Unconventional Superconductivity in CeCoIn₅Studied by the Specific Heat and Magnetization Measurements

Abstract

We measured the low-temperature specific heat in magnetic fields up to 80 kOe, together with the magnetization for the heavy-fermion superconductor CeCoIn 5 with the transition temperature T c = 2.25 K. CeCoIn 5 is a strong-coupling superconductor with a large jump in the specific heat Δ C / C n ( T c ) = 4.7. The heavy-fermion state is significantly formed below 1 K, reaching at least 1070 mJ/K 2 ·mol in magnetic fields. This large electronic specific heat coefficient at 0.25 K is, however, reduced with increasing magnetic field, ranging from 1070 mJ/K 2 ·mol at 50 kOe to 820 mJ/K 2 ·mol at 80 kOe. The upper critical field H c2 at 0 K is estimated to be 116 kOe for H ∥[100] and 49.5 kOe for H ∥[001]. The present anisotropy of H c2 is well explained by the anisotropic effective mass, but the magnitude of H c2 is reduced strongly by the paramagnetic effect for both field directions.