Observation of Magnetic Moments in the Superconducting State of YBa2Cu3O6.6

Neutron scattering measurements for YBa2Cu3O6.6 have identified small magnetic moments that increase in strength as the temperature is reduced below T* and further increase below T-c. An analysis of the data shows the moments are antiferromagnetic between the Cu-O planes with a correlation length of longer than 195 Angstrom in the a-b plane and about 35 Angstrom along the c axis. The origin of the moments is unknown, and their properties are discussed both in terms of Cu spin magnetism and orbital bond currents.