Noise probe explores the glassiness of Ferromagnetic Insulating (FMI) state in manganites

The ferromagnetic insulating (FMI) state of low hole doped manganites forms a disordered electronic system showing Efros-Shklovskii variable range hopping (ESVRH) type hoping at low temperature with evidence of a soft Coulomb gap of Δ_CG. The temperature dependent noise identified a freezing temperature where the freezing process is kinetically governed with the time scale determined by an activation energy similar to Δ_CG. The activation barrier determined from noise matches closely with Δ_CG obtained from transport measurement. At low temperatures the fluctuation develops a non-Gaussian component. Using higher order statistics of fluctuations we experimentally address the evidence of slowly driven kinetics and correlated motion of charge carriers in FMI states.