Nematic electron and phonon dynamics in SnS crystals

Tin sulfide (SnS) is one of the promising materials for the applications of optoelectronics and photovoltaics. This study determines the nematic dynamics of photoexcited electrons and phonons in SnS single crystals using polarization-dependent pump-probe spectroscopy at various temperatures. As well as the fast (0.21-1.38 ps) and slow (>5 ps) relaxation processes, a 36-41 GHz coherent acoustic phonon with a sound velocity of 4883 m/s that is generated by the thermoelastic effect is also observed in the transient reflectivity change (ΔR/R) spectra. Electrons and coherent acoustic phonons show significant in-plane anisotropy from 330 to 430 K due to strong electron-phonon coupling. However, this in-plane anisotropy weakens dramatically in the low-temperature (<330 K) and high-temperature (>430 K) phases. These results add to the knowledge about the anisotropy of electrons and coherent acoustic phonons that give SnS applications in photovoltaic or optoelectronic devices.