Heavy-fermion superconductivity: AnX-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 implies in lower values associated to the maximum of the superconducting critical temperature Tc, indicating that the real charge transfer between bands tends to destabilizes 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 ρ f (µ) have sufficiently high values and it was found both for configurations where the system presents intermediate valence and heavy fermion behavior, as experimentally observed. Finally, as the total occupation is raised and for larges 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.

Superconductivity in the Anderson lattice: a finite-Uslave boson description

“…However, using the slave boson method it was found [13] that, for infinite coupling, superconductivity prevails in a regime where the heavy electron filling is smaller than the light electron filling. This was confirmed by the X-boson approach [14]. In these works the relative stabilities of the various pairing symmetries were studied, and the basic conclusion is that the critical temperatures for the various symmetries are in general similar and the dominant one varies as the parameters of the model change (see however [18,19] where a quantum phase transition is predicted for d-wave symmetry when antiferromagnetism and superconductivity coexist).…”

“…The Anderson model is generally accepted as appropriate to describe heavy-fermion systems [12]. Using slave boson descriptions both magnetic and superconducting instabilities have been successfully studied [7,[13][14][15][16][17], as have their competition/coexistence [18,19].…”

“…This problem was studied before in the case of finite U using a perturbative approach [31] and in the U = ∞ limit a slave boson method [13] and the X-boson method [14] were used. It was predicted in the perturbative approach that for large enough U superconductivity disappears.…”

Flat-band superconductivity for tight-binding electrons on a square-octagon lattice

“…Presently, we argue that the two-dome phase diagram observed in unconventional superconductors can be related to a single pairing mechanism, especially when it is taken into account the multiband aspect of the microscopic models that describe them. In fact, the two-dome phase diagram with a single pairing mechanism have been previously obtained for strongly correlated systems, such as the heavy fermions compounds since it also appears in the periodic Anderson model in the context of a hybridization gap [58].…”

Interplay between charge, magnetic, and superconducting order in a Kondo lattice with attractive Hubbard interaction

“…Heavy fermion superconductors are usually considered to be a nodal unconventional superconductor where the nonlocal Cooper pairing is mediated by magnetic fluctuations [15][16][17][18][19][20]. However, very recently the pairing mechanism of the first heavy fermion superconductor CeCu 2 Si 2 is controversially discussed [21][22][23][24][25][26].…”