Quantum many-body intermetallics: Phase stability of ${\mathrm{Fe}}_3\mathrm{Al}$ and small-gap formation in ${\mathrm{Fe}}_2\mathrm{VAl}$

Various intermetallic compounds harbor subtle electronic correlation effects. To elucidate this fact for the Fe-Al system, we perform a realistic many-body investigation based on a combination of density functional theory with dynamical mean-field theory in a charge self-consistent manner. A better characterization and understanding of the phase stability of bcc-based $D{0}_3-{\mathrm{Fe}}_3\mathrm{Al}$ through an improved description of the correlated charge density and the magnetic energy is achieved. Upon replacement of one Fe sublattice with V, the Heusler compound ${\mathrm{Fe}}_2\mathrm{VAl}$ is realized, known to display bad-metal behavior and increased specific heat. Here we document a charge-gap opening at low temperatures in line with previous experimental work. The gap structure does not match conventional band theory and is reminiscent of (pseudo)gap characteristics in correlated oxides.

Figure 1

Relevant crystal structures. From left to right: $D{0}_3-{\mathrm{Fe}}_3\mathrm{Al}, L{1}_2-{\mathrm{Fe}}_3\mathrm{Al}$, and $L{2}_1-{\mathrm{Fe}}_2\mathrm{VAl}$. Fe (red/light gray), Al (green/dark), and V (blue/gray).

Figure 2

Projected local $\mathrm{Fe}\left(3d\right)$ orbitals in $L{1}_2-{\mathrm{Fe}}_3\mathrm{Al}$. On-site level energies: ${\varepsilon }_{\alpha }=\{-624,-699,-843,-843,-998\}\mathrm{meV}$ for the effective orbitals $\alpha =\{x^2-y^2,z^2,xz,yz,xy\}$.

Figure 3

Spectral functions of $L{1}_2-{\mathrm{Fe}}_3\mathrm{Al}$. (a) Total, (b) local Fe from GGA, and (c) local Fe from DFT+DMFT. Insets in (b) and (c) are low-energy blowups.

Figure 4

Spectral functions of $D{0}_3-{\mathrm{Fe}}_3\mathrm{Al}$. (a) Total, (b) local Fe1, and (c) local Fe2. Insets in (b) and (c) are low-energy blowups.

Figure 5

Relevant charge-density plots in $D{0}_3-{\mathrm{Fe}}_3\mathrm{Al}$ around Fe1 (left) and Fe2 (right) with the $c$ axis perpendicular to the plotting plane. (a) GGA bonding charge density (see text). (b) DFT+DMFT bonding charge density. (c) Charge difference $n_{\mathrm{DFT}+\mathrm{DMFT}}-n_{\mathrm{GGA}}$.

Figure 6

Comparison of ${\mathrm{Fe}}_3\mathrm{Al}$ formation-energy curves for the $D{0}_3$ and the $L{1}_2$ structure within NM-GGA and PM-DFT+DMFT. The dashed line marks the experimental equilibrium volume.

Figure 7

Spectral function of $L{2}_1-{\mathrm{Fe}}_2\mathrm{VAl}$. Top: Total with DFT+DMFT for two different temperatures. Middle: V local. Bottom: Fe local.