Fractional quantum conductance in gold nanowires

The conductance of a nanoscopic wire decreases in steps when it is stretched until it breaks. This is due to narrowing of the wire whereby quantized conductance channels sequentially close. However the conductance plateaus seldom occur at integral multiples of the quantum of conductance G(0) and most steps are much smaller than G(0). High speed precision measurements of the conductance steps reveal that the nanowires are composed of not one but several quantized conductors in series and that a step is caused by a quantized conductance change in one of the elements in the sequence. Resolved series conductance quanta up to 20 G(0) have been observed at room temperature. The effect is explained in terms of elastic electronic scattering and has important consequences for nano-electronic circuitry.