On additional conductance quantization and related effects of an electric field in 2D quantum point contacts

Influence of the electric field on the quantum point contact (QPC) differential conductance is studied in two cases of well-developed transmission spectrum of(a) step-like and(b) resonance character. These are exemplified by a symmetric rectangular constriction and double-bend constriction in two-dimensional electron gas. It is shown that an additional structure in the constriction-conductance dependence on the Fermi energy (referred sometimes as half integer quantization) reflects the specific field distribution in the contact region at moderate fields and is washed out by nonlinear field effects produced by the potential variation inside the contact. To study held effects, we suggest an analytical expression for the transmission probability, which includes as particular cases two models used previously to confirm and to reject the possibility of the QPC conductance quantization by value e(2)/h. We also briefly discuss the case of resonance doubling accompanied by two-times decrease of the resonance intensity, representing another example of transformations in the QPC conductance, which have the same origin.