INDIVIDUAL electrons have been observed in a flowing current for the first time.
Current is usually measured indirectly, for example by detecting the drop in voltage across a resistor. Now, a team from Chalmers University of Technology in Gothenburg, Sweden, has successfully counted each electron in a current after getting them to line up in single file.
To do this, they used an array of 50 microscopic, superconducting electrodes separated by gaps a micron across. The set-up was cooled to 30 millikelvin and a voltage applied across the array. At that temperature, the individual electrons tunnelled through the array from electrode to electrode, the repulsion between the electrons being such that only one could enter the array at a time. 鈥淭hey line up just like a train,鈥� says team member Per Delsing (Nature, vol 434, p 361).
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At the end of the array the team used a highly sensitive single electron detector to count each passing electron. Delsing says the technique could be used to create a new standard for measuring electrical current, 鈥渋f you could define a current in terms of the number of electrons passing each second鈥�.
