Anisotropic thermal conductivity of c-axis aligned Bi2Sr2CaCu2Ox superconductor in high magnetic fields

The anomalous behavior of the thermal conductivity, kappa, of high temperat ure superconductors (HTS) has been attributed to two conflicting theories ( phonon domination and electron domination) since the discovery of HTS. Chan ge in kappa due to a magnetic field is a direct consequence of additional s cattering processes between the phonons, the charge carriers, and the flux lines. The existing theories predict different scattering effects for the p honons and the electrons. Therefore, knowing magnetothermal conductivity ca n provide useful information for the nature of heat carriers in HTS and the understanding of the vortex dynamics. We have measured the in-plane therma l conductivity of a c-axis aligned Bi2Sr2CaCu2Ox superconductor in magnetic fields up to 17 T. The magnetic field was applied both parallel and perpen dicular to the c axis and always perpendicular to the direction of heat flo w. The results are compared to existing electronic and phononic models. It has been discovered that the electronic thermal conductivity, kappa(e), cal culated from the Wiedemann-Franz law, does not pl edict the measured behavi or of the thermal conductivity. Rather, the phonon thermal conductivity, ka ppa(ph), calculated from the extended BRT (Bardeen, Richayzen, and Tewordt) theory, reproduces the experimental results accurately. The anisotropy of the in-plane magnetothermal conductivity is also investigated. (C) 1998 Ame rican Institute of Physics.