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Free keywords:
high pressure; heavy-fermion superconductivity; non-fermi liquid
Abstract:
The hybridization between a periodic lattice of almost localized (core like) electrons (of lanthanides or actinides) and band electrons has challenged researchers for over 30 years to unravel its microscopic origin and the many puzzling physical phenomena related to it. Among such phenomena are very unusual normal state properties, which differ strongly from Landau-Fermi liquid (FL) behavior or exciting unconventional forms of superconductivity. Here, we report on experimental studies of a recently discovered new class of these heavy fermion superconductors: CeTIn5 (T: transition metal). Our studies point towards the realization of unconventional superconductivity in these compounds. In both CeIrIn5 and in CeCoIn5 the specific heat C(T), thermal conductivity kappa(T) and nuclear spin-relaxation rate decrease as a power law of temperature instead of exponentially for T < T-c. We present results of measurements of the heat capacity of CeCoIn5 at hydrostatic pressures p less than or equal to 1.6 GPa. In CeCoIn5 (as well as in CeIrIn5), T-c increases with increasing pressure, while the effective mass of the quasiparticles, m(eff), decreases as indicated by the ratio C/T(T greater than or equal to T-c) As a working hypothesis based on theories of a nearly antiferromagnetic FL this may be interpreted as the stabilization of the superconducting state by the increase of the characteristic spin-fluctuation temperature T-SF(T-SF infinityk(F)(2)/m(eff)). F Interestingly, in CeIrIn5 the ratio DeltaC/gammaT(c) = 0.8 is small and almost stays constant with increasing pressure, while in CeCoIn5 DeltaC/gammaT(c) approximate to 5 is extremely large but starts to decrease rapidly at pgreater than or equal to0.8 GPa where T-c(p) approaches a maximum. (C) 2002 Elsevier Science B.V. All rights reserved.
