Classification of coherent peaks in two-terminal quantum devices into normal and anomalous Kondo peaks

TL;DR

This paper classifies coherent peaks in two-terminal quantum devices into normal and anomalous Kondo peaks based on spin dynamics and scaling functions, providing a new framework for understanding zero-bias peaks in quantum transport.

Contribution

It introduces a novel classification scheme for Kondo peaks in quantum devices, distinguishing normal and anomalous types by their spin dynamics and scaling behavior.

Findings

Normal Kondo peaks involve spin exchange and have scaling temperature equal to half FWHM.

Anomalous Kondo peaks arise without spin exchange and have different scaling properties.

Reproduced experimental conductance line shapes support the classification.

Abstract

Coherent peaks arising in the differential conductance of quantum dot (QD) and quantum point contact (QPC) devices are classified into two categories, normal and anomalous Kondo peaks, according to the underlying spin dynamics and the form of the scaling function to which the scaled temperature-dependent linear conductance collapses. The zero-bias peaks (ZBPs) observed in QPCs and in the triplet state of the even sector of quantum dot single-electron transistors (QDSETs) are identified as normal Kondo peaks, formed by spin dynamics involving spin exchange, a symbolic characteristic of the Kondo effect. For these ZBPs, the scaling temperature coincides with half the full width at half maximum (FWHM). In contrast, the ZBP observed in the odd sector of QDSETs and all finite-bias coherent peaks, including the coherent side peaks of QPCs and the split ZBP in the singlet state of the QDSET even sector, are identified as anomalous Kondo peaks, because they arise from spin dynamics without spin exchange, and their scaling temperature does not coincide with half the FWHM. To support these findings, we reproduce gate-voltage-dependent differential conductance line shapes measured in the odd sector of a QDSET, demonstrating that its ZBP originates from a combination of two coherent side peaks explicitly observed in QPCs.