Heat capacity under pressure of CeCoIn₅

Among heavy-fermion (HF) superconductors, CeCoIn5 exhibits a record high value of T-c = 2.3 K at ambient pressure [1]. CeCoIn5 belongs to a new class of HF-superconductors that crystallize in the tetragonal HoCoGa5-structure. This structure can be regarded as alternating layers of CeIn3 and CoIn2. Bulk CeIn3 undergoes a transition from an antiferromagnetic (AFM) state at ambient pressure (T-N = 10.2 K) to a superconducting state with very low T-C = 0.15 K at a critical pressure p(c) = 2.8 GPa [2] at which long range magnetic order vanishes. It is, therefore, regarded as a possible candidate for magnetically mediated superconductivity (SC). We report on measurements of the heat capacity of CeCoIn5 at hydrostatic pressures p less than or equal to 1.5 GPa. While T-c increases with increasing pressure, the effective mass of the quasi-particles m(eff) decreases, as indicated by the ratio C/T\(Tc). As a working hypothesis based on theories of a nearly antiferromagnetic Fermi-liquid (NAFFL), this may be interpreted as the stabilization of the superconducting state by an increase of the characteristic spin fluctuation temperature T-SF (T-SF proportional tok(F)(2)/m(eff))