Electrically-induced polarization selection rules of a graphene quantum dot

TL;DR

This paper theoretically investigates the polarization-dependent far-infrared absorption spectra of a triangular zigzag graphene quantum dot under uniform in-plane electric fields, revealing specific polarization selection rules and their effects on electronic transitions.

Contribution

It introduces a detailed analysis of polarization selection rules in graphene quantum dots and how electric fields influence their optical absorption spectra, which is a novel insight.

Findings

Intraband transitions are forbidden when light is polarized along the electric field.

Absorption is polarized perpendicular to the electric field direction.

Selection rules depend on the electric field orientation and wave function parity.

Abstract

We study theoretically the single-electron triangular zigzag graphene quantum dot in uniform in-plane electric fields. The far-infrared absorption spectra of the dot are calculated by the tight-binding method. The energy spectra and the distribution of wave functions are also presented to analyse the far-infrared spectra. The orthogonal zero-energy eigenstates are arranged along to the direction of the external field. The remarkable result is that all intraband transitions and some interband transitions are forbidden when the absorbed light is polarized along the direction of the electric field. With x-direction electric field, all intraband absorption is y polarized due to the electric-field-direction-polarization selection rule. Moreover, with y-direction electric field, all absorption is either x or y polarized due to the parity selection rule as well as to the electric-field-direction-polarization selection rule. Our calculation shows that the formation of the FIR spectra is co-decided by the polarization selection rules and the overlap between the eigenstates of the transition.