In high-purity ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$, the (weak-field) thermal Hall conductivity ${\kappa }_{\mathrm{xy}}$ is observed to increase a thousand-fold between 90 and 30 K. The inferred quasiparticle lifetime $\tau$ increases a hundred-fold starting below 90 K, in disagreement with a recent photoemission experiment. We show that ${\kappa }_{\mathrm{xy}}$ exhibits a specific scaling behavior below $\sim 30K$. This scaling may bear on the issue of whether Landau quantization of the quasiparticle states occurs.

• Received 1 June 2000

DOI:https://doi.org/10.1103/PhysRevLett.86.890