Heavy-fermion superconductivity: An X-boson treatment

Abstract

We use the X-boson method to study the heavy-fermion superconductivity phase, employing an extension of the periodic Anderson model in the U=∞ limit with a nearest-neighbor attractive interaction between the localized f electrons. We show that higher values of the hybridization parameter imply lower values associated with the maximum of the superconducting critical temperature Tc, indicating that the real charge transfer between bands tends to destabilize the Cooper pairing. Moreover, we show that the superconductivity is constrained to the vicinity of a range of densities where the f-band density of states at the Fermi level ρf(μ) has sufficiently high values, and it was found both for configurations where the system presents intermediate-valence and heavy-fermion behaviors, as experimentally observed. Finally, as the total occupation is raised and for large hybridization parameter V there is an insulator-superconductor transition, which is related to the existence of a hybridization gap that cannot be accessed by the slave-boson method, because when the chemical potential lies in or above the gap the system suffers the second-order phase transition characteristic of that method.

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