Topological half-metallic features in alkali metal doped $\mathrm{Cr}{\mathrm{Cl}}_3$ monolayers

Two-dimensional (2D) topological half metals, namely, empowering nontrivial topological states with 100% spin-polarized 2D systems, may find important applications in low-dissipation spintronics. However, exploration of such intriguing materials is still very challenging. The recently discovered 2D magnetic materials provide unprecedented opportunities to realize 2D topological half-metallic state. Using first-principles calculations, we first find that the ferromagnetism of $\mathrm{Cr}{\mathrm{Cl}}_3$ monolayer can be well reserved by doping alkali metals, in fact, whose Curie temperature can be enhanced from 23 to 66 K after doping K. Then, we notice that semiconducting to Dirac half-metallic phase transition is achieved via Na and K doping, where the linear Dirac dispersion originates from the honeycomb lattice formed by Cr atoms. Most strikingly, Na- and K doped $\mathrm{Cr}{\mathrm{Cl}}_3$ exhibit quantum anomalous Hall effect (QAHE) with Chern number $C=1$, while the Li-doped one harbors high Chern number QAHE with $C=-2$. Thus, our work provides a theoretical guideline to realize 2D topological half-metallic state, rendering it as a promising platform for future applications.

Figure 1

Top (a) and side (b) views of alkali metal doped monolayer (ML) $\mathrm{Cr}{\mathrm{Cl}}_3$, where, blue, green, and yellow represent Cr, Cl, and Li/Na/K atoms, respectively. Here, red dashed lines in (a) denote the $1\times 1$ unit cell. Charge-difference density of Na doped ML $\mathrm{Cr}{\mathrm{Cl}}_3$ is given in (b), where magenta and cyan colors represent electron gaining and losing, respectively. (c) Phonon spectrum of Na doped ML $\mathrm{Cr}{\mathrm{Cl}}_3$.

Figure 2

Normalized magnetic moment (a) and specific heat $C_v$ (b) of pristine and alkali metal doped ML $\mathrm{Cr}{\mathrm{Cl}}_3$ as a function of temperature obtained from the Monte Carlo simulations.

Figure 3

Band structures of the Na doped ML $\mathrm{Cr}{\mathrm{Cl}}_3$ without (a) and with (c) spin-orbit coupling (SOC). (b) and (d) are the magnified bands near the Fermi level in (a) and (c). (e) The 3D band structure of Na doped ML $\mathrm{Cr}{\mathrm{Cl}}_3$.

Figure 4

(a) Band structure of Na doped ML $\mathrm{Cr}{\mathrm{Cl}}_3$ obtained from Wannier function (cyan lines) and DFT calculations (black lines). Here, the orange dotted lines denote the 1D Berry curvature distribution. (b) Corresponding Hall conductance as a function of Fermi energy. (c) Corresponding edge states. Here, the Fermi level is tuned into the global band gap.

Figure 5

Band structures of Li doped ML $\mathrm{Cr}{\mathrm{Cl}}_3$ without (a) and with (c) SOC. (b) Magnified bands near the Fermi level in (a). (d) Band structures obtained from Wannier 90 package and DFT calculations. Here, the orange lines denote the 1D Berry curvature. (e) Corresponding edge states. (f) Schematic diagrams of non-Dirac and Dirac bands of Li doped ML $\mathrm{Cr}{\mathrm{Cl}}_3$. In order to identify its topological property, the Fermi level is tuned into the global band gap in (d) and (e).