Strongly correlated regimes in a double quantum dot device

The transport properties of a double quantum dot device with one of the dots coupled to perfect conductors are analyzed using the numerical renormalization group technique and slave-boson mean-field theory. The coupling between the dots strongly influences the transport through the system, leading to a nonmonotonic dependence of the conductance as a function of the temperature and the magnetic field. For small interdot coupling and parameters such that both dots are in the Kondo regime, there is a two-stage screening of the dot’s magnetic moments that is reflected in the conductance. In an intermediate-temperature regime Kondo correlations develop on one of the dots and the conductance is enhanced. At low temperatures the Kondo effect takes place on the second dot, leading to a singlet ground state in which the conductance is strongly suppressed.

Figure 1

(Color online) Schematic representation of the device. A QD molecule with only one of the dots coupled to the leads.

Figure 2

(Color online) Magnetic moment of the DQDD as a function of the temperature for different values of the interdot coupling. From top to bottom, $t_{ab}=0$, $t_{ab}=0.002–0.0046$ in steps of 0.0002, and $t_{ab}=0.02$. Parameters are $U=0.5$, $\epsilon =-0.25$, and $\Delta =0.035$. Inset: binding energy of the $a\text{−}b$ singlet $T_{ab}$ estimated using the NRG (see text). The solid line is a fit based on Eq. (30).

Figure 3

Spectral density of dot $a$ at $T=0$. Parameters are $U=0.5$, $\Delta =0.035$, and $t_{ab}=0.0022$. The broadened atomic levels of dot $a$ are clearly seen at $\omega =\pm U∕2$. The left inset shows the central Kondo peak of width $T_K^0\sim 7\times {10}^{-4}$. The right inset shows the Kondo hole of width $T_0\sim 1.78\times {10}^{-10}$.

Figure 4

Upper panel: magnetic moment of the DQDD at zero field as a function of temperature for $t_{ab}=0.003$. The other parameters are as in Fig. 2. Lower panel: conductance through the device at zero field as a function of the temperature. Three regimes can be clearly seen both in the conductance and the magnetic moment.

Figure 5

(Color online) Upper panel: magnetic moment of the DQDD as a function of magnetic field at $T=0$. Lower panel: conductance as a function of the magnetic field at low temperatures. Inset: field dependence of the $T=0$ conductance. The coupling between the dots $t_{ab}=0.003$. The other parameters are as in Fig. 2.

Figure 6

Conductance through the double dot system as a function of the gate voltage $V_g=-{\epsilon }_a=-{\epsilon }_b=-\epsilon$ and different temperatures. Parameters are $U_a=U_b=0.25$, $t_{ab}=0.025$, and $\Delta =0.125$.

Figure 7

Same as in Fig. 6 but for a different set of parameters: $U_a=U_b=0.5$, $t_{ab}=0.05$, and $\Delta =0.063$.

Figure 8

Same as in Fig. 7 but for $t_{ab}=0.25$. The curves correspond to temperatures ranging from $9.2\times {10}^{-3}{T}_K^0$ to $18.4T_K^0$ from bottom to top (in the central region). Each curve corresponds to a temperature that is twice as high as that of the previous one.