Conductance Quantization in Metallic Nanowires

Abstract

Recent investigations carried out in our group concerning theconductance quantization of metallic nanowires are reviewed. Theseinclude: i) The formation of metallic nanowires between macroscopicelectrodes, including liquid metals, demonstrating that at the laststages of the contact breakage, a nanowire exists, independently of theinitial contact size. ii) A statistical study of the conductance usingthousands of consecutive contact breakage experiments, both at room andat liquid helium temperatures. These histograms, totally reproducible,present clear peaks close to integer values of the quantum ofconductance G(0)=2e(2)/h for diamagnetic metals like Gold, Silver,Copper, Sodium, Platinum.... Ferromagnetic metals, Iron, Cobalt andNickel, exhibit a flat conductance histogram. This effect is attributedto the combination of the lifting of the spin degeneracy in theferromagnetic nanowires and the effect of geometry and disorder. Themeasured conductance histograms are basically independent of thetemperature, iii) A discussion of the position and width of the observedpeaks. Just geometrical effects can not explain the large conductancepeak shifts observed experimentally, and disorder, behaving as aresidual resistance, has to be invoked to explain them. iv) Firstrealization of conductance quantization in Bi at 4K. Conductanceplateaus lasting 20-100 nm electrode separation are presented; thehistogram displays also clear peaks. v) A statistical study of theconductance plateau duration, demonstrating a broad distribution of thisduration, 0.05-0.4 nm, with an average value that decreases asconductance increases. vi) A discussion of force and energy quantizationwithin a resonant energy model of two reservoirs connected by aballistic channel. vii) Experiments performed in ultra high vacuum,where we manage to stabilize the nanowires for hours and study switchingand current voltage characteristics for different quantum conductancechannels with remarkable accuracy. viii) Visualization inside scanningand transmission electron microscopes of the metallic contact betweentwo macroscopic electrodes at the micron and nanometer scales. Theseexperiments provide experimental evidence of the formation of aconnective neck between the electrodes. ix) Experiments on lightemission from breaking nanowires. A plausible explanation for thisphenomenon is presented.