Anomalies of conductivity behavior near the paramagnetic-antiferromagnetic transition in single-crystals La_{2}CuO_{4+\delta}

摘要

The temperature dependences of resistance, R(T), of two single-crystalsLa_{2}CuO_{4+\delta} samples have been studied with the aim to detect apossible change in the R(T) behavior induced by paramagnetic-antiferromagnetic(PM-AFM) transition. One of the samples with \delta \lesssim 0.01, was fairlyhomogeneous in oxygen distribution (not phase-separated) with Neel temperatureT_{N}\approx 266 K. Conductivity of this sample has been determined by Mott'svariable-range hopping below T_N. The other, far less resistive, sample with\delta \approx 0.05, was inhomogeneous (phase-separated) showing both PM-AFM(T_N\approx 205 K) and superconducting (T_c\approx 25 K) transitions. It isfound that for the homogeneous sample the resistivity decreases above T_N farfaster with temperature than below it (for both directions of measuringcurrent, parallel and perpendicular to basal CuO_2 planes). A similar behaviorof conductivity near PM-AFM transition is also found for the phase-separatedand less resistive sample. In this case a clear kink in R(T) curve nearT_N\approx 205 K can be seen. Furthermore, a transition to metallic (dR/dT>0)behavior occurs far enough above T_N. The observed behavior of the samplesstudied is related to increased delocalization of charge carriers above T_N.This is in accordance with decrease in the AFM correlation length andcorresponding enhancement of the hole mobility above T_N known for low-dopedlanthanum cuprates.