Comparing Y−Ba−Cu−O superconductors by Cu,O and Ba NMR/NQR

This paper discusses various NMR/NQR studies performed by the resonance group at the Physik-Institut on the structurally related compounds YBa₂Cu₃O₇ and YBa₂Cu₄O₈. Employing different isotopes and comparing similar measurements offers the possibility to gain new insights into these compounds. The discussion addresses the following topics: Electric field gradients and their temperature and pressure dependence;T _c enhancement by Ca doping; Cu and O Knight shifts; Ba relaxation. The wide range of applicability of the resonance methods in superconductivity research is demonstrated.