Aharonov-Bohm Signature for Neutral Polarized Excitons in Type-II Quantum Dot Ensembles

The Aharonov-Bohm effect is commonly believed to be a typical feature of the motion of a charged particle interacting with the electromagnetic vector potential. Here we present a magnetophotoluminescence study of type-II $\mathrm{InP}/\mathrm{GaAs}$ self-assembled quantum dots, revealing the Aharonov-Bohm–type oscillations for neutral excitons when the hole ground state changes its angular momentum from ${\ell }_h=0$ to ${\ell }_h=1$, 2, and 3. The hole-ring parameters derived from a simple model are in excellent agreement with the structural parameters for this system.

Figure 1

Sketches of the type-II $\mathrm{InP}/\mathrm{GaAs}$ QDs: (a) conduction and valence band profiles, indicating the spatial separation of electrons and holes; (b) top view of the QD plane, indicating the holes confined to a ring around the QD due to the Coulomb interaction with the electron trapped into the dot.

Figure 2

PL spectra of the InP QDs for $B=0$ (circles) and $B=12\mathrm{T}$ (triangles). Solid lines are Gaussian fits to the data. The total energy shift is 4.5 meV for 12 T.

Figure 3

(a) The PL peak position as a function of the applied magnetic field (solid circles). Three plateaulike structures are clearly observed. The error bars are smaller than the solid circles. (b) Hole energy dependence on the magnetic field (open squares), showing the Aharonov-Bohm oscillations with period ${\varphi }_0$. The error bars are the uncertainties on the peak position after the Gaussian fits. The dashed curves are parabolas following Eq. (2) shifted upward by arbitrary energy. Calculated $E_h$ [Eq. (2)] for a QD ensemble described by a Gaussian size distribution for $R$, with $R_{\mathrm{peak}}=19.1\mathrm{nm}$ and full width at half maximum of $2\Delta R_{\mathrm{CV}}=1.6\mathrm{nm}$ is shown by the solid curve. Note the progressive offsets of the parabola minima for increasing ${\ell }_h$.