Kondo effect in a side-coupled double-quantum-dot system embedded in a mesoscopic ring

Details Kondo effect in a side-coupled double-quantum-dot system embedded in a mesoscopic ring Kondo effect in a side-coupled double-quantum-dot system embedded in a mesoscopic ring

2009-08-05

arxiv.org/abs/0908.0589v2

Phys. Rev. B 81, 195305 (2010)

Physics

Condensed Matter

Mesoscale and Nanoscale Physics

17 pages, 12 figures, references and additional affiliation added

Scientific paper

We study the finite size effect of the Kondo screening cloud in a double-quantum-dot setup via a large-N slave-boson mean-field theory. In this setup, one of the dots is embedded in a close metallic ring with a finite size $L$ and the other dot is side-coupled to the embedded dot via an anti-ferromagnetic spin-spin exchange coupling with the strength K. The antiferromagnetic coupling favors the local spin-singlet and suppresses the Kondo screening. The effective Kondo temperature T_k (proptotional to the inverse of the Kondo screening cloud size) shows the Kosterlitz--Thouless (KT) scaling at finite sizes, indicating the quantum transition of the KT type between the Kondo screened phase for K < K_c and the local spin-singlet phase for K > K_c in the thermodynamic limit with K_c being the critical value. The mean-field phase diagram as a function of 1/L and K shows a crossover between Kondo and local spin-singlet ground states for K < K_c (L=4n, 4n+1, 4n+3) and for K>K_c (L=4n+2). To look into the crossover region more closely, the local density of states on the quantum dot and the persistent current at finite sizes with different values of $K$ are also calculated.

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