Spin state of a single Mn atom embedded in an InAs quantum dot

The spin states of single Mn atoms embedded in InAs quantum dots (QD) were investigated by optical means. In (In,Ga)As, the Mn impurity acts both as acceptor and a magnetic moment. In the low density limit, which is relevant here, the acceptor is in the neutral state A⁰ with an effective spin J = 1. Using magneto-photoluminescence experiments, we probed the exchange interaction between the dot confined carriers and the Mn spin. Peculiar properties are found such as a large influence of the QD strain field on the acceptor spin states, a ferromagnetic hole-Mn spin coupling and a very small interaction with electrons. The Mn atoms were deposited during the QD growth by molecular beam epitaxy. Although the substrate temperature favored large segregation of the Mn atoms, we could measure a few dots containing single magnetic impurities. The zero-magnetic field exciton of a Mn-doped single dot shows a complex spectrum consisting of two doublets and a singlet. They correspond to the excitonic recombination of electron-hole pairs, affected by the exchange coupling with the Mn magnetic moment in the Jz = ±1, 0 states. The fine structure of each doublet is due to the QD in-plane anisotropy which partially mixes the Jz = ±1 states. The magnetic field dependence exhibits even more striking modifications, with several crossing and anti-crossing again linked to the QD strain field. We developed a model taking into account the spin interactions between the Mn impurity and the carriers in the dot. A very good agreement is found with the experimental data. © 2009 SPIE.