Aharonov-Bohm effect of a quantum ring in the Kondo regime

We investigate a small tuneable quantum ring fabricated by direct local oxidation using an atomic force microscope. The device contains very few electrons and is tuned into the Kondo regime. We study this Kondo effect by temperature dependent measurements. At finite bias voltages we observe additional peaks. These vanish with increasing temperature indicating Kondo correlations for these excited states. Additionally, the geometry of our device allows to study Aharonov-Bohm oscillations in the Kondo regime for a device containing less than ten electrons. We observe a modulation of the Kondo effect with a reduced Aharonov-Bohm period explained by electron-electron interaction in our small quantum ring.