Quantum dot contact

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A quantum point contact (QPC) is a taper between two extensive conductive areas, the width of which is in the range of the electron wavelength. It was first examined in 1988 by Bart van Wees , Henk van Houten, Carlo Beenakker and colleagues. Today, quantum dot contacts are a fundamental component for transport studies in mesoscopic structures.

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 metal gates that are close to one another on a modulation-doped (Al) GaAs wafer. By applying an electrical voltage to the gates, the two-dimensional electron gas of the GaAs heterostructure is reduced to one dimension and becomes wire-shaped.

If current is passed through the quantum point contact, then practically only electrons near the Fermi edge take part in the charge transport in n-doped semiconductors and metals . This applies all the more strictly, the lower the temperature is compared to the Fermi temperature. A uniform Fermi wavelength can be assigned to the electrons participating in the transport. Since only electrons of a certain wavelength participate in the transport, the quantum point contact shows properties similar to those of a waveguide . If the width of the quantum point contact is varied by changing the voltage applied to the metallic gates, only an integer number of modes can participate in the transport. Since every mode corresponds to a quantum mechanical state, it can only be occupied by one electron at a certain point in time due to the Pauli principle . Each of these channels contributes a quantum of conductance to the overall conductance . This creates the typical step shape of the conductance when the gate voltage changes. The fact that the steps are at is due to the fact that each spatial state can be occupied by two electrons with different spins.

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