Abstract
is a layered material that has been recently identified as a two-dimensional (2D) electride, an unusual ionic compound in which electrons serve as anions. The electronic properties of 2D electrides attract considerable interest as the anionic electrons, which form a 2D layer sandwiched between atomic planes, are highly mobile as they are not attached to any ion. Here, on the basis of first-principles time-dependent density-functional theory calculations, we investigate the collective excitations of the electrons—i.e., the plasmons—in as a function of wave vector . Our calculations reveal an intrinsic negative in-plane dispersion of the anionic plasmon, in striking contrast with the homogeneous electron gas. Moreover, for wave vectors normal to the planes, we find a long-lived plasmon that continues to exist well beyond the first Brillouin zone. This is a mark of the electronic inhomogeneities in the charge response that shares with other layered materials like transition-metal dichalcogenides and . Finally, we compare the plasmon properties of in its bulk and monolayer forms, which shows the effect of the different electronic structures and dimensionalities.
1 More- Received 18 July 2017
DOI:https://doi.org/10.1103/PhysRevB.96.125131
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