Observation of non-Gaussian conductance fluctuations at low temperatures in Si:P(b) at the metal-insulator transition.

We report investigations of conductance fluctuations (with 1/f(alpha) power spectra) in doped silicon at low temperatures (T<20 K) as it is tuned through the metal-insulator transition (MIT) by changing the carrier concentration n. The scaled magnitude of noise, gamma(H), increases with decreasing T following an approximate power law gamma(H) approximately T-beta. At low T, gamma(H) diverges as n decreases through the critical concentration n(c), accompanied by a growth of low-frequency spectral weight. The second spectrum and probability density of the fluctuations show strong non-Gaussian behavior below 20 K as n/n(c) decreases through 1. This is interpreted as the onset of a glassy freezing of the electronic system across the MIT.