Cu Nuclear Spin-Lattice Relaxation Study of A- and B-Sites in La_1.80Sr_0.20CuO₄ (T_c=30K)

Abstract

We report the temperature(T)-dependence of the planar ⁶³Cu nuclear spin-lattice relaxation rate, 1/T₁, both at the Cu(A)-site (77.3K≤ T≤ 500K) and at the Cu(B)-site (77.3K≤ T≤ 300K) in the high-T_c Cu oxide, La_1.80Sr_0.20CuO₄ (T_c-- 30K), measured by the Cu NQR spin-echo technique. We found that 1/T₁ at the Cu(B)-site is different from that at the Cu(A)-site, and that 1/T₁ at the Cu(A)-site has a superlinear T-dependence in the T-range of 300-- 500K. Comparisons of the present 1/T₁ are made with the data for other systems. The difference in 1/T₁ between two Cu sites is discussed from the viewpoint of local inhomogeneous electronic states.