Theory of intrinsic acoustic plasmons in twisted bilayer graphene
Lorenzo Cavicchi, Iacopo Torre, Pablo Jarillo‐Herrero, Frank H. L. Koppens, Marco Polini
Abstract
The authors theoretically investigate here the intrinsic plasmonic properties of twisted bilayer graphene as a function of twist angle $\ensuremath{\theta}$, temperature, and filling factor. Using the random phase approximation, the authors consider the layer-pseudospin degree of freedom, spatial nonlocality of the density-density response function, crystalline local field effects, and Hartree self-consistency. Their findings reveal a smooth transition in the plasmonic spectrum of TBG from a strongly coupled regime ($\ensuremath{\theta}$ $\ensuremath{\lesssim}$ 2\ifmmode^\circ\else\textdegree\fi{}) with a weakly dispersive intraband plasmon, to a weakly coupled regime ($\ensuremath{\theta}$ $\ensuremath{\gtrsim}$ 2\ifmmode^\circ\else\textdegree\fi{}), where an acoustic plasmon clearly emerges.