Quantum point contact

A quantum point contact (English Quantum Point Contact; QPC ) is a taper between two extended conductive regions whose width is in the range of the electron wave length. It was the first time in 1988 by B. J. van Wees, Henk van Houten, Carlo Beenakker and colleagues studied. Today, quantum point contacts are a basic component for transport studies in mesoscopic structures dar.

A quantum point contact is a one-dimensional quantum mechanical structure, similar to the quantum wire. It can be produced for example by applying two closely spaced metal gate on a modulation-doped (Al) GaAs wafer. By applying an electrical voltage to the gates of the two dimensional electron gas of the GaAs heterostructure is reduced to one dimension, and is wire-shaped.

When current is passed through the quantum point contact, so take the charge transport in n- doped semiconductors and metals practically only electrons near the Fermi level part. This is all the more severe, the lower the temperature is compared with the Fermitemperatur. Participating in the electron transport, a uniform Fermi wavelength can be assigned. Because only electrons of a certain wavelength to participate in the transport of the quantum point contact has similar characteristics as a waveguide. Variation in the width of the quantum point contact by changing the gate voltage applied to the metal can always participate in the transport of only an integer of modes. Since each mode corresponds to a quantum mechanical state, it can be occupied because of the Pauli principle at any given time only one electron. Each of these channels contributes to the total conductance in a Leitwertsquantum of. Thus, the typical step-like shape is formed at the conductivity change of the gate voltage. The fact that the levels are at is to establish the fact that each local state can be occupied by two electrons of different spins.