arXiv subjects
Publications and source records attributed to Lizardo H. C. M. Nunes.
From an extension of the periodic Anderson model (PAM) in the $ U=\infty $ limit taking into account the effect of a nearest neighbor attractive interaction between $ f $-electrons, we compare the obtained superconducting phase diagram of a two dimensional d-wave superconductor with the results obtained for an isotropic s-wave superconductor employing the X-boson method.
We use the X-boson method to study the heavy fermion superconductivity employing an extension of the periodic Anderson model in the $ U = \infty $ limit with a nearest neighbor attractive interaction between the localized $ f $-electrons and we show that higher values of the hybridization parameter implies in lower values associated to the maximum of the superconducting critical temperature $ T_{c} $, indicating that the real charge transfer between bands tends to destabilizes the Cooper pairing. Moreover, we show that superconductivity are constrained to the vicinity of a range of occupations where the $ f $-band density of states at the Fermi level $ ρ_{f} (μ) $ have sufficiently high values, though superconductivity was found both for configurations where the system present intermediate valence and heavy fermion behavior, as experimentally observed. Finally, as the total occupation is raised and for increased hybridization parameter $ V $ there is a transition insulator-superconductor, which is related to the existence of a hybridization gap that cannot be obtained by the slave-boson method.
We show that there is an effect of nonextensivity acting upon the BCS model for superconductors in the ground state that motivates its study in the Tsallis' statistical framework. We show that the weak-coupling limit superconductors are well described by $q \sim 1$, where q is a real parameter which characterizes the degree of nonextensivity of the Tsallis' entropy. Nevertheless, small deviations with respect to q = 1 provide better agreement when compared with experimental results. To illustrate this point, making use of an approximated Fermi function, we show that measurements of the specific heat, ultrasonic attenuation and tunneling experiments for tin (Sn) are better described with q = 0.99.