The Transmission Phase Shift of a Quantum Dot with Kondo Correlations

Jan von Delfta, Ulrich Gerlanda, Theo Costib, and Yuval Oregc
a Institut fuer Theoretische Festkoerperphysik, Universitaet Karlsruhe, D-76128 Karlsruhe, Germany
b Theoretische Physik III, Universitaet Augsburg, 86135 Augsburg, Germany
cLyman Laboratory of Physics, Harvard University, Cambridge MA 02198, USA
vondelft@tfp-physik.uni-karlsruhe.de

The Kondo effect, which occurs in metals containing magnetic impurities, has been studied for more than thirty years, yet one of its most fundamental properties has so far eluded direct experimental verification: at sufficiently low temperatures, a conduction electron scattering off a spin-1/2 impurity is predicted [1,2,3] to experience a resonance phase shift of pi/2, without any phase randomization. A direct observation of this phase shift, not possible in bulk systems, has now become feasible using quantum dots, due to two recent experimental breakthroughs: Kondo-type correlations were observed in dots strongly coupled to leads [4-8], and the transmission phase shift of a dot was measured by Aharanov-Bohm interferometry [9,10]. By combining these two experiments, it should be possible to directly measure the transmission phase shift of a Kondo-correlated dot -- this would elucidate phase-coherent transport of electrons traversing a strongly-interacting environment (the dot-lead system) that is tunable from being uncorrelated at high temperatures through a strongly-correlated crossover regime to a Fermi liquid at sufficiently low temperatures. I give a detailed introduction to the two types of experiments, and explain what could be expected to happen if they were combined, including how the pi/2 phase shift would manifest itself.

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