Cryogenic THz Nano Imaging and Spectroscopy of Graphene/α-RuCl₃Heterostructures

Several recent studies have shown that graphene can be heavily doped via a charge transfer process when it shares an interface with a number of different materials. One such material is α-RuCl₃, which has been shown to dope graphene to a Fermi energy of roughly 0.6 eV. One question of interest is what effect this charge transfer process has on α-RuCl₃. Namely, is α-RuCl₃ doped into a metallic state. To investigate this claim, we probe graphene/ α-RuCl₃ heterostructures in the low-energy THz regime to understand how their Drude characteristics differ from pristine graphene. Using our home-built cryogenic microscope, we image a graphene/ α-RuCl₃ stack using THz light and extract local spectra from 0.5 - 1.5 THz, all with nanoscale resolution. In our nanoimaging measurements, we observe clear contrast between the three different regions of our heterostructure stack: graphene/RuCl_3, graphene, and α-RuCl₃. Changes in contrast is evidence of substantial changes in the number of Drude carriers between the three regions. Further, at physical graphene edges on α-RuCl₃, we observe local contrast in both amplitude and phase, which is indicative of a local plasmonic response. Finally, we will report the analysis of nano-spectra of both graphene/α-RuCl₃ and graphene.