Optical signatures of nonlocal plasmons in graphene

TL;DR

This paper explores how nonlocal plasmon effects in graphene can be detected through optical scattering, highlighting significant deviations from local models at small wavelengths and specific conditions.

Contribution

It provides a theoretical analysis of nonlocal plasmon signatures in graphene using optical scattering and compares local versus nonlocal conductivity models.

Findings

Nonlocal effects cause up to 20% deviation in plasmon wavelength from local models.

Differences in scattering amplitudes are significant at small grating periods.

Nonlocal signatures are prominent at low temperatures and small wavelengths.

Abstract

We theoretically investigate under which conditions nonlocal plasmon response in monolayer graphene can be detected. To this purpose, we study optical scattering off graphene plasmon resonances coupled using a subwavelength dielectric grating. We compute the graphene conductivity using the Random Phase Approximation (RPA) obtaining a nonlocal conductivity and we calculate the optical scattering of the graphene-grating structure. We then compare this with the scattering amplitudes obtained if graphene is modeled by the local RPA conductivity commonly used in the literature. We find that the graphene plasmon wavelength calculated from the local model may deviate up to $20\%$ from the more accurate nonlocal model in the small-wavelength (large-$q$) regime. We also find substantial differences in the scattering amplitudes obtained from the two models. However, these differences in response are pronounced only for small grating periods and low temperatures compared to the Fermi temperature.