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June 13, 2006

Supercurrent in quantum dots and electron control in nanowires

Researcher have places quantum dots on semiconducting nanowire. He can achieve supercurrent in the dots. He can precisely control the electrons in the quantum dot using an external charge. Low temperature and pure nanowires are needed. Improved nanowire quality was also part of the research.

Jorden van Dam, researcher at the Kavli Institute of Nanoscience Delft, has succeeded in largely controlling the transportation of electrons in semiconductor nanowires. He was able to make a quantum dot in a semiconductor nanowire. Van Dam moreover discovered how to observe a divergent type of supercurrent in these wires. Nanowires have superior electronic properties which in time could improve the quality of our electronics In recent years, many possible applications for semiconductor nanowires have emerged, such as in lasers, transistors, LEDs and bio-chemical sensors.

Van Dam has enabled total control over the number of electrons that can be confined in a quantum dot. He can control this number by means of an externally introduced charge. A crucial factor for the extreme degree of control that Van Dam has achieved is the quality (for example the purity) of the nanowires, which were supplied by Philips. It is above all the quality of the material used (wires and electrodes) that was greatly improved during Van Dam's research.

In the improved nanowires, Van Dam achieved for the first time the realisation and observation of a (theoretically already predicted) divergent type of supercurrent (a supercurrent is the current that occurs in superconductivity). In a quantum dot, the electrons normally pass through one by one. In superconductivity, the passage of electrons occurs in pairs. Van Dam, with the help of superconductor electrodes, has now achieved a supercurrent in the quantum dot, whereby the pairs of electrons pass through one by one.

Van Dam has also - under specific conditions - achieved a reversal in the direction of the supercurrent. He is able to control this reversal by varying the number of electrons confined in the quantum dot. With this, the Delft University of Technology researcher has achieved a largely controllable superconductor connection in semiconductor nanowires.

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