Theoretical analysis of the thermal conductivity of YBa2Cu3O7−δ single crystals

Abstract

We analyze the in-plane thermal conductivity of single-crystal ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$. Our theoretical fit provides an excellent description of the experimental data throughout the temperature range 10 K<T<200 K. From this fit, we can extract information about the lattice microstructure and the electronic contribution to the total thermal conductivity. Our calculations indicate that long-wavelength phonons, with mean free paths of the order of the crystal thickness, contribute significantly to the thermal conductivity up to ∼75 K. The phonon-electron coupling strength λ for the phonons which dominate in the heat-conduction process is calculated to lie in the range 0.03<λ<0.08. In addition, we extract a value of (1.6±0.3)${\mathrm{\Delta }}_{\mathrm{BCS}}$ for the superconducting energy gap.