π- plasmon dispersion in free-standing graphene by momentum-resolved electron energy-loss spectroscopy
Journal
Physical Review B - Condensed Matter and Materials Physics
Journal Volume
91
Journal Issue
4
Pages
045418-1 - 045418-7
Date Issued
2015
Author(s)
Abstract
The π-plasmon dispersion in graphene was scrutinized by momentum-resolved electron energy-loss spectroscopy with an improved momentum q resolution and was found to display the square root of the q dispersion characteristic of the collective excitation of two-dimensional electron systems, in contrast to previous experimental and theoretical studies which reported a linear q dispersion. Our theoretical elaborations on the q-dependent spectra affirm this square root of q relation and further unveil an in-plane electronic anisotropy. The physical property of the π plasmon is thoroughly compared to that of the two-dimensional plasmon due to carriers of the Dirac fermions. A clear distinction between the π plasmon and the two-dimensional Dirac plasmon is demonstrated, clarifying the common notion about correlating the linearly dispersed Dirac cones with the linear dispersion of the π plasmon previously reported.
SDGs
Publisher
American Physical Society
Type
journal article