Magnetic Splitting of the Zero Bias Peak in a Quantum Point Contact with a Variable Aspect Ratio

TL;DR

This study investigates a zero-bias peak in a quantum point contact that splits under magnetic field, revealing spin-related mechanisms distinct from the Kondo effect, with detailed experimental validation of Zeeman energy correlation.

Contribution

It demonstrates the magnetic splitting of the zero-bias peak in a QPC and distinguishes its origin from the conventional Kondo effect, supported by precise Zeeman energy measurements.

Findings

Zero-bias peak splits in magnetic field matching Zeeman energy

Peak is independent of gate voltage, indicating spin involvement

The mechanism differs from the Kondo effect in quantum dots

Abstract

We report a zero-bias peak in the differential conductance of a Quantum Point Contact (QPC), which splits in an external magnetic field. The peak is observed over a range of device conductance values starting significantly below $2e^2/h$. The observed splitting closely matches the Zeeman energy and shows very little dependence on gate voltage, suggesting that the mechanism responsible for the formation of the peak involves electron spin. Precision Zeeman energy data for the experiment are obtained from a separately patterned single-electron transistor located a short distance away from the QPC. The QPC device has four gates arranged in a way that permits tuning of the longitudinal potential, and is fabricated in a GaAs/AlGaAs heterostructure containing 2-dimenional electron gas. We show that the agreement between the peak splitting and the Zeeman energy is robust with respect to moderate distortions of the QPC potential. We also show that the mechanism that leads to the formation of the ZBP is different from the conventional Kondo effect found in quantum dots.