Enhanced magneto-optical response due to the flat band in nanoribbons made from the $\alpha-T_3$ lattice

TL;DR

This paper investigates how a magnetic field influences the magneto-optical response of $oldsymbol{ extalpha{-}T_3}$ lattice nanoribbons, revealing tunable absorption features and valley effects that could enable advanced magneto-optical devices.

Contribution

It demonstrates the magnetic field-induced gap opening and enhanced optical response in $oldsymbol{ extalpha{-}T_3}$ nanoribbons, highlighting the role of the flat band in magneto-optical modulation.

Findings

Magnetic field opens a gap and induces a new absorption peak in $oldsymbol{ extalpha{-}T_3}$ nanoribbons.

Enhanced magneto-optical response due to the flat band compared to graphene ribbons.

Valley degeneracy lifting and valley splitting observed under magnetic field.

Abstract

We study the optical response of nanoribbons made from the $\alpha-T_3$ lattice under a weak magnetic field in the terahertz to far-infrared regime. It is found that the magnetic field can open a gap in the band structure and induce a new absorption peak with much reduced frequency in metallic armchair ribbons and a class of zigzag ribbons with particular boundaries. This tunable magneto-optical modulation effect is attributed to the interband transitions between the flat band and the propagating bands. By contrast, this magnetic modulation of gap opening and optical conductance is much weaker in metallic armchair graphene ribbons (the case of $\alpha=0$) in which the flat band is absent. The enhancement in the $\alpha-T_3$ model is analytically investigated and explained within the perturbation theory for metallic armchair ribbons. The magnetic field induced valley degeneracy lifting and valley splitting of the absorption peak are also discussed in the case of zigzag ribbons. These findings pave the way for magneto-optics devices based on the $\alpha-T_3$ model materials.