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

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.

6+4 pages, 4+4 figures

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• Multiple Mechanisms for Emerging Conductance Plateaus in Fractional Quantum Hall States
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• Half-integer thermal conductance in the absence of Majorana mode
• Experimentally Motivated Order of Length Scales Affect Shot Noise
• Single electron interference and capacitive edge mode coupling generates ${\Phi }_0/2$ flux periodicity in Fabry-Perot interferometers
• Edge reconstruction of compressible Quantum Hall fluid in the filling fraction range 1/3 to 2/3
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• Collapse of edge reconstruction in compressible Quantum Hall fluid within filling fraction range 2/3 to 1