Molecular phases in coupled quantum dots

We present excitation energy spectra of few-electron vertically coupled quantum dots for strong and intermediate interdot coupling. By applying a magnetic field, we induce ground state transitions and identify the corresponding quantum numbers by comparison with few-body calculations. In addition to atomiclike states, we find novel molecularlike phases. The isospin index characterizes the nature of the bond of the artificial molecule and this we control. Like spin in a single quantum dot, transitions in isospin leading to full polarization are observed with increasing magnetic field.