Fig. 1. Crystal and magnetic structures of Mn₃Sn and the THz longetudinal conductivity spectra.

a, b A 3D schematic view of atomic configuration (a) and top view along c-axis (b) of the magnetic structures of Mn₃Sn at room temperature where the magnetic moments form an inverse triangular spin structure in the ab plane. c The X-ray diffraction measurement for the 50-nm-thick film of Mn_3+xSn_1−x (x = 0.02) on a SiO₂ substrate. d A schematic of our sample configuration. $E_x^{\mathrm{in}}$ the incident electric field polarized along the x direction, J_x the longitudinal current, J_y the Hall current. e, f The real and imaginary parts of THz longitudinal conductivity spectra of Mn_3+xSn_1−x thin films (x = 0.02) on a SiO₂ substrate at various temperatures. The solid curves are the results of the Drude-model fitting. The inset shows temperature dependence of the scattering time obtained from the fitting.