Angle dependence of the transverse thermal conductivity in YBa2Cu3O7 single crystals: Doppler shift and Andreev scattering contributions - art. no. 167006

We have measured the transverse thermal conductivity kappa (xy) of twinned and untwinned YBa2Cu3O7 single crystals as a function of angle theta betwee n the magnetic field applied parallel to the CuO2 planes and the heat curre nt direction. For both crystals we observed a clear twofold variation in th e field-angle dependence Of kappa (xy) (theta) kappa (0)(xy) (T, B) sin(2 t heta). We have found that the oscillation amplitude kappa (0)(xy) depends o n temperature and magnetic field. Our results show that kappa (0)(xy) = aB ln(1/bB) with the temperature- and sample-dependent parameters a and b. We discuss our results in terms of Andreev scattering of quasiparticles by vor tices and a recently proposed theory based on the Doppler shift in the quas iparticle spectrum.