Lateral tunneling in point contacts

The Shubnikov--de Haas oscillations of the resistance of a point contact formed in the two-dimensional electron gas of Alₓ{Ga}_{1{{-}}x}$As/GaAs heterostructures via the lateral field effect are investigated for a series of values of the confining gate voltage ${V}g$. Giant magnetoresistance oscillations are observed for values of ${V}g$ close to the threshold voltage. An analysis of the differential channel resistance dV/dI as a function of the voltage drop V over the point contact shows that these oscillations are due to lateral tunneling through the point contact.