NQR and NMR studies of Cu in the superconducting La 2CuO 4+δ

Abstract

In the superconducting La 2CuO 4+δ obtained by annealing in high pressure mixture gas of oxygen and argon, nuclear quadrupole resonance (NQR) signals of 63Cu and 65Cu have been observed around 33.1 and 36.0 MHz together with the antiferromagnetic Cu NMR signal around 70–100 MHz. The ratio of the resonance frequency of 63Cu and 65Cu is the same as that of the quadrupole moment of each Cu nucleus, indicating no internal magnetic field (paramagnetic) at Cu site. The nuclear spin-lattice relaxation time, T 1, of Cu NQR indicates that the paramagnetic phase is in the superconducting state at low temperatures. The NQR intensity is roughly proportional to the partial pressure of the oxygen gas. The NQR result suggests that the volume fraction of paramagnetic phase in La 2CuO 4+δ increases with increasing oxygen content.