Fig. 3: Exciton and continuum absorption in few-layer BP.
From: The optical conductivity of few-layer black phosphorus by infrared spectroscopy
a The frequency-integrated conductivity σI of the 1 s exciton as a function of layer number, in the unit of eV·σ0. For each layer number, at least three samples were measured, the squares denote the average values. The solid curve is the fitting to the E11 data using the relation σI = h/(χ0 + Nχ1), with χ0 and χ1 describing the screening effect from the PDMS substrate and single-layer BP, respectively. h is the only fitting parameter, extracted to be 5.78 eV·σ0·Å. The dashed curve shows the 1/N relation for guideline. b The continuum height of each subband transition near the corresponding band edge (ħω ≈ Eg) is plotted as a function of layer number. The continuum absorption nearly shows a constant value, independent of the material thickness. The black dashed line indicates the well-known universal conductivity σ0 = e2/4ħ for guideline. Data are extracted from Fig. 2 with error bars indicating sample-to-sample variation.
