CONDUCTANCE QUANTIZATION HISTOGRAMS OF GOLD NANOWIRES AT 4 K

Driving a scanning tunneling microscope (STM) tip into a metallic surf ace and pulling it out afterwards results in the formation of a nanome ter-sized wire (nanowire) between the electrodes. The electrical condu ction measured during this process shows signs of quantized conductanc e in units of G(0) = 2(e)2/h. Due to the inherent irreproducibility of the measured conductance curves, the standard technique has been to c onstruct histograms with a few hundred selected curves. These histogra ms, for gold nanowires at room temperature, have shown three to four p eaks at integer values of 2e(2)/h, while in a low-temperature mechanic ally controlled break junction study, with statistics using only 65 cu rves, only the first peak has been reported. A proposed explanation fo r this apparent experimental discrepancy has been a higher nanowire te mperature arising from the higher retraction speed used in scanning tu nneling microscopy measurements. However, our simple estimation using macroscopic heat transport theory produces a very low temperature rise , less than 1 mu K. In this work, an improved statistical study is pre sented, where histograms built with thousands of consecutive gold cont act breakage experiments at 4 K show up to seven conductance peaks. Th us, no significant differences with our previous room-temperature (RT) studies are observed, pointing to a conductance quantization behavior that is the same at low, intermediate, and high (RT) temperatures.