T. Xiang et Jm. Wheatley, SUPERFLUID ANISOTROPY IN YBCO - EVIDENCE FOR PAIR TUNNELING SUPERCONDUCTIVITY, Physical review letters, 76(1), 1996, pp. 134-137
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.