Phys. Rev. Lett. 87, 167006 (2001)
R. Ocaña and P. Esquinazi
Abstract
We have measured the transverse thermal conductivity κxy of twinned and untwinned YBa2Cu3O7 single crystals as a function of angle θ between the magnetic field applied parallel to the CuO2 planes and the heat current direction. For both crystals we observed a clear twofold variation in the field-angle dependence of κxy(θ) = -κxy0(T,B)sin(2θ). We have found that the oscillation amplitude κxy0 depends on temperature and magnetic field. Our results show that κxy0 = aBln(1/bB) with the temperature- and sample-dependent parameters a and b. We discuss our results in terms of Andreev scattering of quasiparticles by vortices and a recently proposed theory based on the Doppler shift in the quasiparticle spectrum.