Low-energy spin dynamics and critical hole concentrations in La2-xSrxCuO4 (0.07 ≤ x ≤ 0.2) revealed by 139La and 63Cu nuclear magnetic resonance

We report a comprehensive La-139 and Cu-63 nuclear magnetic resonance study on La2-xSrxCuO4 (0.07 <= x <= 0.2) single crystals. The La-139 spin-lattice relaxation rate T-139(1)-1 is drastically influenced by Sr doping x at low temperatures. A detailed field dependence of T-139(1)-1 at x = 1/8 suggests that charge ordering induces the critical slowing down of spin fluctuations toward glassy spin order and competes with superconductivity. On the other hand, the 63Cu relaxation rate T-63(1)-1 is well described by a Curie-Weiss law at high temperatures, yielding the Curie-Weiss temperature Theta as a function of doping. Theta changes sharply through a critical hole concentration x(c) similar to 0.09. x(c) appears to correspond to the delocalization limit of doped holes, above which the bulk nature of superconductivity is established.