Field-Angle-Dependent Specific Heat Measurements and Gap Determination of a Heavy Fermion Superconductor URu2Si2

To identify the superconducting gap structure in URu₂Si₂, we perform field-angle-dependent specific heat measurements for the two principal orientations in addition to field rotations, and a theoretical analysis based on microscopic calculations. The Sommerfeld coefficient γ(H)’s in the mixed state exhibit a distinctly different field dependence. This comes from point nodes and the substantial Pauli paramagnetic effect of URu₂Si₂. These two features combined give rise to a consistent picture of superconducting properties, including a possible first order transition of H_c2 at low temperatures.