Counter-propagating charge transport in the quantum Hall effect regime

TL;DR

This paper investigates charge transport in the quantum Hall regime, revealing upstream charge currents in hole-conjugate states, challenging the traditional downstream-only picture and highlighting the role of upstream modes in certain conditions.

Contribution

It provides experimental evidence of upstream charge transport in the $ u=2/3$ hole-like state, demonstrating a departure from the conventional chiral edge mode model.

Findings

Upstream charge current observed in spin-unpolarized $ u=2/3$ state.

Upstream modes are significant at short propagation distances.

Traditional downstream-only transport does not hold for all quantum Hall states.

Abstract

The quantum Hall effect, observed in a two-dimensional electron gas subjected to a perpendicular magnetic field, imposes a 1D-like chiral, downstream, transport of charge carriers along the sample edges. Although this picture remains valid for electrons and Laughlin's fractional quasiparticles, it no longer holds for quasiparticles in the so-called hole-conjugate states. These states are expected, when disorder and interactions are weak, to harbor upstream charge modes. However, so far, charge currents were observed to flow exclusively downstream in the quantum Hall regime. Studying the canonical spin-polarized and spin-unpolarized $\nu=2/3$ hole-like states in GaAs-AlGaAs heterostructures, we observed a significant upstream charge current at short propagation distances in the spin unpolarized state