Nuclear spin-lattice relaxation of ¹³⁹La in (La_1−xSr_x)₂CuO₄

We report here the data of ¹³⁹La nuclear spin-lattice relaxation times T₁ taken from 4.2K to 275K in (La_1−xSr_x)₂CuO₄, concentrating on a region from x=0.075 (superconducting with highest T_c to x=0.15 (metallic). In the superconducting state of the compounds with x=0.075 and 0.10, T₁⁻¹ just below T_c decreases rapidly without any enhancement. In the metallic sample of x=0.15, T₁ follows a Korringa law within our experimental range of 4.2-77K. On the other hand, in the normal state for x=0.075, T₁⁻¹ shows anomalous increase from 70K to ~150K and then levels off at high temperatures. This anomalous behavior is considered to be originated in a change of the density of state at the Fermi level near to the La sites, probably caused by the orthorhombic-to-tetragonal phase transition.