Evolution of the pseudogap in Sr_1-xY_xAl ₂Si₂ (x=0, 0.05, 0.1, and 0.15) probed via Al27 nuclear magnetic resonance

With the aim of providing microscopic information about the electronic characteristics of SrAl₂Si₂ and effects of chemical substitution on its pseudogap features, we carried out a study on Sr _1-xY_xAl₂Si₂ (x= 0, 0.05, 0.1, and 0.15) by means of Al27 nuclear magnetic resonance (NMR) spectroscopy. For stoichiometric SrAl₂Si₂, 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.