Enhanced valley polarization of graphene on hBN under circularly polarized light irradiation

TL;DR

This study numerically investigates how circularly polarized light induces valley polarization in graphene on hBN, revealing optimal conditions for valleytronics device design, especially in infrared and terahertz regions.

Contribution

It provides a detailed numerical analysis of valley polarization in G/hBN under circularly polarized light, highlighting the effects of twist angle and doping.

Findings

Valley polarization is most pronounced near zero twist angle in non-doped G/hBN.

Valley polarization is insensitive to twist angle in hole-doped G/hBN.

Optimal valley polarization occurs in the infrared and terahertz frequency regions.

Abstract

Graphene on hBN (G/hBN) has a long period moir\'{e} superstructure owing to the lattice mismatch between two materials. Long periodic potential caused by the moir\'{e} superstructure induces modulation of electronic properties of the system. In this paper, we numerically calculate optical conductivity of G/hBN under circularly polarized light irradiation. The lack of spatial inversion symmetry in G/hBN induces the valley polarization. In further, the valley polarization becomes most pronounced in the infrared and terahertz regions if the twist angle between two materials is close to zero for non-doping case, however, insensitive with twist angle for hole-doped case. These results will serve to design the valleytronics devices using G/hBN.