Cadmium Arsenides: Structure, Synthesis of Bulk and Film Crystals, Magnetic and Electrical Properties (Review)

The Cd-As system is distinguished by metastable states; three compounds, namely, Cd3As2, CdAs2, and CdAs4, are formed in the system under normal pressures. The last-listed compound, CdAs4, is metastable and can be prepared, as a rule, together with other phases that stabilize it, e.g., with isostructural CdP4. The focus of research is Cd3As2. This compound was first regarded as a narrow-gap semiconductor with an abnormally high electron mobility. More recently, Cd3As2 has been rediscovered as a 3D topological semimetal, positioned as a bulk analogue of graphene that has a negative magnetoresistance (NMR) and superconductivity. The conduction band and valence band of cadmium arsenide have a linear dispersion law and touch each other in the 3D Brillouin zone to form Dirac points. Provided the time reversal and inverted symmetry, the Dirac points are doubly degenerate. Symmetry breaking leads to splitting of a Dirac point. A magnetic field transforms the Weyl semimetal, generating NMR and giving rise to superconducting properties. The second stable compound of the three listed, CdAs2, is a semiconductor with a moderate bandgap width, and is distinguished by a high anisotropy of optical, electrical, and thermoelectrical properties. This compound is interesting due to the high value of birefringence in the IR. The review analyzes the synthetic methods to prepare single crystals and thin films. Data are presented on thermodynamic properties, the effects of doping with donor and acceptor dopants, types of defects, and their relations to optical and electrical properties. Present-day studies are reviewed.