NMR probe of pseudogap characteristics inFe2+xV1−xAl

Abstract

We report the results of a ${}^{51}\mathrm{V}$ nuclear magnetic resonance (NMR) study of ${\mathrm{Fe}}_{2+x}{\mathrm{V}}_{1-x}\mathrm{Al},$ near the ordered composition with $x=0,$ at temperatures between 4 and 500 K. All compositions are found to be metallic or semimetallic, though electrical resistivity has indicated a metal-insulator transition at $x=0.\mathrm{}$ The low-temperature NMR relaxation rates for stoichiometric $\mathrm{}(x=0\mathrm{})\mathrm{}$ and nonstoichiometric $(x=0.10\mathrm{}$ and $-0.05)$ compounds follow a Korringa law, associated with a finite density of carriers at the Fermi level. High-temperature relaxation rates for $x<~0$ go over to a semiconductorlike activated form, providing information about the gap structure near the Fermi energy. The results are consistent with pseudogap features identified by recent band-structure calculations, although with smaller energy splittings. We analyze pseudogap changes vs composition, and compare the band-filling behavior to a recent coherent potential approximation calculation.