Complex Susceptibility of High-T_c Superconductor ErBa₂Cu₃O_6+x

Abstract

The magnetic response of ErBa 2 Cu 3 O 6+ x has been studied in terms of complex susceptibility χ=χ'- i χ''. In the superconducting transition, χ' reflects the Meissner effect and χ'' forms a single peak. Careful measurements revealed that the onset temperature of χ' is slightly higher than that of χ'' and there exist two superconducting phases. χ' and χ'' of the lower phase are very sensitive to the field amplitude. The upper phase may be interpreted as a bulk superconductivity while the lower phase corresponds to a weak coupling between bulk superconducting inclusions.