Anomalous magnetic and transport properties of laterally connected graphene quantum dots

We investigate the magnetic, electronic, and transport properties of chemically modified Clar's goblets and laterally connected graphene quantum dots (GQDs) using density functional theory. The chemical modification includes full or partial edge passivation with 2H, O, and F atoms. We report transformation of antiferromagnetic spin ordering of Clar's goblet to ferromagnetic ordering with a nonzero net spin such as S = 1 by full passivation with 2H or S = 2.5 by partial passivation with 2H. The full and partial passivation of Clar's goblet with 2H isolates correspondingly 2 and 5 electrons with the same spin alignment which boosts the ferromagnetism. We also report the spin density localization on one side of the goblet by doping the other side with Li-atom. For laterally connected triangular GQDs, we reveal unconventional net spin. Contrary to Lieb's rule, the laterally connected triangular GQDs host not S = 0 but S = 4 net spin. This anomalous ferromagnetic state occurs due to the twisting of GQDs with respect to one another. Due to the symmetry breaking between spin up and spin down energy states, the corresponding spin up and down energy gaps are strongly affected by the modification. For instance, the spin down energy gap increased/decreased by partial passivation with F/O atoms leading to tunable transport properties. I-V characteristics indicate that the edge modification increases conduction due to the enhanced dipole moment and the number of conducting charges. Transport through latterly connected GQDs show quantum tunneling effect due to the overlap between spin up and spin down molecular orbitals which makes these systems promising as ferromagnetic tunneling diodes.

Automated summary

In this study, we investigated the magnetic, electronic, and transport properties of chemically modified Clar's goblets and laterally connected graphene quantum dots (GQDs) using density functional theory. We found that the magnetic ordering of Clar's goblet can be transformed from antiferromagnetic spin ordering to ferromagnetic ordering by chemical passivation, and the net spin can be controlled by full or partial passivation with 2H. For laterally connected triangular GQDs, we observed unconventional net spin due to the twisting of GQDs. The modification strongly affects the energy gaps and leads to tunable transport properties. Additionally, the edge modification enhances conduction and allows for quantum tunneling effects, making the latterly connected GQDs promising for ferromagnetic tunneling diodes.