Geometry-diversified Coulomb excitations in trilayer AAB stacking graphene

TL;DR

This paper investigates the unique Coulomb excitations in trilayer AAB-stacked graphene, revealing diverse electronic behaviors, plasmon modes, and the effects of Fermi energy variations, highlighting differences from other stacking types.

Contribution

It provides a detailed theoretical analysis of Coulomb excitations and plasmon modes specific to trilayer AAB-stacked graphene, a less-studied stacking configuration.

Findings

Nine interband excitations with unique spectral features.

Existence of a low-frequency acoustic plasmon similar to narrow gap nanotubes.

Fermi energy significantly influences electron-hole boundaries and plasmon properties.

Abstract

The lower-symmetry trilayer AAB-stacked graphene exhibits rich electronic properties and thus diverse Coulomb excitations. Three pairs of unusual valence and conduction bands create nine available interband excitations for the undoped case, in which the imaginary (real) part of the polarizability shows 1D square root asymmetric peaks and 2D shoulder structures (pairs of antisymmetric peaks and logarithm type symmetric peaks). Moreover, the low frequency acoustic plasmon, being revealed as a prominent peak in the energy loss spectrum, can survive in a narrow gap system with the large-density-of-states from the valence band. This type of plasmon mode is similar to that in a narrow gap carbon nanotube. However, the decisive mechanism governing this plasmon is the intraband conduction state excitations. Its frequency, intensity and critical momentum exhibit a non-monotonic dependence on the Fermi energy. The well-defined electron-hole excitation boundaries and the higher frequency optical plasmons are transformed by varying the Fermi energy. There remain substantial differences between the electronic properties of trilayer AAB, ABC, AAA and ABA graphene stackings.