Electric-Switchable Chiral Magnons in PT-Symmetric Antiferromagnets

Abstract

The magnons in antiferromagnetic insulators (AFIs) exhibit dual chirality, each carrying opposite spin angular momentum. However, in AFIs that are protected by PT symmetry, the magnon bands remain degenerate. In this work, we introduce a new class of PT - preserving AFIs in which the giant chiral splitting of magnons can be induced and reversibly controlled by an external electric field. Unlike ordinary cases, such AFIs host a hidden dipole coupled to the antiferromagnetic order, which allows an external electric field to break the magnon sublattice symmetry and thereby largely lift the band degeneracy. Through group theory analysis, we identify the possible magnetic layer groups that support electric-field-induced magnon band splitting. Promisingly, by density-functional- theory and spin wave calculations, the magnon band splitting of Cr2CBr2 reach up to 27meV induced by an electric field of 0.2V/Å, equivalent to the 230T under a uniform magnetic field. In addition, since chiral splitting is directly coupled to the electric field, the corresponding magnon-mediated spin current can be switched by the electric field. Our Letter opens a door for developing electric-field-controlled spintronics based on the magnons.

Figures (4)

• Figure 1: The illustration of the magnons antiferromagnet with ${\cal PT}$ symmetry. (a) The degenerate magnons when the local dipole ($d_{l}$) is absent, where only the Zeeman field can split the bands. (b) The degenerate magnons undergo electric-field-induced splitting in the presence of local polarization. Here, the red circle and blue circle represent the right-hand and left-hand chirality of magnons.
• Figure 2: (a)-(b) The side and top view of of the monolayer $\hbox{Cr}_{2}\hbox{C}X_{2}$ where $X$ = $\hbox{F}$, $\hbox{Cl}$, $\hbox{Br}$. (c) The changes in the NN spin exchange ${\cal J}_{a}$, ${\cal J}_{b}$ and ${\cal J}_{ab}$ on $E_{z}$. Here, only the relative energy differences between the cases with and without the $E_{z}$ are presented, denoted as $\Delta{\cal J}_{a}$, $\Delta{\cal J}_{b}$ and $\Delta{\cal J}_{ab}$, respectively. The relative band splitting energies with (d), $E_{z}$$>$${0}$ and (e) $E_{z}$$<$${0}$. (f) The changes in the splitting strength at high symmetry points on $E_{z}$.
• Figure 3: (a) DFT calculated $E_{z}$ dependence of normalized $\frac{\Delta^{1}_{c}-\Delta^{2}_{c}}{gap}$ of for $\hbox{Cr}_{2}\hbox{C}X_{2}$. Here, $\Delta^{1}_{c}$ and $\Delta^{2}_{c}$ refer to the crystal field splitting within the first layer and second layer of $\hbox{Cr}^{3+}$ ions, respectively, and $gap$ refers to the band gap of the material. (b) The band splitting of varies material candidates with $E_{z}$$=$$0.2\,\hbox{V/\AA}$. The $\text{T}_{N}$ of candidates is also listed.
• Figure 4: Illustration of electric switchable spin currents mediated by the magnons in antiferromagnetic insulators. Here, the transition from red to blue represents the distribution of the applied temperature gradient.