Magneto optics of a doubly charged quantum dot -- Observation of a negative diamagnetic shift

We present magneto-optical studies of a self-assembled semiconductor quantum dot, concentrating specifically on the case in which the dot is doubly positively charged, studying this way the confined hole - hole exchange interaction. A simple harmonic potential model, which we extend to capture the influence of an externally applied magnetic field in Faraday configuration fully describe the observed polarization sensitive magneto-photoluminscence spectra. We deduce the effective composition of the quantum dot from its measured electronic g-factor. Using this value we determine the dot effective permittivity and quantitatively describe various measured excitonic transitions, their measured Zeeman splittings and their diamagnetic shifts. In particular, the model quantitatively accounts for an observed pronounced negative diamagnetic shift, which provides a direct measure for the hole-hole exchange interaction and its dependence on the externally applied magnetic field strength.