Thermal conductivity of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ in a magnetic field: Can κ(H) probe the vortex state?

We investigate the behavior of the thermal conductivity κ(H) of both twinned and untwinned single crystals of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ in a magnetic field. Remanant field data are examined in the framework of the Bean critical state model and thermally activated flux creep. In-field data are shown to depart from conventional superconductor models. The κ(H) profie is fitted by a phenomenological form and is suggested to originate from Bloch wave travel of phonons through a vortex array which becomes more regular as the field increases.