Monday, 8 April 2013

Terahertz Conductivity of Twisted Bilayer Graphene

Physical Review Letters 110, 067401 (2013)  Received 9 April 2012; published 7 February 2013

Authors: Xingquan Zou1, Jingzhi Shang1, Jianing Leaw1, Zhiqiang Luo1, Liyan Luo1, Chan La-o-vorakiat1, Liang Cheng1, S. A. Cheong1, Haibin Su2, Jian-Xin Zhu3, Yanpeng Liu4, Kian Ping Loh4, A. H. Castro Neto5, Ting Yu1, and Elbert E. M. Chia1
  1. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 637371 Singapore
  2. Division of Materials Science, School of Materials Science and Engineering, Nanyang Technological University, 639798 Singapore
  3. Theoretical Division and Center for Integrated Nanotechnologies, +Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
  4. Department of Chemistry, +National University of Singapore , 3 Science Drive 3, 117543 Singapore
  5. Graphene Research Centre and Physics Department, National University of Singapore, 6 Science Drive 2, 117546 Singapore
More details at:


Using terahertz time-domain spectroscopy, the real part of optical conductivity [σ1(ω)] 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 σ1(ω) at ∼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, which is caused by the presence of a van Hove singularity arising from a commensurate twisting of the two graphene layers.
© 2013 +American Physical Society

... The transmission THz spectra of the BLG were measured using a conventional THz-TDS system (TeraView TPS Spectra 3000)... THz TDS has proven to be a very useful noncontact technique to study material properties such as dielectric response, complex conductivity and refractive index in the far-infrared range without the need for Kramers-Kronig analysis ...