Universal absorption of two-dimensional systems
Universal absorption of two-dimensional systems
We discuss the optical conductivity of several non-interacting two-dimensional (2D) semiconducting systems focusing on gapped Dirac and Schr\"odinger fermions as well as on a system mixing these two types. Close to the band-gap, we can define a universal optical conductivity quantum of $\sigma_0=\frac{1}{16}\frac{e^2}{\hbar}$ for the pure systems. The effective optical …