EVIDENCE FOR STRONG ELECTRON-PHONON COUPLING IN THE THERMAL-CONDUCTIVITY OF YBA2CU3O7-DELTA

We have measured the ab-plane thermal conductivity (kappa) on single-crystal YBa2Cu3O7-delta (delta almost-equal-to 0.08) in the temperature range 10 less-than-or-equal-to T less-than-or-equal-to 300 K. Our main focus is an analysis of the slope change in kappa(T), which occurs just below the superconducting transition. The reduced-temperature (t = T/T(c)) derivative of the normalized thermal conductivity, -d(kappa(s)/kappa(n))/dt\t = 1, as determined from the data, is rather small, less-than-or-equal-to 1.1. From measurements of the electrical conductivity on the same specimens and application of the Wiedemann-Franz law, we determine the relative contributions to the heat conduction from the carriers and the lattice, and discuss the normal-state phonon-scattering mechanisms. Employing these results we calculate the slope of the lattice thermal conductivity at T(c) and infer that the slope of the carrier conductivity must by very large, greater-than-or-equal-to 6. This result implies strong coupling for some of the carriers.