Anisotropic thermal conductivity of c-axis aligned Bi₂Sr ₂CaCu₂O_x superconductor in high magnetic fields

The anomalous behavior of the thermal conductivity, κ, of high temperature superconductors (HTS) has been attributed to two conflicting theories (phonon domination and electron domination) since the discovery of HTS. Change in κ due to a magnetic field is a direct consequence of additional scattering processes between the phonons, the charge carriers, and the flux lines. The existing theories predict different scattering effects for the phonons and the electrons. Therefore, knowing magnetothermal conductivity can provide useful information for the nature of heat carriers in HTS and the understanding of the vortex dynamics. We have measured the in-plane thermal conductivity of a c-axis aligned Bi₂Sr ₂CaCu ₂O_x superconductor in magnetic fields up to 17 T. The magnetic field was applied both parallel and perpendicular to the c axis and always perpendicular to the direction of heat flow. The results are compared to existing electronic and phononic models. It has been discovered that the electronic thermal conductivity, κ_e, calculated from the Wiedemann-Franz law, does not predict the measured behavior of the thermal conductivity. Rather, the phonon thermal conductivity, κ_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.