Nuclear Quadrupole Resonance of Cu in Superconducting (La_0.925Sr_0.075)₂CuO₄

Abstract

Nuclear quadrupole resonance (NQR) signals of ⁶⁵Cu and ⁶³Cu have been discovered in the high-T_c superconducting oxide (La_0.925Sr_0.075)₂CuO₄ at 33.0 MHz and 35.3 MHz, respectively. The temperature dependence of the nuclear spin-lattice relaxation rate 1⁄T₁ was similar to that of Cu(II) (CuO₂ plane) in the YBa₂Cu₃O_7−δ system (Y system). From the behavior of 1⁄T₁, it is pointed out that the relaxation arises from the same mechanism as that of the CuO₂ plane in the Y system, where the relaxation in the normal state is considered to be dominated by the spin fluctuations of the nearly localized Cu-3d holes.