Two level telegraphic conductivity fluctuations in ferromagnetic insulating manganite single crystals

Robust two-level telegraph conductivity noise in phase separated ferromagnetic insulating manganite La _0.86 Ca _0.14 MnO ₃ has been observed in exceptionally wide temperature range 130 K - 185 K in the low-resistivity metastable state of the system. The switching rate of the telegraphic noise was found not to depend on applied magnetic field and bias current. In contrast, the amplitude of the telegraphic noise varies in a non monotonic way with decreasing temperature and goes through a clear maximum around 160 K. The amplitude decreases exponentially with increasing bias current in exactly the same manner as the sample resistance increases with the current. This features point out to the dynamic current redistribution between distinct percolation paths in the phase separated material as a possible mechanism behind the robust two-level conductivity fluctuations.