In this talk, I will discuss three topics concerned with quantum-interference electron transport phenomena in metallic nanowires at liquid-helium temperatures.

(1) I will discuss the weak-localization and weak-antilocalization effects in tin-doped indium oxide (ITO) nanowires. In this class of metallic nanowires, we found that the electron dephasing length is
very long, reaching above 500 nm at 1 K. Furthermore, we found that the spin-orbit coupling in this material can be enhanced by disorder. [Y. W. Hsu et al., Phys. Rev. B 82, 195429 (2010).]

(2) I will discuss our recent observation of time-dependent universal conductance fluctuations (UCF) in metallic ruthenium dioxide (RuO_2) nanowires. The conductance fluctuation amplitudes increase with decreasing temperature. The root-mean-square amplitude reaches a fraction of the quantum conductance (e^2/h) below 1 K. These UCF are shown to originate from the scattering of conduction electrons with
mobile defects (moving scattering centers) which behave like two-level systems. In sharp contrast, inITO nanowires, the defects are “stable” in space, and hence the usual magnetic-field dependent UCF are observed.

(3) If time permits, I will briefly discuss the electronic conduction processes through “nanocontacts” which inevitably form at every interface between a metallic nanowire and a lithographic contacting electrode. We found that, in many cases, the charge conduction
processes can be explained in terms of the theoretical model of fluctuation-induced tunneling conduction across a mesoscopic tunnel junction previously formulated by Ping Sheng. [Y. H. Lin et al., Nanotechnology 19, 365201 (2008).]