NQR AND NMR OF HIGH-Tc SUPERCONDUCTING OXIDES (La1-xBax)2CuO4-y AND YBa2Cu3O7–y

Abstract

In (La1-xBax)2CuO4-y, the antiferromagnetic and superconducting phase diagram have been investigated from both 139La nuclear quadrupole resonance (NQR) and resistivity measurements. It is concluded that the magnetic phase boundary is around x = 0.025-0.03 where the superconductivity starts to appear around 2 K. In YBa2Cu3O7-y, both NQR and NMR of 63Cu and 65Cu have been made at zero and high fields up to 135 kOe. Two pairs of Cu NQR lines have been observed at 31.5, 29.5 MHz, and 22.1, 20.4 MHz, corresponding to two inequivalent Cu sites. From the high-field NMR measurement, two Cu sites with the lower and higher NQR frequencies were reasonably assigned to the Cu sites situated in Cu–O chains and planes, respectively.