Ultrafast Terahertz Photocurrents in Semi-metal and semiconductor few monolayer PtSe2

PtSe
2
is a promising 2D material for the THz range as its bandgap that can be tuned from an indirect semiconductor to a semimetal with the number of atomic layers, unlike other transition metal dichalcogenides. Here we use Terahertz (THz) emission time domain spectroscopy (TDS) to investigate PtSe
2
as a function of number of 2D layers. We demonstrate the THz emission from this material for the first time and show that this is a result of second order nonlinear photocurrents in PtSe
2
, with contributions from photon drag and photogalvanic effects. We also show how the PtSe
2
bandstructure dependence on the number of 2D layers radically changes its THz emission properties, rendering PtSe
2
a promising material for THz photonics.