Quantum interference and sharp spin polarization on a double quantum dot: Role of the Rashba spin-orbit interaction

We analyze the spin-dependent conductance spectrum of a double quantum dot with Rashba spin-orbit and electron-electron interactions based on the Keldysh nonequilibrium Green's function formalism. A clear physical picture emerges from the single-particle analysis of electron-transfer pathways in a quantum dot molecule. It provides an insight into the mechanism that underlies the evolution of bonding resonances. This study demonstrates both numerically and analytically that the mechanism of quantum interference is altered, as either component of the Rashba spin-orbit interaction is modulated. Most importantly, the bonding state can be controlled by tuning the Rashba parameter: a bound state in the continuum becomes unbound upon gate control and vice versa, mediated by the transverse Rashba spin-orbit component. A spin-polarized current is shown to be produced by the interplay of the spin-resolved interference effect with the magnetic flux. Sharp spin polarization that arises from the negative differential conductance, observed over a wide range of values of relevant parameters, is discussed.

Figure 1

Double quantum dot with Rashba spin-orbit interaction and onsite Coulomb repulsion, coupled laterally to leads denoted as $L$ and $R$.

Figure 2

Consider $V=0.02$, $U=2$, and $k_{B}T=0.02$. (a) Conductance spectrum for ${\varphi }_1={\varphi }_2=1.3687$. Differential conductance with ${\varepsilon }_1={\varepsilon }_2\equiv \varepsilon$ for (b) ${\varphi }_1={\varphi }_2$, (c) fixed ${\varphi }_2=1.3687$, and (d) ${\varphi }_1={\varphi }_2=1.3687$. Corresponding $t_{d_1{d}_2}^R=0.4\exp \left(0.2021\right)$ in (a), (c), and (d).

Figure 3

Consider $V=0.02$, $U=2$, $k_{B}T=0.02$, $t_{d_1{d}_2}^R=0.4\exp \left(0.2021\right)$, and fixed ${\varphi }_2=1.3687$. (a) Differential conductance with ${\varepsilon }_1={\varepsilon }_2\equiv \varepsilon$ for ${\varphi }_1=2$ and ${\varphi }_M=\pi /4$. (b) Spin polarization for ${\varphi }_M=\pi /4$, and the sum and difference of spin-dependent conductance in (a), denoted as s and d, respectively, plotted in the inset. (c) Conductance difference $G_{\uparrow }-G_{\downarrow }$ for ${\varphi }_1=2$. (d) Electron occupation on the first dot for ${\varphi }_M=\pi /4$. Dashed lines in (a) and inset in (b) indicate the zero conductance.