Thermal Conductivity as a Probe of Quasi-Particles in the Cuprates

In underdoped YBa2Cu3Ox (x = 6.63), the low- T thermal conductivity K xx varies steeply with fieldB at small B, and saturates to a nearly field- independent value at high fields. The simple expression [1 + p(T) |B|]-1 provides an excellent fit to K xx (B) over a wide range of fields. Prom the fit, we extract the zero-field mean-free-path, and the low temperature behavior of the QP current. The procedure also allows the QP Hall angle θ Q to be obtained. We find that θ Q alls on the 1/T 2 curve extrapolated from the electrical Hall angle above Tc. Moreover, it shares the same T dependence as the field scalep(T) extracted from K xx . We discuss implications of these results.