Carrier-induced spin splitting of an individual magnetic atom embedded in a quantum dot

The influence of the number of confined carriers on the spin splitting of a single magnetic ion $\left({\mathrm{Mn}}^{2+}\right)$ embedded in a semiconductor quantum dot is evidenced. Investigating both the biexciton and the exciton transitions in the same Mn-doped quantum dot, we analyze the impact of the Mn-exciton exchange interaction on the fine structure of the quantum dot emission. A single electron-hole pair is enough to induce a spontaneous splitting of the exciton-Mn system. The injection of a second electron-hole pair cancels the exchange interaction with the Mn ion and the Mn spin splitting is significantly reduced. A detailed analysis of the biexciton-Mn transitions reveals that the carriers’ orbital wave functions are perturbed by the interaction with the magnetic ion.

Figure 1

PL spectra of a single Mn-doped QD for different excitation intensities. $X\text{−}\mathrm{Mn}$ denotes the exciton-Mn emission while $X_2\text{−}\mathrm{Mn}$ corresponds to the recombination of the two-exciton-Mn (biexciton) states. The insets give a detail of the $X\text{−}\mathrm{Mn}$ emission spectra at low-excitation density ($X_b\text{−}\mathrm{Mn}$ corresponds to the bright excitons and $X_d\text{−}\mathrm{Mn}$ corresponds to the dark excitons) and the evolution of the integrated intensities of $X\text{−}\mathrm{Mn}$ and $X_2\text{−}\mathrm{Mn}$ as a function of the total emission intensity.

Figure 2

(Color) Intensity contour plot of the magnetic field dependence of the excitonic and biexcitonic transitions of a single Mn-doped QD. The bright areas correspond to the high PL intensity. The anticrossings observed for the exciton are symmetrically reproduced on the biexciton transitions.

Figure 3

(a) Exciton-Mn $\left(X\text{−}\mathrm{Mn}\right)$ and biexciton-Mn $\left(X_2\text{−}\mathrm{Mn}\right)$ transition energies as functions of a magnetic field after removing the diamagnetic shift. (b) The diamagnetic shift of the exciton-Mn and biexciton-Mn complexes. The dotted lines are parabolic fits with a diamagnetic shift coefficient ${\Gamma }_{X\text{−}\mathrm{Mn}}={\Gamma }_{X_2\text{−}\mathrm{Mn}}=0.00245\mathrm{meV}{\mathrm{T}}^{-2}$.

Figure 4

Scheme of optical transitions from the exciton-Mn and biexciton-Mn states at zero magnetic field. The right-hand side scheme illustrates the effect of a perturbation of the carriers’ orbital wave functions by the exchange coupling with the ${\mathrm{Mn}}^{2+}$ ion. Mn spin projections are indicated on the horizontal scale.

Figure 5

(a) Detail of the exciton-Mn and biexciton-Mn transitions at zero magnetic field showing the irregular spacing of the transition energies. (b) Biexciton energies $(E_{X_2}+E_X)$ and biexciton binding energies $(E_{X_2}-E_X)$ deduced from the optical transitions presented in (a). The biexciton energies scale is translated by 4065.225 meV.