Electronic structures of AlB2-type superconducting YbGa1+xSi1−x alloys probed by NMR and Seebeck coefficient

Abstract

We report the electronic properties of the AlB2-type compounds YbGa1+xSi1−x (x=0, 0.15, and 0.3) studied by means of the nuclear magnetic resonance (NMR) and the Seebeck coefficient measurements. These materials are of current interest due to the presence of superconductivity with Yb element. From the analysis of G69a NMR spin-lattice relaxation rates, we deduce the Ga 4s partial Fermi level density of states Ns(EF) for these compounds. The result indicates a gradual increase in Ns(EF) with increasing x in YbGa1+xSi1−x. In addition, the evolution of the Seebeck coefficient feature can be understood well within the band-filling scenario. From the Seebeck coefficient analysis, we find that the variation in the total Fermi level density of states N(EF) is not consistent with the trend of superconducting temperature Tc which shows a gradual decrease with Ga content. These observations support the hypothesis that the electronic Fermi level density of states is not the key factor in determining the superconducting transition temperature of YbGa1+xSi1−x.