Recently, a research team from Zhejiang University revealed an astonishing phenomenon of graphene quantum dots under light irradiation, particularly the anomalous inverse Faraday effect under twisted light (light vortex). This discovery provides new insights into controlling fundamental phenomena in two-dimensional materials. The researchers found that when graphene quantum dots are subjected to light with a helical phase, the light-induced magnetic moment not only arises but also exhibits opposite magnetic moment directions in certain regions, leading the rotation direction of the current to be opposite to that of the light. This unexpected behavior is due to the complex interaction between the light's phase and the material's properties, opening a new understanding of how the angular momentum of light is converted into magnetism.
In this study, the scientists constructed a framework to explore the interaction between graphene quantum dots and light, particularly the transfer of the orbital angular momentum (OAM) of light. By analyzing the behavior of graphene quantum dots irradiated by light vortex beams, the research team focused on the generation of photoelectric currents and the transfer of angular momentum. The study selected a hexagonal graphene quantum dot composed of 54 atoms and performed computational simulations on it, revealing a low-frequency peak in its absorption spectrum at 1.847 eV (672 nm), closely related to the low-energy transitions and degenerate excited states of OAM transfer.
jrhz.infoThrough the irradiation of light vortex beams, the researchers discovered the generation of two different types of photoelectric currents: Type II current oscillates synchronously with the planar electric field, while Type III current forms quasi-stable vortices around the center of the quantum dot, showing an acquired OAM in the z direction, manifested as an anomalous inverse Faraday effect. To quantify this effect, the research team systematically moved the graphene quantum dot within the laser beam field and calculated the corresponding orbital magnetic moment (OMM). The results showed that the OMM distributions under modes LG01, LG02, and LG13 exhibited sign reversals in both radial and angular coordinates, with their oscillation periods matching the LG node indices.
Furthermore, the study revealed an anomalous phenomenon where graphene quantum dots acquired negative OAM under light vortex beam irradiation, challenging the expected direction of traditional models. Through detailed analysis of the torque effect of light on electrons, the researchers confirmed the self-consistency of this phenomenon, indicating that the phase structure of light vortices induced a position-dependent phase difference and rotational dynamics. This research establishes a new framework for understanding light-driven responses in two-dimensional materials, providing potential applications for developing novel optoelectronic devices and manipulating chiral light.
