Magnetic field dependence of low-temperature specific heat inSr2RuO4

Abstract

The magnetic field $(H)$ dependence of the Sommerfeld coefficient $\ensuremath{\gamma}(H)$ of the low-temperature specific heat in ${\text{Sr}}_{2}{\text{RuO}}_{4}$ is analyzed by numerically solving the microscopic Eilenberger equation. By taking account of the strong Pauli-paramagnetic effect, we find that $\ensuremath{\gamma}(H)$ exhibits a systematic change from a concave function $\sqrt{H}$ to a convex function ${H}^{\ensuremath{\alpha}}(\ensuremath{\alpha}>1)$ at high fields when the orientation of the magnetic field is varied, explaining experimental results. The magnetization is found to be consistent with this behavior. This implies either singlet pairing or triplet pairing with the $d$ vector locked in the basal plane. Based on this conclusion, we explain other properties of this compound.