Clar's goblet on graphene: field modulated charge transfer in a hydrocarbon heterostructure

TL;DR

This study uses first-principles DFT calculations to explore how adsorption and electric fields modulate the magnetic and electronic states of Clar's goblet molecules on graphene, revealing potential for qubit applications.

Contribution

It demonstrates the effects of adsorption and electric fields on the magnetic states and charge transfer in graphene-Clar's goblet heterostructures using DFT, highlighting controllable magnetic transitions.

Findings

HOMO in FM state aligns with the Fermi surface, enabling hybridization.

Electric fields induce transitions between FM and AFM states.

Charge realignment correlates with magnetic state changes.

Abstract

In certain configurations, the aromatic properties of benzene ring structured molecules allow for unpaired, reactive valence electrons (known as radicals). Clar's goblets are such molecules. With an even number of unpaired radicals, these nanographenes are topologically frustrated hydrocarbons in which pi-bonding network and topology of edges give rise to the magnetism. Clar's goblets are therefore valued as prospective qubits provided they can be modulated between magnetic states. Using first principles DFT, we demonstrate the effects of adsorption on both molecule and substrate in a graphene-Clar's goblet heterostructure. We look at the energy difference bewteen FM and AFM states of the system and discuss underlying physical and chemical mechanisms in reference to the highest occupied molecular orbital (HOMO) and second HOMO (HOMO-1). We find that the HOMO of the molecule in the FM state is right at the Fermi surface, which leads to the hybridization between molecular state and the graphene state near the Dirac point. Furthermore, we investigate qualitative changes in charge realignment and magnetic state under variable electric field. Transitions from FM to AFM and back to FM states are observed.