Enhanced ponderomotive force in graphene due to interband resonance

Abstract

We analyze intrinsic nonlinearities in two-dimensional (2D) polaritonic materials interacting with an optical wave. Focusing on the case of graphene, we show that the second-order nonlinear optical conductivity due to carrier density fluctuations associated with the excitation of a plasmon polariton is closely related to the ponderomotive force due to the oscillating optical field. A recent study (Sun et al 2018 Proc. Natl Acad. Sci. USA 115 3285–9) derived this force in the hydrodynamic regime of a generic Dirac fluid, and suggested that inclusion of interband transitions could have interesting implications. Here we reproduce the Drude-like result in a more general fashion on the basis of thermodynamics, which makes extension to other regimes straightforward. We find that for zero temperature a diverging nonlinearity is found at the interband threshold. By including finite-temperature effects this is regularized, but remains quite significant even at room temperature. Going further beyond, we include nonlocal corrections as a second potential source of regularization, and find that they do not lead to broadening (as one would usually expect e.g. due to Landau damping), but rather to a splitting of the ponderomotive interband resonance, providing a very characteristic signature of nonlocality. Our analysis should prove useful to the open quest for exploiting nonlinearities in graphene and other 2D polaritonic materials, through effects such as photon drag.

Keywords

• graphene nonlinearities
• ponderomotive force
• nonlocal response