Variable-range hopping conductivity and absence of a true metal–insulator transition in La[sub 0.7−δ] Ca[sub 0.3]Mn[sub 1−y]Fe[sub y]O[sub 3]

2002 ◽  
Vol 91 (10) ◽  
pp. 7400 ◽  
Author(s):  
R. Laiho ◽  
E. Lähderanta ◽  
J. Salminen ◽  
K. G. Lisunov ◽  
V. S. Zakhvalinskii ◽  
...  
Keyword(s):  
Insulator Transition ◽  
Variable Range Hopping ◽  
Metal Insulator Transition ◽  
Metal Insulator ◽  
Hopping Conductivity ◽  
Variable Range

Metal–insulator transition and variable-range hopping conductivity of n-CdSb in magnetic field

2007 ◽  
Vol 68 (2) ◽  
pp. 272-279 ◽  
Author(s):  
R. Laiho ◽  
A.V. Lashkul ◽  
K.G. Lisunov ◽  
E. Lähderanta ◽  
M.O. Safonchik ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Insulator Transition ◽  
Variable Range Hopping ◽  
Metal Insulator Transition ◽  
Metal Insulator ◽  
Hopping Conductivity ◽  
Variable Range

Hopping Conduction Near the Metal-Insulator Transition in CdMnTe:In and Evidence for a Magnetic Hard Gap in the Density of States

1994 ◽  
Vol 08 (07) ◽  
pp. 905-912 ◽  
Author(s):  
I. Terry ◽  
T. Penney ◽  
S. von Molnár ◽  
P. Becla
Keyword(s):  
Carrier Concentration ◽  
Density Of States ◽  
Low Temperatures ◽  
Localization Length ◽  
Insulator Transition ◽  
Variable Range Hopping ◽  
Coulomb Interactions ◽  
Metal Insulator Transition ◽  
Metal Insulator ◽  
Magnetic Polarons

A series of resistivity curves is obtained as a function carrier concentration in just one sample of the dilute magnetic persistent photoconductor Cd0.91Mn0.09Te:In. The measurements, made at carrier concentrations approaching the metal-insulator transition, reveal a cross-over from an exp(To/T)1/2 dependence to an exp(EH/T) form when lowering temperature. The exp(To/T)1/2 dependence is characteristic of variable range hopping in the presence of Coulomb interactions, while the energy EH in the activated form is associated with a hard gap in the density of states that is magnetic in origin. All the data are shown to scale onto a single curve. The localization length. ξ, is found to have the same critical dependence on carrier concentration as that of the measured dielectric constant, κ, when approaching the metal-insulator transition. The temperature dependence of the resistivity is interpreted in terms of the orientation of Mn spins by carriers due to the s-d exchange interaction (the formation of magnetic polarons). This model can also account for the large positive and negative magnetoresistance observed in Cd0.91Mn0.09Te:In at low temperatures.

ANOMALOUS CROSSOVER FROM EFROS–SHKLOVSKII TO MOTT VARIABLE RANGE HOPPING IN SILICON MOSFETs

2013 ◽  
Vol 27 (21) ◽  
pp. 1350146 ◽  
Author(s):  
L. LIMOUNY ◽  
A. EL KAAOUACHI ◽  
S. DLIMI ◽  
A. SYBOUS ◽  
A. NARJIS ◽  
...  
Keyword(s):  
Electron System ◽  
Zero Magnetic Field ◽  
Variable Range Hopping ◽  
Dimensional Electron ◽  
Metal Insulator Transition ◽  
Metal Insulator ◽  
Exponential Factor ◽  
Coulomb Gap ◽  
Variable Range ◽  
Dimensional Electron System

In this paper, we investigate the temperature dependence of the electrical resistivity of a two-dimensional electron system in n-channel Si -MOSFETs at zero magnetic field down to 0.2 K. At low electron densities, near the metal–insulator transition point from the insulating side, our results show the existence of a crossover, from Efros–Shklovskii variable range hopping (ES-VRH), which is consistent with the existence of a Coulomb gap, where ρ = ρ0 exp (T ES /T)1/2 to Mott regime, where ρ = ρ0 exp (T M /T)1/3. With ρ0 is a pre-exponential factor that is found to be close to 2 (h/e2), this crossover occurs when T ~ 1 K .

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