We investigate the relation of electronic and optical properties to ultrafast strain in topological antiferromagnet Mn$_3$Sn thin films using near-infrared femtosecond laser pulses. Coherent acoustic phonon oscillations are generated and clearly identified with a remarkably large amplitude exceeding 1% in differential transmission. Quantitative analysis reveals that near-infrared photoelastic coefficient in Mn$_3$Sn is several times larger than that in typical materials. These results establish a quantitative approach for understanding the large optical responses to ultrafast strain in the topological kagome antiferromagnet, suggesting potential opto-spintronic and optoacoustic applications even at telecommunications wavelength.
Categories: cond-mat.mtrl-sci