Fig. 1: Strain-induced moiré superlattices and stacking-dependent magnetism of CrBr3.
From: Moiré magnetism in CrBr3 multilayers emerging from differential strain
a Moiré superlattices commonly originate from a small twist angle θ between identical vdW layers. They can also arise from interlayer biaxial (b) and uniaxial (c) differential strain, which cause adjacent layers to have slightly different lattice vectors. Red and blue honeycomb lattices represent atoms in the two layers. d Top view of the lattice structure of monolayer CrBr3 and its unit cell, displaying the honeycomb lattice formed by Cr atoms (blue balls) within the edge-sharing octahedra of Br atoms (white balls). e Depending on how layers are stacked, three distinct (meta)stable structures of CrBr3 are known, with different interlayer exchange coupling: the M (monoclinic) and AA stackings lead to antiferromagnetic (AFM) interlayer coupling; the rhombohedral (AB) stacking leads to interlayer ferromagnetic (FM) ordering (only the Cr atoms are depicted; red and blue balls represent Cr atoms in the two layers). f In differentially strained CrBr3 layers, the spatial dependence of the interlayer exchange spontaneously results in the formation of non-collinear spin textures (i.e., moiré magnetism). g the tunneling magnetoconductance δG(H, 2 K) of FM barriers (data measured on a four-layer AB stacked CrBr3 junction) is small (2%) at low temperature and exhibits characteristic “lobes” near TC as shown in h. In contrast, AFM barriers (data measured on a four-layer M stacked CrBr3 junction) exhibit a large low-T magnetoconductance (i) due to the spin-flip transitions of the inner and outer layers, which is suppressed as T is increased, and which vanishes above TN (j see ref. 28. for the analogous data measured in an AA stacked AFM CrBr3 barrier and for more information about the devices used to measure the data shown in this figure).
