Molecular states observed in a single pair of strongly coupled   self-assembled InAs quantum dots
  Molecular states in a SINGLE PAIR of strongly coupled self-assembled InAs quantum dots are investigated using a sub-micron sized single electron transistor containing just a few pairs of coupled InAs dots embedded in a GaAs matrix. We observe a series of well-formed Coulomb diamonds with charging energy of less than 5 meV, which are much smaller than those reported previously. This is because electrons are occupied in molecular states, which are spread over both dots and occupy a large volume. In the measurement of ground and excited state single electron transport spectra with magnetic field, we find that the electrons are sequentially trapped in symmetric and anti-symmetric states. This result is well-explained by numerical calculation using an exact diagonalization method. 
T. Ota, M. Stopa, M. Rontani, T. Hatano, K. Yamada, S. Tarucha, H. Z.   Song, Y. Nakata, T. Miyazawa, T. Ohshima, N. Yokoyama