Electron phase shift at the zero-bias anomaly of quantum point contacts

TL;DR

This study provides phase-sensitive experimental evidence supporting the Kondo effect as the origin of the zero-bias anomaly in quantum point contacts, using a scanning gate microscope to observe a characteristic phase shift.

Contribution

First phase-sensitive measurement of the zero-bias anomaly in quantum point contacts, demonstrating a phase shift consistent with Kondo physics.

Findings

Observed a half-period shift in interference fringes within the zero-bias anomaly range

Behavior cannot be explained by single-particle models, indicating many-body effects

Provides experimental evidence supporting the Kondo effect as the cause of the zero-bias anomaly

Abstract

The Kondo effect is the many-body screening of a local spin by a cloud of electrons at very low temperature. It has been proposed as an explanation of the zero-bias anomaly in quantum point contacts where interactions drive a spontaneous charge localization. However, the Kondo origin of this anomaly remains under debate, and additional experimental evidence is necessary. Here we report on the first phase-sensitive measurement of the zero-bias anomaly in quantum point contacts using a scanning gate microscope to create an electronic interferometer. We observe an abrupt shift of the interference fringes by half a period in the bias range of the zero-bias anomaly, a behavior which cannot be reproduced by single-particle models. We instead relate it to the phase shift experienced by electrons scattering off a Kondo system. Our experiment therefore provides new evidence of this many-body effect in quantum point contacts.