Graphene plasmons are highly tunable and display the typical dispersion relation 10 \(\omega _p \sim \sqrt q\) of an ideal 2D electron gas for q → 0, and can be observed with techniques ranging from electron-energy loss spectroscopy (EELS) to nano-imaging of interference patterns generated with atomic-force microscopy (AFM) tips 1, 2, 4, 11.īesides graphene, plasmons in other atomically thin quasi-2D metals have been reported 12, 13, 14, some displaying intriguing dispersion relations. In addition, there has been great interest in plasmons in atomically thin (one to a few atomic layer) crystalline metals such as graphene 5, 6, 7, 8, 9. Since these propagating collective modes are strongly affected by boundary/geometric effects, plasmon modes can be tuned by assembling nanostructured materials with repeated patterns, or by selectively exciting modes that only exists on the surface of metals, such as the surface plasmon polaritons (SPPs) 1, 2, 3, 4. Plasmons are quantum collective motions of electrons in solids arising from the long-range Coulomb interaction. This opens the possibility of tracking plasmon wave packets in real time for novel imaging techniques in atomically thin materials. Moreover, our ab initio calculations reveal that plasmons of monolayer metallic transition metal dichalcogenides are tunable, long lived, able to sustain field intensity enhancement exceeding 10 7, and localizable in real space (within ~20 nm) with little spreading over practical measurement time.
This stems from a broken continuous translational symmetry which leads to interband screening so, dispersionless plasmons are a universal intrinsic phenomenon in quasi-2D metals. Here we show that the plasmons in real quasi-2D metals are qualitatively different, being virtually dispersionless for wavevectors of typical experimental interest. However, besides graphene, plasmons in real, atomically thin quasi-2D materials were heretofore not well understood. Plasmons depend strongly on dimensionality: while plasmons in three-dimensional systems start with finite energy at wavevector q = 0, plasmons in traditional two-dimensional (2D) electron gas disperse as \(\omega _p \sim \sqrt q\).
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