Exciton states in a circular graphene quantum dot: magnetic field induced intravalley to intervalley transition

TL;DR

This study investigates how magnetic fields influence exciton states in circular graphene quantum dots, revealing significant excitonic effects, valley-dependent behaviors, and tunable optical transitions due to magnetic and geometric confinements.

Contribution

It provides a detailed analysis of intravalley and intervalley excitons in CGQDs under magnetic fields, highlighting their different magnetic dependencies and the possibility of tuning valley-specific optical transitions.

Findings

Excitonic effects are enhanced by confinement and reduced screening.

Distinct magnetic-field responses for intravalley and intervalley excitons.

Magnetic field induces an intravalley to intervalley exciton transition.

Abstract

The magnetic-field dependence of the energy spectrum, wave function, binding energy and oscillator strength of exciton states confined in a circular graphene quantum dot (CGQD) are obtained within the configuration interaction (CI) method. We predict that: (1) excitonic effects are very significant in the CGQD as a consequence of a combination of geometric confinement, magnetic confinement and reduced screening; (2) two types of excitons (intravalley and intervalley excitons) are present in the CGQD because of the valley degree of freedom in graphene; (3) the intravalley and intervalley exciton states display different magnetic-field dependencies due to the different electron-hole symmetries of the single-particle energy spectra; (4) with increasing magnetic field, the exciton ground state in the CGQD undergoes an intravalley to intervalley transition accompanied by a change of angular momentum; (5) the exciton binding energy does not increase monotonically with the magnetic field due to the competition between geometric and magnetic confinements; and (6) the optical transitions of the intervalley and intravalley excitons can be tuned by the magnetic field and valley-dependent excitonic transitions can be realized in CGQD.