Low-frequency random telegraphic noise and 1/f noise in the rare-earth manganite Pr0.63Ca0.37MnO3 near the charge-ordering transition -: art. no. 174415

We have studied low-frequency resistance fluctuations (noise) in a single crystal of the rare-earth perovskite manganite Pr0.63Ca0.37MnO3, which shows a charge-ordering transition at a temperature T(CO)approximate to245 K. The measurements were made across the charge-ordering transition covering the temperature range 200 K<T<330 K and frequency range 10(-3) Hz<f<10 Hz. The noise measurements were made using an ac bias with and without a dc bias current imposed on it. We find that the spectral power S-V(f) contains two components-one broad band 1/f part that exists for all frequency and temperature ranges and a single-frequency Lorentzian of frequency f(c), which is strongly temperature dependent. The Lorentzian in S-V(f) that appears due to random telegraphic noise (RTN) as seen in the time series of the fluctuation is seen in a very narrow temperature window around T-CO where it makes the dominating contribution to the fluctuation. When the applied dc bias is increased beyond a certain threshold current density J(th), the electrical conduction becomes nonlinear and one sees the appearance of a significant Lorentzian contribution in the spectral power due to RTN. We explain the appearance of the RTN as due to coexisting charge-ordered (CO) and reverse orbitally ordered (ROO) phases. These phases are in dynamical equilibrium over a mesoscopic length scale (approximate to30 nm), the kinetics being controlled by an activation barrier E(a)approximate to0.45 eV. The destabilization of the CO phase to the ROO phase causes nonlinear conductivity as well as the appearance of a RTN-type fluctuation when the bias current exceeds a threshold. The 1/f noise is low for T>T-CO but increases by nearly two orders in a narrow temperature range as T-CO is approached from above and the probability distribution function (PDF) deviates strongly from a Gaussian dependence. We explain this behavior as due to approach of charge localization with correlated fluctuators which make the PDF non-Gaussian.