Mesoscopic Kondo effect of a quantum dot embedded in an Aharonov-Bohm ring with intradot spin-flip scattering

– We study the Kondo effect in a quantum dot embedded in a mesoscopic ring taking into account intradot spin-flip scattering R. Based on the finite-U slave-boson mean-field approach, we find that the Kondo peak in the density of states is split into two peaks by this coherent spin-flip transition, which is responsible for some interesting features of the Kondo-assisted persistent current circulating the ring: (1) strong suppression and crossover to a sine function form with increasing R; (2) appearance of a “hump” in the R-dependent behavior for odd parity. R-induced reverse of the persistent current direction is also observed for odd parity. Intensive attention has been paid to the Kondo effect in a quantum dot (QD), [1, 2] in which formation of a bound state between the local spin and conduction electrons induces a Kondo peak in the density of states (DOS) at the Fermi level EF, consequently leading to strong enhancement of the linear conductance ultimately to the ideal value 2e/h below the bulk Kondo temperature T 0 K. Associated with this energy scale, the characteristic length of the bound state wave-function, the so-called Kondo screening cloud defined as ξ K ≈ h̄vF/T 0 K (vF is the Fermi velocity), is itself mesoscopic size (of the order of 1 μm). The easy control of major parameters of these artificial atoms in a wide range makes it possible to study the Kondo effect even when the size of the lead is comparable to the size of screening cloud ξ K. Recently, Affleck and Simon [3] suggested that the setup of a QD embedded in a closed mesoscopic Aharonov-Bohm (AB) ring is an ideal tool to detect this cloud because their perturbation calculations found that the persistent current (PC) in such a geometry is a universal scaling function of ξ K/L (L is the ring circumference), and crosses over from the saw-tooth of perfect ring in the limit ξ K/L ≪ 1 to a sine function with vanishing magnitude at ξ K/L ≫ 1. Besides, slave-boson mean-field (SBMF) evaluation disclosed that this finite size effect affects drastically the Kondo resonance in a way that depending on the