Gate-controlled two-stage Kondo effect in a metal-free polycyclic aromatic hydrocarbon diradical molecular switch: A...

Strong correlation behaviors play a pivotal role in realizing novel, high-performance, low-power nanoscale electronic devices. In this study, we theoretically design a molecular switch based on a metal-free polycyclic aromatic hydrocarbon diradical molecule dominated by strong electron-electron repulsions. By establishing a customized simulation framework that combines density functional theory with the numerical renormalization group method, and with the aid of a side-coupled two-orbital Anderson model, we systematically simulate the quantum transport governed by various kinds of Kondo effects. When the central energy level sweeps upward, the linear conductance tends to reach its unitary limit in the low-temperature regime, driven by the broadening two-stage Kondo effect window. As the side energy increases, a quantum phase transition from the two-stage Kondo effect to the spin-1/2 Kondo effect emerges, resulting in a stable, full conductance plateau. Furthermore, by tuning the exchange coupling between the central and the side orbitals, we simulate the impact of precisely adjusting the intramolecular dihedral angle of the molecule on the transport properties. The linear conductance exhibits a transition from zero to the unitary limit as the molecule smoothly evolves from the antiferromagnetic to the ferromagnetic regime. These findings provide valuable insights into the dynamical and thermodynamical properties of complex polycyclic aromatic hydrocarbon systems. Our suggested "ab initio + model calculation" theoretical framework may offer a promising methodology for exploring the complex Kondo physics in real magnetic nanosystems.