Electronic structure, magnetic and Fermi surface calculations of heavy-fermions superconductors compounds based on Nb3Sn

We report a theoretical investigation of the electronic structures and Fermi surface of the heavy-fermion superconductors Nb3Sn. The electronic structures are investigated ab-initio on the basis of full-potential local orbital minimum-basis band- structure calculations (FPLO), adopting both the scalar- and fully relativistic formulations within the framework of the local spin-density approximation (LSDA). The possibility of a partial 4d localization occurring for compounds is discussed. The electronic structures of the Nb3Sn compounds are computed to be rather similar to the literature. Our total-energy calculations predict paramagnetic and ferromagnetic order to be favorable for Nb3Sn materials, which is, however, observed experimentally. Also, the calculated magnetic moment is 0.35 ?B. Furthermore, the theoretical Fermi surfaces topology and the possible origins of the superconductivity are discussed. The Bardeen, Cooper and Schreiffer (BCS) energy gap and the Ginzburg-Landau (GL) parameter K for these compounds have been calculated from the Fermi velocity. We found strong indication suggesting the existence of a second superconducting (SC) gap in Nb3Sn. In addition, the average superconductivity-gap at zero temperature is calculated for this compound. The knowledge of energy gap value gives important information on the coupling scenarios. Our results provide an explanation between the electronic structures, the Fermi surface (FS) topology and two-band model of the superconductivity