We present the temperature dependence of the thermal conductivity kappa(T) of the unconventional superconductor Sr_2RuO_4 down to low temperatures (100 mK). In T -> 0 K limit we found a finite residual term in kappa/T, providing clear evidence for the superconducting state with an unconventional pairing. The residual term remains unchanged for samples with different T_c, demonstrating the universal character of heat transport in this spin-triplet superconductor. The low-temperature behavior of kappa suggests the strong impurity scattering with a phase shift close to pi/2. A criterion for the observation of universality is experimentally deduced.
@article{arxiv.cond-mat/0201010,
title = {Universal Heat Transport in Sr2RuO4},
author = {M. Suzuki and M. A. Tanatar and N. Kikugawa and Z. Q. Mao and Y. Maeno and T. Ishiguro},
journal= {arXiv preprint arXiv:cond-mat/0201010},
year = {2009}
}