Magnetic field dependence of low-temperature specific heat in Sr2RuO4

The magnetic field (H) dependence of the Sommerfeld coefficient gamma(H) of the low-temperature specific heat in Sr(2)RuO(4) is analyzed by numerically solving the microscopic Eilenberger equation. By taking account of the strong Pauli-paramagnetic effect, we find that gamma(H) exhibits a systematic change from a concave function root H to a convex function H(alpha)(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.