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Abstract

Studies of a new family of heavy fermion (HE) superconductors CeMIn5 (M: transition metal) point toward the realization of unconventional superconductivity (SC): the specific heat, 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 CeCoIn5 at hydrostatic pressures pless than or equal to1.5 GPa. In this compound, T-c increases with increasing pressure, while the effective mass of the quasi- particles m(eff) decreases, as indicated by the ratio C/T (Tgreater than or equal toT(c)). As a working hypothesis, this may be interpreted as the stabilization of the superconducting state by an increase of the characteristic spin fluctuation temperature T-SF (T(SF infinity)k(F)(2)/m(eff)). Interestingly, in CeCoIn5 the ratio DeltaC/gammaT(c) approximate to 5 is extremely large but starts to decrease rapidly with increasing p at p > 0.8 GPa where T,(p) approaches a maximum. (C) 2002 Elsevier Science B.V. All rights reserved.