Non-trivial evolution of the Dirac cone in chromium doped Dirac semimetal Cd3As2

Abstract

The magnetic doping of Dirac semimetals breaks their time-reversal symmetry thus giving rise to anomalous transport phenomena promising for applications. While the Dirac cone (DC) manifestations were observed in the electron transport of (Cd1−xCrx)3As2 alloys up to x = 0.06, their mechanism remains challenging. To address this challenge, we performed DFT calculations of the (Cd0.96Cr0.04)3As2 alloy with the non-magnetic (NM), ferromagnetic (FM), and antiferromagnetic (AFM) spin orders. It was found that the NM state is unstable, while the FM state has the lowest energy. The band structure analysis revealed that Cr 3d states are distributed in energy not uniformly, but with Cr-free windows, in which the Dirac spectrum can survive. The only exception is the Dirac point vicinity, where a narrow gap is formed. Outside the window, the DC band strongly hybridizes with the Cr 3d states and disappears. Near EF, such a Cr-free window with the DC band exists only in the FM↓ state and is absent in the NM, FM↑, and AFM states. The Fermi surface of FM (Cd1−xCrx)3As2 has two parts: the DC↓ sheet with the velocity vF ≈ 1∙106 m/s and several sheets with low vF, originating from Cr 3d↑ states. As an example of transport properties, the dc conductivity of FM (Cd1−xCrx)3As2 was estimated. We found that at T→0 K the DC↓ electrons have a very large transport lifetime and therefore dominate in the conductivity. In this dominance, the role of the Cr-free window is double: it ensures the DC↓ surviving and greatly reduces an admixture of Cr 3d↓ orbitals to DC↓ states, so suppressing the scattering of DC↓ electrons by doped Cr atoms. This mechanism looks rather general and may be applied to the design of magnetic topological alloys.