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Abstract

In the quest for new superconductor compounds which adopt the superconducting state at increasingly higher transition temperatures T-c, a non-phonon mediated coupling between the charge carriers seems to play a key role. In order to enhance our understanding of such unconventional coupling mechanisms, we studied a new family of heavy fermion (HF) superconductors CeTIn5 (T: transition metal) whose properties point toward the realization of unconventional superconductivity (SC): the specific beat, thermal conductivity and nuclear spin-lattice relaxation rate of CeIrIn5 and CeCoIn5 decrease as a power law of temperature instead of exponentially for T < T-c. We report on measurements of the heat capacity of CeIrIn5 and CeCoIn5 at hydrostatic pressures p less than or equal to 1.6 GPa. In both compounds, T. increases with increasing pressure, while the 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 to k(F)(2)/m(eff)).