Single electron spectroscopy in a single pair of weakly coupled self-assembled InAs quantum dots

Using a single electron transistor containing a single pair of weakly coupled self-assembled InAs quantum dots, we have studied the transport properties of elastic and inelastic single electron tunneling. We found a series of Coulomb diamonds above pinch off voltage and, below it, characteristic irregular structures in the current vs. source-drain voltage and gate voltage, consisting of "vertical lines" and "kinks". Based on a simple calculation, the vertical lines are assigned to elastic tunneling between aligned states of the two dots. The kinks come from change of electron number in the dots, observed in the inelastic tunneling regime through off-resonant states in the two dots.