We present results of an experimental study of magnetoresistance (MR) in insulating NbSi amorphous alloys
sample showing Variable Range Hopping (VRH) conductivity ; The MR is found to be negative in a wide range
of low temperature (4.2-20 K) and in the range of moderate magnetic fields (0-4 T). We made tentative analysis
using three theoretical models which are the model of quantum interference, the model of Zeeman effect and the
model of localized magnetic moments.
We present measurements of the electrical conductivity of barely metallic n-type GeSb that are driven to the metal-insulator transition (MIT) by impurity concentration. The experiments were carried out at low temperature in the range (4.2 -0.066 K) and with impurity concentrations up 6.41017 cm−3 . On the metallic side of the MIT, the electrical conductivity is found to behave like σ =σ0 + mT1/2 down to 66 mK. Physical explanation to the temperature dependence of the conductivity is given in metallic side of the MIT using a competition between two effects involved in the mechanisms of conduction, like electron-electron interaction effect, and weak localization effect.
On the insulating side of the metal-insulator transition (MIT), the study of the effect of low Temperatures T on
the electrical transport in amorphous silicon-nickel alloys a-Si1-yNiy:H exhibits that the electrical conductivity
follows, at the beginning, the Efros-Shklovskii Variable Range Hopping regime (ES VRH) with T-1/2. This
behaviour showed that long range electron-electron interaction reduces the Density Of State of carriers (DOS) at
the Fermi level and creates the Coulomb gap (CG). For T higher than a critical value of temperature TC, we
obtained the Mott Variable Range Hopping regime with T-1/4, indicating that the DOS becomes almost constant
in the vicinity of the Fermi level. The critical temperature TC decreases with nickel content in the alloys.
We present results of an experimental study of magnetoresistance phenomenon in an amorphous siliconnickel
alloys a-Si1-yNiy:H (where y=0.23) on the insulating side of the metal-insulator transition (MIT) in
presence of magnetic field up to 4,5T and at very low temperature. The electrical resistivity is found to
follow the Efros-Shklovskii Variable Range Hopping regime (ES VRH) with T -1/2. This behaviour
indicates the existence of the Coulomb gap (CG) near the Fermi level.
Longitudinal and positive magnetoresistance behaviour was used to determine what of the Variable Range Hopping (VRH) conduction regime is found in insulating InSb sample, Mott VRH regime or Efros- Shklovskii (ES) VRH regime. Experimental results are reported on field longitudinal magnetoresistance in insulating n-type InSb sample in which range hopping occurs at low temperatures. Positive magnetoresistance associated with VRH conduction has been observed. Experimental data are tentatively compared with available theoretical models in the insulating regime.
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