Strong Non-Ohmicity in Vertical Transport in Multilayered Quantum Hall Systems

Vertical transport in GaAs/AlGaAs superlattices has been studied in the quantum Hall regime. Both the in-plane and out-of-plane resistances exhibit an Arrhenius-type temperature dependence with small values of activation energy. At very low temperatures, the out-of-plane conductance becomes almost temperature independent and its values scale with the sample perimeter, indicating that the current is carried by the chiral surface states. The vertical transport in this regime exhibits distinct non-Ohmicity, suggesting the onset of bulk transport at high bias voltages. Rather strong non-Ohmicity is also observed in the low bias voltage region where the chiral surface state is responsible for the vertical transport.