Effect of pressure on unconventional superconductivity in CeCoIn5

Abstract

Studies of a new family of heavy fermion (HF) 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<Tc. We report on measurements of the heat capacity of CeCoIn5 at hydrostatic pressures p⩽1.5GPa. In this compound, Tc increases with increasing pressure, while the effective mass of the quasi-particles meff decreases, as indicated by the ratio C/T (T⩾Tc). As a working hypothesis, this may be interpreted as the stabilization of the superconducting state by an increase of the characteristic spin fluctuation temperature TSF (TSF∝kF2/meff). Interestingly, in CeCoIn5 the ratio ΔC/γTc≈5 is extremely large but starts to decrease rapidly with increasing p at p≳0.8GPa where Tc(p) approaches a maximum.