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Electronic and optical properties of topological semimetal Cd 3 As 2

View Article: PubMed Central - PubMed

ABSTRACT

K: Using ab initio density functional theory the band structure and the dielectric function of a bct Cd3As2 crystal are calculated. We find a Dirac semimetal with two Dirac nodes ± near the Γ point on the tetragonal axis. The bands near the Fermi level exhibit a linear behavior. The resulting Dirac cones are anisotropic and the electron-hole symmetry is destroyed along the tetragonal axis. Along this axis the symmetry-protected band linearity only exists in a small energy interval. The Dirac cones seemingly found by ARPES in a wider energy range are interpreted in terms of pseudo-linear bands. The behavior as 3D graphene-like material is traced back to As p orbital pointing to Cd vacancies, in directions which vary throughout the unit cell. Because of the Dirac nodes the dielectric functions (imaginary part) show a plateau for vanishing frequencies whose finite value is proportional to the Sommerfeld fine structure constant but varies with the light polarization. The consequences of the anisotropy of the Dirac cones are highlighted for the polarization dependence of the infrared optical conductivity.

No MeSH data available.


(a) Electronic band structures of bct Cd3As2 along the ΓZ line with (solid black lines) and without SOI (dashed blue lines) (b) Zoom for significantly reduced energies.
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f7: (a) Electronic band structures of bct Cd3As2 along the ΓZ line with (solid black lines) and without SOI (dashed blue lines) (b) Zoom for significantly reduced energies.

Mentions: Most interesting is the behavior of the band structure near the Fermi energy EF and the BZ center Γ in Fig. 6. Far away from Γ there are no allowed band states in the low-energy region. Despite the band folding effect due to the larger unit cell, the bands around Γ in Fig. 6 show seemingly some similarities to those in Fig. 3. There are As p bands crossing the Fermi level. However there are also differences: the Cd s-derived band crossing the Fermi level in the small cube here disappeared. As more clearly visible in Fig. 7 for an extremely small energy interval, around Γ a small gap of about 0.02 eV is opened. However, along the ΓZ line (and consequently along the opposite Γ line) twofold degenerate linear bands cross at , thereby forming two fourfold-degenerate Dirac points at the Fermi level. Therefore the centrosymmetric bct Cd3As2 forms a topological Dirac semimetal with two Dirac points on the tetragonal axis in a distance ±k0 from Γ. Similar to graphene, ideal bct Cd3As2 may be also identified as a multivalley zero-gap semiconductor. In the non-centrosymmetric case1315 small band splittings occur and hence Weyl points arise. Around Γ and EF the band structures in Figs 6 and 7 are in agreement with symmetry considerations28. The inverted band structure, already found for the building blocks consisting of two formula units Cd3As2, cannot open up an energy gap due to the C4 rotational symmetry around the tetragonal axis. It protects two 3D Dirac cones touching at two special points k± along the ΓZ line13. Actually, the linearity of the bands at the Dirac points holds just in a very small energy range, as shown in Fig. 6. Therefore, Dirac fermions only appear for excitation energies much lower as claimed discussing ARPES measurements (see discussion below).


Electronic and optical properties of topological semimetal Cd 3 As 2
(a) Electronic band structures of bct Cd3As2 along the ΓZ line with (solid black lines) and without SOI (dashed blue lines) (b) Zoom for significantly reduced energies.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5382546&req=5

f7: (a) Electronic band structures of bct Cd3As2 along the ΓZ line with (solid black lines) and without SOI (dashed blue lines) (b) Zoom for significantly reduced energies.
Mentions: Most interesting is the behavior of the band structure near the Fermi energy EF and the BZ center Γ in Fig. 6. Far away from Γ there are no allowed band states in the low-energy region. Despite the band folding effect due to the larger unit cell, the bands around Γ in Fig. 6 show seemingly some similarities to those in Fig. 3. There are As p bands crossing the Fermi level. However there are also differences: the Cd s-derived band crossing the Fermi level in the small cube here disappeared. As more clearly visible in Fig. 7 for an extremely small energy interval, around Γ a small gap of about 0.02 eV is opened. However, along the ΓZ line (and consequently along the opposite Γ line) twofold degenerate linear bands cross at , thereby forming two fourfold-degenerate Dirac points at the Fermi level. Therefore the centrosymmetric bct Cd3As2 forms a topological Dirac semimetal with two Dirac points on the tetragonal axis in a distance ±k0 from Γ. Similar to graphene, ideal bct Cd3As2 may be also identified as a multivalley zero-gap semiconductor. In the non-centrosymmetric case1315 small band splittings occur and hence Weyl points arise. Around Γ and EF the band structures in Figs 6 and 7 are in agreement with symmetry considerations28. The inverted band structure, already found for the building blocks consisting of two formula units Cd3As2, cannot open up an energy gap due to the C4 rotational symmetry around the tetragonal axis. It protects two 3D Dirac cones touching at two special points k± along the ΓZ line13. Actually, the linearity of the bands at the Dirac points holds just in a very small energy range, as shown in Fig. 6. Therefore, Dirac fermions only appear for excitation energies much lower as claimed discussing ARPES measurements (see discussion below).

View Article: PubMed Central - PubMed

ABSTRACT

K: Using ab initio density functional theory the band structure and the dielectric function of a bct Cd3As2 crystal are calculated. We find a Dirac semimetal with two Dirac nodes ± near the Γ point on the tetragonal axis. The bands near the Fermi level exhibit a linear behavior. The resulting Dirac cones are anisotropic and the electron-hole symmetry is destroyed along the tetragonal axis. Along this axis the symmetry-protected band linearity only exists in a small energy interval. The Dirac cones seemingly found by ARPES in a wider energy range are interpreted in terms of pseudo-linear bands. The behavior as 3D graphene-like material is traced back to As p orbital pointing to Cd vacancies, in directions which vary throughout the unit cell. Because of the Dirac nodes the dielectric functions (imaginary part) show a plateau for vanishing frequencies whose finite value is proportional to the Sommerfeld fine structure constant but varies with the light polarization. The consequences of the anisotropy of the Dirac cones are highlighted for the polarization dependence of the infrared optical conductivity.

No MeSH data available.