Effect of magnetic field on thermal conductivity of YBa2Cu3O7- delta 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{\ensuremath{-}}\mathrm{\ensuremath{\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 \ensuremath{\kappa} is very sensitive to the presence of fluxoids which are strong scatterers of phonons. The degradation of \ensuremath{\kappa} is particularly large when the magnetic field H is oriented perpendicular to the Cu-O planes. The anisotropic behavior of \ensuremath{\kappa}(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 \ensuremath{\kappa} on the field.