Non-Equilibrated Counter Propagating Edge Modes in the Fractional Quantum Hall Regime

TL;DR

This paper presents evidence of non-equilibrated counter-propagating edge modes in short fractional quantum Hall regions, revealing conductance behaviors that suggest the presence of upstream neutral modes and non-equilibrated channels.

Contribution

It demonstrates the existence of non-equilibrated counter-propagating edge channels in short fractional quantum Hall regions, including at ${ u}=1/3$, which was previously unobserved due to short equilibration lengths.

Findings

Observation of conductance approaching $G_Q=e^2/h$ in fractional regions.

Evidence of upstream neutral modes coexisting with downstream modes.

Detection of non-equilibrated ${ u}=1$ channels in short fractional regions.

Abstract

It is well established that 'density reconstruction' at the edge of a two dimensional electron gas takes place for 'hole-conjugate' states in the fractional quantum Hall effect (such as ${\nu}=2/3, 3/5,$ etc.). Such reconstruction leads, after equilibration between counter propagating edge channels, to a downstream chiral current edge mode accompanied by upstream chiral neutral modes (carrying energy without net charge). Short equilibration length prevented thus far observation of the counter propagating current channels - the hallmark of density reconstruction. Here, we provide evidence for such non-equilibrated counter-propagating current channels, in short regions $(l=4{\mu}m$ and $l=0.4{\mu}m)$ of fractional filling ${\nu}=2/3$, and, unexpectedly, ${\nu}=1/3$, sandwiched between two regions of integer filling ${\nu}=1$. Rather than a two-terminal fractional conductance, the conductance exhibited a significant ascension towards unity quantum conductance $(G_Q=e^2/h)$ at or near the fractional plateaus. We attribute this conductance rise to the presence of a non-equilibrated downstream ${\nu}=1$ channel in the fractional short regions.