Robust integer and fractional helical modes in the quantum Hall effect

TL;DR

This paper introduces a novel platform using double quantum wells in GaAs to create and study protected integer and fractional helical edge modes in the quantum Hall regime, with potential applications in topological quantum computing.

Contribution

The work demonstrates a new method to generate and control helical and fractional helical edge modes in quantum Hall systems using electrostatic gating in a double quantum well structure.

Findings

Helical modes remain ballistic over large distances due to spin protection.

Electrostatic gating enables formation of counter propagating integer and fractional edge modes.

Platform allows for artificial induction of fractional edge modes and interferometer construction.

Abstract

Electronic systems harboring one dimensional helical modes, where the spin and momentum of the electron are locked, have lately become an important field of its own. When coupled to a conventional superconductor, such systems are expected to manifest topological superconductivity, a unique phase that gives rise to exotic Majorana zero modes. Even more interesting are fractional helical states which have not been observed before and which open the route for the realization of the generalized para fermions quasiparticles. 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 one dimensional helical and fractional helical edge modes in the quantum Hall regime. The novel platform is based on a carefully designed double quantum well structure in a high mobility GaAs based system. In turn, the quantum well hosts two sub bands of 2D electrons, each tuned to the quantum Hall effect regime. By electrostatic gating of different areas of the structure, counter propagating integer, as well as fractional, edge modes, belonging to Landau levels with opposite spins are formed, rendering the modes helical. We demonstrate that due to spin protection, these helical modes remain ballistic, without observed mixing for large distances. In addition to the formation of helical modes, this new platform can be exploited as a rich playground for an artificial induction of compounded fractional edge modes, as well as construction of interferometers based on chiral edge modes.