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Dresden 2003 – scientific programme

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HL: Halbleiterphysik

HL 17: Symposium Quantenringe

HL 17.2: Talk

Tuesday, March 25, 2003, 11:30–12:00, POT/81

Fractional Aharonov-Bohm oscillations in a Kondo correlated few-electron quantum ring — •U. F. Keyser1, C. Fühner1, R. J. Haug1, W. Wegscheider2, and M. Bichler31Institut für Festkörperphysik, Universität Hannover — 2Angewandte und Experimentelle Physik, Uni Regensburg, D-92040 Regensburg — 3Walter Schottky Institut, TU München, D-85748 Garching

We investigate a small quantum ring (electronic diameter ∼ 300 nm) fabricated by local oxidation with an atomic force microscope [1]. For high 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. With transport spectroscopy in a perpendicular magnetic field we show that we can tune the electron number on our small quantum ring between three and seven electrons [2]. The well-known Aharonov-Bohm effect leads to transitions between ground states of a ring structure with every flux quantum h/e added. 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 density. When our device contains only five electrons, we observe in our experiment a level transition when about a fifth of a flux quantum is added to the ring area [2]. These frequent level transitions lead also to a modulation of the Kondo conductance in our small quantum ring. [1] U. F. Keyser et al., Semicon. Sci. Technol. 17, L22 (2002). [2] U. F. Keyser et al., cond-mat/0206262.

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