Transmission Phase of a Quantum Dot with Kondo Correlation near the Unitary Limit

The complex transmission amplitude of a quantum dot (QD) with Kondo correlation was measured near the unitary limit. The transmission phase was observed to evolve almost linearly over a range of about $1.5\pi$ when the Fermi energy was scanned through a spin degenerate energy level of the QD. Surprisingly, the phase in the Coulomb Blockade regime, with one more electron entering the dot, was strongly affected by a preexistence of Kondo correlation. These results suggest that a full explanation of the Kondo effect may go beyond the framework of the Anderson model.