The Kondo effect in a one- and two-electron quantum dot

We study the Kondo effect in a vertical quantum dot holding only one- or two-electrons. We observe clear Kondo features in the temperature and bias voltage dependence of the conductance when there is only one electron in the dot (spin S=1/2). The estimated Kondo temperature is much higher than in previous reports due to large dot-lead tunnel coupling on the order of View the MathML source. We also observe a Kondo enhancement of the conductance when the two-electron ground state makes a transition from a spin singlet (S=0) to a triplet (S=1) at a magnetic field of View the MathML source. The bias voltage dependence of the differential conductance at this transition field shows weak features that may be related to the Zeeman splitting of the triplet state.