Thermal conductivity of Sr3Ru2O7 was measured down to 40 mK and at magnetic fields through the quantum critical endpoint at H_c = 7.85 T. A peak in the electrical resistivity as a function of field was mimicked by the thermal resistivity. In the limit as T -> 0 K we find that the Wiedemann-Franz law is satisfied to within 5% at all fields, implying that there is no breakdown of the electron despite the destruction of the Fermi liquid state at quantum criticality. A significant change in disorder (from ρ0(H=0T) = 2.1 μΩ cm to 0.5 μΩ cm) does not influence our conclusions. At finite temperatures, the temperature dependence of the Lorenz number is consistent with ferromagnetic fluctuations causing the non-Fermi liquid behavior as one would expect at a metamagnetic quantum critical endpoint.
@article{arxiv.cond-mat/0602469,
title = {Thermal conductivity in the vicinity of the quantum critical endpoint in Sr3Ru2O7},
author = {F. Ronning and R. W. Hill and M. Sutherland and D. G. Hawthorn and M. A. Tanatar and J. Paglione and Louis Taillefer and M. J. Graf and R. S. Perry and Y. Maeno and A. P. Mackenzie},
journal= {arXiv preprint arXiv:cond-mat/0602469},
year = {2009}
}