Probing Electronic Structure and Carrier Dynamics in the Ferromagnetic Semiconductor CrSiTe3

The layered ferromagnetic semiconductor CrSiTe3 (CST) has attracted great scientific attention due to its potential as a 2-dimensional ferromagnet with higher Tc than in its bulk form. In order to understand the nature of magnetic correlations and possible magneto-optoelectronic applications, it is crucial to understand the electronic structure and photoinduced response near the band-edge in nanoscale samples. Here we present transient optical spectroscopy on exfoliated CST nanosheet samples at 300 K as well as at 10 K over an extended photon energy: 0.3 – 1.2 eV. We find clear signatures of optical transitions around 0.5 and 1.15 eV, which agree well with theoretical calculations of the indirect and direct conduction band edges. Photoexcited carriers are thermalized within a ps to the lattice through strong coupling to optical phonons and the subsequent decay persists over a nanosecond before undergoing recombination. Our work not only demonstrates direct measurements of the band structure but also sheds light on scattering behavior of photoexcited carriers in CST, which are critical for its future applications.