Conductance quantization and dequantization in gold nanowires due to multiple reflection at the interface

Abstract

The conductance of gold $⟨110⟩$ nanowires was measured, along with simultaneous observation of their atomic structure in a transmission electron microscope. The conductance histogram obtained from 300 thinning processes of the nanowires showed a series of peaks whose conductance values increased nearly in steps of the conductance quantum, ${G}_{0}=2{e}^{2}/h$. However, thick nanowires above $10{G}_{0}$ showed dequantization, where the increment was only $0.9{G}_{0}$. The structure for each peak was found to be either an atomic sheet or a hexagonal prism. The number of conductance channels calculated for each determined atomic structure by first-principles theory, coincided well with the peak index in the conductance histogram. The observed decrease in the conductance from the quantized number of conductance channels was explained by partial transmission of electrons due to the multiple reflection at the interfaces between the nanowire and the electrodes. The present study shows that the $⟨110⟩$ nanowires behave as ballistic conductors, and a conductance peak appears whenever the conductance channel is open one by one.