Electronic Characterization of a Charge-Transfer Complex Monolayer on Graphene

TL;DR

This study uses low-temperature STM/STS to characterize a 2D charge-transfer complex monolayer of TTF and F4TCNQ on graphene, revealing a correlated ground state and opening avenues for exploring exotic electronic phenomena.

Contribution

It provides the first detailed electronic characterization of a 2D charge-transfer complex monolayer on graphene, demonstrating the formation of a correlated ground state at low temperatures.

Findings

Confirmation of charge-transfer complex formation via spectroscopy and imaging.

Observation of a zero-bias gap indicating correlated ground state.

Potential for studying exotic electronic effects in 2D monolayers.

Abstract

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.