Fractional Aharonov-Bohm Oscillations in a Kondo Correlated Few-Electron Quantum Ring

Abstract

We investigate a small quantum ring fabricated by local oxidation with an atomic force microscope. For strong tunnel coupling to the leads we observe a Kondo-effect which shows the temperature-, gate voltage-, and magnetic field dependence predicted for a spin-1/2 Anderson impurity. Using transport spectroscopy in a perpendicular magnetic field we prove that we can tune the electron number on our small quantum ring between one and seven electrons. The well-known Aharonov-Bohm effect leads to transitions between ground states of a ring structure separated by the flux quantum h/e. However, for our low electron numbers electron-electron interaction dominates the level spectrum. This leads to more frequent level crossings compared to devices with high electron densities. When our device contains only five electrons, we observe a level transition when about a fifth of a flux quantum is added to the ring area. These frequent level transitions lead also to a modulation of the Kondo conductance in our small quantum ring.