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Bias Dependent 1/f Conductivity Fluctuations in Low-Doped La$_{1-x}$Ca$_{x}$MnO$_3$ Manganite Single Crystals

Low frequency noise in current biased La$_{0.82}$Ca$_{0.18}$MnO$_{3}$ single crystals has been investigated in a wide temperature range from 79 K to 290 K. Despite pronounced changes in magnetic properties and dissipation mechanisms of the sample with changing temperature, the noise spectra were found to be always of the 1/f type and their intensity (except the lowest temperature studied) scaled as a square of the bias. At liquid nitrogen temperatures and under bias exceeding some threshold value, the behavior of the noise deviates from the quasi-equilibrium modulation noise and starts to depend in a non monotonic way on bias. It has been verified that the observed noise obeys Dutta and Horn model of 1/f noise in solids. The appearance of nonequilibrium 1/f noise and its dependence on bias have been associated with changes in the distribution of activation energies in the underlying energy landscape. These changes have been correlated with bias induced changes in the intrinsic tunneling mechanism dominating dissipation in La$_{0.82}$Ca$_{0.18}$MnO$_{3}$ at low temperatures.