Two-stage Kondo effect in a four-electron artificial atom

TL;DR

This paper investigates the two-stage Kondo effect in a four-electron artificial atom, revealing a narrow dip in conductance at zero bias and analyzing its dependence on temperature and magnetic field.

Contribution

It demonstrates the observation of the two-stage Kondo effect in a four-electron artificial atom and compares low energy scales derived from conductance measurements.

Findings

Observation of a Kondo peak with a narrow dip at zero bias.

Good agreement between temperature and magnetic field energy scales.

Discrepancy in voltage scale possibly due to nonequilibrium effects.

Abstract

An artificial atom with four electrons is driven through a singlet-triplet transition by varying the confining potential. In the triplet, a Kondo peak with a narrow dip at drain-source voltage V_ds=0 is observed. The low energy scale V_ds* characterizing the dip is consistent with predictions for the two-stage Kondo effect. The phenomenon is studied as a function of temperature T and magnetic field B, parallel to the two-dimensional electron gas. The low energy scales T* and B* are extracted from the behavior of the zero-bias conductance and are compared to the low energy scale V_ds* obtained from the differential conductance. Good agreement is found between kT* and |g|muB*, but eV_ds* is larger, perhaps because of nonequilibrium effects.