**Probing spin helical surface states in topological HgTe nanowires** - Johannes Ziegler

The Dirac-like surface states of an ideal topological insulator nanowire form a conducting cylinder around an insulating bulk. A magnetic field applied along the wire axis modifies the 1D subband structure and results in Aharonov-Bohm oscillations. The band structure exhibits a gap for zero magnetic flux phi=0 and gapless states for half a flux quantum phi_0=h/e, which constitutes a switching from topological to trivial band structure.
Magnetotransport experiments of gated nanowires fabricated from 80 nm strained HgTe along with a theoretical analysis are presented. The widths of investigated wires range from 160 to 310 nm, with lengths of 1-2 µm. We observe phi_0=h/e periodic conductance oscillations, clearly indicating that transport is quasi-ballistic. A quantitative analysis of the gate-induced oscillations, reflecting the subband spacing, demonstrates the topological nature of the surface states.