Spintronic Terahertz Emission from Metal/PtSe₂ Heterostructures

Spintronic emitters have become an important THz source with gapless broadband THz emission and the ability to magnetically control the emitted polarization through ultrafast spin-to-charge conversion (SCC). This work has recently driven investigations of two-dimensional (2D) materials for new types of spintronic THz sources. Indeed 2D materials are ideal platforms for spin-to-charge conversion (SCC) as a result of their strong spin-orbit coupling and low crystal symmetries. One of such 2D materials is the transition-metal dichalcogenide PtSe2. In this work we present THz spintronic sources based on high quality epitaxially grown CoFeB/PtSe2/graphene heterostructures, with PtSe2 thicknesses ranging from 1 to 15 monolayers. The unique thickness dependent electronic structure of PtSe2 permits to demonstrate the different origins of the THz emission - from the inverse Rashba-Edelstein effect in monolayer PtSe2 to the inverse spin Hall effect for multilayers through the strength of the THz emission. This unique bandstructure flexibility makes PtSe2 an ideal candidate as a THz spintronic 2D material and to further study and explore the underlying mechanisms and engineering of the SCC for THz emission.