Precise period doubling of the Aharonov-Bohm effect in a quantum dot at high magnetic fields

We report a clear and sudden period doubling in the Aharonov-Bohm oscillations (ABO), observed in the low-temperature magneto-resistance of a small quantum dot. The doubling occurs over a well-defined range of magnetic field, outside of which the ABO revert back to their single period. The precise nature of the doubling is reflected in the Fourier spectra of the oscillations, and suggests an interpretation in terms of the single-particle energy-level spectrum of the dot.