Numerical Simulation of Conductance through Quantum Point Contacts with an Embedded Impurity

The conductance through a QPC is calculated when a hill like impurity potential, due to the nonuniform distribution of ionized impurities in the modulation doping layer, is added to smooth varying saddle like QPC potential. It was found that a weakly localized state can form between the QPC center and the impurity. Anomalous plateau appeared around 0.7 × 2e2/h when the conductance via the localized state is added to the QPC conductance. The results imply that the resonance due to quasi-bound state formed by the impurity potential in the QPC is one of the possible origins of anomalous conductance plateau.