Johannes Ziegler1 Raphael Kozlovsky1 Cosimo Gorini1 Klaus Richter1 Dieter Weiss1

1, Universität Regensburg, Regensburg, , Germany

Nanowires with helical surface states represent key prerequisites for observing and exploiting phase-coherent
topological conductance phenomena, such as spin-momentum locked quantum transport or topological super-
conductivity. We demonstrate in a joint experimental and theoretical study that gated nanowires fabricated from
high-mobility strained HgTe, known as a bulk topological insulator, indeed preserve the topological nature of
the surface states, that moreover extend phase-coherently across the entire wire geometry. The phase-coherence
lengths are enhanced up to 5 μm when tuning the wires into the bulk gap, so as to single out topological trans-
port. The nanowires exhibit distinct conductance oscillations, both as a function of the flux due to an axial
magnetic field, and of a gate voltage. The observed h/e-periodic Aharonov-Bohm-type modulations indicate
surface-mediated quasi-ballistic transport. Furthermore, an in-depth analysis of the scaling of the observed
gate-dependent conductance oscillations reveals the topological nature of these surface states. To this end we
combined numerical tight-binding calculations of the quantum magneto-conductance with simulations of the
electrostatics, accounting for the gate-induced inhomogenous charge carrier densities around the wires. We
find that helical transport prevails even for strongly inhomogeneous gating and is governed by flux-sensitive
high-angular momentum surface states that extend around the entire wire circumference.