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In this work we review the investigations of conductance fluctuations in doped silicon at low temperatures (2K < T < 20K) as it is tuned through the metal-insulator transition by changing the carrier concentration n. Spectral power, S(f), of the conductance fluctuation retains a generic 1/fα dependence. In the metallic regime (n>nc) the doped Si is like a weakly-localized electron system and the conductance fluctuation is governed by the mechanism of Universal conductance fluctuations. The relative variance of fluctuation follows the temperature dependence ∝ T-β, where β≈1/2. However, the noise diverges by orders of magnitude as n decreases through the critical concentration nc and the fluctuation also becomes strongly temperature dependent with β>> 1. At the transition (n/nc≈1) the fluctuation becomes strongly non-Gaussian below 20K as observed through the second spectrum S(2)(f). At T=4.2K, we find that after subtracting the Gaussian background , S(2)(f)∝ 1/fp where p is small (< 0.5) for metallic samples (n/nc≥ 1.5) and it grows to > 1 for samples close to the transition n/nc ≈1. The growth of non-Gaussianity is accompanied by a growth in low frequency spectral weight as seen through a significant enhancement of α from close to 1 (n>nc) to nearly 1.4 for n/nc ≈1. The growth of non-Gaussian fluctuation of extremely large magnitude with significant low frequency component points to a correlated low frequency dynamics of charge fluctuation near the insulator-metal transition. This has been interpreted as the onset of a glassy freezing of the electronic system across the transition.
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