Mapping of few-electron wave-functions in semiconductor nanocrystals -   evidence of exchange interaction
  The influence of the tip-substrate bias induced electric field in a scanning-tunneling-spectroscopy experiment on charged InAs nanocrystals is studied. Calculating the ground and first excited many-particle state for five electrons occupying the quantum dot reveals a Stark-induced reordering of states by increasing the electric field strength. It is shown that this reordering of states is accompanied by a symmetry change of the local density of states (LDOS), which in principal is observable in a wave-function mapping experiment. Since in the usually performed experiments the electric field can not be directly controlled, we investigate the crystal size dependence of the 5-electron LDOS symmetry. It is found that the symmetry changes from spherical to torus-like by increasing the nanocrystal radius. 
Michael Tews and Daniela Pfannkuche