Berry curvature engineering by gating two-dimensional antiferromagnets

Recent advances in tuning electronic, magnetic, and topological properties of two-dimensional (2D) magnets have opened a new frontier in the study of quantum physics and promised exciting possibilities for future quantum technologies. In this study, we find that the dual-gate technology can well tune the electronic and topological properties of antiferromagnetic (AFM) even septuple-layer (SL) ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ thin films. Under an out-of-plane electric field that breaks $\mathcal{PT}$ symmetry, the Berry curvature of the thin film could be engineered efficiently, resulting in a huge change of anomalous Hall (AH) signal. Beyond the critical electric field, the double-SL ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ thin film becomes a Chern insulator with a high Chern number of 3. We further demonstrate that such 2D material can be used as an AFM switch via electric-field control of the AH signal. These discoveries inspire the design of low-power memory prototypes for future AFM spintronic applications.

Figure 1

(a) Schematic of AFM double layer with $\mathcal{PT}$ symmetry. The purple balls in each layer represent magnetic atoms whose magnetic orientations (out of plane) are depicted by arrows (e.g., Mn atoms in double-SL ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$). (b) Schematic of AFM double layer with an out-of-plane electric field in which $\mathcal{PT}$ symmetry is broken. (c)–(e) Schematics of band structures for AFM double-SL ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ thin film without and with electric field. The colors of blue and green stand for states with different spin. In (c), each band is doubly degenerate. In (d) and (e), under the electric field, $\mathcal{PT}$ symmetry is broken. The dot lines in (e) stand for the original bands without electric field.

Figure 2

(a) Lattice structure of double-SL ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ thin film and the first BZ. Red arrows mark magnetic orientations on Mn atoms. Band structures of double-SL ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ thin film under electric fields: (b) $E$ = 0 V/$\AA$, (c) $E$ = 0.010 V/$\AA$, (d) $E$ = 0.021 V/$\AA$, (e) $E$ = 0.023 V/$\AA$, (f) $E$ = 0.027 V/$\AA$, and (g) $E$ = 0.029 V/$\AA$. The Fermi levels marked by the black dashed lines are set to be zero. (h) 2D electronic structures around the Fermi level and the $\mathrm{\Gamma }$ point when electric field is 0.021 V/$\AA$. Band crossing points are marked as red stars. (i) Schematic of edge states when the double-SL ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ thin film is a QAH insulator with a Chern number of 3. The magnetic Mn atoms are indicated by the purple balls with arrows and the black arrow indicates the direction of the electric field. Distributions of the Berry curvature in the first BZ for double-SL ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ thin film under (j) $E=0.021$ V/$\AA$ and (k) $E=0.029$ V/$\AA$. Corresponding energy levels are marked as red dashed lines in (e) and (g).

Figure 3

(a) Edge states in double-SL ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ thin film under the electric field of $E=0.023$ V/$\AA$. (b) AH signal as a function of chemical potential and external perpendicular electric fields. The chemical potentials are aligned to Fermi levels. The phase regions I, II, and III represent the trivial semiconducting phase, QAH phase, and trivial AFM metal phase, respectively. The black dashed lines show the energy positions of the conduction and valence band edges in phase regions I and II. (c) AH conductance with varying chemical potential in double-SL ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ thin film under the electric field of $E=0.023$ V/$\AA$. The chemical potential scale is marked as the red solid line in (b).

Figure 4

(a) Top view of schematics for a Hall bar device. The blue arrows indicate the edge current direction. The red areas show the double-SL ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ thin film. The gray and yellow areas represent the substrate and attached electrodes, respectively. (b) Schematic operation for the AFM memory device. “On” and “Off” states are for double-SL ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ thin film in the trivial semiconductor phase and QAH phase. (c), (d) AH conductance with varying temperature in double-SL ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ thin film under the electric field of $E=0.010$ and 0.023 V/$\AA$. The temperature is normalized to Néel temperature $T_N=25$ K.