Effect of controlled disorder on quasiparticle thermal transport in Bi₂Sr₂CaCu₂O₈

Low-temperature thermal conductivity κ of optimally doped Bi₂Sr₂CaCu₂O₈ was studied before and after the introduction of point defects by electron irradiation. The amplitude of the linear component of κ remains unchanged, confirming the universal nature of heat transport by zero-energy quasiparticles. The induced decrease in the absolute value of κ at finite temperatures allows us to resolve a nonuniversal term in κ due to conduction by finite-energy quasiparticles. The magnitude of this term provides an estimate of the quasiparticle lifetime at subkelvin temperatures.