Fig. 1: Experimental geometry.
From: Efficient spin excitation via ultrafast damping-like torques in antiferromagnets
a Projection of the YMnO3 crystal structure onto the basal plane. Mn3+ ions (violet) in grey and white areas are located in planes at z = 0 and z = c/2, respectively. The three sublattice magnetisations Mi point along equivalent x axes xi as indicated in the coordinate system. Note that spins in HoMnO3 point along equivalent y axes for TSR < T < TN (Supplementary Fig. 1). b Schematic of the setup. The pump and probe pulses are circularly and linearly polarised, respectively. P polariser, λ/4 quarter-wave plate, WP Wollaston prism, BPD balanced photodiode. c Visualisation of optical Z-mode excitation with field-like and damping-like torques \({{\mathcal{T}}}_{{\rm{FL}}}\) and \({{\mathcal{T}}}_{{\rm{DL}}}\) exerted by the effective field HIFE of the IFE on the magnetisation \({{\bf{M}}}_{i}\parallel {\hat{{\bf{x}}}}_{i}\) (\({\hat{{\bf{x}}}}_{i}\) denotes the unit vector in the direction xi). Black lines illustrate the ensuing strongly elliptical spin precession. Dashed ellipses show the expected trajectory without spin excitation via \({{\mathcal{T}}}_{{\rm{DL}}}\). Precession amplitudes are significantly reduced.
