SUPERFLUID ANISOTROPY IN YBCO - EVIDENCE FOR PAIR TUNNELING SUPERCONDUCTIVITY

Proximity effect and pair tunneling models are applied as alternative scenarios to explain the recently measured ab-plane and c-axis compone nts of the superfluid tensor in copper-oxide superconductors which con tain chains, such as YBa2Cu3O6.95. It is argued that conventional prox imity effect models, which couple chains and planes via single electro n tunneling only, are incompatible with the experimental observations. On the other hand, several surprising features of the experimental da ta are readily explained by the presence of a microscopic pair tunneli ng process.