Transport properties of a Si/SiGe quantum point contact in the presence of impurities.

Abstract

The conductance of a quantum point contact, defined in a Si/SiGe heterostructure by a short split gate, shows Aharonov-Bohm oscillations between the quantized plateaus in the presence of magnetic fields above B\ensuremath{\approxeq}2 T. Their period increases with decreasing gate bias, indicating that they arise from the point-contact geometry itself. A more detailed analysis demonstrates, however, that their origin is also associated with an impurity state close to or in the constriction. This interpretation is further supported by distinct conductance peaks which appear at gate voltages close to the channel ``pinch-off'' and which result from resonant tunneling through such impurity states.