Alex Greilich, Ştefan C. Bădescu, Danny Kim, Allan S. Bracker, Daniel Gammon
Two electron spins in quantum dots coupled through coherent tunneling are generally acknowledged to approximately obey Heisenberg isotropic exchange. This has not been established for two holes. Here we obtain the spectrum of two holes and of two electrons in two vertically stacked self-assembled InAs quantum dots using optical spectroscopy as a function of electric and magnetic fields. We find the exchange to be dominantly isotropic for both systems, with observed anticrossing singularities that can only be explained by asymmetric mixing. The latter arises from spin-orbit and Zeeman interactions combined with spatial asymmetries. Such asymmetric contributions to the isotropic Hamiltonian for electrons are of the order of a few percent while those for holes are an order of magnitude larger.
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http://arxiv.org/abs/1209.0920
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