Vertical absorption edge and universal onset conductance in semi-hydrogenated graphene

TL;DR

This paper investigates the optical and conductance properties of semi-hydrogenated graphene with sub-lattice energy differences, revealing a universal onset conductance and how absorption edges are affected by these differences.

Contribution

It introduces the concept of a universal onset conductance in systems lacking inversion symmetry, independent of the band gap size, and analyzes the impact of sub-lattice energy differences on optical absorption.

Findings

Universal conductance at the band edge is $rac{ ext{pi} e^2}{2h}$, regardless of band gap.

Optical absorption edge is determined by the sub-lattice energy difference $$.

Conductance near the band edge varies as $1/^2$ with frequency.

Abstract

We show that for graphene with any finite difference in the on-site energy between the two sub-lattices ($\Delta$), The optical absorption edge is determined by the $\Delta$. The universal conductance will be broken and the conductance near the band edge varies with frequency as $1/\omega^2$. Moreover, we have identified another universal conductance for such systems without inversion symmetry, i.e., the onset conductance at the band edge is $% \sigma_c=2\sigma_0=\pi e^2/2h$, independent of the size of the band gap. The total integrated optical response is nearly conserved despite of the opening of the band gap.