surface state from being accessible in
transport experiments. This interpretation is supported by low-field
magneto-transport experiments demonstrating the coexistence of n-conducting
topological surface states and p-conducting Volkov-Pankratov states at the
relevant gate voltages.

Mesoscale and Nanoscale Physics