SUPERCONDUCTIVITY EFFECTS IN HOPPING CONDUCTIVITY OF LA2CUO4 SINGLE-CRYSTAL WITH EXCESS OXYGEN

hopping conductivity of La2CuO4+delta single crystal with excess oxyge n has been studied. It is found that the transition from variable-rang e hopping (with the temperature dependence of resistance R proportiona l to exp(T-0/T)(1/4)) to simple activation conductivity (R proportiona l to exp(Delta/kT)) occurs at a temperature lower than 20 K. This tran sition is accompanied with significant changes in the behavior of magn etoresistance and current-voltage characteristics. It is shown that su ch a behavior of hopping conductivity below 20 K is due to the presenc e of superconducting inclusions in insulating sample due to phase sepa ration of La2CuO4+delta. The observed peculiarities in the conducting properties are in good agreement with the known effects of competition between electron localization and superconductivity in homogeneous sy stems. (C) 1997 American Institute of Physics.