Giant random telegraph noise (RTN) in the resistance fluctuation of a macro
scopic film of perovskite-type manganese oxide La2/3Ca1/3MnO3 has been obse
rved at various temperatures ranging from 4 to 170 K, well below the Curie
temperature (T-C approximate to 210 K). The amplitudes of the two-level flu
ctuations 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 cluste
rs switch back and forth between two phases that differ in their conductivi
ty and magnetization.