High frequency cut-off in 1/f conductivity noise of hole-doped La_1-xCa_xMnO₃ manganite single crystals

High frequency bias and temperature-dependent Lorentzian cut-off has been observed in the 1/f spectra of the conductivity fluctuations in low holedoped ferromagnetic insulating La_1-xCa_xMnO₃ manganite at low temperatures. The cut-off frequency depends on dc current bias and temperature. The high frequency cut-off has been tentatively associated with intrinsic limits of the appearance of 1/f noise in the hopping regime of the Coulomb glass state. The assumption is validated by the fact that the Efros-Shklovskii temperature T_ES, estimated from the fit of the model to the experimentally measured temperature dependence of the cut-off frequency, has the same value as the temperature T_ES evaluated independently from the temperature dependence of the resistivity in the corresponding temperature range.