139La Pure Quadrupole Resonance of High Tc Superconducting Materials (La1-xMx)2CuO4 (M=Ba, Sr)

Pure Quadrupole Resonance (PQR) of 139La in high T c superconductor, (La1-x M x )2CuO4 with M=Ba, Sr, has been observed at zero external field between 1.3 K and 4.2 K. In undoped La2CuO4, the PQR spectrum is very complicated, reflecting the orthorhombic structure, while in the superconducting compounds, the spectrum exhibits a drastic change and becomes more simple due to the tetragonal structure. The alloying is suggested to be responsible not only for the change of crystal structure but also for the change of microscopic electronic state.