¹³⁹La NMR Study of Charge and Spin Order in La_1.885Sr_0.115CuO₄ Single Crystal

Recent technological advancements have made the detection of charge order in La_2-xSr_xCuO₄ (x ~ 1/8) possible using x-ray diffraction nearly two decades after NMR measurements showed that the superconducting La_2-xSr_xCuO₄ (x ~ 1/8) share nearly identical anomalies as Nd-codoped La_1.48 Nd_0.2Sr_0.12CuO₄ at the charge order transition of the latter. We revisit the elusive charge ordered state in La_1.885Sr_0.115CuO₄ by measuring the ¹³⁹La NMR linewidth and relaxation rate 1/T₁. Our data demonstrates that the NMR linewidth broadens and 1/T₁T is enhanced below the charge order temperature T_charge = 80 K. In view of our recent finding that two different types of ⁶³Cu NMR signals exist below T_charge, we analyze 1/T₁ using a two-component fit. We estimate the fractions of ¹³⁹La nuclear spins with fast and slow 1/T₁ components. The temperature dependence of slow 1/T₁ exhibits qualitatively the same behavior as the optimally superconducting phase even below T_charge down to T_c = 30K, but its volume fraction decreases with temperature. In contrast, 1/T₁T of the fast component begins to increase immediately below T_charge. We also show that the fast 1/T₁ exhibits very strong magnetic field dependence below T_c.