Variable-range hopping conduction and metal–insulator transition in amorphous Re_xSi_1−xthin films

Abstract

Resistivity, ρ(T), of the amorphous Re x Si 1−x thin films with x = 0.285-0.351 is investigated in the interval of T ∼ 300-0.03 K. At x = 0.285-0.324 the activated behavior of ρ(T) is governed by the Mott and the Shklovskii-Efros variable-range hopping (VRH) conduction mechanisms in different temperature intervals and the three-dimensional regime of the hopping. Between x = 0.328 and 0.351 the activationless dependence of ρ(T) takes place. The critical behavior of the characteristic VRH temperatures and of the Coulomb gap, , pertinent to proximity to the metal-insulator transition at the critical value of x c ≈ 0.327, is observed. The analysis of the critical behavior of yields directly the critical exponent of the dielectric permittivity, η = 2.1 ± 0.2, in agreement with the theoretical prediction, η = 2. On the other hand, the values of the critical exponent of the correlation length ν ∼ 0.8-1.1 close to the expected value of unity can be obtained from the analysis of the critical behavior of the VRH characteristic temperatures under an additional assumption of a strong underbarrier scattering of hopping charge carriers in conditions, when the concentration of scattering centers considerably exceeds the concentration of sites involved in the hopping.

Transport properties of β-FeSi2

“…( 6) within two decades of Δ and four decades of T 3 02 =T 04 . 79) However, in the β-FeSi 2 single crystals, doped with Cr, Co, and Mn, Eq. ( 6) is violated.…”