Fig. 1: Magnetic lattice, phase diagram, and magnon modes in a 2-SL MBT.
From: Magnons and magnetic fluctuations in atomically thin MnBi2Te4
a Illustration of two triangular magnetic lattices formed by Mn ions in the top (bottom) layer indicated by dark (light) purple spheres. The layers follow an ABC stacking order. D and Jc represent anisotropy and interlayer exchange coupling. b Phase diagram as a function of temperature and an applied magnetic field perpendicular to the 2D plane. c Magnons in antiferromagnetic (AFM) phase: spins from two layers oscillate with different amplitudes, corresponding to two magnon modes. Illustrations of spins before and after applying a time-reversal \({{{{{{{\mathcal{T}}}}}}}}\), inversion \({{{{{{{\mathcal{I}}}}}}}}\) and two-fold rotational (\({{{{{{{\mathcal{C}}}}}}}}\) w.r.t x-axis) operator (\({{{{{{{\mathcal{ITC}}}}}}}}\)). d Magnons in canted AFM (c-AFM) phase: the spin are canted at an angle with respect to the applied magnetic field. Illustrations of spins before and after time-reversal and two-fold rotational (y-axis) operator (\({{{{{{{\mathcal{CT}}}}}}}}\)). e Magnons in ferromagnetic (FM) phase: spins in the two layers oscillate in-phase or out of phase. Illustrations of spins before and after inversion operator (\({{{{{{{\mathcal{I}}}}}}}}\)). Shaded modes are either Raman silent or near zero frequency. ωL (ωH) refers to the magnon branch with a higher (lower) frequency in the left (right) column.
