Giant Excitonic Exchange Splittings at Zero Field in Single Colloidal CdSe Quantum Dots Doped with Individual Mn Impurities.

Replacing a single atom of a host semiconductor nanocrystal with a functional dopant can introduce completely new properties potentially valuable for "solotronic" information-processing applications. Here, we report successful doping of colloidal CdSe quantum dots with a very small number of manganese ions-down to the ultimate limit of one. Single-particle spectroscopy reveals spectral fingerprints of the spin-spin interactions between individual dopants and quantum-dot excitons. Spectrally well-resolved emission peaks are observed that can be related to the discrete spin projections of individual Mn ions. In agreement with theoretical predictions, the exchange splittings are enhanced by more than an order of magnitude in these quantum dots compared to their epitaxial counterparts, opening a path for solotronic applications at elevated temperatures.