The penetration depth in the interlayer tunnelling model for high-temperature superconductors

We investigate numerically the temperature dependence of the London penetration depth within the mean-field treatment of the interlayer pair tunnelling model for the copper oxide superconductors. It is found that the assumption that the pair tunnelling is the dominant pairing mechanism in YBCO (yttrium-barium-copper oxide) is not consistent with the experimental results on this material. We also consider the Knight shift and the dynamic spin susceptibility at a low temperature within the model. We find that the experimental results for these quantities are consistent with a relatively small contribution of the interlayer pair tunnelling to the pairing channel provided that, at least in the case of the dynamic susceptibility, the in-plane pairing produces a gap of d(x2-y2)-wave symmetry which is non-zero within at most a few tens of meV off the Fermi line. (author)