Strong non-ohmicity in vertical transport in multilayered quantum Hall systems

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