Magnetism and Electrical Conduction in Lightly-Doped Single-Layer High- T c Cuprate La 2 CuO 4+ δ

The temperature dependences of magnetization and electrical resistivity as well as their magnetic field dependences have been examined in lightly-doped single-layer cuprate La 2 CuO 4+ δ [LCO, hole-doping level p(2δ) ≅ 0.03] single crystals, in comparison with those in the extremely low doping region of p [Formula: see text] 0.015 to uncover the intrinsic magnetism and electrical conduction of the Cu–O plane that exhibits both antiferromagnetic (AF) and superconducting (SC) orders simultaneously. In p ≅ 0.03 SC LCO, the sub-lattice moments on Cu sites and their AF couplings are only ∼15% smaller than those of the Mott-insulator parent material, suggesting that the localization of Cu3d electrons remains very strong. Furthermore, we report that in the SC LCO, two-dimensional AF spin correlations develop rapidly from T * ≅ 280 K towards Néel temperature T N = 266 K, where the out-of-plane resistivity starts to decrease largely. This might be responsible for the AF ordering at such a high temperature in the SC single-layer cuprate with p ≅ 0.03.