Low-frequency random telegraphic noise and 1/f noise in the rare-earth manganite Pr_0.63Ca_0.37MnO₃ near the charge-ordering transition

Abstract

We have studied low-frequency resistance fluctuations (noise) in a single crystal of the rare-earth perovskite manganite Pr_0.63Ca_0.37MnO₃, which shows a charge-ordering transition at a temperature T_CO≈245K. The measurements were made across the charge-ordering transition covering the temperature range 200K<T<330K and frequency range 10⁻³Hz<f<10Hz. 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 (≈30nm), the kinetics being controlled by an activation barrier E_a≈0.45eV. 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.