Noise Probe of the Dynamic Phase Separation inLa2/3Ca1/3MnO3

Giant random telegraph noise (RTN) in the resistance fluctuation of a macroscopic film of perovskite-type manganese oxide ${\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_3$ has been observed at various temperatures ranging from 4 to 170 K, well below the Curie temperature ( $T_C\approx 210\mathrm{K}$). The amplitudes of the two-level fluctuations vary from $0.01\%$ to $0.2\%$. We discuss the origin of the RTN to be a dynamic mixed-phase percolative conduction process, where manganese clusters switch back and forth between two phases that differ in their conductivity and magnetization.