Nonequilibrium Spintronic Transport through an Artificial Kondo Impurity: Conductance, Magnetoresistance, and Shot Noise

We investigate the nonequilibrium transport properties of a quantum dot when spin flip processes compete with the formation of a Kondo resonance in the presence of ferromagnetic leads. Based upon the Anderson Hamiltonian in the strongly interacting limit, we predict a splitting of the differential conductance when the spin flip scattering amplitude is of the order of the Kondo temperature. We discuss how the relative orientation of the lead magnetizations strongly influences the electronic current and the shot noise in a nontrivial way. Furthermore, we find that the zero-bias tunneling magnetoresistance becomes negative with increasing spin flip scattering amplitude.

Figure 1

(a) Differential conductance $\mathcal{G}$ versus bias voltage $V_{\mathrm{d}\mathrm{c}}$ in the parallel case with lead magnetizations ${\eta }_L={\eta }_R=\eta =0.5$ for four different values of the spin flip amplitude $R$. (b) Dependence of the $\mathcal{G}–V_{\mathrm{d}\mathrm{c}}$ curves on $\eta$ for $R=0.75T_K^0$. Inset: Kondo temperature of the QD ($T_K$) as a function of $R$ for the lead polarizations depicted in (b). The crossing points with the straight line $T_K=R$ mark the transition to a nonzero splitting in $\mathcal{G}(V_{\mathrm{d}\mathrm{c}})$.

Figure 2

(a) $\mathcal{G}–V_{\mathrm{d}\mathrm{c}}$ curves in the antiparallel case for ${\eta }_L=-{\eta }_R=0.5$ and different values of $R$. Inset: $T_K$ as a function of $R$. Notice that this curve is independent of $\eta$ so that the transition to the splitting in $\mathcal{G}(V_{\mathrm{d}\mathrm{c}})$ takes place at the same point independently on the value of $\eta$. (b) Tunneling magnetoresistance $M$ at $\eta =0.5$ as a function of the bias voltage $V_{\mathrm{d}\mathrm{c}}$ for the first four values of $R$ plotted in Fig. 2a.

Figure 3

Fano factor versus bias voltage as a function of $R$ for the parallel alignment with ${\eta }_L={\eta }_R=0.5$. (b) Voltage dependence of the shot noise for the unpolarized, parallel, and antiparallel case at $R=0$. Inset: Transmission probability as a function of energy (the origin is taken at $E_F=0$) for the same values of $R$ as in (a).