The electronic pseudo band gap states and electronic transport of the full-Heusler compound Fe2VAl

Abstract

For Fe2VAl the temperature-dependent Seebeck coefficientS(T) and electrical resistivityρ(T) were calculated within the framework of density functional theory (DFT). The DFT calculations were extended in terms of a DFT/LDA+Uapproach withU−Jvalues attributed to Fe-d-like states. For simulating the general features of the measured data, a large range ofU−Jvalues was scanned withU−J= 2.145 eV as the recommended value. For this value a very small negative indirect gap ofE(X) −E(Γ) = −0.0093 eV is found, which is significantly reduced as compared to the DFT-GGA value of −0.164 eV. Charge transfer was derived by Bader's approach, resulting in a significant transfer of 0.75 electronic charges to each Fe atom from Al (1.03) and V (0.48). The pseudogap states around the Fermi energy were analyzed in detail in terms of density of states, band structures and charge density contours. These states almost exclusively governS(T) andρ(T). They have large dispersions and are centered atΓandX. They consist of tails of localized V and Fe states dangling to the Al site. The dispersion of the band along thekspace directionX-Γwas modelled in terms of a tight-binding ansatz, resulting ink-dependent matrix elements. From our DFT study, based on the findings forS(T) andρ(T), it appears that Fe2VAl has a very small negative indirect gap in the electronic structure. By fitting the temperature-dependent Seebeck coefficient within a parabolic band model, a tiny positive band gap of around 0.003 eV is revealed which qualitatively agrees with the DFT results.