Half-integer conductance plateau at the $\nu = 2/3$ fractional quantum Hall state in a quantum point contact

TL;DR

This study observes a robust half-integer conductance plateau at 0.5 e^2/h in a quantum point contact at the ν=2/3 fractional quantum Hall state, supporting a model of edge mode transition influenced by confining potential sharpness.

Contribution

It demonstrates the emergence of a half-integer conductance plateau at ν=2/3, providing experimental evidence for edge mode structure transition based on confining potential sharpness.

Findings

Robust 0.5 e^2/h conductance plateau observed in multiple QPCs.

The plateau is consistent with full reflection of an inner -1/3 edge mode.

Different heterostructure with softer confinement shows a 1/3 e^2/h plateau.

Abstract

The $\nu = 2/3$ fractional quantum Hall state is the hole-conjugate state to the primary Laughlin $\nu = 1/3$ state. We investigate transmission of edge states through quantum point contacts fabricated on a GaAs/AlGaAs heterostructure designed to have a sharp confining potential. When a small but finite bias is applied, we observe an intermediate conductance plateau with $G = 0.5 \frac{e^2}{h}$. This plateau is observed in multiple QPCs, and persists over a significant range of magnetic field, gate voltage, and source-drain bias, making it a robust feature. Using a simple model which considers scattering and equilibration between counterflowing charged edge modes, we find this half-integer quantized plateau to be consistent with full reflection of an inner counterpropagating -1/3 edge mode while the outer integer mode is fully transmitted. In a QPC fabricated on a different heterostructure which has a softer confining potential, we instead observe an intermediate conductance plateau at $G = \frac{1}{3} \frac{e^2}{h}$. These results provide support for a model at $\nu = 2/3$ in which the edge transitions from a structure having an inner upstream -1/3 charge mode and outer downstream integer mode to a structure with two downstream 1/3 charge modes when the confining potential is tuned from sharp to soft and disorder prevails.