EXCITONIC CORRELATIONS IN THE INTERMETALLIC FE2VAL

The intermetallic compound Fe2VAl looks nonmetallic in transport and s trongly metallic in thermodynamic and photoemission data. It has in it s band structure a highly differentiated set of valence and conduction bands leading to a semimetallic system with a very low density of car riers. The pseudogap itself is sensitive to the presence of Al states, but the resulting carriers have only minor Al character. The effects of generalized gradient corrections to the local density band structur e are shown to be important, reducing the carrier density by a factor of 3. Spin-orbit coupling results in a redistribution of the holes amo ng pockets at the Brillouin zone center. Doping of this nonmagnetic co mpound by 0.5 electrons per cell in a virtual crystal fashion results in a moment of 0.5 mu(B) and destroys the pseudogap. We assess the ten dencies toward the formation of an excitonic condensate and toward an excitonic Wigner crystal and find both to be unlikely. We propose a mo del in which the observed properties result from excitonic correlation s arising from two interpenetrating lattices of distinctive electrons (e(g) on V) and holes (t(2g) on Fe) of low density (one carrier of eac h sign per 350 formula units).