Going Ballistic

Beating electrical resistance usually brings to mind superconductivity. But electrons can also travel unimpeded if they're in a wire so narrow that electrons can move in only one direction. Such quantum wires must not have defects or imperfections over their lengths that can trip up the electrons. (A quantum wire isn't considered superconducting because the electrons are not paired up in a way indicative of the superconducting state.) Past experiments, however, always revealed that such "ballistic" electrons encountered some resistance. Those speed bumps are now thought to arise from the contacts at the ends of the wire, not from the wire itself. Researchers from Lucent Technologies and Columbia University grew a layered structure that could conduct electrons ballistically and permitted the voltage in the wire to be measured without disrupting the flow. Their finding that the resistance is in the contacts only, described in the May 3 Nature, has implications for the design of future circuits based on quantum wires.

   
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