Reexamination of Spin Dynamics in La₂CuO₄by Cu-NQR

Abstract

The nuclear spin-lattice relaxation rate 1/ T 1 and the indirect nuclear spin-spin relaxation rate 1/ T 2g for 63 Cu in La 2 CuO 4 ( 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/ T 1 is in good agreement with the previous result, while 1/ T 2g decreases more rapidly with temperature. The temperature dependences of both 1/ T 1 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/ T 1 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.