Ansys Insight: Scattering rate in surface conductivity of graphene
The 2D surface conductivity model of graphene used in Lumerical’s optical solvers (FDTD and MODE) requires the user to specify the scattering rate for graphene in units of energy (eV), which is a common way to quote this parameter in the literature.
However, this can be confusing when looking at the expressions for the surface conductivity:
In these expressions the scattering rate parameter Γ should have units of inverse time. How is Γ related to the “scattering rate (eV)” parameter in the material database? The answer is simple: Γ is just the result of dividing the “scattering rate (eV)” parameter by hbar, ℏ, in appropriate units.
Another common parameter found in the literature is the electron relaxation time, τ, which is typically deduced from a comparison with the Drude model and is related to Γ by τ=1/(2Γ). In some references they also relate the scattering rate to the electron mobility.