THz conductivity of graphene on boron nitride

TL;DR

This paper investigates the terahertz and infrared conductivity features of graphene on boron nitride, revealing how moiré patterns and Fermi level tuning influence optical responses, with implications for understanding 2D material interactions.

Contribution

It provides a detailed analysis of THz and IR conductivity features in graphene on boron nitride, linking them to moiré band structures and Fermi level effects, which was not previously characterized.

Findings

Strong THz and IR features occur when lattices are aligned.

Features are prominent near Fermi levels close to ±150 meV.

Substrate-induced band splitting causes sharp IR features in p-doped graphene.

Abstract

The conductivity of graphene on a boron nitride substrate exhibits features in the terahertz (THz) and infrared (IR) frequency regimes that are associated with the periodic moir\'e pattern formed by the weakly coupled two-dimensional materials. The THz and IR features are strongest when the two honeycomb lattices are orientationally aligned, and in this case are Pauli blocked unless the Fermi level is close to $\pm 150$ meV relative to the graphene sheet Dirac point. Because the transition energies between moir\'e bands formed above the Dirac point are small, ac conductivity features in n-doped graphene tend to be overwhelmed by the Drude peak. The substrate-induced band splitting is larger at energies below the Dirac point, however, and can however lead to sharp features at THz and IR frequencies in p-doped graphene. In this Letter we focus on the strongest few THz and IR features, explaining how they arise from critical points in the moir\'e-band joint density-of-states, and commenting on the interval of Fermi energy over which they are active.