Optical study of the three-dimensional Weyl semimetal Mn3Sn

The three-dimensional Weyl semimetal Mn3Sn has attracted tremendous attention due to its great application potential. However, the complex magnetic structures at different temperature intervals make it extremely difficult to unravel the underlying electronic structures of Mn3Sn. Here, we perform temperature-dependent optical spectroscopy measurements on single-crystalline Mn3Sn to investigate its charge dynamics. We find that both the optical reflectivity R(omega) and conductivity sigma 1(omega) evolve very smoothly across the magnetic phase transition at TM = 285 K, where the giant anomalous Hall effect (AHE) at room temperature drops significantly. Furthermore, linearly increasing segments of sigma 1(omega) are observed in the whole temperature range from 300 K to 10 K, indicating that the existence of Weyl fermions is very robust against the magnetic phase transition. In addition, the Weyl points closest to the Fermi level EF are identified to be located about 101 meV away from EF at 10 K, and the associated Fermi velocity is about 2.50 x 107 cm/s. Our results reveal that the phase transition at TM only generates subtle modification to the band structure, which helps to further uncover the mechanism of the dramatic change of AHE in Mn3Sn.