Electronic Characterization of a Charge-Transfer Complex Monolayer on Graphene.
Organic charge-transfer complexes (CTCs) formed by strong electron acceptor and strong electron donor molecules are known to exhibit exotic effects such as superconductivity and charge density waves. We present a low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) study of a two-dimensional (2D) monolayer CTC of tetrathiafulvalene (TTF) and fluorinated tetracyanoquinodimethane (F4TCNQ), self-assembled on the surface of oxygen-intercalated epitaxial graphene on Ir(111) (G/O/Ir(111)). We confirm the formation of the charge-transfer complex by dI/dV spectroscopy and direct imaging of the singly occupied molecular orbitals. High-resolution spectroscopy reveals a gap at zero bias, suggesting the formation of a correlated ground state at low temperatures. These results point to the possibility to realize and study correlated ground states in charge-transfer complex monolayers on weakly interacting surfaces.
['Kumar|Avijit|A|https://orcid.org/0000-0001-8665-810X', 'Banerjee|Kaustuv|K|', 'Ervasti|Mikko M|MM|', 'Kezilebieke|Shawulienu|S|https://orcid.org/0000-0003-4166-5079', 'Dvorak|Marc|M|https://orcid.org/0000-0001-9653-2674', 'Rinke|Patrick|P|https://orcid.org/0000-0003-1898-723X', 'Harju|Ari|A|', 'Liljeroth|Peter|P|https://orcid.org/0000-0003-1253-8097']
charge-transfer complex TTF F4TCNQ epitaxial graphene charge density wave (CDW) scanning tunneling microscopy (STM)