▎ 摘　　要

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 similar to 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. DOI: 10.1103/PhysRevLett.110.067401