Enhancement of Kondo Effect in Multilevel Quantum Dots(<SPECIAL TOPICS>Kondo Effect-40 Years after the Discovery)
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概要
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We theoretically study enhancement mechanisms of the Kondo effect in multilevel quantum dots. In quantum dots fabricated on semiconductors, the energy difference between discrete levels △ is tunable by applying a magnetic field. With two orbitals and spin 1/2 in the quantum dots, we evaluate the Kondo temperature T_K as a function of △, using the scaling method. T_K is maximal around △=0 and decreases with increasing |△|, following a power law, T_K(△)=T_K(0)・(T_K(0)/|△|)^γ, which is understood as a crossover from SU(4) to SU(2) Kondo effect. The exponents on both sides of a level crossing, γ_L and γ_R, satisfy a relation of γ_L・γ_R=1. We compare this enhanced Kondo effect with that by spin-singlet-triplet degeneracy for an even number of electrons, to explain recent experimental results using vertical quantum dots.
- 2005-01-15
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