Influence of energy level alignment on tunneling between coupled quantum dots

We have measured the nonlinear transport properties of two GaAs/Al_xGa_1-xAs quantum dots connected in series. At high source-drain bias the Coulomb oscillations develop a sharp overstructure. The behavior of this overstructure is studied as a function of the electrostatic potentials of the dots. The structure is shown to arise from the modulation of interdot tunneling that occurs as the quantum levels in the two dots are aligned and dealigned.