Half-Integer Conductance Plateau at the ν=2/3 Fractional Quantum Hall State in a Quantum Point Contact.

Area of Science:

• Condensed Matter Physics
• Quantum Hall Effect

Background:

• The fractional quantum Hall effect (FQHE) exhibits exotic electronic states at low temperatures and high magnetic fields.
• The ν=2/3 FQHE state is the hole conjugate of the primary Laughlin ν=1/3 state.
• Understanding edge state behavior in FQHE is crucial for characterizing these states.

Purpose of the Study:

• To investigate the transmission properties of edge states in the ν=2/3 FQHE state through quantum point contacts (QPCs).
• To explore the influence of confining potential sharpness on edge state behavior.
• To validate theoretical models of FQHE edge states.

Main Methods:

• Fabrication of GaAs/AlGaAs heterostructures with sharp and soft confining potentials.
• Measurement of electrical conductance through QPCs at varying magnetic fields, gate voltages, and source-drain biases.
• Analysis of conductance plateaus and comparison with theoretical models.

Main Results:

• An intermediate conductance plateau at G=0.5(e^2/h) was observed in QPCs with sharp confining potentials.
• This plateau is a robust feature, persisting across various experimental parameters.
• In QPCs with softer potentials, an intermediate plateau at G=(1/3)(e^2/h) was observed.

Conclusions:

• The observed 0.5(e^2/h) plateau supports a model where an inner upstream -1/3 edge mode is fully reflected, while the outer integer mode is transmitted.
• The transition to a (1/3)(e^2/h) plateau in softer potentials suggests a change to two downstream 1/3 charge modes.
• These findings provide experimental evidence for the role of confining potential in determining FQHE edge state structure.