Figure 1

Photoluminescence from a single charge-tunable quantum dot (QD-A). (a) Contour plot of the PL intensity (log scale) as a function of applied bias voltage under linear polarized excitation and detection $[({\sigma }^y,{\sigma }^y)]$. The excitation is at 1.35615 eV, which corresponds to the $p$-shell resonance for $X^0$; $\sim 40.4\mathrm{meV}$ above $X^0$. (b), (c) Degree of circular PL polarization ${\rho }_c^{\pm }$ of PL for $X^{+}$ (b) and $X^{-}$ (c) under (${\sigma }^{\pm }$) excitation with energy $\sim 35$ and 40 meV above $X^{-}$ and $X^{+}$ lines, respectively. ${\rho }_c$ depends strongly on bias voltage and weakly on pump power (not shown).Reuse & Permissions

Figure 2

Spin splitting induced by the Overhauser field. (a) High-spectral-resolution $X^{-}$ PL spectra measured with a Fabry-Perot scanning interferometer (spectral resolution $\sim 1\mu \mathrm{eV}$) under $B_{\mathrm{ext}}=0$ and 20 mT for QD-B. (b) $X^{+}$ PL spectra under $B_{\mathrm{ext}}=0$. Under circularly polarized excitation (${\sigma }^{\pm }$), the detection polarization is cocircular (red curves) or cross circular (black) with respect to the pumping polarization. Spin splitting of $\sim 13\mu \mathrm{eV}$ and $\sim 17\mu \mathrm{eV}$ are observed under ${\sigma }^{\pm }$ excitation for $X^{-}$ and $X^{+}$, respectively. For $B_{\mathrm{ext}}=0$ and linearly polarized excitation (${\sigma }^y$), colinear or cross-linear polarized PL are detected. In contrast to circular polarization, linear polarization is not preserved. The spin splitting of $X^{-}$ at $B_{\mathrm{ext}}=20\mathrm{mT}$ under linearly polarized excitation is attributed to Zeeman splitting.Reuse & Permissions

Figure 3

Spin splitting (a) and PL polarization (b) as a function of applied external magnetic field $B_{\mathrm{ext}}$. Here the spin splitting is determined by a weighted average of the $X^{-}$ spectral lines measured by the spectrometer. The solid black and red curves in (a) are fits according to the model described in the text. Observation of correlated dips in spin splitting and in polarization as a function of $B_{\mathrm{ext}}$ suggests an average Knight field $B_e\simeq 6\mathrm{\text{Gauss}}$ seen by the nuclei. Blue curves in the polarization data shown in (b) are fits obtained from Eq. (3), using averaged values of the data in (a). Under ${\sigma }^{+}$ (${\sigma }^{-}$) excitation, $B_e$ is parallel (antiparallel) to the wave vector $\mathbf{k}$ of laser excitation. The schematic in the inset of (b) sketches the orientations of the laser wave vector and the external magnetic field.Reuse & Permissions