Evidence for strong electron-phonon coupling from the specific heat of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$

We report precise measurements of the relative enthalpy of polycrystalline ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ at high temperatures (273 K<T<700 K). From these data, we determine the lattice and electronic contributions to the specific heat. We find that the specific heat of the charge carriers follows the temperature dependence of a Fermi liquid with a Sommerfeld constant of 25±3 mJ/mole ${\mathrm{K}}^2$. By comparing our data to measurements made at low temperatures, we determine that the electron-phonon coupling is strong in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ and adequate to account for the high transition temperature.