Nuclear Spin-Lattice Relaxation of ¹³⁹La in Superconducting (La_1−xSr_x)₂CuO₄

Abstract

Nuclear spin-lattice relaxation times T₁ of ¹³⁹La in high-T_C superconductor (La_1−xSr_x)₂CuO₄ (x=0.075, 0.10) have been measured in zero field. T₁⁻¹ in the superconducting state decreases rapidly, indicating a superconducting energy gap formation, but no signs of T₁⁻¹ enhancement are observed just below T_C. T₁⁻¹ in the normal state shows slightly stronger temperature dependence than that expected from the Korringa relation (T₁T=const.) observed in a highly Sr-doped, nonsuperconducting compound with x=0.15.