Aharonov-Bohm Interference in Neutral Excitons: Effects of Built-In Electric Fields

We report a comprehensive discussion of quantum interference effects due to the finite structure of neutral excitons in quantum rings and their first experimental corroboration observed in the optical recombinations. The signatures of built-in electric fields and temperature on quantum interference are demonstrated by theoretical models that describe the modulation of the interference pattern and confirmed by complementary experimental procedures.

Figure 1

(a) AFM image of an uncapped InAs QR sample (3D ring profile in inset). (b) plan-view bright-field TEM image of a ring taken close to the $[001]$ zone axis with $[220]$ reflecting planes. (c) High-resolution TEM image on cross-section samples providing ring thickness and confirming that they lie on $\{001\}$ planes. (d) PL spectra of the InAs QRs for $B=0\mathrm{T}$ and $B=15\mathrm{T}$ at 2 K. For both spectra there are two radiative channels, QR 1 and QR 2.

Figure 2

PL energy peak position vs magnetic field from emission band (a) QR1, with visible AB-oscillations and (b) QR2, with unclear AB-oscillations. (c) and (d) show the integrated PL intensity of QR1 and QR2 vs magnetic field, respectively, both displaying clear AB-oscillations. The higher transition energy and the larger average radius of QR2, suggests it may present smaller ring width and height than QR1.

Figure 3

(a) Magnetic flux dependence of the (HH)-exciton spectrum (binding energy $E_b=4.35\mathrm{meV}$). (b) OS as a function of magnetic flux for a (HH) exciton at various temperatures. (c) Probability density of finding the electron and (HH) angular positions differing by $\theta$. (d) Ground-state OS for the (HH) exciton (solid curve) and the (LH) exciton (dashed curve) as a function of the magnetic flux at two values of an in-plane electric field.

Figure 4

(a) Series of the PL emission for increasing excitation powers from $0.36\mathrm{mW}/{\mathrm{cm}}^2$ to $16.4\mathrm{kW}/{\mathrm{cm}}^2$. (b) Position of emission peaks vs excitation power. The inset shows the log-log relative area (ratio of peak 2 area to peak 1 area), which displays two distinct lines, at low and high excitation power, the fingerprint of excitons in semiconductors nanostructures.

Figure 5

(a) PL integrated intensity normalized to the value at $T=10\mathrm{K}$, for the emission bands QR1 and QR2, respectively. (b) Calculated OS (normalized to the value at $T=0$) for three values of the in-plane electric field $F$. The increase of PL intensity at low temperatures can be understood as an electric field effect. Inset: PL spectra at low temperature are dominated by the emission band QR2, whereas above 160 K, they become dominated by QR1, which is attributed to the transference of carriers between QRs, via wetting layer, favoring the lower energy states, as also observed in QD systems.