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We theoretically study the Kondo effect in double quantum dots connected in parallel [1], using the scaling and NRG methods. The double quantum dots are capacitively coupled to each other, whereas they are attached to separate leads. The SU(4) Kondo effect is realized with an electron when the energy levels are matched between the quantum dots. We show that (i) the Kondo temperature T_K decreases with increasing |Δ, where Δ is the level separation between the dots, obeying a power law. This is due to the crossover from SU(4) to SU(2) Kondo effect. (ii) The exponent of the power law is not universal. This is an evidence of the marginal fixed point of SU(4) Kondo effect [2,3]. (iii) The conductance through one of the dots may show an anomalous behavior as a function of temperature T (e.g., increases, decreases and increases again with T) although the total conductance is a universal function of T/T_K.
[1] A. Huebel, J. Weis and K. von Klitzing, 17th International Conference on the Electronic Properties of Two-Dimensional Systems (EP2DS, 2007). [2] L. Borda et al., Phys. Rev. Lett. 90, 026602 (2003). [3] M. Eto, J. Phys. Soc. Jpn. 74, 95 (2005). |
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