Quasiparticle band structure of the almost-gapless transition-metal-based Heusler semiconductors

Abstract

Transition-metal-based Heusler semiconductors are promising materials for a variety of applications ranging from spintronics to thermoelectricity. Employing the GW approximation within the framework of the FLAPW method, we study the quasi-particle band structure of a number of such compounds being almost gapless semiconductors. We find that in contrast to the sp-electron based semiconductors such as Si and GaAs, in these systems the many-body corrections have a minimal effect on the electronic band structure and the energy band gap increases by less than 0.2 eV, which makes the starting point density functional theory (DFT) a good approximation for the description of electronic and optical properties of these materials. Furthermore, the band gap can be tuned either by the variation of the lattice parameter or by the substitution of the sp-chemical element.

Half-metallicity and magnetism in the Co2MnAl/CoMnVAl heterostructure

“…The BZ was again sampled with a dense Monkhorst-Pack grid of 16 × 16 × 16 k-points. We obtained an equilibrium lattice constant of 5.74Å, which is in line with the values obtained with a pseudo-potential plane-wave method [75] and with a full-potential linearized augmented plane-wave (FP-LAPW) method [73], respectively 5.76Å and 5.74Å. The calculated lattice constant is in reasonable agreement with the experimental value reported above, leading to an error of about 1%.…”

“…6. In LSDA we obtain a value of -0.14 eV, which is in fair agreement with the value of -0.07 eV obtained in GGA with a FP-LAPW code [73]. In LSDA+DMFT, instead, we obtain a value of -0.21 eV, which corresponds to a variation of around 0.07 eV with respect to the LSDA value.…”

“…The valence band crosses the Fermi level at the Γ-point, while the conduction band goes below it at the X-point. These semi-metallic features have been reported in prior works [39,73]. Further insight into the band structure can be obtained by analysing projections over real spherical (cubic) harmonics (data not shown).…”

“…Among the quaternary Heusler compounds, one is more likely to find small-gap SCs, since the unit cell contains three different transition metals [74]. CoMnVAl was in fact predicted to be a nonmagnetic SC through first principles calculations [39,74], although the presence of an indirect negative gap formally makes it a semi-metal [39,73]. The lattice constant measured in experiments amounts to 5.80Å [70], which is rather close to that of Co 2 MnAl.…”

“…The dominant Co-Mn coupling is enhanced in LSDA+U , which reflects the increase of the magnetic moment reported in Table I [70]. The primitive cell contains 24 valence electrons and, according to the Slater-Pauling rule [71,72], should be expected to be a semiconductor (SCs), either magnetic or non-magnetic [73]. Among the quaternary Heusler compounds, one is more likely to find small-gap SCs, since the unit cell contains three different transition metals [74].…”