Chern Insulators from Heavy Atoms on Magnetic Substrates

We propose searching for Chern insulators by depositing atomic layers of elements with large spin-orbit coupling (e.g., Bi) on the surface of a magnetic insulator. We argue that such systems will typically have isolated surface bands with nonzero Chern numbers. If these overlap in energy, a metallic surface with large anomalous Hall conductivity will result; if not, a Chern-insulator state will typically occur. Thus, our search strategy reduces to looking for examples having the Fermi level in a global gap extending across the entire Brillouin zone. We verify this search strategy and identify several candidate systems by using first-principles calculations to compute the Chern number and anomalous Hall conductivity of a large number of such systems on MnTe, MnSe, and EuS surfaces. Our search reveals several promising Chern insulators with gaps of up to 140 meV.

Figure 1

(a) Top view and (b) side view of the tripled surface unit cell of MnTe with $2/3\mathrm{ML}$ Pb. Pb is in green, Mn in gray, Te is dark blue and I in cyan.

Figure 2

(a)–(b) Band structure of $2/3$ Pb on MnTe with spins in (a) the $\pm z$ direction, and (b) the $\pm x$ direction. Bands with the most Pb character are highlighted in thick (blue) lines; bulklike MnTe bands are in thin (black) lines. Chern numbers of gaps near the Fermi level are labeled. (c)–(d) Anomalous Hall conductivity of band structures in (a)–(b), in units of $e^2/h$. Quantized plateaus are highlighted.

Figure 3

Band structures of atoms on $-2\%$ epitaxially strained MnSe. Top: $1/3\mathrm{ML}$ Br, $1/3\mathrm{ML}$ Bi, Bottom: $2/3\mathrm{ML}$ Pb, $1/3\mathrm{ML}$ I. Majority spin-up surface bands are in red; majority spin-down surface bands are in blue; bulklike bands are in thin black lines. Chern numbers near the Fermi level are labeled.