The Crystal and Electronic Structures of Cd₃As₂, the Three-Dimensional Electronic Analogue of Graphene

Abstract

The structure of Cd3As2, a high-mobility semimetal reported to host electrons that act as Dirac particles, is reinvestigated by single-crystal X-ray diffraction. It is found to be centrosymmetric rather than noncentrosymmetric as previously reported. It has a distorted superstructure of the antifluorite (M2X) structure type with a tetragonal unit cell of a = 12.633(3) and c = 25.427(7) Å in the centrosymmetric I41/acd space group. The antifluorite superstructure can be envisioned as consisting of distorted Cd6□2 cubes (where □ = an empty cube vertex) in parallel columns, stacked with opposing chirality. Electronic structure calculations performed using the experimentally determined centrosymmetric structure are similar to those performed with the inversion symmetry absent but with the important implication that Cd3As2 is a three-dimensional (3D)-Dirac semimetal with no spin splitting; all bands are spin degenerate and there is a 4-fold degenerate bulk Dirac point at the Fermi energy along Γ-Z in the Brillouin zone. This makes Cd3As2 a 3D electronic analogue of graphene. Scanning tunneling microscopy experiments identify a 2 × 2 surface reconstruction in the (112) cleavage plane of single crystals; needle crystals grow with a [110] long axis direction.

Pressure-induced superconductivity in the three-dimensional topological Dirac semimetal Cd3As2

“…In Figure 4, the XRD patterns below 2.60 GPa can be well indexed as the tetragonal phase in space group I4 1 /acd. 30 All the peaks are slightly shifted to higher angle with increasing pressure, due to the shrink of the lattice. However, when the pressure increases to 4.67 GPa and above, a set of new peaks emerges, which is clearly different from that of low-pressure tetragonal phase.…”

“…Figure 1a shows the crystal structure of Cd 3 As 2 . 30 The cubic Cd lattice with two vacancies resides in a face-centred cubic As lattice. Figure 1b plots a typical resistivity curve of Cd 3 As 2 single crystal at 0 GPa.…”

A new form of Ca3P2 with a ring of Dirac nodes

“…17,19,41 One of the prominent examples of a 3D Dirac semimetal is Cd 3 As 2 , which has recently gained a lot of attention. [37][38][39][42][43][44][45] Although Cd 3 As 2 crystallizes in a very different crystal structure, 42 the chemical relation to Ca 3 P 2 is still apparent. The other currently known 3D Dirac semimetal, Na 3 Bi, is much more air-sensitive 40 than Ca 3 P 2 .…”

Molecular beam epitaxy of Cd3As2 on a III-V substrate

“…19 Its preferred growth surface is the (112). 20,21 The atom arrangements near the (112) growth plane can be compared with those in the (111) planes of III-V semiconductors with the cubic zincblende structure, such as GaAs or GaSb, as shown in Fig. 1 epitaxial III-V layers.…”

“…Three different polymorphs of Cd 3 As 2 have been reported. 21 The low-temperature Dirac semimetal can be described as containing ordered Cd vacancies, 21 in contrast to the high temperature Fm3m cubic phase. An intermediate-temperature structure with P4 2 /nm symmetry has also been found.…”