Evolution of the pseudogap in Sr1−xYxAl2Si2(x=0, 0.05, 0.1, and 0.15) probed viaAl27nuclear magnetic resonance

Abstract

With the aim of providing microscopic information about the electronic characteristics of SrAl${}_{2}$Si${}_{2}$ and effects of chemical substitution on its pseudogap features, we carried out a study on Sr${}_{1\ensuremath{-}x}$Y${}_{x}$Al${}_{2}$Si${}_{2}$ ($x=$ 0, 0.05, 0.1, and 0.15) by means of $^{27}\mathrm{Al}$ nuclear magnetic resonance (NMR) spectroscopy. For stoichiometric SrAl${}_{2}$Si${}_{2}$, the temperature-dependent NMR Knight shift and spin-lattice relaxation rate are associated with a sharp feature in the electronic density of state within a pseudogap at around the Fermi level. On the other hand, the NMR observations for Y-substituted compounds exhibit ordinary metallic behavior, suggesting that the Fermi level has moved out of the pseudogap for these materials, resulting in the dominant Korringa process responsible for the observed relaxation rates.