Optically controlled periodical chain of quantum rings

We demonstrated theoretically that a circularly polarized electromagnetic field substantially modifies electronic properties of a periodical chain of quantum rings. Particularly, the field opens band gaps in the electron energy spectrum of the chain, generates edge electron currents, and induces the Fano-like features in the electron transport through the finite chain. These effects create physical prerequisites for the development of optically controlled nanodevices based on a set of coupled quantum rings.

Figure 1

Sketch of the system under consideration: (a) The periodical chain of quantum rings irradiated by a circularly polarized electromagnetic wave with the electric field amplitude ${\tilde{E}}_0$. (b) The elementary cell of the chain consisting of a quantum ring with the radius $R$, two leads with the length $d/2$, and two quantum point contacts (QPCs). The arrows correspond to electron waves traveling in different ways with the amplitudes $A_{\pm },B_{\pm },C_{\pm },D_{\pm }$, and $T$ is the period of the chain.

Figure 2

Electron energy spectrum of the chain of GaAs-based quantum rings with the radius $R=30$ nm and the period $T=100$ nm in the presence of a circularly polarized electromagnetic field with the frequency $\omega =12\times {10}^{12}\mathrm{rad}/\mathrm{s}$.

Figure 3

Probability of electron transmission through a finite chain consisting of five quantum rings at the irradiation-induced phase shift ${\varphi }_0=\pi /9$. The shaded-green regions correspond to the band gaps in Fig. 2.

Figure 4

Distribution of electron density in the chain $\mathcal{R}={\mathcal{R}}_{+}-{\mathcal{R}}_{-}$ as a function of the irradiation-induced phase shift ${\varphi }_0$ at $kT=\pi /4$ for the four lowest energy bands pictured schematically in the lower insert, where ${\mathcal{R}}_{+}$ and ${\mathcal{R}}_{-}$ are the probabilities of the electron staying in the upper and lower segments of the rings, respectively. The upper insert shows the edge currents corresponding to the cases of ${\mathcal{R}}_{\pm }=1$.