Charge carrier dynamics in 2D materials probed by ultrafast THz spectroscopy

In this review, we discuss the rich ultrafast response at terahertz (THz) frequencies of two-dimensional (2D) materials. Thanks to their unique optoelectronic properties and exceptional tunability, van der Waals organic and inorganic 2D materials, such as graphene, transition metal dichalcogenides (TMDs), and 2D perovskites, are emerging as promising platforms for the development of nano-electronic and nano-photonic devices in the THz range. The investigation of the ultrafast charge carriers dynamics resulting from their reduced dimensionality is crucial for guiding the engineering route towards novel nanotechnologies. Here, we first give a brief overview of the state-of-the-art experimental schemes for inspecting the ultrafast response of 2D materials in the THz range, including the generation and the detection of THz light and the prototypical optical pump - THz probe setup. Then, we present and discuss the most relevant results, reviewing the THz ultrafast signatures of charge carriers and excitons dynamics in graphene, TMDs, and 2D perovskites. Finally, we provide a vision of the emerging tools for characterizing the ultrafast THz dynamics at the nanoscale.