The transparency of graphene and other direct-gap two dimensional materials

Abstract

Graphene and other two-dimensional materials display remarkable optical properties, including a simple light transparency of $T\approx 1-\pi \alpha$ for light in the visible region. Most theoretical rationalizations of this "universal" opacity employ a model coupling light to the electron's crystal momentum and put emphasis on the linear dispersion of the graphene bands. However, such a formulation of interband absorption is not allowable within band structure theory, because it conflates the crystal momentum label with the canonical momentum operator. We show that the physical origin of the optical behavior of graphene can be explained within a straightforward picture with the correct use of canonical momentum coupling. Its essence lies in the two-dimensional character of the density of states rather than in the precise dispersion relation, and therefore the discussion is applicable to other systems such as semiconductor membranes. At higher energies the calculation predicts a peak corresponding to a van Hove singularity as well as a specific asymmetry in the absorption spectrum of graphene, in agreement with previous results.

APS PHYSICS Synopsis: http://physics.aps.org/synopsis-for/10.1103/PhysRevB.94.205439

References in corpus (9)

• The electronic properties of graphene
• Universal Dynamic Conductivity and Quantized Visible Opacity of Suspended Graphene
• Measurement of the Optical Conductivity of Graphene
• Optical properties of graphene
• Spectroscopic ellipsometry of graphene and an exciton-shifted van Hove peak in absorption
• Seeing many-body effects in single- and few-layer graphene: Observation of two-dimensional saddle-point excitons
• Electronic structure of multilayer graphene
• Low frequency optical conductivity in graphene and in other scale-invariant two-band systems
• Tree-level electron-photon interactions in graphene

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• Optical absorption in two-dimensional materials with tilted Dirac cones
• Polarized photoluminescence clocks ultrafast pseudospin relaxation in graphene
• Optical Transparency in an effective model for Graphene
• Optical Conductivity in an effective model for Graphene: Finite temperature corrections
• Universal transparency and fine band structure near the Dirac point in HgTe quantum wells
• Sub-Sharvin conductance and incoherent shot-noise in graphene disks at magnetic field