The Transmission Properties of Quantum Dots at High Magnetic Fields

We have fabricated quantum dot structures in GaAs/AlGaAs heterostructures using metallic surface gates defined by electron beam lithography and lift-off. Electrical transport measurements were performed on the dots at low temperatures (10 mK-1.5 K) and in magnetic fields of up to 8 T. Here we discuss the experimental characteristics of the devices, which include the observation of time dependent resistance changes at fixed gate voltage as well as a hysteresis in the resistance as the gate voltage is swept in different directions. These results demonstrate the influence of the dynamical nature of individual defects, charged states, or impurities, on the device behaviour. The corresponding magnetoresistance was found to show resonant peaks on the quantum Hall plateaus. Once the magnetoresistance exceeded the quantum resistance ( h / e 2 ), however, periodic oscillations were observed in the magnetoresistance. We discuss these observations with respect to the scattering between different edge states, as well as Coulomb blockade effects, in high magnetic fields.