Giant enhancement of the thermal Hall conductivity kappa_(xy) in the superconductor YBa₂Cu₃O₇

In high-purity crystals of YBa_2Cu_3O_7, the quasiparticle (qp) lifetime \tau and the (weak-field) thermal Hall conductivity \kappa_{xy} undergo dramatic increases below 90K. We present a detailed picture of the behavior of \kappa_{xy} at low temperature, in particular its scaling properties, which are directly relevant to the issue of whether Landau quantization of the qp states occurs.