Scanning of electronic states in a quantum point contact using asymmetrically biased side gates

The conductance of a trench-type quantum point contact (QPC) with side gates has been experimentally investigated over a wide range of gate voltages. The performed measurements, in which the asymmetric gate bias modifies the confinement potential while the sum of the gate voltages populates it with electrons, made it possible to scan the electron states in the QPC. Analysis of the experimental data revealed an unusual four-well shape of the confining potential in a single QPC. The rather complicated transconductance plot measured can be divided into its component parts — the contributions of the four separate conducting channels. Different electron states observed in the experiment have been associated with a certain number of filled one-dimensional (1D) subbands belonging to different channels. A whole network of degeneration events of 1D subbands in parallel channels has been found. Almost every such event was experimentally manifested by anticrossings observed both for small and large numbers of filled 1D subbands.