Interference effects on Kondo-assisted transport through double quantum dots

We systematically investigate electron transport through double quantum dots with particular emphasis on interference induced via multiple paths of electron propagation. By means of the slave-boson mean-field approximation, we calculate the conductance, the local density of states, and the transmission probability in the Kondo regime at zero temperature. It is clarified how the Kondo-assisted transport changes its properties when the system is continuously changed among the serial, parallel and T-shaped double dots. The obtained results for the conductance are explained in terms of the Kondo resonances influenced by interference effects. We also discuss the impacts due to the spin-polarization of ferromagnetic leads.

Figure 1

DQD system connected by the interdot tunneling $t_c$: ${\Gamma }_{m,m\sigma }^{\alpha }$ ($\alpha =L,R$ and $m=1,2$) represents the resonance width due to transfer between the $m\text{th}$ dot and the $\alpha \text{th}$ lead for an electron with spin $\sigma$. By changing the ratio of tunneling amplitudes, we continuously change the system among the serial, parallel and T-shaped DQD.

Figure 2

(a) Serial DQD system, which is a special case of Fig. 1 $({\Gamma }_{1,1\sigma }^R={\Gamma }_{2,2\sigma }^L=0)$. (b) T-shaped DQD system realized at${\Gamma }_{2,2\sigma }^L={\Gamma }_{2,2\sigma }^R=0$ in Fig. 1.

Figure 3

Linear conductance as a function of $x={\Gamma }_{1,1\sigma }^R={\Gamma }_{2,2\sigma }^L$, where we set ${\Gamma }_{2,2\sigma }^R={\Gamma }_{1,1\sigma }^L=1$.

Figure 4

(a)DOS for $t_c=1.5$: $x=0.2$, 0.5, and 0.8. Inset shows the DOS at $x=0$. (b) The transmission probability $T\left(\epsilon \right)$ for $t_c=1.5$. (c) Enlarged picture of (b) around $\epsilon =0$.

Figure 5

Linear conductance as a function of the spin-polarization strength $p$ for $t_c=1.5$ and $x=0.8$. The contribution from up-spin and down-spin electrons is also shown.

Figure 6

(a) DOS of up-spin and down-spin electrons connected to normal leads $(p=0)$ and ferromagnetic leads $(p=0.6)$. We assume $t_c=1.5$ and $x=0.8$. Inset: Enlarged picture around $\epsilon =0$. (b) Transmission probability $T\left(\epsilon \right)$ of up-spin and down-spin electrons.

Figure 7

DOS of (a) dot-1 and (b) dot-2 around the Fermi energy. (c) The corresponding transmission probability $T\left(\epsilon \right)$. We set $t_c=2$ and ${\epsilon }_1={\epsilon }_2=-3.0$.

Figure 8

DOS of the dot-1 for the T-shaped DQD $(y=0)$: (a) ${\epsilon }_2=-3.0$ and (b) ${\epsilon }_1=-3.0$. The interdot coupling is chosen as $t_c=2.0$.

Figure 9

Linear conductance as a function of the bare energy level: we change ${\epsilon }_1$ (filled circles), by keeping ${\epsilon }_2=-3.0$ fixed, while we change ${\epsilon }_2$ (open circles) by keeping ${\epsilon }_1=-3.0$ fixed. The interdot coupling for these plots is $t_c=2.0$. For reference we plot the conductance for the single dot system $(t_c=0)$ as filled triangles.

Figure 10

DOS of the dot-1 for the T-shaped DQD: nonpolarized leads $(p=0)$ and spin-polarized leads $(p=0.8)$. We choose ${\epsilon }_1=-1.5$, ${\epsilon }_2=-3.0$, and $t_c=2.0$. Inset: DOS of the dot-1 drawn in a wider energy range.

Figure 11

Linear conductance as a function of the strength of the spin-polarization $p$. The contribution from up-spin and down-spin electrons is also shown.