Metal-insulator transition in amorphousSi1−xNix:Evidence for Mott’s minimum metallic conductivity

Abstract

We study the metal-insulator transition in two sets of amorphous ${\mathrm{Si}}_{1-x}{\mathrm{Ni}}_x$ films. The sets were prepared by different, electron-beam-evaporation-based technologies: evaporation of the alloy, and gradient deposition from separate Ni and Si crucibles. The characterization included electron and scanning tunneling microscopy, glow discharge optical emission spectroscopy, energy dispersive x-ray analysis, and Rutherford back scattering. Investigating the logarithmic temperature derivative of the conductivity, $w=\mathrm{d}\ln \sigma /\mathrm{d}\ln T,$ we observe that, for insulating samples, $w\left(T\right)\mathrm{}$ shows a minimum, increasing at both low and high T. Both the minimum value of w and the corresponding temperature seem to tend to zero as the transition is approached. The analysis of this feature of $w(T,x)\mathrm{}$ leads to the conclusion that the transition in ${\mathrm{Si}}_{1-x}{\mathrm{Ni}}_x$ is very likely discontinuous at zero temperature in agreement with Mott’s original views.