The magnetic nature of the altermagnet candidate RuO2 remains under debate. It has been recently shown from quantum oscillations and angle-resolved photoemission spectroscopy (ARPES) that the high-quality RuO2 bulk single crystal is a paramagnetic metal. Here we report the specific heat and magnetic susceptibility in ultra-clean RuO2 single crystals with residual resistivity ratio up to 1200. The magnetic susceptibility increases with temperature and is phenomenologically fitted with an inclusion of Tln(T/T0) over a wide temperature range up to 400 K. In contrast, the energy dependence of the density of states and thermal activation of quasiparticles lead to a decrease with temperature. Such characteristic temperature dependence, similar to that observed in other d-electron metals, is attributable to an enhanced orbital contribution arising from lattice-expansion-induced changes in the band structure. The electronic specific heat, the magnetic susceptibility, and the T2 coefficient in resistivity point to a weakly-correlated 3D Fermi-liquid state with a modest electron correlation, as supported by the Wilson and Kadowaki-Woods ratios.
@article{arxiv.2512.03108,
title = {Fermi-liquid behavior and characteristic temperature-dependent susceptibility in clean RuO$_2$ crystal},
author = {Shubhankar Paul and Atsutoshi Ikeda and Hisakazu Matsuki and Giordano Mattoni and Jörg Schmalian and Kunihiko Yamauchi and Chanchal Sow and Shingo Yonezawa and Yoshiteru Maeno},
journal= {arXiv preprint arXiv:2512.03108},
year = {2026}
}