  We investigated the electron transport properties of parallel-coupled double
quantum dot (DQD) devices under magnetic fields. When a low magnetic field was
applied, electron tunneling through parallel-coupled DQDs was observed. Under a
high magnetic field, we observed both electron tunneling through parallel- and
series-coupled DQDs under nonlinear transport conditions. In addition, the
Pauli spin blockade was observed, indicating tunneling through the
series-coupled DQDs. We attribute these behaviors to the magnetic-field-induced
changes in the tunnel-couplings that allow the coexistence of the current paths
of the parallel and series configurations.
