Low-temperature nonlinear effects in the conductivity of lightly doped cuprates La2−xSrxCuO4 in antiferromagnetic state

Low-temperature conductivity of antiferromagnetic cuprates La2−xSrxCuO4 prepared by solid-phase synthesis was investigated. The concentration of strontium in the samples was 0.01, 0.005 and 0.001. In the temperature range T < 100 K for all the samples the conduction mechanism corresponded to 3D variable-range hopping. For T > TN (where TN is the Neel temperature) a transition to the metallic type of conductivity was observed. Nonlinear effects in low-temperature conductivity, magnetoresistivity, as well as current-controlled negative differential resistance were found. It was established that the nonlinear behavior of conductivity intensified with decreasing the strontium concentration. For temperatures T < 10 K, the effect of positive magnetoresistance was observed. It is suggested that this effect can be attributed to the presence of a new low-temperature magnetic phase (spin density waves).