Graphene's πα

Plate 58 speaks for itself: “2.3% dark.”

The Physics

Electrons in graphene behave like massless Dirac particles with a linear dispersion. As a result a single atomic layer absorbs a fraction πα of visible light, set only by the fine-structure constant.

E = ± ħ v_F |k|

• E: electron energy, J
• ħ: reduced Planck constant, J s
• v_F: Fermi velocity ≈ 10⁶ m s⁻¹
• k: wavevector from the Dirac point, m⁻¹
• α: fine-structure constant, dimensionless

One layer absorbs πα ≈ 2.29%. It depends only on α.

Sources

• R. R. Nair et al., Science 320, 1308 (2008).

On the poster

Plate 058, “Graphene's πα”: the pixel-art plate with its slogan “2.3% dark.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.