Reexamination of Spin Dynamics in La₂CuO₄ by Cu-NQR

抄録

The nuclear spin-lattice relaxation rate 1/T₁ and the indirect nuclear spin-spin relaxation rate 1/T_2g for ⁶³Cu in La₂CuO₄ (T_N=312, K) were reexamined from 400, K to 1000, K, expanding the temperature range of the first observation by Imai et al. The temperature dependence of 1/T₁ is in good agreement with the previous result, while 1/T_2g decreases more rapidly with temperature. The temperature dependences of both 1/T₁ and 1/T_2g closely follow the renormalized classical (RC) formula below about 600, K, but deviate from the RC prediction above 600, K. The scaling relation between 1/T₁ and 1/T_2g was not confirmed above 600, K, in conflict with the theoretical prediction for the quantum critical (QC) regime. Hence, we argue that the deviation from the RC formula above 600, K does not necessarily correspond to a crossover from the RC to the QC regime.