Transmission phase of a singly occupied quantum dot in the Kondo regime.

We report on the phase measurements on a quantum dot containing a single electron in the Kondo regime. Transport takes place through a single orbital state. Although the conductance is far from the unitary limit, we measure directly, for the first time, a transmission phase as theoretically predicted of pi/2. As the dot's coupling to the leads is decreased, with the dot entering the Coulomb blockade regime, the phase reaches a value of pi. Temperature shows little effect on the phase behavior in the range 30-600 mK, even though both the two-terminal conductance and amplitude of the Aharonov-Bohm oscillations are strongly affected. These results also suggest that previous phase measurements involved transport through more than a single level.

Zero-dimensional spin accumulation and spin dynamics in a mesoscopic metal island.

We have measured electron spin accumulation at 4.2 K and at room temperature in an aluminum island with all dimensions (400 nm x 400 nm x 30 nm) smaller than the spin relaxation length. For the first time, we obtain uniform spin accumulation in a four-terminal lateral device with a magnitude exceeding the Ohmic resistance in the island. By controlling the magnetization directions of the four magnetic electrodes that contact the island, we have performed a detailed study of the spin accumulation. Spin precession measurements confirm the uniformity of our system and provide an accurate method to extract the spin relaxation time.