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2009 SEMICONDUCTORS AND NANOSTRUCTURESSpectroscopy and optical manipulation of a single Mn spin in a CdTe-basedquantum dot in high magnetic fieldQuantum dots containing single magnetic ions have recentlyattracted significant interest as systems close to theultimate limit of information storage miniaturization. Anefficient optical read-out of the Mn spin state has beendemonstrated [Besombes et al., Phys. Rev. Lett. 93,207403 (2004)] as well as the writing and storing of theinformation using the Mn spin state. It has been shown thatit is possible to optically manipulate the single Mn spin byinjecting the spin-polarized excitons into the quantum dot,either by direct quasi-resonant excitation of the dot with circularlypolarized light [Le Gall et al., Phys. Rev. Lett. 102,127402 (2009)] or by using a spin-conserving transfer ofthe excitons between two coupled quantum dots [Goryca etal., Phys. Rev. Lett. 103, 087401 (2009)].We have applied the micro-photoluminescence measurementsto directly probe states of a single Mn atom embeddedin a CdTe quantum dot in high magnetic fields.The sample was placed in a micro-photoluminescence setupconsisting of precise piezo-electric three-dimensional stageand a microscope objective. The micro-photoluminescencesystem was kept at the temperature of 4.2 K in a cryostatplaced in a resistive magnet producing magnetic field up to28 T. The field was applied parallel to the the growth axisof the sample (Faraday configuration).Figure 70: Color-scale plot of the photoluminescence intensityof a single Mn-doped QD as a function of emission energy andmagnetic field. The branches of emission lines can be assigned tobright (X) and dark (DX) exciton transitions.The photoluminescence of the QD’s was excited by circularlypolarized tunable dye laser in the range 570−610 nm.The excitation beam and the collected PL signal werepassed though a mono-mode fiber connected directly to themicroscope objective. Optical spectra have been recordedfor both circular polarization of light.An example of the PL measurement of a neutral excitonspectrum of a single Mn-doped QD as a function of themagnetic field is shown in figure 70. It reveals not only detailsof the optical transitions of the so called bright excitons(excitons with J = 1), but also transitions of dark excitons(J = 2) are clearly visible (5 lines in the low energy partof the spectra). This is due to the mixing of electron spinstates by electron-Manganese exchange interaction and opticalorientation of the spin of the Mn ion.Calculated excitonic transitions in a dot containing a singleMn ion is shown in figure 71. It is clearly visible that inthe case of dark excitons we should indeed observe only 5lines, in contrast to bright excitons (two upper branches oflines in figure 71), where 6 strong lines should be visiblein each circular polarization for detection. The number ofthese lines reflects the 6 possible spin projections of the Mnion (S = 5/2) onto the quantization axis.Figure 71: Calculated optical transitions of a single Mn-dopedQD. Line width reflects the oscillator strength, colors indicate circularpolarization of the emitted light (red - σ + , blue - σ − )M. Goryca, P. Plochocka, P. Kossacki, M. PotemskiP. Wojnar (Institute of Physics, Polish Academy of Sciences, Warsaw), J. A. Gaj (Institute of Experimental Physics,University of Warsaw)51