Activationless percolating transport of charge carriers in TbMnO3 films at low temperature with low electric field

Au/TbMnO₃/YBa₂Cu₃O_7–x capacitors were fabricated on SrTiO₃ substrates by pulse laser deposition technique, of which electric properties were investigated in the temperature range from 25 to 300 K. Both current-voltage characteristics and junction resistances with bias voltages showed remarkable temperature dependence, in which obvious thermally excited relaxation processes were found between 150 and 200 K. At the temperatures lower than the activation process, the leakage currents of the capacitors were studied. Interestingly, at high electric field, the mechanism of the leakage was Poole-Frenkel emission. However, at low electric field, the conduction was not Ohmic, and ideal lnJ∝E^1/4 characteristics were observed. Analysis showed that the possible origin was related to the inherent inhomogeneous nature of activationless percolating transport.