Optical transparency of graphene as determined by the fine-structure constant

Understand

The observed 97.7% optical transparency of graphene has been linked to the value 1/137 of the fine structure constant, by using results for noninteracting Dirac fermions.

• The agreement in three significant figures requires an explanation for the apparent unimportance of the Coulomb interaction.
• Using arguments based on Ward identities, the leading corrections to the optical conductivity due to the Coulomb interactions are correctly computed (resolving a subtle theoretical issue) and shown to amount to only 1-2%, corresponding to 0.03-0.04% in the transparency.