Fast two-dimensional long-wavelength plasmons in atomically thin MoS2
Journal
Physical Review Research
Journal Volume
8
Journal Issue
2
Start Page
023072
ISSN
26431564
Date Issued
2026-04-01
Author(s)
Wu, Chien-Ting
Hsu, Chih-En
Huang, Chih-Ying
Hsu, Yung-Ning
Lee, Che-Lun
Huang, Ssu-Yen
Hsueh, Hung-Chung
Chu, Ming-Wen
Abstract
Plasmons are bosonic wavelike charge oscillations in solids and the plasmon group velocity (vg), the first derivative of momentum (q)-dependent dispersions, depicts the many-body electron motions of critical electronic importance. The profound characteristics of vg in either three-dimensional (3D) or two-dimensional (2D) electron systems are nonetheless short of quantitative scrutiny. Using q-resolved electron energy loss spectroscopy, we tackle the q-dependent vg of π and π + σ plasmons in 3D-bulk and 2D-monolayer (ML) MoS2 semiconductors, with the 2D MoS2 being the model transition-metal dichalcogenide (TMD) for emergent atomically thin electronics. vg along with the underlining electronic parameters of the charge density, effective mass, and screening length in 2D for the plasmon dispersions is quantitatively elaborated. 2D vg is further compared to those evaluated from metallic ML-TMD TaS2 and graphene, and the scaling over the single-particle Fermi velocity (vF) unveils a vg/vF function generally obeyed by the semiconducting and metallic TMD and graphene of distinctly different massive and relativistic characters, respectively. Beyond the pertinent critical q (on the order of 10−2Å−1) where one observes vg=vF, electric-field lines connecting the oscillating 2D charges would turn from vacuum into the atomically thin matters, concomitant with the increasing plasmon damping and reducing vg (vgvF), with high-speed application merits. Conversely, 3D plasmons in bulk MoS2 never exceed vF
Publisher
American Physical Society
Type
journal article