Who: Cosimo Gorini, Universitšt Regensburg
Place: Donostia International Physics Center
Date: Tuesday, 11 September 2018, 12:00
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 superconductivity. 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 ?m when tuning the wires into the bulk gap, so as to single out topological transport. 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 quasiballistic 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 magnetoconductance with simulations of the electrostatics, accounting for the gate-induced inhomogeneous 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.
We also discuss the magneto-conductance through shaped (tapered, curved) nanowires. The nanowire non-constant radius implies a competition between effects due to quantum confinement and to a spatially varying enclosed magnetic flux, and offers the possibility of studying quantum Hall physics in curved space.
Host: Dario Bercioux