Impurity effects on the Aharonov-Bohm optical signatures of neutral quantum-ring magnetoexcitons

We study the role of impurity scattering on the photoluminescence (PL) emission of polarized magnetoexcitons. We consider systems where both the electron and hole are confined on a ring structure (quantum rings) as well as on a type-II quantum dot. Despite their neutral character, excitons exhibit strong modulation of energy and oscillator strength in the presence of magnetic fields. Scattering impurities enhance the PL intensity on otherwise “dark” magnetic field windows and nonzero PL emission appears for a wide magnetic field range even at zero temperature. For higher temperatures, impurity-induced anticrossings on the excitonic spectrum lead to unexpected peaks and valleys on the PL intensity as function of magnetic field. Such behavior is absent on ideal systems and can account for prominent features in recent experimental results.

Figure 1

Schematic representation of a polarized neutral exciton in a quantum ring (top) and in a type-II quantum dot (bottom)

Figure 2

(Color online) Electron (red thick line) and hole (black thin line) energy levels as function of magnetic field for the unperturbed (top) and impurity-distorted (bottom) cases.

Figure 3

(Color online) Hole probability ground-state distribution for attractive (red line and insets) and repulsive (black line) impurities at ${\theta }_0=\pi ∕2$ (top panel) and two impurities at ${\theta }_0=\pi ∕2$ and ${\theta }_0=3\pi ∕2$ (bottom panel). Dashed line shows the uniform ${\left(2\pi \right)}^{-1}$ probability density for the unperturbed case.

Figure 4

(Color online) Excitonic energy levels as function of magnetic field on a type-II quantum dot for one impurity (left-hand side) and two symmetrical impurities (right-hand side). Some level crossings are restored in the symmetrical configuration, as indicated by arrows.

Figure 5

Photoluminescence intensity as function of magnetic field for unperturbed (top) and single impurity-distorted (bottom) cases at different temperatures: $T=0\mathrm{K}$ (dashed line), $T=0.5\mathrm{K}$ (circles), $T=1\mathrm{K}$ (triangles), $T=2\mathrm{K}$ (diamonds), and $T=4\mathrm{K}$ (thick line). The vertical lines in the bottom panel are guides to the eye, displaying the magnetic field values for ${\Phi }_{h\left(e\right)}∕{\Phi }_0=n∕2$.

Figure 6

PL intensity as function of magnetic field for the impurity-distorted case for $T=2\mathrm{K}$. Diamonds denote the intensity for fixed $R_h=19\mathrm{nm}$ and $R_e=16\mathrm{nm}$. Thick and dashed lines denote size-averaged intensities, with Gaussian dispersions $\Delta R=0.8\mathrm{nm}$ and $\Delta R=2\mathrm{nm}$, respectively.

Figure 7

Photoluminescence intensity as function of magnetic field for a electron-hole pair on a type-II QD with one (top) and two symmetric impurities (bottom). Curves for $T=0.5\mathrm{K}$ (solid), $T=2\mathrm{K}$ (diamonds), $T=4\mathrm{K}$ (filled circles) are shown. Vertical lines are guides to the eye, representing ${\Phi }_h∕{\Phi }_0=n∕2$. Inset, intensity curves for the no-impurity case.