Nonlinear Quantum Conductance of a Lateral Microconstraint in a Heterostructure

Finite source-drain voltage V causes smearing of quantum steps in the I(d) function of microconstraint (d is the diameter of a constraint, I the current through it). The number of steps is restricted by the value n@u similar to = 2E sub(F)/eV, where E sub(F) is the Fermi energy of the 2D electron gas. In the differential conductance G = partial differential I/ partial differential V additional steps occur, their width is proportional to V and their heights are multiples of half-integer quanta e super(2)/2 pi h-bar . As a by-product we derive the d(V sub(G)) function (V sub(G) is the gate voltage) that could be compared with the experimental data on G(V sub(G)).