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 Si 1−x 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 = d ln σ/d ln T , we observe that, for insulating samples, w(T ) 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) leads to the conclusion that the transition in Si 1−x Ni x is very likely discontinuous at zero temperature in agreement with Mott's original views. 71.30.+h,71.23.Cq, Typeset using REVT E X

Electron-electron interaction and weak localization effects in badly metallicSrRuO3

“…16͒ or more sophisticated analysis proposed to avoid unphysical fitting of the low-temperature conductivity when approaching the in- sulating regime. 17 We consider that the films are thick enough ͑1000 Å͒ as to discard effects coming from twodimensional behavior. At least from the point of view of magnetic properties, the high Curie temperatures observed support this assumption.…”

Metal–insulator transition in amorphous alloys

“…On the other hand, Fig. 1 of [97] and [78,77]. The samples 1-5 (+) were prepared by electron-beam evaporation of the alloy [78], the samples e and f (•) were deposited by a gradient technique based on co-evaporation of the elements [78], and the samples α and β ( ) were sputtered [77].…”

“…The samples 1-5 (+) were prepared by electron-beam evaporation of the alloy [78], the samples e and f (•) were deposited by a gradient technique based on co-evaporation of the elements [78], and the samples α and β ( ) were sputtered [77]. Ni content: x = 0.149, 0.164, 0.167, 0.189, 0.221 (RBS) for samples 1-5, respectively; x = 0.235, 0.248 (EDX, these values exceed related RBS data by roughly 0.06 [78]) for samples e and f, respectively; x = 0.207, 0.271 (EDX) for samples α and β, respectively.…”

“…This quantity contains still more information [78]: A fingerprint of the character of the MIT at T = 0 can be contained in the graph of w(T, x = const.) for a set of samples measured at finite T .…”

“…The data presented were obtained from measurements in three different cryostats, where several months passed between the investigations. Samples g and h are metallic films [78], included for comparison; for sample f, a conclusion on the character of the conduction could not be drawn within [78]. [91].…”