Conductance quantization in nanowires formed between micro and macroscopic metallic electrodes

In this work we present experimental results concerning conductance quantization at room temperature in metallic nanowires. The experiments are performed both at ambient presure and in ultrahigh vacuum using scanning tunneling microscopy (STM)-like devices. Both microscopic and macroscopic electrodes are used. The obtained results are independent of the electrode size, indicating that nanowires form at the last stages of the contact-breakage process, independently of the initial size and shape of the contact. In addition, we study (a) the stability of the nanowires, finding their lifetimes remarkably long, an the order of minutes; (b) the I-V curves for different quantum channels; (c) nanowires formed and visualized using a STM inside a scanning electron microscope (SEM); (d) the statistical behavior of the conductance, sampling tens of thousands of consecutive conductance experiments, showing clear quantized peaks up to five quanta of conductance; and (e) the length of the conductance plateaus, that might indicate the chaotic behavior of the quantum states formed at the nanowire. The statistical study of the conductance plateau lengths shows a broad Wigner-like distribution with an average value of 0.13 nm for the first quantum channel. This is at variance with a constant length, predicted and experimentally observed, in the plateaus between force jumps.