Effect of the Phonon-Electron Interaction on Anisotropy in the Thermal Conductivity of YBCO Crystals

Experimental results on the anisotropic thermal conductivity K for the directions of the a-, b- and c-axis in YBCO crystals, have been analyzed comprehensively to make clear the mechanism of the high Tc superconductivity. By comparing these results to the Tewordt and Wolkhausen (T-W) theory, the anisotropic phonon-carrier interaction coefficients γa, γb, and γc are evaluated. It is concluded that γa≥γb≥γc, and the larger the value of γ in a direction, the higher the density of the Cooper pairs in that direction. From the maximum increment of K below Tc, AK, at each direction, phonons are concluded to be much more mobile along the ab-plane than along the c-axis.