Pressure Effects on Unconventional Superconductivity in Electronically Low Dimensional Compounds CeTIn5 (T: Ir, Co)

Abstract

Experimental studies of the new class of heavy fermion (HF) superconductors CeTIn5 (T: transition metal) point towards the realization of unconventional superconductivity (SC): in both CeIrIn5 and in CeCoIn5 the specific heat C(T), thermal conductivity κ(T) and nuclear spinrelaxation rate 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 ≤ 1.6 GPa. In both compounds, T c increases with increasing pressure, while the effective mass of the quasiparticles, m eff, decreases as indicated by the ratio C/T(T≥ T c). 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 the increase of the characteristic spin fluctuation temperature. Interestingly, in CeIrIn5 the ratio is small and almost stays constant with increasing pressure, while in CeCoIn5 is extremely large but starts to decrease rapidly at P ≥ 0.8 GPa where T c(p) approaches a maximum.