Effect of magnetic field on thermal conductivity of YBa2Cu3O7−δ single crystals

Abstract

We report measurements of the thermal conductivity in a magnetic field on single crystals of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$. Unlike in sintered samples, the zero-field thermal conductivity of these crystals above the superconducting transition temperature shows a marked decrease with increasing temperature, demonstrating the importance of phonon-phonon processes and the high quality of the crystals. We find that the thermal conductivity κ is very sensitive to the presence of fluxoids which are strong scatterers of phonons. The degradation of κ is particularly large when the magnetic field H is oriented perpendicular to the Cu-O planes. The anisotropic behavior of κ(H) is in qualitative agreement with a geometric argument based on the anisotropy of the superconducting coherence length. We detect hysteresis at the level of several percent in the dependence of κ on the field.