Robust Integer and Fractional Helical Modes in the Quantum Hall Effect

Electronic systems harboring one-dimensional helical modes, where spin and momentum are locked, have lately become an important objective. When coupled to a conventional superconductor, such systems are expected to manifest topological superconductivity; a unique phase hosting Majorana zero modes. Even more interesting are fractional helical modes, yet to be observed, which open the route for realizing generalized para-fermions. Possessing non-abelian exchange statistics, these quasiparticles may serve as building blocks in topological quantum computing. Here, we present a new approach to form protected helical and fractional helical modes in the quantum Hall regime. The novel platform is based on a carefully designed double-quantum-well structure in a GaAs based system hosting two electronic sub-bands; each tuned to the quantum Hall regime. By gating different areas of the system, counter-propagating integer as well as fractional edge modes with opposite spins are formed. We demonstrate that due to spin protection, these helical modes remain ballistic for large distances. In addition to formation of helical modes, this platform can serve as a rich playground for artificial induction of compounded fractional edge modes, and for construction of edge modes based interferometers.