Novel Phase Separation and Spin Dynamics of Lightly Doped La_(2-x)Sr_2CuO_4 Probed by La-Nuclear Quadrupole Resonance

摘要

We report novel magnetic properties in the slightly hole-doped Mott-insulator La_(2-x)Sr_xCuO_4 via the La-nuclear quadrupole resonance (NQR) measurements. At x = 0.018, the antiferromagnetic (AFM) La-NQR spectrum affected by internal fields comes out as the temperature decreases below T_N ～ 150 K, whereas the nonmagnetic one persists to be observed down to a temperature T_f ～ 20 K at which the nuclear-relaxation rate has a pronounced peak. This demonstrates that the phase separation of nonmagnetic and AFM phases occurs between T_f and T_N. The novel phase separation is suggested as due to the partial destruction of the AFM phase caused by mobile holes via the formation of an extended spin-singlet state between Cu-derived spins and hole spins.