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.