Terahertz conductivity of twisted bilayer graphene

Xingquan Zou, Jingzhi Shang, Jianing Leaw, Zhiqiang Luo, Liyan Luo, Chan La-o-vorakiat, Liang Cheng, Haibin Su, Jian-Xin Zhu, Yanpeng Liu, Kian Ping Loh, A. H. Castro Neto, Ting Yu, Elbert E. M. Chia

Published 2013-02-18Version 1

Using terahertz time-domain spectroscopy, the real part of optical conductivity [$\sigma_{1}(\omega)$] of twisted bilayer graphene was obtained at different temperatures (10 -- 300 K) in the frequency range 0.3 -- 3 THz. On top of a Drude-like response, we see a strong peak in $\sigma_{1} (\omega)$ at $\sim$2.7 THz. We analyze the overall Drude-like response using a disorder-dependent (unitary scattering) model, then attribute the peak at 2.7 THz to an enhanced density of states at that energy, that is caused by the presence of a van Hove singularity arising from a commensurate twisting of the two graphene layers.