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HL: Halbleiterphysik
HL 12: Quantenpunkte und -dr
ähte: Transporteigenschaften II
HL 12.3: Vortrag
Montag, 24. März 2003, 15:45–16:00, POT/81
Transmission phase in a ring interferometer with two quantum dots — •Martin Sigrist1, Andreas Fuhrer1, Thomas Ihn1, Klaus Ensslin1, Werner Wegscheider2, and Max Bichler3 — 1Solid State Physics Laboratory, ETH Hönggerberg, CH-8093 Zürich — 2Inst. f. angew. und exp. Physik, Univ. Regensburg , 93040 Regensburg — 3Walter Schottky Institut, TU München, Am Coulombwall, 85748 Garching
We report transport measurements on a quantum ring interferometer fabricated by AFM-lithography on a Ga[Al]As heterostructure. Individual Coulomb-blockaded quantum dots can be induced by plunger gates in each of the two interfering paths. Four terminal measurements have been performed with the aim of studying the relative transmission phase.
The 1 µm ring is investigated at a temperature of 50 mK. The conductance exhibits h/e-periodic Aharonov-Bohm oscillations in a magnetic field applied normal to the ring plane. In a symmetric four-terminal configuration, the transmission phase of h/e-periodic oscillations is investigated with a single quantum dot induced in each of the interfering paths. Clear phase shifts in the oscillations are measured across a Coulomb peak of one dot while keeping the other dot on a conductance peak. The overall behaviour of the phase in such measurements is a monotonous increase of the phase by about π in agreement with resonant tunnelling arguments. Phase shifts are also investigated in the situation when both dots are tuned through a Coulomb resonance simultaneously. The results agree qualitatively with the expected phase shift of 0 and 2π depending on the sweep direction.