Righi–Leduc effect in Y- and Bi-based high- Tc superconductors

Abstract

Measurements of the transverse ( k xy ) and longitudinal ( k xx ) thermal conductivity in the superconducting state of single crystals of YBa 2Cu 3O 7− δ (YBCO) and Bi 2Sr 2CaCu 2O 8− δ (BSCCO) are presented in applied magnetic fields up to 14 T. We separate the electronic thermal conductivity ( k xx el) of the CuO 2-planes from the phononic thermal conductivity ( k xx ph) using k xy and the magnetic field dependence of k xx . Our main results are: (1) In YBCO k xx el( T) shows a pronounced maximum. We attribute this to a rapid increase of the quasiparticle scattering time τ below T c. The maximum of k xx el( T) in BSCCO is much smaller due to stronger impurity scattering. The maximum of k xx is strongly suppressed by a magnetic field, presumably because of scattering of QPs on vortices. (2) Our data analysis reveals that below T c a transport ( τ) and Hall ( τ H) relaxation time must be distinguished as in the normal state. Whereas τ is strongly enhanced below T c, τ H displays the same temperature dependence as above T c.