EFFECT OF DISORDER ON THE ELECTRICAL PROPERTIES OF AMORPHOUS CONDUCTING CARBON FILMS: OBSERVANCE OF FIELD INDUCED METAL-INSULATOR TRANSITION?

2000 ◽  
Vol 14 (02n03) ◽  
pp. 224-229 ◽  
Author(s):  
V. MEENAKSHI ◽  
S. V. SUBRAMANYAM
Keyword(s):  
Magnetic Field ◽  
Electrical Properties ◽  
External Magnetic Field ◽  
Low Temperature ◽  
Carbon Films ◽  
Electronic Systems ◽  
Metal Insulator Transition ◽  
Preparation Temperature ◽  
Metal Insulator ◽  
Effect Of Disorder

In this work, the influence of disorder on the electrical properties (DC conductivity and Magnetoresistance) of amorphous conducting carbon films, prepared by the pyrolysis of Tetra chloro phthalic anhydride, is reported and discussed. The low temperature electrical properties are analyzed in terms of the various models developed for disordered electronic systems. The results indicate the possibility of a metal - insulator (M-I) transition, both as a function of preparation temperature and an external magnetic field.

Particle Size Dependent Magnetoresistance And Magnetothermoelectric Power Of La0.5Pb0.5MnO3 Showing Metal-Insulator Transition

2002 ◽  
Vol 718 ◽  
Author(s):  
Aritra Banerjee ◽  
S Pal ◽  
B K Chaudhuri
Keyword(s):  
Magnetic Field ◽  
Particle Size ◽  
Low Temperature ◽  
Nearest Neighbor ◽  
Small Polaron ◽  
Insulator Transition ◽  
Metal Insulator Transition ◽  
Metal Insulator ◽  
Polaron Hopping ◽  
Size Dependent

AbstractParticle size dependent transport properties (resistivity and thermopower) of La0.5Pb0.5MnO3 has been investigated both in presence and in absence of magnetic field B=0.0-1.5T (maximum). All the samples show metal-insulator transition (MIT) with a peak at the MIT temperature (Tp). Magnetic field decreases the resistivity with an increase in the peak temperature Tp. Particle size, conductivity and Tp of the sample increase with increasing annealing time. High temperature semiconducting (insulating) part of the resistivity curve is divided into two distinct regimes. Resistivity data for T>qθ/2, can be well fitted with the nearest neighbor small polaron hopping (SPH) model. Polaron hopping energy (WH) decreases with increase of particle size. The lower temperature part (Tp>T>qθ/2) of the semiconducting (insulating) regime is found to follow variable range hopping (VRH) model. With the increase of particle size, the temperature range of validity of the VRH mechanism decreases. The low temperature metallic regime (for T<Tp) of the resistivity (both in absence and in presence of field) data fit well with ρ = ρ0 +ρ2.5 T2.5 and transport mechanism in this region is mainly dominated by magnon-carrier scattering (∼T2.5). Particle size has, however, comparatively little effect on Seebeck coefficient (S). In all the samples with different particle sizes, S changes sign below Tp. In contrast to magnetoresistance, application of magnetic field increases S at low temperature (T<Tp) for these samples. Similar to the resistivity results, thermopower data in the metallic phase (both for B=0.0 and 1.5T) can also be analyzed by considering magnon-scattering term along with an additional spin-wave fluctuation term (∼T4).

scholarly journals Behaviour of the conductivity in metallic 70 Ge:Ga close to the metal-insulator transition

2021 ◽  
Vol 229 ◽  
pp. 01056
Author(s):  
Mohamed Errai ◽  
Said Amrane
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Low Temperature ◽  
Electrical Transport ◽  
Weak Localization ◽  
Insulator Transition ◽  
Electrical Transport Properties ◽  
Metal Insulator Transition ◽  
Metallic Behavior ◽  
Metal Insulator

The electrical transport properties in sample 1 of impurity concentration n=xx of the 70Ge: Ga system are studied in the absence of a magnetic field and at low temperature in the range 0.53 to 0.017 K. It is noted that the electrical conductivity of sample 1 exhibits a metallic behavior. We found that the exponent S is equal to 0.5 (σ=σ(T=0)+mTs). This result is in agreement with the theory of weak localization (WL) at 3D and the theory of electronelectron interactions (EEI). We also found that sample 1 is located near the metal-insulator transition (MIT) of the metallic side.

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