Effects of the Antiferromagnetic Spin Coupling and Interdot Coulomb Repulsion on Kondo Effects in Serial Double Quantum Dots

We theoretically study the effects of the antiferromagnetic (AF) spin coupling and the interdot Coulomb repulsion on the Kondo effects in serial double quantum dots by means of the slave-boson mean-field approximation. Our results indicate that in the weak coupling regime, the AF spin coupling strengthens the Kondo resonance, while the interdot Coulomb repulsion suppresses them for the equilibrium case. In the non-equilibrium case, the AF spin coupling strengthens the Kondo resonance only when J>2.5T_K⁰, while the interdot Coulomb repulsion does not suppress Kondo peaks. In the strong coupling regime, the bias voltage has no effects on the Kondo resonance in this system, and the AF spin coupling increases the height of Kondo peaks only when J<2.5T_K⁰. However, the inter-dot Coulomb repulsion suppresses the spin Kondo effect, which induces the orbit Kondo effect. Moreover, the relevant underlying physics of these problems are discussed.