THERMAL-CONDUCTIVITY OF HIGH-T(C) CRYSTALS - DEPENDENCE ON MAGNITUDE AND ORIENTATION OF MAGNETIC-FIELD, AND EFFECT OF ZN DOPING

We present precise measurements of in-plane thermal conductivity for s uperconducting single crystals of YBa2Cu3O7-x (YBCO) with T(c)=92 and 60 K, Bi2Sr2CaCu2O8 (BSCCO), and of Zn-doped YBCO. Magnetization and t hermal conductivity data obtained with the same 90 K YBCO crystal demo nstrate a close relationship between the magnetic thermal resistivity and the internal magnetic field B in a superconductor in the mixed sta te. For all superconductors studied here, the magnetic thermal resisti vity is a sublinear function of magnetic field. The origins of the non linearity are discussed. Angular dependences of the magnetic thermal r esistivity have been shown to depart from the anisotropic 3D supercond uctor model and are in quantitative agreement with a quasi-2D model. I mplications for spatial modulation of the order parameter are made.